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WO2025190504A1 - Microlasers comestibles, leurs procédés de préparation et leurs utilisations - Google Patents

Microlasers comestibles, leurs procédés de préparation et leurs utilisations

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Publication number
WO2025190504A1
WO2025190504A1 PCT/EP2024/057096 EP2024057096W WO2025190504A1 WO 2025190504 A1 WO2025190504 A1 WO 2025190504A1 EP 2024057096 W EP2024057096 W EP 2024057096W WO 2025190504 A1 WO2025190504 A1 WO 2025190504A1
Authority
WO
WIPO (PCT)
Prior art keywords
edible
microlaser
mixtures
wax
oil
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/EP2024/057096
Other languages
English (en)
Inventor
Matjaz Humar
Abdur Rehman ANWAR
Marusa MUR
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Institut Jozef Stefan
Original Assignee
Institut Jozef Stefan
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Institut Jozef Stefan filed Critical Institut Jozef Stefan
Priority to PCT/EP2024/057096 priority Critical patent/WO2025190504A1/fr
Publication of WO2025190504A1 publication Critical patent/WO2025190504A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/0627—Construction or shape of active medium the resonator being monolithic, e.g. microlaser
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/06—Luminescent, e.g. electroluminescent, chemiluminescent materials containing organic luminescent materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/168—Solid materials using an organic dye dispersed in a solid matrix
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/20—Liquids
    • H01S3/213—Liquids including an organic dye
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/169—Nanoparticles, e.g. doped nanoparticles acting as a gain material

Definitions

  • the present invention belongs to the field of lasers, i.e., devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range, more precisely to the field of microlasers for sensing and/or barcoding.
  • the invention relates to edible microlasers, i.e., combinations of compounds that can emit light upon excitation, while at the same time being safe for consumption. Further, the invention also relates to methods for preparation of said edible microlasers and to uses thereof.
  • Microbarcodes serve the same purpose as macroscopic barcodes, but at a much smaller scale.
  • One type of microbarcodes are based on microlasers.
  • Figure 1 shows characteristic properties of microlasers, which have a very narrow emission, a highly nonlinear output when the input power is increased, they typically have a polarized output and sometimes distinguishable spatial modes and a directional output. These properties can be used for barcoding and sensor development. Therefore, microlasers have the potential for tracking, labeling, biodetection, cell tagging, information security, and anticounterfeiting (Shikha, et al., Chem. Soc. Rev., 46(22): 7054-7093, 2017; Leng et al., Chem. Soc.
  • Microcavity- and microlaser-based barcodes can be used for product labeling as an authentication tool to reduce counterfeiting (Anwar et al., ACS photonics, 10(5):1202-1224, 2023).
  • the microcavity-based microlasers have a narrow emission spectrum and therefore have the potential to generate millions of unique microbarcodes/tags (Dannenberg et al., Opt. Express, 29(23):38109-38118, 2021 ; Martino et al., Nat. Photonics, 13(10):720- 727, 2019).
  • microlasers are ideal candidates for this since the cavity itself modifies the emission characteristics of the fluorescent gain material within (Fig. 1). Most notably, while the fluorescence emission width is of the order of 50 nm, microlasers have a much narrower emission, frequently below 0.1 nm. Since the emission linewidth is several hundred times narrower, the number of distinguishable “colors” is larger by the same factor.
  • the output intensity is highly nonlinear when increasing the input intensity and a clear lasing threshold is observed. Both below and above the lasing threshold, the emitted light can be polarized and well-defined spatial modes are present. The modes can be observed as a particular intensity pattern and as a directional output.
  • the output of a microlaser can be used in various ways to encode the actual barcode.
  • the encoding variables can be, for example, the wavelength of a single or multiple spectral lines, the size of the microlaser (calculated from the spectrum), and the value of the laser threshold.
  • the barcode can be random, due to the random properties of the microlasers, or more rarely, it can be predefined, so that some useful information can be encoded.
  • the most obvious encoding choice is in the case of single-mode lasers, where simply the central emission wavelength is the barcode (Fig. 4a).
  • the most common single-mode microlasers are small WGM lasers where the FSR is large enough so that only one mode is within the gain region.
  • the other common type of single-mode laser is distributed feedback (DFB) laser, where the emission wavelength is directly related to the periodicity of the structure.
  • the maximum number of barcodes that can be generated is proportional to the wavelength range where the emission can be generated and inversely proportional to the width of the spectral peaks (either limited by the microlaser itself or by the detection system).
  • the spectral lines can be used as unique identifiers in various ways (Fig. 4b). Wavelength, width and the intensity of each spectral peak can be considered.
  • the lasing peaks are relatively independent of each other, so the positions and possibly the intensities of all the peaks can be used as a barcode.
  • the position of the bars can be defined as the central wavelengths of the spectral peaks and the width of the bars can be defined as the fluorescence intensity of each peak.
  • the modes are not independent of each other. For example, in a simple Fabry-Perot cavity, the modes are equally spaced and the positions of all the peaks are defined by the optical length of the cavity (Fig. 4c). Therefore, a single parameter, i.e., the size of the cavity, should be used as a barcode (Fig. 4d). For more complex cavity geometries, more parameters influence the cavity modes and can be independently used as the barcoding quantities.
  • WGM microlasers are one example where size can be used as a barcode.
  • the width of the particle size distribution in this particular case is calculated from the mean diameter and the CV is 3.2 pm. If the diameters are spaced perfectly in 1 nm intervals, this can give a theoretical maximum number of barcodes equal to 3200.
  • the pumping power at which the lasing threshold is reached can be used for barcoding (Fig. 4e).
  • the threshold is measured by increasing the pumping power until the microlaser starts to emit laser light.
  • the threshold behavior is very typical of laser cavities and it is not exhibited by other optical probes. Therefore, it can be easy to distinguish it from the background.
  • To measure the threshold no spectrometer is needed, since only the intensity of the light is measured. Threshold barcoding is especially useful for anti-counterfeiting applications. Random barcode generation versus predefined information encoding
  • Unique barcodes are generated through the inherent randomness of their manufacturing, such as the polydispersity in their size (Fig. 4f). For most barcoding applications this randomness is desirable. On one hand, it facilitates the production of very complex barcodes that are practically impossible to replicate (physical unclonable function), which is favorable for anticounterfeiting applications. On the other hand, it enables the generation of a large number of unique barcodes. This is useful when many entities need to be tagged, for example, in cell tagging. However, if some information is to be encoded into the barcode, as is usually the case with macroscopic barcodes, then the manufacturing process needs to be accurately controlled. A limited number of cases have been demonstrated for the generation of predefined microlaser barcodes.
  • the number of bits that can be encoded by one microlaser can be calculated using Iog2(n), where n is the number of unique barcodes that can be generated.
  • n is the number of unique barcodes that can be generated.
  • a seemingly large number of unique combinations only gives a modest amount of encoded information. For example, 1000 unique spectra can encode only ⁇ 10 bits of information.
  • a microfluidics device can be used to produce microlasers with a controllable size.
  • the coefficient of variation for droplets produced with standard microfluidics setups is of the order of 1 % and sometimes down to 0.1%. For example, in the size range 20-40 pm and with a CV of 1% it would be possible to generate ⁇ 100 unique barcodes. In this way, monodispersed droplets are produced. These droplets can also be turned into solid spheres, either by making them at a higher temperature material (e.g. wax) and solidification at a lower temperature or by making the droplets from a material dispersed in a solvent, which diffuses out leaving a solid microbead.
  • a higher temperature material e.g. wax
  • microbeads that can be made in bulk quantities.
  • the microbeads are coated with a fluorescent dye and used as WGM lasers.
  • microspheres have a CV of 1-3%.
  • Fig. 4g there are size distributions of 13 samples of spheres, as provided by the commercial supplier. In this particular case, about 20 different sizes could be used in this size range without a significant overlap. With a larger size range and a smaller CV, at least 50 distinguishable sizes could be made.
  • a single property of a microlaser e.g., the microlaser lasing wavelength and the threshold size
  • the number of unique barcodes can be increased via multiplexing, i.e., by combining two or more principles of encoding to generate a multi-dimensional barcode.
  • Two or more microlasers can be joined together to generate a single barcode, or two different properties of a single microlaser (e.g., the emission wavelength and the lasing threshold) can be used to create a barcode.
  • the microlaser-based encoding can also be combined with other optical barcoding techniques, such as graphical encoding.
  • microsphere size as the microlaser property used for encoding.
  • the microsphere size is chosen for clarity, as it is easily depicted. However, instead of the size of the microspheres, different microlaser properties (as well as different types of microlasers) can be used in actual cases.
  • N (D!) I (ml (D-m)l), where m is the number of microlasers, and each microlaser can exist in one out of D possible unique states (e.g., number of unique emission spectra or number of unique sizes).
  • N (D!) I (ml (D-m)l)
  • m the number of microlasers
  • each microlaser can exist in one out of D possible unique states (e.g., number of unique emission spectra or number of unique sizes).
  • the barcode containing several microlasers is read by taking a single spectrum. From it, it is impossible to deduce how many microlasers with the same spectrum are present in the barcode. Therefore, the equation for the number of combinations without repetition is used.
  • the number of combinations is 7x10 7 .
  • the number of unique barcodes increases rapidly with a larger number of microlasers in the group. Consequently, this strategy could be employed for multiplexing applications that require a huge number of unique barcodes.
  • the sizes of the microlasers are random, there is a probability that two barcodes will be the same. As the total number of microlasers is increased, this probability also increases. If the barcode contains multiple microlasers, then the probability that such a barcode is identical to some other barcode is much lower than for barcodes containing only one microlaser.
  • the number of microlasers is not fixed. Information is encoded through the presence (T) or absence (’O’) of certain values of a chosen microlaser property (e.g., a certain size, a certain lasing emission wavelength, a certain lasing threshold) in the sample, as shown schematically in Fig. 5b.
  • microlaser-based encoding can be arranged in a particular graphical pattern.
  • an ordered group e.g., ordered in a line, Fig. 5c
  • the number of unique barcodes is larger by a factor of ml compared to the case when the order is not important (compare to the previous equation).
  • M D m .
  • the number of unique barcodes is slightly higher at 10 10 .
  • microlasers can also be positioned into a two-dimensional pattern, creating a graphic pattern. In terms of the number of unique barcodes, this case is equivalent to the microlasers being ordered in a line. However, when a large number of microlasers is used to produce a barcode, for some applications it might be beneficial to use a more compact 2D shape rather than a long line. Multiplexing can also be achieved by combining two or more properties of the microlasers. For example, different gain media (with different emission spectra) can be used in addition to the microlaser sizes, to increase the number of unique barcodes (Fig. 5d).
  • Barcodes and sensors based on microlasers have been developed, as for example described in documents US20110256577A1 , US11289879 and US20230272372A1 , however they have been till now only applied to biomedical applications and were not made from edible materials.
  • the technical problem which is solved by the present invention, is the design of edible microlasers and their use in labelling food and/or pharmaceutical products, as well as other products in need of reliable labels and/or sensors for ensuring quality, safety and authenticity of products.
  • Prior art is the design of edible microlasers and their use in labelling food and/or pharmaceutical products, as well as other products in need of reliable labels and/or sensors for ensuring quality, safety and authenticity of products.
  • microlasers where either the gain material or the cavity material is edible.
  • Solid microspheres dyed with different non-edible dyes have been produced from numerous edible materials, such as bovine serum albumin, pectin and cellulose by Ta et al. (Adv. Opt. Mater., 5: 1601022, 2017), chicken and goose egg white by Mai et al. (Soft Matter, 16: 9069-9073, 2020) and Nguyen et al.( J. Phys. D: Appl. Phys., 53: 445104, 2020), respectively, polyvinyl alcohol (PVA) by Ta et al. (Opt.
  • PVA polyvinyl alcohol
  • riboflavin as a gain material also in a spherical droplet of water and glycerol, producing a completely edible laser supported on a non-edible super-hydrophobic substrate needed for the operation of the microlaser.
  • Van Spotify et al. demonstrate another type of cavity, containing riboflavin as a gain material. They dope gelatine with the riboflavin and produce a distributed feedback microlaser, by spin-coating the gelatine on a micro- structured non-edible substrate. Similarly, Choi et al. (Lab Chip, 15: 642-645, 2016) use riboflavin-dyed silk to produce a free-standing distributed feedback microlaser that is completely edible.
  • the present invention addresses the technical problem of providing edible microlasers for sensing and/or barcoding and aims to overcome the disadvantages of known solutions as defined in the independent claims, while preferred embodiments are defined in dependent claims.
  • Microlaser comprises a microcavity containing gain material. When optically pumped above the lasing threshold, it emits laser light, whereas below the lasing threshold, it acts in the spontaneous emission regime.
  • Barcoding is a process of encoding random or predefined information into an object that can be later read by the user.
  • Sensorics is the ability to read one or more properties of an object, such as temperature, pH, concentration of chemical substances, presence of bacteria, etc.
  • Water soluble gain Gain materials that are soluble in water, such as riboflavin, riboflavin material sodium phosphate, saffron, norbixin (annatto), beetroot red, NADH, quinine, tartrazine, quinoline yellow WS, sunset yellow FCF, cochineal, carmoisine, amaranth, ponceau 4R, erythrosine, allura red AC, patent blue V, indigo carmine, brilliant blue FCF, chlorophyllin, copper complexes of chlorophylls and chlorophyllin, green S, plain caramel, caustic sulphite caramel, ammonia caramel, sulphite ammonia caramel, betanin, anthocyanins, pigment rubine, tangeretine, vanillin.
  • riboflavin riboflavin material sodium phosphate
  • norbixin annatto
  • beetroot red NADH
  • quinine quinine
  • tartrazine quinoline yellow
  • Oil soluble gain Gain materials that are soluble in oil, such as chlorophyll, material bixin(annatto), porphyrin, porphine, curcumin, paprika oleoresin, alpha-carotene, beta-carotene, gamma-carotene, capsanthin, capsorubin, lycopene, beta-apo-8'-carotenal, ethyl ester of beta-apo- 8'-carotenic acid, lutein, zeaxanthin, retinol, citrus red 2, vitamin E
  • the essence of the invention is that the microlasers according to the invention are made from completely edible materials, thus allowing their safe use in/on food, pharmaceutical products, and also other products, such as cosmetics.
  • the microlaser according to the invention comprises at least an edible gain (active) material that can fluoresce and an edible optical cavity (resonator) for receiving said gain material.
  • a usual component of lasers is also a pumping source, however, according to this invention, the pumping source is external, i.e. provided in the device for reading the signal from the microlaser.
  • the gain medium provides optical gain through stimulated emission when it is pumped either optically or electrically.
  • the optical microcavity is responsible for trapping the light and confining it within the cavity. When the total optical gain in the cavity matches or exceeds the total optical losses, the system reaches the lasing threshold, resulting in laser emission.
  • microcavities can be categorized into different types such as WGM, FP, DFB, and random lasers, wherein all these types can be achieved with edible materials as described further below and defined in the claims.
  • the microcavity confines light to a small volume, with typical dimensions in the range from below a micrometer to a few hundred micrometers.
  • Its eigenmodes comprise a particular set of transverse and longitudinal cavity modes.
  • the number of cavity modes is proportional to the volume of the microcavity.
  • the optical path travelled in one round trip must be equal to an integer multiple of the resonant wavelength.
  • the spacing between the wavelengths of two consecutive modes is called the free spectral range (FSR).
  • the resonator’s performance is characterized by the quality factor Q, which is directly proportional to the time that the light stays trapped inside the cavity.
  • Q quality factor
  • Different cavity modes can experience different losses in the cavity, resulting in different Q-factors for each of the modes.
  • the Q-factor is inversely proportional to the resonance line-width.
  • the cavity When the cavity contains gain material, it can act as a laser. If pumped above the lasing threshold, population inversion is achieved in the gain medium, enabling the amplification of resonant light through the process of stimulated emission. Sharp laser lines emerge in the emission spectrum at the positions of the resonant wavelengths. Due to the cavity losses becoming compensated by gain, the line width decreases considerably. The overlap of the gain region with the resonant modes determines how many modes will be visible. If the gain region is narrower than the FSR, then only one mode will start lasing, resulting in a single-mode laser. Sharp spectral lines can also be present below the lasing threshold due to the Purcell effect. If pumped below the lasing threshold, the microlaser output is governed by spontaneous emission. Depending on the microcavity type, spectral peaks can be present at positions of resonant wavelengths also in this regime. If present, spectral peaks can be used for barcoding and sensing in the same way as lasing peaks.
  • any edible material which displays fluorescence can be used. These can be either artificial compounds, such as colorants, or natural compounds or mixtures, such as various extracts.
  • compounds with low fluorescence are useful, for example, compounds with quantum yield below 0.2.
  • the fluorescence quantum yield of the dye used should be relatively high, for example above approximately 0.2.
  • the edible and fluorescent gain material is preferably selected in the group comprising: curcumin, riboflavin, riboflavin sodium phosphate, tartrazine, quinoline yellow WS, sunset yellow FCF, cochineal, carmoisine, amaranth, ponceau 4R, erythrosine, allura red AC, patent blue V, indigo carmine, brilliant blue FCF, chlorophylls, chlorophyllins, copper complexes of chlorophylls and chlorophyllins, green S, plain caramel, caustic sulphite caramel, ammonia caramel, sulphite amonia caramel, alpha-carotene, beta-carotene, gamma-carotene, annatto (bixin), paprika oleoresin, capsanthin, capsorubin, lycopene, beta-apo-8'-carotenal, ethyl ester of beta-apo-8'-carotenic acid, lutein, can
  • the gain material may be dissolved in the cavity material.
  • the FP microlasers have a cavity between the mirrors filled with a solution of the selected gain material in oil or water, depending on the solubility of the selected gain material in oil or water.
  • random laser gain material in powder form may be used.
  • the edible dye with a high enough quantum yield is selected in the group comprising: riboflavin, riboflavin sodium phosphate, chlorophylls, and bixin.
  • the edible and fluorescent gain material is selected in the group comprising: riboflavin, riboflavin sodium phosphate, chlorophylls, bixin, porphine, and porphyrin.
  • the minimum required concentration of fluorescent dye is approximately 50 pM if working above the lasing threshold and approximately 1 pM if working in the spontaneous emission regime. Upper concentrations are limited by the solubility of each dye in a particular solvent. The concentration of the dye in dry form can be as high as 100% if the laser cavity is made entirely from the dye.
  • optical cavity of the microlasers according to the invention can be made from various materials including but not limited to:
  • - edible oil or mixtures thereof for example olive oil, sunflower oil, anise oil, cinnamon oil, mineral oil;
  • - edible wax for example carnauba wax, beeswax, paraffin wax, petrolatum, rice bran wax, spermaceti wax, wax esters;
  • lipids for example methyl esters of fatty acids, montanic acid esters, montan acid esters, lanolin, cholesterol, vaseline, butter;
  • polysaccharides or mixtures thereof for example chitin, starch, shellac, gelatine, agar, starch, pectin, cellulose, and its derivatives,
  • BSA bovine serum albumin
  • poly(vinyl alcohol), polyethylene glycol such as poly(vinyl alcohol), polyethylene glycol
  • the microlasers according to the invention may comprise supplementary materials, which are not strictly required for the functioning of the lasers, but enhance their stability and/or functionality.
  • the microlasers as described above can thus comprise one or more of the following in any possible combination: preservatives, antioxidants, acidity regulators, pH regulators, anti-caking agents, glazing agents, emulsifiers. These additional components may be separate components or they can be incorporated in the selected cavity material.
  • microlasers can be designed in any possible manner known to the skilled person based on the targeted use as barcodes and/or sensors.
  • the types of microcavities and microlasers may be whispering-gallery-mode (WGM) microcavities and microlasers, Fabry-Perot (FP) microcavities/lasers, random lasers, and distributed feedback (DFB) lasers, which will be further described in the detailed description of the invention.
  • WGM whispering-gallery-mode
  • FP Fabry-Perot
  • random lasers random lasers
  • DFB distributed feedback
  • the size (diameter or the longest side) of optical cavities of microlasers, preferably of microlasers for barcoding, is at least 1 .m, preferably from 1 .m to 1 cm, and the number of needed microlasers is at least one, but preferably more to achieve a barcode of sensible length.
  • Microlaser readout depends on how the microlasers are operated - above or below their laser threshold.
  • an appropriate light source preferably a pulsed laser
  • continuous wave laser or LED can be used.
  • a filter or dichroic mirror should be used to filter out the excitation light and only let through fluorescent light.
  • the signal is collected by a lens and/or optical fiber and sent to a detector. If the information is encoded in the spectrum, a spectrometer is used. If the information is encoded into the lasing intensity or threshold, then a simple photodiode may be used.
  • the illumination and detection can be designed as a compact handheld reader, which preferably comprises:
  • microlaser(s) such as a pulsed laser, a continuous wave laser or an LED light
  • - optics such as a filter or dichroic mirror for filtering out the excitation light and allowing passage of the fluorescent light and a lens and/or an optical fiber for signal collection,
  • a detector arranged to detect the emission spectrum in the case of spectral information encoding, or emission intensity in the case of encoding by lasing intensity or threshold,
  • a display for displaying the results of measurements which can comprise information from the barcode (expiration date, manufacturer information, additional data from an external online database) or information on the freshness of the product, - a suitable software for analysing the signal from the detector and converting it to a human- or machine-readable information, comparing it to an internal/external database and displaying it.
  • microlasers There are two preferred applications of edible microlasers according to the invention, i.e., barcoding and sensing, which will be discussed in further detail below.
  • the microlasers according to the invention use materials of different types and properties according to the intended use of the microlasers.
  • the invention as described is primarily intended for labelling food products, pharmaceutical products, as well as other products intended for consumption. Therefore, the invention also relates to a product comprising at least one edible microlaser according to the invention.
  • the microlaser is embedded inside or on the surface of the product or inner/outer surface or inside packaging material, depending on its intended function and properties.
  • the present invention could also be used for tracing, biomarking and anti-counterfeiting of cosmetics, textiles, products used in agriculture, industrial materials and sustainable environmental sensing, including drinkable water tracking and monitoring.
  • the edible microlasers can be used as biodegradable photonic sensors, which could be released in the environment to perform monitoring, for example water or soil, and left there without any harm to the environment.
  • the characteristic spectrum from the sensors would also serve as a barcode, having thousands of unique combinations, and would be used to distinguish different populations of sensors. This could enable the release of the sensors into different streams of water and later collect them in a common reservoir to determine their origin and environmental parameters of their respective sources.
  • Figure 1 Characteristic properties of a microlaser, the emission spectrum, nonlinearity of the output, polarization, and the existence of spatial modes.
  • FIG. 2 Schematics of different types of lasers a) FP, b) WGM, c) random, and d) DFB.
  • a) FP, b) WGM, c) random, and d) DFB For each type of laser, its exemplary lasing spectrum is shown in the bottom panels.
  • FIG. 3 Placement of lasers according to the invention in packaged products (panel a) and in unpackaged products (panel b).
  • Figure 4 Principles of using microlasers for barcoding, a) for single-mode emission, the wavelength of the spectral line defines each barcode, b) for multi-mode emission multiple independent spectral lines can be used to define the barcode, c) for well-defined cavities the modes have, for example, well- defined spacings, which are dependent on the cavity's optical size, d) the size or some similar property can be used as the barcode, e) laser threshold values can also be used to encode the barcode, f) size distribution of a commercial sample of polydispersed polystyrene microbeads, which can be used as random barcodes, and g) size distributions of 13 samples of commercially available monodispersed microspheres, which can be used for barcodes with predefined information. An additional 7 sizes could be fitted in this range, resulting in a total of 20 distinguishable sizes.
  • microlaser property that encodes the information is represented by the microsphere's size, although other microlaser properties, such as the spectrum and threshold (and other microlaser types) can be used as well, a) a single barcode can be composed of more than one microlaser, which greatly increases the number of possible unique barcodes, b) barcoding principle where any number of unique states can be selected to make a single barcode. This is in contrast to (a) where a fixed number of microlasers make up the barcode.
  • the barcode is encoded by the presence (T) or absence ('0') of a certain state, c) microlasers positioned into a line, as a simple example of combining microlaser-based and graphical encoding, and d) the number of unique barcodes can be increased by using two (or more) different properties of the microlaser, for example, different gain media (with different emission spectra) can be used in addition to using several microlasers of different sizes.
  • Figure 6 a) Lasing spectrum of chlorophyll-doped oil droplet immersed in a water solution of Tween20 , b) output of the chlorophyll-oil droplet laser dependence on the input energy (typical threshold behavior), c) schematic diagram of the edible FP cavity laser, and d) lasing spectrum of the chlorophyll-based FP cavity.
  • FIG. 7 Chlorophyll-oil droplets, a, b) bright-field images of the monodisperse droplets of two different samples i.e., 40 and 100 pm approximately, and c, d) lasing spectra of both samples.
  • Figure 8 a) Lasing spectrum of the riboflavin-doped water micro-droplet on a spinach leaf, b) droplets of 14 different sizes (diameters) produced by a droplet chip and demonstration of information encoding of a specific binary code, and c) possibility to increase the information encoding capacity by increasing the number of unique sizes.
  • Figure 9 a) Variation of the refractive index with the change of glucose concentration measured with an edible WGM laser, b) swelling behavior of the chitosan film in different pH mediums, c) lasing spectrum from an edible FP cavitybased pH sensor, d) the changes of the FSR with respect to the change of pH, e) a proof-of-concept demonstration of an edible sensor: the change of the milk’s pH over a period of time at room temperature, f) emission spectrum from the edible temperature sensor before and after crossing the melting temperature (inset figure), and g) schematic diagram of the edible FP cavity-based pH sensor.
  • the microlasers according to the invention may be designed either as WGM, FP, DFB or random lasers comprising at least an edible gain material and an edible cavity material configured to receive the gain material.
  • WGM WGM
  • FP FP
  • DFB random lasers comprising at least an edible gain material and an edible cavity material configured to receive the gain material.
  • Possible gain and cavity materials are listed above, wherein specific exemplary embodiments will be described further below.
  • microlasers according to the invention can be designed in any possible manner known to the skilled person based on the targeted use as barcodes and/or sensors.
  • the possible types of microcavities and microlasers are schematically shown in Figure 2.
  • Panel a) shows a FP microcavity, wherein light bounces between two parallel flat mirrors. Peaks in the spectrum correspond to the wavelengths at which a standing wave forms in the cavity and constructive interference occurs.
  • Panel b) shows a WGM microcavity. Due to the total internal reflection at the resonator's boundary, the light circulates the cavity along its perimeter. Spectral peaks appear at resonant wavelengths, for which the optical path, travelled in a round trip, equals an integer multiple of the wavelength.
  • Random laser configuration is shown in panel c).
  • the prolonged optical path is enabled by strong scattering in the gain medium.
  • the spectral peaks appear due to the light propagating in close loops between the scatterers, resembling conventional optical cavities.
  • Panel d) depicts a DFB laser. Light exhibits Bragg scattering on a periodic variation of the refractive index. The periodicity of the structure determines the emission wavelength.
  • a Fabry-Perot cavity typically comprises two mirrors with a gain medium between them. Light bounces between the two mirrors and forms a standing wave. With every passing the light is amplified. In such a cavity, the lasing spectrum can be tuned by changing the gain medium, the cavity length, the mirror shape and by inserting objects into the cavity.
  • the mirrors are made from edible metals, including silver, gold or aluminium. The mirrors may be made from the same materials or from different materials.
  • a FP-type cavity can also be realized as an (elongated) object made of a high-refractive-index material, with two parallel, flat surfaces acting as mirrors.
  • An example of such a FP cavity is an organic single-crystalline waveguide, where the end crystal facets act as mirrors.
  • Edible dye-doped single crystals from different materials such as sugar, acetic acid, ascorbic acid and its salts, as well as any salt-forming crystals, for example sodium chloride, sodium iodate, sodium citrate, ascorbinates, sodium hydrogen carbonate, sodium fluoride, potassium chloride, potassium nitrite, potassium hydrogen carbonate, magnesium chloride, magnesium hydrogen carbonate calcium chloride, calcium carbonate and calcium hydrogen carbonate, could be used for this purpose.
  • a whispering-gallery-mode microcavity is realized as a micro-object with a circular crosssection: a microsphere, a microdisk, a microtoroid, etc.
  • these micro-objects need a smooth surface and a larger refractive index than the material they are immersed in. In this way, due to total internal reflection at the surface of the microcavity, light is guided along the perimeter.
  • the modes have either transverse electric (TE) or transverse magnetic (TM) polarization. They circulate close to the boundary and have an evanescent tail, extending out of the cavity. Through this tail the WGMs are coupled with the surrounding medium.
  • the positions of the spectral lines depend on three parameters: the microcavity size, the internal and the external refractive index.
  • the other two can be calculated by fitting the spectral position of the peaks to the equations describing the WGMs as known from the article Deep tissue localization and sensing using optical microcavity probes, (2022, Nature Communications, 13, 1 , 1269).
  • the fact that the resonances depend on the size of the microcavity and its refractive index makes it possible to create an abundance of distinct microcavities with distinguishable spectra, which can serve as barcodes.
  • the WGM microcavity When a gain material is present in the WGM microcavity at least partly or even only at its surface, lasing can be achieved. Below as well as above the threshold the WGM spectrum exhibits a series of narrow lines, corresponding to subsequent cavity modes.
  • the gain material In edible microlasers the gain material is preferably realized in the form of edible fluorescent dyes.
  • the WGM microcavities can be made from liquid materials (oils), as droplets dispersed in an immiscible medium, or they can have a form of solid beads or disks made of waxes, gels, etc. The operation principles are the same as for the WGM microlasers made from non-edible materials.
  • Random lasers are another type of lasers.
  • the prolonged optical path through the optical gain material in random lasers results not from reflections at the cavity edges, but rather from scattering.
  • a random laser can be made in several different ways. For example, it can consist of scattering particles in a non-scattering gain material (e.g., fat and protein globules in fluorescently labelled milk). In this case the lasing threshold depends strongly on the density of the scattering particles.
  • Another way is to use a highly scattering material (e.g., meat, powdered material such as flour, sugar, salts) and label it with an edible gain material, preferably a fluorescent dye.
  • a random laser can also be entirely made of a highly scattering material that acts as a gain material at the same time (e.g., edible fluorescent dye powder).
  • the random laser spectrum is narrowed due to the non-resonant feedback.
  • a random laser with a strongly scattering medium where the light is scattered frequently, photons can travel in closed loops. This provides resonant feedback that results in sharp peaks in the spectrum. These peaks could in principle be used as a barcode, but they are dependent on precise location and orientation of the sample with respect to the excitation light and the detector. Therefore, for random lasers other approaches to barcoding are preferred, for example threshold barcoding in combination with graphical barcoding.
  • the cavity is realized as a longitudinal periodic variation of the refractive index, either in the gain medium itself or in the material into which the gain medium is embedded.
  • On the periodic structure light exhibits Bragg reflection and is thus continuously being returned to the cavity.
  • a DFB laser usually operates in single mode.
  • the emission wavelength is determined by the periodicity of the structure and can be used as a barcode.
  • the periodic structure is made in various ways, for example.
  • microlasers use materials of different types and properties according to the intended use of the microlasers.
  • microlasers are used for barcoding, they have to be made from materials that are stable in time, so that the emission properties and therefore the barcode, does not change in time.
  • some code is written into the microlasers.
  • the purpose of the barcodes is labelling of the products for their traceability and authenticity. It can also be used to tag unpackaged goods, where a barcode or other information (expiration date, manufacturer code, etc.) can be placed into the product itself, since there is no packaging.
  • the information can be predetermined, for example a serial number, or it can be random. In the latter case each item of the same product would have a different code, which needs to be read for each individual item at for example the production facility and be stored in a database.
  • the microlasers are used for sensing they should be made from materials responsive to a particular parameter that is to be detected.
  • the microlaser can be made from materials of similar properties as the food in which they may be embedded in, so the microlaser will degrade at the same rate as the food and show if it is still safe to eat the food.
  • This possible embodiment of the microlasers according to the present invention thus comprises any gain material identified in this description in combination with any optical cavity material, which is susceptible to a change in a particular environmental condition (such as temperature, pH, presence of bacteria, etc.) or degradable in a particular time and/or condition, for example at high or low temperatures, at particular pH values, etc.
  • the cavity is made from a pH sensitive material such as chitosan, or from gelatine prepared with water so it can degrade in presence of bacteria (gelatinase).
  • a pH sensitive material such as chitosan
  • gelatine prepared with water so it can degrade in presence of bacteria
  • Various embodiments of this type are possible depending on the aimed function of the microlaser-based sensor.
  • Microlasers are very sensitive to the properties of the surface of the optical cavities, so any surface change such as degradation of the food material will clearly be observed as a change in the lasing spectrum, drastically increased lasing threshold or cease of the lasing. Similarly, cooking or freezing will change the lasing indicating if food is cooked or has been frozen before.
  • the gain materials can be susceptible to change due to particular environmental conditions resulting in a change of lasing spectrum or cease of lasing.
  • the microlasers according to the invention are reliable indicators of food safety.
  • microlasers used as sensors are arranged to detect a change in the product, wherein one microlaser per product is sufficient to determine the status of the product.
  • examples of said product changes are change in temperature, pH, glucose concentration, bacterial growth, etc.
  • the microlaser emission output light
  • more than one microlaser per product may be used in case of detection of more than one parameter change, a larger volume, separate packaging, or similar.
  • microlasers There are several important aspects specific for labelling food or similar products with microlasers according to the invention, the placement of the microlasers in/on the products, the readout and their stability.
  • the edible microlasers according to the invention can be inserted directly on and/or into food products, pharmaceuticals or other non-edible products such as cosmetics, cleaning products, agricultural products, etc.
  • the microlasers are provided on the packaging, either on the outer surface of the packaging or more preferably on the inner surface of the packaging.
  • Figure 3 shows possible placements of lasers in packaged products (panel a) and in unpackaged products (panel b). If the packaging is transparent the lasers can be placed also on the internal surface of the packaging or inside the food product. If the food product is transparent the lasers can be placed also inside, otherwise on the surface.
  • the lasers can also be free-floating in a liquid or gel or can be dispersed in a solid or granular material.
  • the lasers can be made of different densities so that in a liquid they can either float on the surface or sink to the bottom or being neutrally buoyant, based on the required application. For example, for a larger bulk liquid that will be transferred from larger containers into smaller containers, the lasers are preferably neutrally buoyant and therefore uniformly dispersed, so that they will be transferred to all smaller containers. On the opposite, for a smaller transparent container, it is better that the lasers either float to the surface or sink to the bottom, where they will be more concentrated and easier to be read. Examples are droplets of sunflower, cinnamon oil or a mixture of sunflower and cinnamon oils, which will be floating, sinking, or be neutrally buoyant, respectively. There are various possible ways for attaching lasers onto solid food or on the package.
  • the lasers can be directly attached to food, on the package or mixed with solid food.
  • the other option is to embed the lasers into an edible micro container, such as a transparent layer, sphere or other shaped form, from materials such as silk, chitosan, agar, cellulose, etc. Such a layer can be used as a patch, which can be then attached to the target.
  • the embedding container has multiple functions. Firstly, it provides mechanical support so that the lasers are mechanically more stable and can be easier to attach to any surface.
  • the container can also float in a liquid.
  • the container can also be made from a responsive material, so that it acts as a sensor.
  • WGM lasers embedded in a chitosan layer can be used as a pH sensor.
  • the container shields the lasers from the environment, which is especially important for barcodes.
  • the container can also enable the use of WGM lasers in high refractive index materials, such as oils and honey, which would be otherwise not possible since WGM lasers require the laser to have a significantly larger refractive index than the surroundings.
  • an external light is used to illuminate them and the collected light is analysed.
  • the microlaser is present on the inner surface of the packaging, the latter has to be transparent to allow reading of the signal.
  • a light source is used for the excitation of the microlasers, such as a pulsed laser, a continuous wave laser or an LED light.
  • the excitation light may be focused on the sample by a lens.
  • the laser light is collected through the same or different path.
  • a filter or a dichroic mirror is used for filtering out the excitation light and allowing passage of the fluorescent light.
  • the light is collected by appropriate optics like a lens or an optical fiber and sent to a detector.
  • the detector is arranged to detect the emitted light, preferably emission spectrum in the case of spectral information encoding, or emission intensity in the case of encoding by lasing intensity or threshold.
  • the lasers can be read all at once or sequentially. For the lasers to be read at the same time, they need to be located close to each other, for example, as described above by embedding them in a small patch. The excitation and detection spot should be large enough to cover the whole area where the lasers are located. If the lasers have different nonoverlapping spectra or otherwise a different emission, the individual contributions can be extracted from only a single measurement. If the lasers are distributed throughout the product, such as for example free-floating in a fluid, then scanning is required to detect them.
  • Scanning can be either 1 D or 2D, and can be implemented in the same way as commercially available barcode readers which use laser scanning, for example with a galvo or rotating mirror.
  • the fluid mixing can stir the lasers so they pass into the excitation beam.
  • Such a readout method could be for example implemented on a food filling line where a fluid or granular material is entering the packaging and the lasers could be read in that time.
  • a barcode is written as the presence or lack of lasers of different emissions, to encode ones and zeros for each bit of information, at least one laser of each bit is required to be detected to reconstruct the barcode. Error correction methods developed for regular barcodes can be implemented here. Scanning can also be used if only one laser is present, so there is no need to precisely point the excitation/detection spot onto the laser.
  • microlasers Another important feature of barcoding is the stability of the microlasers, particularly when present in food products.
  • WGM lasers based on oil droplets function in waterbased food. In case they were used in oil, the oil droplets would mix with the oil and the gain material would not be present inside the optical cavity anymore. Hence, no lasing would be achieved.
  • These adaptations and selections of proper microlasers for a particular product are easily determined by the skilled person based on the properties of microlasers and products, particularly based on solubility and/or degradability.
  • Table 1 Examples of combinations of dye and cavity materials, in the form of WGM and FP types of lasers, which operate successfully above the lasing threshold.
  • Pump/Lasing stands for pump and lasing emission wavelengths, respectively.
  • QY stands for the fluorescent quantum yield of the gain material.
  • the positions of the WGM spectral lines are sensitive to the size, external and internal refractive index.
  • the other two i.e., size of the laser and external refractive index can be calculated by fitting the spectral position of the peaks.
  • Any WGM laser droplet or solid bead
  • the most important substance, which changes the refractive index is sugar (sucrose, glucose, fructose etc.).
  • chlorophyll-doped oil droplets were used to demonstrate the concentration of glucose in water.
  • the edible pH sensor made completely out of edible materials was demonstrated.
  • the sensor was based on a FP cavity laser, which is a linear cavity consisting of two mirrors with a gain medium between them (Fig. 6c).
  • the most reflective edible materials are silver, gold and aluminum in the form of extremely thin leaves. They are usually used as decorations for some foods and drinks.
  • An edible laser was developed by using two edible mirrors, designed by attaching the silver leaves on agar layers used for structural support. The mirrors were separated by an additional agar layer positioned at the mirror edges to form a cavity that was filled with a 2 mM chlorophyll solution in oil or with a 5 mM riboflavin sodium phosphate in water.
  • One mirror was intentionally made shorter to enable the excitation light to enter the cavity and the resulting laser light to exit the cavity.
  • sharp, equally spaced peaks appeared in the emission spectrum, indicative of lasing within the FP cavity (Fig. 6d).
  • a chitosan film was additionally introduced into the laser cavity as shown in Fig. 9g.
  • the modified FP-cavity (edible sensor) was additionally sealed by using an edible sealant, to increase its mechanical stability.
  • the edible sealant was prepared by dissolving 0.5 g of agar and 0.75 g of glycerol in 20 ml of water, and then continuously stirring the solution on a hot plate at 80°C.
  • the pH sensitive behavior of the chitosan is widely reported - the swelling of a chitosan film increases with the decrease of the pH [https://doi.Org/10.1016/j.addr.2009.07.019],
  • the chitosan film was prepared by following a similar procedure as explained in this reference [https://doi.Org/10.1016/j.lwt.2010.01.021],
  • the 0.2 g of chitosan (low molecular weight, Sigma Aldrich) was dissolved in 20 ml of 2% acetic acid.
  • the well-mixed solution was poured into the cup cake mold. Then, it was placed in the oven overnight at 50°C for the evaporation of acetic acid.
  • the film was detached and cut into pieces of required sizes and washed with the ethanol solution.
  • the final thickness of the 1% chitosan film was 0.5 mm.
  • the final thickness of the film was around 0.5 mm.
  • the chitosan film was immersed in the solutions with different pH i.e., 5, 6.7, and 7.2. Its weight was measured at different time points over the period of 1 hour as shown in Fig. 9b. Then, the edible FP cavity containing the chitosan film was pumped with a blue pulsed laser and its spectrum was collected as shown in Fig. 9c and further analyzed. The FSR value was calculated by fitting the peak positions of the emission spectrum.
  • Example 3 Edible sensors for sensing bacteria
  • FP-cavity based bacteria sensor was assembled in a similar way as in Figure 6c, except the agar was replaced by gelatine (120 g/L). Additionally, the nutrients (casein at 5 g/L and yeast extract at 3 g/L) were added to the gelatine matrix. An FP-cavity was assembled by using these gelatine layers, edible silver leaf, and chlorophyll-vegetable oil solution (see Figure 6c).
  • the FP-cavity-based sensor was designed in a similar way as the Example 3.
  • the cavity was filled with the chlorophyll oil solution.
  • the temperature up to 30°C the gelatine began to melt and the shape of the cavity was deformed. Therefore, after heating, the lasing was no longer observed. Once the cavity shape is degraded, it cannot be reversed.
  • the chlorophyll-butter microbeads were also used as an edible temperature sensor.
  • butter to make solid spherical WGM cavities.
  • the chlorophyll was entrapped within or on the surface of the cavity as a gain medium.
  • the chlorophyll-butter bead exhibited WGM lasing upon pumping with the blue pulsed laser.
  • the butter began to melt and the shape of the cavity was degraded. After that, the lasing was no longer observed. Once the cavity shape is degraded, it cannot be reversed.
  • these sensor can be a valuable tool to monitor the food storage condition. It can be placed inside the food packaging or in contact with food itself because it is entirely made of edible materials.
  • the transition temperature can be varied by using different materials or mixtures of materials with different melting points.
  • Example 5 Edible barcodes based on monodispersed oil droplets
  • the solution of chlorophyll in oil was prepared in the same way as in Example 1.
  • the hydrophilized droplet generator chip- Fluidic 440 (Chip-Shop) was used. This chip was composed of four different channels with nozzle sizes from 50-80 pm. Each channel contained two inlets - one for the flow of dispersed phase and the other for the continuous phase - and one outlet for the collection of droplets.
  • the Elveflow OB1 pressure controller was used. To reduce the flow of air into the channels, a low pressure (10-20 millibar) was applied to both reservoirs (chlorophyll solution in oil and water comprising 1 % Tween20 surfactant) until the solution started dripping out from both tubes. Then, both tubes were connected to their corresponding inlets of the chip. Highly monodisperse droplets were produced with diameters in the range of 38-95 pm with less than 1 % CV by varying the pressure and using different channels.
  • Figure 7 shows the prepared oil monodisperse droplets with diameter of approximately 40 pm (Fig. 7a) and approximately 100 pm (Fig. 7b) and corresponding lasing spectra of a chlorophylloil droplet from each set of droplets (Figs. 7c, d).
  • Figure 8a shows the lasing spectrum of the riboflavin micro-droplet on a spinach leaf.
  • Fig 8b shows a concept of barcoding using prepared oil droplets of 14 different sizes produced by a droplet chip and demonstration of information encoding a date.
  • Fig. 8c shows the possibility to increase the information encoding capacity by increasing the number of unique sizes.
  • Example 6 Barcoding with monodispersed silica spheres
  • the stirring time can vary depending on the desired size and dispersity of the silica beads.
  • a small amount of ammonium hydroxide was added to the mixture to initiate the hydrolysis and condensation reaction of TEOS.
  • the concentration of ammonium hydroxide can be adjusted based on the desired pH of the reaction mixture.
  • v. Continue stirring and aging: Allow the mixture was continued to be stirred and aged for a specific period of time depending on the desired size and morphology of the silica beads.
  • centrifuging was done to separate the silica beads from the solution and the beads were washed several times with ethanol to remove any unreacted precursors or impurities and dried under vacuum or at a low temperature.
  • the specific concentrations, timings, and conditions may vary depending on the desired properties of the silica microbeads and the specific fluorescent dye being used.
  • the sizes appropriate for barcoding are in the range from 5 urn to 150 urn.
  • the coefficient of variation (CV) of the size of such beads is usually less than 10%. Due to such a narrow CV, a large number of sizes can be distinguished without a large overleap, for example sizes for barcoding could be 50, 55, 60, 65 .m, etc.
  • first nonfluorescent beads can be produced and then later a thin coating (1 - 1000 nm) containing the dye can be coated using known methods (Nanoscale, 2023,15, 8611-8618, htps://doi.org/10.1039/D2NR06965B).
  • the silica beads can be used also for sensing. They can be embedded or coated with a material that changes the optical properties depending on some environmental parameter. For example, pH ca be measured by silica beads embedded in (or coated by) chitosan, which is pH responsive.
  • Example 7 Solid wax lasers
  • the paraffin was dissolved in dichloromethane (DCM) at a concentration of 4 wt. %. Then, the porphine was added to the same solution at a concentration of 2 mM.
  • the water phase was prepared by adding 1 wt. % of polyvinyl alcohol (PVA) in water as a surfactant to stabilize the dispersion. Then, the DCM solution (including paraffin) was added at 1 % to the water phase (1 % PVA solution) and shaken to produce polydisperse droplets. Monodispersed droplets could be generated by a microfluidic device as described in Example 5. This dispersed solution was placed inside the ultrasonic bath for a few minutes.
  • the dispersion was left for 20 hours so the DCM evaporated from the solution/droplets, resulting in the solid microbeads.
  • the resultant microbeads were in the size range of 150-200 pm.
  • a microbead was illuminated by a blue CW laser to excite the fluorescent dye (porphine).
  • the emitted fluorescent light was sent to the spectrometer revealing the spectral peaks corresponding to the WGMs. From the WGMs, we can measure the size of the bead in nanometer precision as the modes are very sensitive to the size of the bead. Therefore, we can also utilize these microbeads for the barcoding applications and sensing in the same way as for example oil droplets or silica microbeads.

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Abstract

La présente invention appartient au domaine des lasers, c'est-à-dire des dispositifs utilisant une émission stimulée de rayonnement électromagnétique dans la gamme des ondes infrarouges, visibles ou ultraviolets, plus précisément dans le domaine des microlasers pour la détection et/ou le codage à barres. L'invention concerne des microlasers comestibles, c'est-à-dire des combinaisons de composés qui peuvent émettre de la lumière lors d'une excitation tout en étant sans danger pour la consommation. En outre, l'invention concerne également des procédés de préparation desdits microlasers comestibles et leurs utilisations.
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