WO2025032582A1

WO2025032582A1 - Composite comprising an elastic polymeric substrate and metal nanostructures and method of making same

Info

Publication number: WO2025032582A1
Application number: PCT/IL2024/050786
Authority: WO
Inventors: Aleksei SOLOMONOV; Alexander Tesler; Ulyana Shimanovich
Original assignee: Yeda Research and Development Co Ltd
Current assignee: Yeda Research and Development Co Ltd
Priority date: 2023-08-06
Filing date: 2024-08-06
Publication date: 2025-02-13
Anticipated expiration: 2026-02-06

Abstract

A composite, an article comprising the composite, and a method of making the composite are disclosed. The composite may include an elastic polymeric substrate and metal nanostructures attached to a surface of the elastic polymeric substrate; wherein: each of said metal nanostructures comprises a first portion embedded within the elastic polymeric substrate and a second portion exposed to an ambient; said metal nanostructures have lateral dimension between 1 to 1000 nm, said metal nanostructures have a thickness of between 5 to 200 nm.

Description

COMPOSITE COMPRISING AN ELASTIC POLYMERIC SUBSTRATE AND

METAL NANOSTRUCTURES AND METHOD OF MAKING SAME

CROSS-REFERENCE TO RELATED APPLICATIONS

[001] This application claims the benefit of priority of Israeli Patent Application No. 304992, titled “COMPOSITE COMPRISING AN ELASTIC POLYMERIC SUBSTRATE AND METAL NANOSTRUCTURES AND METHOD OF MAKING SAME”, filed August 6, 2023. The contents of all these applications are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

[002] The present invention generally relates to chemiresistor sensors. More particularly, the present invention relates to nanoparticles for chemiresistor sensors.

BACKGROUND OF THE INVENTION

[003] When dimensions of noble metals including gold (Au), silver (Ag), copper (Cu), and others reduce to a less then or comparable wavelength of the incident light, they exhibit distinct optical characteristics derived from the excitation of localized surface plasmon (LSP) polaritons in or close to, the visible spectral range. LSPs are collective charge density oscillations confined within the final volume of a metallic nanoparticle (NP). When the frequency of incident light is equal to the plasma frequency of the free electrons, resonance occurs resulting in strong light scattering, the appearance of intense LSP absorption bands, and the enhancement of the local electromagnetic field near the metal surface.

[004] Furthermore, the wavelength and extinction intensity of the localized surface plasmon resonance (LSPR) band are sensitive to variations in the dielectric properties of the surrounding environment. Such changes near the NP surface can be induced, for instance, by binding molecules to the metal structures, displacing air by solvent, or changes in the oxidation state of the substrate. The latter forms the basis for applying LSPR systems as optical sensors, and transducers for chemical and biological sensing.

[005] Tuning the wavelength of the LSPR band is vital for applications such as photothermal therapy, plasmon-enhanced luminescence, optical imaging, labeling of biological systems, photo and photoelectrocatalysis. The LSP band position can be tuned through (i) the nanostructure shape such as rod-like nanostructures that display transverse and longitudinal SP bands, (ii) the nanoparticle size, and (iii) their nature, i.e., single or multicomponent metal nanoparticles (NPs) (e.g., Au, Ag, and/or Cu).

[006] There are various ways to synthesize noble metal nanostructures, however, as optical transducers, they can be used either as freestanding NPs dispersed in solution or deposited as a thin metal film on solid transparent substrates such as glass or quartz.

[007] Various applications require the incorporation of plasmonic NPs not just onto/into solid inorganic materials but organic polymers (PMMA, PDMS), biopolymers (proteins), and polysaccharides, known as plasmonic nanocomposites. In recent years, controlled assembly of NPs directly on/in polymeric substrates has been proposed based on the selfassembly of NPs from solution. Growing Au NPs on a flexible substrate enables simple mechanical control of the plasmonic coupling via its stretching/shrinkage. Plasmon-coupled Au NPs incorporated in flexible stretched shape-memory polymers were demonstrated for mechanical and thermal sensing, and opto-mechanic devices. Flexible plasmonic materials were prepared by NPs deposition on solid state substrates followed by polymer coating and peeling out, layer-by-layer assembly, particularly of polyurethane, by Au NPs led to stretchable conductive material fabrication. Polymeric “three-in-one” platform for rapid sampling, photo-controlled release, and surface-enhanced Raman scattering (SERS) detection of pathogens was demonstrated. Also, stencil lithography was used to create plasmonic nano-antennae on a flexible substrate.

[008] Therefore, there is a need for a method of forming the plasmonic nanocomposites, that provide additional functionality such as substrate flexibility. There is also a need for a unique plasmonic nanocomposites having a new structure and applications.

SUMMARY OF THE INVENTION

[009] Some aspects of the invention are directed to a composite comprising an elastic polymeric substrate and metal nanostructures attached to a surface of the elastic polymeric substrate; wherein: each of said metal nanostructures comprises a first portion embedded within the elastic polymeric substrate and a second portion exposed to an ambient; said metal nanostructures have lateral dimension between 1 to 1000 nm, said metal nanostructures have a thickness of between 5 to 200 nm. In some embodiments, the metal nanostructures consist essentially of a metal in an elemental state and are substantially devoid of a metal salt, a metal complex, or both.

[0010] In some embodiments, a relative volume of said first portion is at least 30% of an average volume of said metal nanostructures, and wherein the relative volume is determined based on a shift of Localized Surface Plasmon Resonance (LSPR) band wavelength relative to said metal nanostructures on a glass. In some embodiments, a surface coverage of the metal nanostructures is between 10 and 50%.

[0011] In some embodiments, said metal nanostructures comprises, at least one of a first type of metal nanostructures and at least one second type of metal nanostructures and wherein the first and second types differ at least in an average lateral dimension. In some embodiments, the average lateral dimension of said first type of metal nanostructures is between 1 to 50 nm and the average lateral dimension of said second type of metal nanostructures is between 60 to 1000 nm. In some embodiments, said first type of metal nanostructures comprises essentially from circular shape nanostructures and said second type of metal nanostructures comprises essentially from truncated ellipsoid shaped nanostructures. In some embodiments, an average thickness of said first type group of metal nanostructures is between 5 to 60 nm and the average thickness said second type of metal nanostructures is between 65 to 200 nm.

[0012] In some embodiments, said composite is characterized by light absorption at a wavelength between 190 to 1100 nm. In some embodiments, said composite is substantially devoid of a metal salt, a metal complex, or both.

[0013] In some embodiments, said metal is selected form Au, Ag, Cu, Ru, Rh, Pd, Re, Os, Ir and Pt, including any combination and any alloy thereof.

[0014] In some embodiments, the elastic polymeric substrate comprises at least one of: a film, and an adhesive layer in contact with a polymeric layer; and wherein the metal nanostructures are embedded within at least one of: the film and the adhesive layer.

[0015] Some additional aspects of the invention are directed to a method of making a composite according to any one of the embodiments disclosed herein, the method may include:

(a) forming an ultrafine metal layer on a donor substrate; (b) annealing the ultrafine metal layer at an elevated temperature, thereby receiving a donor substrate covered by metal nanostructures, the ultrafine metal layer has an average thickness between 1 and 20 nm;

(c) applying an elastic polymer substrate on top of the annealed nanostructures; and

(d) embedding the nanostructures in the elastic polymer substrate, thereby forming the composite.

[0016] In some embodiments, the donor substrate is a rigid substrate.

[0017] In some embodiments, the method may further include applying a selective reduction of the surface energy of the annealed substrate following step (b). In some embodiments, the method may further include: selecting the type of nanostructures; and determining the thickness of the ultrafine metal layer based on the selected type.

[0018] In some embodiments, said composite is characterized by light absorption at a wavelength between 190 to 1100 nm. In some embodiments, said composite is substantially devoid of a metal salt, a metal complex, or both.

[0019] In some embodiments, said metal is selected form Au, Ag, Cu, Ru, Rh, Pd, Re, Os, Ir and Pt, including any combination and any alloy thereof.

[0020] Some additional aspects of the invention may be directed to an article comprising a composite according to any one of the embodiments disclosed herein, the article may be in a form of an antimicrobial patch, photothermal patch, optical sensor, and transducer. In some embodiments, the article may be in a form of the antimicrobial patch, wherein at least 80% of the metal nanostructures characterized by an average lateral dimension of between 1 to 50 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: [0022] Figs. 1A, IB and 1C are an illustration, image and a High-Resolution Scanning Electron Microscope (HRSEM) image of a composite according to some embodiments of the invention;

[0023] Fig. ID shows images of a composite according to some embodiments of the invention;

[0024] Figs. 2A and 2B are an illustration and flowchart of a method of making a composite according to some embodiments of the invention;

[0025] Figs. 2C and 2D are illustrations and chemical representation of the silanization stage according to some embodiments of the invention;

[0026] Fig. 3A shows HRSEM images of metal nanostructures attached to an elastic polymeric substrate according to some embodiments of the invention;

[0027] Fig. 3B shows graphs of distribution statistics of metal nanostructures attached to an elastic polymeric substrate at different nominal thicknesses according to some embodiments of the invention;

[0028] Fig. 3C shows graphs of nanostructures diameter, density, aspect ratio, area fraction as a function of nominal thickness according to some embodiments of the invention;

[0029] Fig. 4 shows images and graphs showing the optical properties of a composite according to somebodies of the invention;

[0030] Fig. 5 shows illustrations and graphs showing the influence of the nanostructures embedding in the surface according to some embodiments of the invention;

[0031] Fig. 6 shows images and graph of sensing characteristics of a composite measured by Raman spectroscopy according to somebodies of the invention;

[0032] Fig. 7 shows images of a composite comprising a medical adhesive tape according to some embodiments of the invention; and

[0033] Fig. 8 shows an image and HRSEM image of a composite comprising a carbon tape according to some embodiments of the invention.

[0034] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0035] One skilled in the art will realize the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting of the invention described herein. Scope of the invention is thus indicated by the appended claims, rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Opening statement

[0036] Some aspects of the invention may be directed to the incorporation of plasmonic NPs onto/into organic polymers (PMMA, PDMS), biopolymers (proteins), liquid Kapton (polyimide), and polysaccharides to form plasmonic nanocomposites, that may provide additional functionality such as substrate flexibility. Fabrication of metal nanostructures in a polymer matrix is challenging since nanostructures usually aggregate alternating their SPR characteristics.

[0037] A composite according to embodiments of the invention may include an elastic polymeric substrate and metal nanostructures attached to a surface of the elastic polymeric substrate.

[0038] In some embodiments, the nanostructures are transferred to the elastic polymeric substrate (e.g., an adhesive tape, a protein tape, etc.) via a soft-printing mechanism. The nanopattems are first formed on a donor substrate and after application of elastic polymeric substrate are automatically transferred to the deposited tape material. One of the advantages of such flexible soft-printed nanostructure-comprised substrates, particularly for sensing applications, is that they can catch target analytes directly from a non-flat surface. On the other hand, as part of an integrated circuit, the nanostructures-based flexible substrates may be utilized in wearable electronics, and flexible optical materials, to name but a few. A soft- printing approach is attractive since it preserves the pattern of nanostructures originally formed on a solid-state substrate.

The composite structure

[0039] Reference is now made to Figs. 1A, IB and 1C which are an illustration, image and HRSEM image of a composite according to some embodiments of the invention. A composite 100 may include an elastic polymeric substrate 10 and metal nanostructures 20 and/or 30 attached to a surface 15 of elastic polymeric substrate 10.

[0040] In some embodiments, elastic polymeric substrate 10 may include any suitable elastic polymer. As used herein, an elastic polymer is a polymer that when shaped in the form of a tape or a film having maximum thickness of 5 mm (e.g., less than 2 mm, 1 mm, 0.5 mm, 0.1 mm and any value in between) can easily be bent, twisted, folded, etc., without applying a force larger than 10 Kgs (e.g., by any human without any external aid). In some embodiment, polymeric substrate 10 may be at least partially optically transparent. In some embodiments, elastic polymeric substrate 10 may include a film, such as, a protein film, a silk film, a Kapton tape and the like. In some embodiments, elastic polymeric substrate 10 may include an adhesive layer in contact with a polymeric layer. In some embodiment, polymeric substrate 10 may be an adhesive tape, e.g., a medical grade adhesive tape. Some nonlimiting examples of suitable elastic polymers may include organic polymers (Poly(methyl methacrylate) (PMMA), Polydimethylsiloxane (PDMS), etc.,), biopolymers (proteins), polysaccharides, and the like. Some nonlimiting examples for elastic polymeric substrate 10 may include transparent adhesive (e.g., Scotch®), medical adhesives, carbon and metallic Mylar (reflective and conductive) tapes and the like.

[0041] In some embodiments, each of metal nanostructures 20 and/or 30 may include a first portion 21 or 31 embedded within elastic polymeric substrate 10, and a second portion 23 or 33 exposed to an ambient. In some embodiments, a relative volume of first portions 23 and/or 33 may be at least about 30% of an average volume of metal nanostructures 20 or 30. In some embodiments, the relative volume is determined based on a shift of Localized Surface Plasmon Resonance (LSPR) band wavelength relative to said metal nanostructures on a glass. For example, the relative portion may be between 30% to 80%, between 30% to 50%, between 40% to 60%, between 35 % to 55%, between 35% to 70% of the average volume of metal nanostructures 20 and/or 30, and any value or range in between. Nonlimiting examples for measuring the shift of the LSPR band is given and discussed with respect to Fig. 4 and the calculation of percentage of embedding is given with respect to Fig. 5.

[0042] In some embodiments, elastic polymeric substrate 10 may include at least one of, a film, and an adhesive layer in contact with a polymeric layer; and wherein the metal nanostructures 20 and 30 may be embedded within the film or the adhesive layer, as disclosed and discussed herein below.

[0043] In some embodiments, the surface coverage of metal nanostructures 20 and/or 30 may be between 10 and 50% from the total surface of substrate 10. For example, the surface coverage of metal nanostructures 20 and/or 30 may be between 10 to 35%, between 15 to 35%, between 15 to 40%, between 20 to 40 %, between 20 to 50%, and any value or range in between.

[0044] In some embodiments, metal nanostructures 20 and/or 30 have a lateral dimension between 1 to 1000 nm. In some embodiments, the lateral dimension is between 1 to 5 nm, between 1 to 10 nm, between 1 to 50 nm, between 1 to 100 nm, between 10 to 50 nm, between 10 to 200 nm, between 100 to 500 nm, between 500 to 1000 nm and any value or range in between.

[0045] In some embodiments, metal nanostructures 20 and/or 30 have a thickness of between 5 to 200 nm. In some embodiments, the thickness is between 10 to 200 nm, 30 to 200 nm, 30 to 150 nm, 50 to 200 nm, 10 to 100 nm and any value of range in between.

[0046] In some embodiments, metal nanostructures 20 and/or 30 have an outer portion 23 or 33 exposed to an ambient, as illustrated. In some embodiments, metal nanostructures 20 and/or 30 consist essentially of a metal in an elemental state and are substantially devoid of a metal salt, a metal complex, or both. The former is due to the unique fabrication method which does not require the use of any organic or inorganic solvent. Metal nanostructures 20 and/or 30 are result of a direct deposition/evaporation of metallic layers on substrate as discussed herein below with respect to Figs. 2A and 2B.

In some embodiments, metal nanostructures 20 and/or 30 comprising a metal is selected form Au, Ag, Ru, Cu, Rh, Pd, Re, Os, Ir and Pt, including any combination and any alloy thereof. Therefore, composite 100 is substantially devoid of a metal salt, a metal complex, or both.

[0047] In some embodiments, metal nanostructures comprise at least a first group/type of metal nanostructures 20 and at least one second group/type of metal nanostructures 30 differ at least in an average lateral dimension. In some embodiments, the average lateral dimension of the first group/type of metal nanostructures 20 is between 1 to 50 nm and the average lateral dimension of the second group/type of metal nanostructures 30 is between 5 to 1000 nm. In some embodiments, the average lateral dimension of the first group/type of metal nanostructures 20 is between 1 to 50 nm and the average lateral dimension of the second group/type of metal nanostructures 30 is between 10 to 100 nm. In some embodiments, the average lateral dimension of the first group/type of metal nanostructures 20 is between 10 to 100 nm and the average lateral dimension of the second group/type of metal nanostructures 30 is between 50 to 200 nm. In some embodiments, the average lateral dimension of the first group/type of metal nanostructures 20 is between 1 to 50 nm and the average lateral dimension of the second group/type of metal nanostructures 30 is between 100 to 300 nm. In some embodiments, the average lateral dimension of the first group/type of metal nanostructures 20 is between 20 to 200 nm and the average lateral dimension of the second group/type of metal nanostructures 300 is between 100 to 500 nm. In some embodiments, the average lateral dimension of the first group/type of metal nanostructures 20 is between 10 to 500 nm and the average lateral dimension of the second group/type of metal nanostructures 300 is between 300 to 800 nm. In some embodiments, the average lateral dimension of the first group/type of metal nanostructures 20 is between 10 to 500 nm and the average lateral dimension of the second group/type of metal nanostructures 30 is between 500 to 1000 nm. Some nonlimiting examples for measurements of the metal nanostructures are given with respect to Figs. 3 A and 3B.

[0048] In some embodiments, the first group/type of metal nanostructures 20 comprises essentially from circular- shape nanostructures, and the second group/type of metal nanostructures 30 comprises essentially from truncated ellipsoid shaped nanostructures, as shown in the HRSEM images in Fig. 1C and 3A and the graphs in Fig. 3C. As used herein, circular- shape nanostructures include any nanostructures with fully circular or at least partially circular (e.g., semi-circular) shape.

[0049] In some embodiments, an average thickness of the first group of metal nanostructures 20 is between 30 to 55 nm and the average thickness said second group of metal nanostructures is between 70 to 200 nm. Some nonlimiting examples for measurements of the thickness are discussed with respect to Fig. 3C. In some embodiments, the thickness is defined by the stochastic process and it is a function of the nominal mass thickness and surface coverage.

[0050] In some embodiments, composite 100 is characterized by light absorption at a wavelength between 190 nm to 1100 nm. For example, composite 100 is characterized by light absorption at a wavelength between 700 nm to 1100 nm (the IR range), between 400 nm to 700 nm (the visible light range), between 190 to 400 nm (the UV range) and any value in between.

[0051] Reference is now made to Fig. ID which includes images of a composite according to some embodiments of the invention. A composite 100 in the form of a tape can be twisted (Fig. ID (a)), bended (Fig. ID (b)) and apply of a user’s skin (Fig. ID (c)). When applied to the user’s skin it may warp an organ (e.g., finger) (Fig. ID (d)) and may be piled of the organ leaving a finger print as shown in Figs. ID (e) and (f). Other nonlimiting examples for composite 100 are given with respect to Figs. 7 and 8.

Method of making the composite

[0052] Reference is now made to Figs. 2A and 2B which are an illustration and flowchart of a method of making a composite according to some embodiments of the invention.

[0053] Step 210 may include forming an ultrafine metal layer on a donor substrate. In a nonlimiting example, ultrathin Au films were prepared by electron beam (e-beam) evaporation of Au on borosilicate glass coverslips with a surface roughness of ca. 1 nm. The nominal (mass) Au thicknesses varied from 1 to 15 nm with a step size of 2 nm. In some embodiments, the donor substrate may include glass, quartz, sapphire, and the like. In some embodiments, the donor substrate may be a rigid substrate, as opposed to elastic substrate 15. As used herein an ultrafine metal layer is a metallic layer having a thickness of at most 30 nm, at most 20 nm, at most 15 nm and any value in between. The metal layer thickness may be determined to form the discreate metal nanostructures defined herein (as opposed to forming semi-continuous structures).

[0054] Step 220 may include annealing the ultrafine metal layer at an elevated temperature, thereby receiving a donor substrate covered by metal nanostructures 20 and 30. In a nonlimiting example, the as deposited ultrathin Au films were exposed to high temperature annealing of 450 °C in air. The annealing triggers a coalescence process which results in forming well defined round shaped nanostructures (e.g., nanostructures 20) and/or well faceted truncated ellipsoid shaped nanostructures (e.g., nanostructures 30). In some embodiments, if the elevated temperature was close to the Tg of the substrate it may result in partial embedding of nanostructures 20 and/or nanostructures 30 in substrate 10, as discussed and shown with respect to Fig. 5. In other to avoid this problem a gap of at least 50 °C may be kept between the annealing temperature and the Tg of the substrate. In some embodiments, very short annealing (e.g., of less than 1 min.) may be performed near Tg (e.g., less than 50 °C).

[0055] Optional Step 230 may include applying a selective reduction of the surface energy of the annealed substrate for example, by conducting silanization,

to increase the substrate’s hydrophobicity. For example, the glass with the annealed Au nanostructures were silanized, as shown and discussed with respect to Figs. 2C and 2D. In another example, phosphonic ester-based chemistry may be used to reduce surface energy of oxide substrates, carboxylic acid-based chemistry can be also used to reduce surface energy of the oxide surfaces. As exemplified herein, PDMS was bound to oxide surfaces by UV-grafting. The same can be done by chemical and thermal grafting.

[0056] Step 240 may include applying an elastic polymer substrate on top of the annealed nanostructures. In a nonlimiting example, an adhesive tape or a film (e.g., substrate 15) may be applied on top of the nanostructures 20 and 30 as shown in Fig. 2A.

[0057] The elastic polymeric substrate may include at least one of: a protein film, and an adhesive layer in contact with a polymeric layer; and wherein the metal nanostructures are embedded within at least one of: the protein films and the adhesive layer In some embodiments, the film may include at least one of, a protein film, a silk film, a Kapton tape, and the like.

[0058] Step 250 may include embedding the nanostructures in the elastic polymer substrate. For example, peeling the adhesive tape from the donor substrate causes the transfer of the nanostructures 20 and 30 onto the adhesive tape (e.g., substrate 15).

[0059] In some embodiments, the method may further include: selecting the type of nanostructures; and determining the thickness of the ultrafine metal layer based on the selected type. For example, if the required type is the first type (e.g., nanostructures 20) the thickness of the ultrafine metal layer may be below 7 nm; and if the required type of the second type (e.g., nanostructures 30) the thickness of the ultrafine metal layer may be above 9 nm and up to 20 nm. In some embodiments, above 20 nm the annealed layer will not form discrete nanostructures, but rather a semi-continuous layer.

[0060] Reference is now made to Figs. 2C and 2D which are illustrations and chemical representation of the silanization step 230 according to some embodiments of the invention. The annealed substrates may be introduced into a chamber under vacuum or N2 atmosphere. Silane molecules may be introduced into the chamber and may bond with the substrate (e.g., glass), as shown in Fig. 2D. Hydrolysis processes may form the required bonds between the silane molecules and the substrate. In some embodiments, if different donor substrate is used, other molecules different form silane molecules may be used to reduce the surface energy of the donor substrate.

[0061] Some aspects of the invention may be directed to an article comprising the composite (e.g., composite 100) according to any embodiment of the invention, Some nonlimiting examples may include an antimicrobial patch, photothermal patch, optical sensor, transducer, and the like. In some embodiments, the article may be in a form of the antimicrobial patch, and at least 80% of the metal nanostructures are the first type of metal nanostructures 20. In some embodiments, smaller nanostructures having average lateral dimension between 1 to 50 nm, may have an antimicrobial effect on tissues.

Experimental results and characterization

[0062] A nonlimiting example of a composite made by depositing Au nanostructures on glass following by the embedding to the nanostructures on an adhesive tape was studied. The composite was made using the method disclosed herein above with respect to Figs. 2A to 2D.

[0063] Reference is now made to Fig. 3A which includes HRSEM images of metal nanostructures attached to an elastic polymeric substrate according to some embodiments of the invention. The morphology of Au nanostructures was characterized by field emission high resolution scanning electron microscopy (FEHRSEM) imaging. FEHRSEM images were taken from the adhesive side of the film that comprises Au nanostructures to ensure that the fringe of Au nanostructures that were in contact with the glass is observed. This fringe is flat and similar to the top [111] facet of bare Au nanostructures. Artificially colored FEHRSEM of Au nanostructures formed by gold film evaporation followed by annealing at 450 °C the different nominal thicknesses of Au films (a - 1 nm, b - 3 nm, c - 5 nm, d - 7 nm, i - 9 nm, j - 11 nm, k - 13 nm, 1- 15 nm), insets - detailed images of the nanostructured gold surface and respective FEHRSEM of the scotch tape films (eh and mp) with Au nanostructures (nominal gold evaporation thickness: e - 1 nm, f - 3 nm, g - 5 nm, h - 7 nm, m - 9 nm, n - 11 nm, o - 13 nm, p - 15 nm), left bottom insets - digital comparison images of Au nanostructures on glass slide before (left) and after (right) scotch tape sticking. The top right insets for (ap) are detailed FEHRSEM images taken with high magnification. Scalebar for FEHRSEM images (ah) is 200 nm, for (il) is 400 nm, and for all the insets is 100 nm.

[0064] Reference is now made to Fig. 3B which shows graphs of distribution statistics of metal nanostructures attached to an elastic polymeric substrate at different nominal thicknesses according to some embodiments of the invention. Nominal mass gold thickness is the thickness as obtained by the read of Quartz Crystall microbalance system used in the e-beam evaporation device. Statistical analysis of the Au nanostructures distribution on the scotch tape shows Au nanostructures allocation patterns across all thicknesses. Distribution statistics of the major and minor diameters, fitted by ellipsoid shape, of metal nanostructures 30 (shown in Fig. 3C) of the Au nanostructures after transferring onto the adhesive tape for different nominal gold evaporation thickness: a - 5 nm, b - 7 nm, c - 9 nm, d - 11 nm, e - 13 nm, and f - 15 nm. As shown quite uniform normal distribution was demonstrated.

[0065] Reference is now made to Fig. 3C which shows graphs of nanostructures diameter, density, aspect ratio, area fraction as a function of nominal thickness according to some embodiments of the invention. The major (maximal) diameter and aspect ratio of the Au nanostructures of metal nanostructures 30 were measured. The density of the Au nanostructures tends to decrease with an increase in nominal Au thickness, while the surface coverage (e.g., area fraction) reaches the maximum value for thicknesses of 3 - 7 nm (ca. 35 %), then decreases as the Au nanostructures size and height increase, i.e., Au tends to dewet/coalesce into large islands with a lower volume to area ratio and reaches the minimum of 18.4 % for 15 nm thick Au films.

[0066] Reference is now made to Fig. 4 which shows images and graphs showing the optical properties of a composite according to somebodies of the invention. The optical characteristics of metal nanostructures on functionalized adhesive films were examined. The obtained films had a uniform color distribution across the entire surface. The color of the substrates changes according to the optical mode, i.e., reflectance or transmittance. In the reflectance mode with a white background, the film color appears from a pale red to purple for metal nanostructures 20 and from violet to yellow for metal nanostructures 30 (Fig. 4 (a)). In the transmittance mode, the films appear from pale red to purple violet for t metal nanostructures 20 and from blue to green and yellow for metal nanostructures 30 (Fig. 4 (b)). In the reflectance mode with a black background, all samples appear metallic gold with increasing intensity from small to large metal nanostructures (Fig. 4 (c)). [0067] In some embodiments, there is a slight difference in the color of the same metal nanostructures films deposited either on glass or polymer substrate (Figs. 4 (df)). This is attributed to the partial embedding of metal nanostructures into the polymeric matrix, i.e., the surrounding environment that has a higher refractive index (n_scotch = -1.47), whereas on glass it was exposed mainly to air (n_air = 1). This change is pronounced when comparing bare glass and glass covered by the polymer film with metal nanostructures. Here, metal nanostructures on bare glass display the LSPR band position in the range of ca. 520 - 725 nm wavelengths (Fig. 4 (d)), whereas the same metal nanostructures on adhesive tape show a redshift to ca. 540 - 850 nm wavelengths covering the green near IR regions (Figs. 4 (ef)). Note that the scotch tape is transparent in UVA, UVB (280 - 400 nm), and partially in UVC (240 - 280 nm) spectral regions offering advances in terms of optical transparency relative to glass/quartz.

[0068] The interaction of metal nanostructures with the tape was further characterized in terms of the LSPR band wavelength and absorbance intensity shifts in the UVV is spectra as summarized in (Figs. 4 (g to i)). Localized Surface Plasmon Resonance (LSPR) is defined as the collective oscillating motion of conduction electrons in nanostructured noble metals like Au and Ag NPs when illuminated by light, leading to the creation of an evanescent electromagnetic field with distinct optical properties. As shown, after embedding metal nanostructures into the polymer, the LSPR band demonstrates a redshift with an increase in metal nanostructures size (Figs. 4 (g, i)). For the metal nanostructures 20 films, the LSPR band wavelength redshifts occur around 20 nm corresponding to -40 nm/RIU sensitivity, while the metal nanostructures 30 films demonstrate a substantial redshift with a maximum of ca. 135 nm for the 15-nm-thick metal nanostructures, corresponding to -300 nm/RIU (Figs. 4 (g, i)). At the same time, the extinction intensity increases in metal nanostructures 20 films with an increase in metal nanostructures size, while decreasing continuously in metal nanostructures 30 films (Figs. 4 (h, i)). These results corroborate our previous findings obtained by the exposure of metal nanostructures films to solvents with increased refractive indices.

[0069] Refence is now made to Fig. 5 shows illustrations and graphs showing the influence of the nanostructures embedding in the surface according to some embodiments of the invention. To verify how Au metal nanostructures embedding onto a polymeric substrate affects the spectral characteristics of the Au metal nanostructures plasmonic band, computational simulations were applied based on the finite element approach. Two sizes of Au metal nanostructures were simulated, corresponding to Au metal nanostructures obtained after annealing ca. 5 and 11 nm thick Au layers,

Au metal nanostructures 20 or 30 films. The substrate was considered to be a layer that simulates soft (polymer) and hard (glass) material having a refractive index close to n = 1.5 in the V is NIR spectral range (400 - 1000 nm). Fig. 5 (a) presents cross sectional images illustrating conditions when 23 nm in diameter Au metal nanostructures are embedded 5, 50, and 95 % in a substrate. The 3D image demonstrates the simulation cell of 130 nm in diameter Au metal nanostructures embedded 50% in a substrate. To emphasize the difference, the shape of the 23 nm in diameter Au metal nanostructures was approximated as spherical, whereas the one of 130 nm in diameter was approximated as an oblate spheroid with a flat top surface (according to the cross sectional FEHRSEM images).

[0070] According to simulations, the LSPR peak is redshifted, and its intensity increases with the degree of embedding. For the 23 nm particles, the relative LSPR shift reaches 17 nm and 38 nm wavelength redshifts, whereas the embedding degree increases from 5 to 50% for 23 and 130 nm islands, respectively. The LSPR redshift is even more pronounced when Au metal nanostructures are embedded at 95%, reaching ca. 25 nm and 61 nm wavelength shifts for 23 and 130 nm Au metal nanostructures, respectively. The LSPR band intensity grows with increasing degrees of embedding.

[0071] Simulations revealed that the LSPR peak position of the 5%embedded Au metal nanostructures of both sizes matched well the LSPR band position of Au metal nanostructures on glass before their transfer to soft material. While comparing the experimental data of the LSPR band position of Au metal nanostructures after the transfer to scotch tape with simulations, it was found that the band position of simulated spectra corresponds to 40 - 60% of Au metal nanostructures 20 and 30 embedded into the soft material of substrate 10. Despite an ideal case scenario of Au metal nanostructure’s location obtained in the numerical simulations and considering spatial order and shape as well as size uniformity, these results correlate well with the tilted SEM images obtained on the soft printed Au metal nanostructures on scotch tape. These models of partial embedding of Au metal nanostructures into a polymeric material with a known refractive index may serve as a plasmonic ruler to develop optical pressure sensors. [0072] Reference is now made to Fig. 6 which shows images and graph of sensing characteristics of a composite measured by Raman spectroscopy according to somebodies of the invention, the sensing characteristics of composites according to some embodiments of the invention were tested by adsorption of Rhodamine 6G (R6G) (Fig. 6 (a)) for Raman spectroscopy measurements) (Fig. 6 (c)) shows an area displayed in (Fig. 6 (b)) taken in a mosaic regime with different scanning areas of the region of interest (ROI). The intensity of the red area in the ROI of this figure is derived from a region of the Raman spectra that were measured in this region between 1335 and 1375 cm^-1. The highest intensity was obtained in area 1 of the ROI (see Fig. 6 (c)), decreasing in the central part (Fig. 6 (b), area 2), and was not observed on the righthand side (see Fig. 6 (c), area 3). Fig. 6 (f)demonstrates a typical spectrum from the region corresponding to area 1 (see Fig. 6 (c)), showing an intense R6G Au NP enhanced Raman spectrum in the fingerprint region. The intensity of the blue color in the ROI is derived from a part of the Raman spectrum measured from this region in the spontaneous (not enhanced) Raman shift range from 1465 to 1495 cm^-1. The highest intensity is in the center of the ROI and a slightly lower intensity is on the left of the ROI, while the righthand side of the ROI is almost dark. Fig. 6 (e)demonstrates a typical Raman map from the region corresponding to area 2 (see Fig. 6 (c)) showing a noisy R6G characteristic spectrum confirming that Au metal nanostructures provide surface enhancement of the R6G Raman spectrum in area 1 but not in area 2. Finally, it was impossible to obtain a characteristic spectrum for the furthest righthand section of the ROI (see Fig. 6 (c), area 3), which has the characteristics of the scotch tape spectrum that under these detection conditions is virtually undetected (not shown).

[0073] Reference is now made to Fig. 7 that shows images of a composite comprising a medical adhesive tape according to some embodiments of the invention. In another nonlimiting example, soft printing Au metal nanostructures procedure was studied for various types of biocompatible medical/surgical adhesive tapes. For example, 3M Durapore™, 3M Micropore™, and 3M Trans pore™ were tested. All the tested adhesives are of medical purposes (Fig. 7 (ac)) but have different textures, porosity, and adhesive characteristics. The soft printing approach works well with these adhesive tapes and Au metal nanostructures of both types can be successfully soft printed to all of them. After the transfer, the tapes remain sticky and can be attached to skin (Fig. 7 (d)). Optical microscopy and FEHRSEM imaging showed the high efficiency of Au metal nanostructures transfer to medical tapes of all types. Such tapes with transferred Au metal nanostructures may serve for medical applications such as phototherapy, transdermal Au supported drug delivery, or as an antibacterial adhesive. Moreover, it is expected that upon transferring Au metal nanostructures to a dissolvable tape and combining it with the patterning ability/electric circuits, islands might be potentially transferred to any kind of surface or skin creating, e.g., tattoo like medical biomonitoring devices.

[0074] Reference is now made to Fig. 8 which is an image and HRSEM image of a composite comprising a carbon tape according to some embodiments of the invention. In some embodiments, soft printing process is not limited to scotch tape but may be applied to a variety of adhesive polymeric materials. Here, carbon and metallic Mylar (reflective and conductive) tapes were used to trap Au metal nanostructures. Metallic Mylar tape, which possesses reflective and conductive properties, was applied to transfer Au metal nanostructures demonstrating comparable transfer efficiency. FEHRS EM images confirmed a transfer efficiency similar to that found on the 3M scotch tape, demonstrating that the soft printing process of Au metal nanostructures is uniform for any adhesive polymeric films.

Applications of a composite according to some embodiments of the invention

[0075] Composite 100 may be used and may be included in several technologies from a variety of areas. For example, composite 100 can be used in LSPR systems as optical sensors and transducers for chemical and biological sensing. In another example, composite 100 may be included in wearable electronics, and flexible optical systems. In another example, composite 100 can be used as a medical/surgical adhesive tape for the use in medical applications, such as phototherapy, transdermal Au supported drug delivery, or as an antibacterial adhesive. In yet another example, composite 100 can be used in reflective and/or conductive tapes.

[0076] Unless explicitly stated, the method embodiments described herein are not constrained to a particular order or sequence. Furthermore, all formulas described herein are intended as examples only and other or different formulas may be used. Additionally, some of the described method embodiments or elements thereof may occur or be performed at the same point in time.

[0077] While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents may occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

[0078] Various embodiments have been presented. Each of these embodiments may of course include features from other embodiments presented, and embodiments not specifically described may include various features described herein.

Claims

1. A composite comprising an elastic polymeric substrate and metal nanostructures attached to a surface of the elastic polymeric substrate; wherein: each of said metal nanostructures comprises a first portion embedded within the elastic polymeric substrate and a second portion exposed to an ambient; said metal nanostructures have lateral dimension between 1 to 1000 nm, said metal nanostructures have a thickness of between 5 to 200 nm, and said metal nanostructures consist essentially of a metal in an elemental state.

2. The composite of claim 1, wherein said metal nanostructures are substantially devoid of a metal salt, a metal complex, or both.

3. The composite of claim 1 or claim 2, wherein a relative volume of said first portion is at least 30% of an average volume of said metal nanostructures, and wherein the relative volume is determined based on a shift of Localized Surface Plasmon Resonance (LSPR).

4. The composite of any one of claims 1 to 3, where a surface coverage of the metal nanostructures is between 10 and 50%.

5. The composite of any one of claims 1 to 4, wherein said metal nanostructures comprises, at least one of a first type of metal nanostructures and at least one second type of metal nanostructures and wherein the first and second types differ at least in an average lateral dimension.

6. The composite of claim 5, wherein the average lateral dimension of said first type of metal nanostructures is between 1 to 50 nm and the average lateral dimension of said second type of metal nanostructures is between 60 to 1000 nm.

7. The composite of claim 5 or claim 6, wherein said first type of metal nanostructures comprises essentially from circular shape nanostructures and said second type of metal nanostructures comprises essentially from truncated ellipsoid shaped nanostructures.

8. The composite according to any one of claims 5 to 7, wherein an average thickness of said type group of metal nanostructures is between 5 to 60 nm and the average thickness said second type of metal nanostructures is between 65 to 200 nm.

9. The composite according to any one of claims 1 to 8, wherein said composite is characterized by light absorption at a wavelength between 190 to 1100 nm.

10. The composite according to any one of claims 1 to 9, wherein said metal is selected form Au, Ag, Cu, Ru, Rh, Pd, Re, Os, Ir and Pt, including any combination and any alloy thereof.

11. The composite according to any one of claims 1 to 10, wherein said metal is Au.

12. The composite according to any one of claims 1 to 11, wherein the elastic polymeric substrate comprises a film, and an adhesive layer in contact with a polymeric layer; and wherein the metal nanostructures are embedded within at least one of: the film and the adhesive layer.

13. A method of making the composite of any one of claims 1 to 12 comprising:

(a) forming an ultrafine metal layer on a donor substrate;

(b) annealing the ultrafine metal layer at an elevated temperature, thereby receiving a donor substrate covered by metal nanostructures; wherein said ultrafine metal layer has an average thickness between 1 and 20nm;

14. The method of claim 13, wherein said donor substrate is a rigid substrate.

15. The method of claim 13, further comprising applying a selective reduction of the surface energy of the annealed substrate following step (b).

16. The method according to any one of claims 13 to 15, wherein said composite is characterized by light absorption at a wavelength between 190 to 1100 nm.

17. The method of any one of claims 12 to 16, further comprising: selecting the type of nanostructures; and determine the thickness of the ultrafine metal layer based on the selected type.

18. The method according to any one of claims 13 to 17 wherein said composite is substantially devoid of a metal salt, a metal complex, or both.

19. The method according to any one of claims 13 to 18, wherein said metal is selected form Au, Ag, Cu, Ru, Rh, Pd, Re, Os, Ir and Pt, including any combination and any alloy thereof.

20. An article comprising the composite of any one of claims 1 to 12, being in a form of an antimicrobial patch, photothermal patch, optical sensor, and transducer.

21. The article of claim 20, being in a form of the antimicrobial patch, wherein at least 80% of the metal nanostructures characterized by an average lateral dimension of between 1 to 50 nm.