RU2620985C1 - Method for measuring fluid flow rates in microchannels - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: method for measuring fluid flow rates in microchannels is characterized in that the composition is prepared as a concentrated solution of anthraquinone not less than ^10-3 mol/l in aliphatic alcohol or anthraquinone solution in the mixture of water and aliphatic alcohol in the ratio of 3:7, which is injected into the microchannel radiated with the ultraviolet constant power light initiating photochemical reactions in the composition to form the fluorescent photoproduct, the appearance time of which depends on the fluid flow rate. Then the appearance time of photoproduct fluorescence is recorded, and the average cross section value of the flow rate in the channel is determined according to the pre-constructed calibration dependence of the fluorescence appearance time on the rate.

EFFECT: eliminating the defects of the inertial measurements that reduces the systematic error and allows to simplify measurements.

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Description

The invention relates to technical physics, in particular to the field of microfluidics and microfluidic devices using small amounts of fluid flowing in channels with characteristic sizes from a few microns to several millimeters, and, in particular, to optical methods for studying the structure of a fluid flow in microchannels. The invention can be used in scientific and laboratory research, in universities.

Microfluidic devices are widely used in various fields of science and technology: from microelectronics (cooling of microchips) to biological and medical research, such as growing protein crystals, DNA microchips, biological and chemical analysis and synthesis (biomicrochips and a laboratory on a chip). Many types of microfluidic devices are made on polymer substrates, in which, using various prototyping methods, they create systems of microchannels, valves, power drives and other elements. In microfluidic devices, the main processes of fluid flow develop in a thin layer of a few microns in size in the near-wall regions of microchannels, which complicates or makes impossible the use of contact measurement methods. In this regard, non-contact optical methods have been developed for measuring various characteristics of liquids in such devices.

Optical methods for measuring fluid flow rates from particle images (Particle Image Velocimetry (PIV)) are widely known.

As applied to microfluidics, these methods were adapted to the small sizes of microchannels and were called micro-PIV. Their detailed review can be found in publications such as: D. Sinton Microscale flow visualization [Microfluid Nanofluid (2004) 1: 2-21] and Steven T. Wereley et al. Recent Advances in Micro-Particle Image Velocimetry [Annu. Rev. Fluid Mech. 2010. 42: 557-76]. No. 6,565,651 to the Micron resolution particle image velocimeter describes a method and apparatus for measuring fluid motion with high spatial resolution. A microchannel with a liquid and fluorescent particles of micron and submicron size is illuminated by light pulses of a certain wavelength and duration. Using a special microscope and a digital camera, at least two consecutive pictures of moving fluorescent particles are taken. The resulting images are divided into equal areas that are correlated between different images in order to measure the most likely local movement of particles and their velocities. The microscope is used both to illuminate the liquid in the microchannel and to register fluorescent microparticles. The microscope has a known depth of focus and focuses on a specific area inside the microchannel. Clearly focused images are obtained only for those microparticles that are in the focus area at the time of shooting, which determines the high spatial resolution of the position of the microparticles. The main disadvantages of the patent and other similar micro-PIV methods are: 1) the complexity of the optical systems used, which require fine tuning both for excitation of fluorescence of particles and for its registration in order to obtain a clear image of microparticles throughout the observation field, and 2) the use of software algorithms for correlation and analysis of images of particle motion and averaging of their velocities, which lead to an increase in the systematic error of measurements, especially for boundary flows near microchannel enok.

There is also a known method of measuring fluid flow rate, based on the phenomenon of photobleaching of fluorescent dyes. In the method under consideration, the dye loses its ability to fluoresce as the solution is irradiated with light in the dye absorption band. For example, in Patent US 7283215 Method and apparatus for fluid velocity measurement based on photobleaching, the flow rate is measured and calculated using the calibration dependence of the dye fluorescence intensity on the flow rate. The higher the flow rate, the less photobleaching and the greater the dye fluorescence intensity. The method and device proposed in the patent allow measuring the local flow velocity at the measurement point and the velocity distribution over the channel cross section with high spatial and temporal resolution. A significant disadvantage of this method is the low signal-to-noise ratio (image contrast), which is an order of magnitude lower compared to other optical methods. Measuring a bright signal against a dark background fundamentally gives more accurate results compared to measuring a dark signal (bleached solution) against a bright background. The measurement error also increases when the movement of the fluorescent regions of the solution is superimposed on areas with a bleached dye due to local gradients of the fluid velocity. This is especially evident when measuring boundary flows near the walls of a microchannel, where evanescent waves are used, the intensity of which is very weak and decreases exponentially from the surface, which further affects the measurement error.

The objective of the present invention is to provide a new method to simplify the optical system for detecting fluid motion in the microchannels of microfluidic devices, to eliminate the disadvantages of inertial measurements and to reduce the systematic error in measuring the velocity of a fluid.

The solution to this problem is achieved by using a fundamentally new way to measure the fluid flow.

A method of measuring fluid flow rates in microchannels, characterized in that the composition is prepared in the form of a concentrated solution of anthraquinone of at least 10 ^-3 mol / L in aliphatic alcohol or a concentrated solution of anthraquinone in a mixture of water and aliphatic alcohol in a ratio of 3: 7, which is introduced into the microchannel irradiated with constant power ultraviolet light, initiating photochemical reactions in this composition with the formation of a fluorescent photoproduct, the time of appearance of which depends on the flow rate of the liquid In addition, the time of the appearance of fluorescence of the photoproduct is recorded, and the value of the average cross-sectional flow velocity in the channel is determined from the velocity dependence of the time of appearance of fluorescence on the preliminary constructed calibration.

The ultraviolet light used to illuminate the microchannel with the liquid can be continuous or pulsating, as well as focused or unfocused. Ultraviolet light can be focused in a certain area along the cross-section of the microchannel in order to accelerate the formation time of the fluorescent photo product in this area.

The invention is illustrated by drawings:

FIG. 1 is a block diagram of an apparatus for implementing the proposed method for measuring flow rates of liquids in microchannels;

FIG. 2 - time dependences of the readings of a photodiode recording the time of appearance of fluorescence of the photoproduct;

FIG. 3 is an example of a calibration dependence of the appearance time of a fluorescent photoproduct on the fluid flow rate.

The implementation of the proposed method, we consider the example of measuring the flow rate of a liquid prepared on the basis of a composition in the form of a concentrated alcoholic solution of anthraquinone (10 ^-3 mol / l), in a quartz tube (1) with an inner diameter of less than 3 mm on a plant, the block diagram of which is shown in FIG. 1. The composition enters the initially empty tube (1) through rubber hoses (2) using a centrifugal pump (3). The flow rate of the composition varies by changing the voltage at the motor power source (4). The excitation of a sample entering the tube is produced by ultraviolet light (wavelength 337 nm) coming from a laser (5). The laser irradiates an arbitrary fixed portion of the tube. The excitation duration is 1 second and is regulated by an electromechanical shutter (8), which is synchronized with another shutter (9), which determines the exposure time of a digital camera (6).

The time of fluorescence of the photoproduct in the irradiation zone of the flow is recorded by the photodiode (7). The initial moment of time t _{0 of} irradiation of the composition, that is, the moment when the composition falls into the irradiation zone of the tube, is fixed and is determined by a sharp decrease in the intensity of the radiation incident on the photodiode (Fig. 2). As a result of the initiated photochemical reactions that occur for some time τ _i , a fluorescent photo product is generated in the composition, the fluorescence of which contributes to the signal recorded by the photodiode. The measured values of the initial instant of time t _{0 for} irradiating the composition and the time t _{1 for the} appearance of fluorescence of the photoproduct in the composition make it possible to determine with high accuracy the generation time of the fluorescent photoproduct as τ _i = t ₁ -t ₀ .

The obtained dependence of the time of occurrence of fluorescence of the anthraquinone photoproduct on the solution flow rate in the tube at a constant laser radiation power of 3 mW is shown in FIG. 3. As can be seen from the graph, the obtained dependence τ _i = ƒ (V _sr ) with a good approximation is linear.

The proposed technical solution eliminates the disadvantages of inertial measurements and high image contrast, which helps to reduce the systematic error and allows us to simplify both the optical scheme and the process of measuring the fluid flow rate.

Claims (1)

A method of measuring fluid flow rates in microchannels, characterized in that the composition is prepared in the form of a concentrated solution of anthraquinone of at least 10 ^-3 mol / L in aliphatic alcohol or a concentrated solution of anthraquinone in a mixture of water and aliphatic alcohol in a ratio of 3: 7, which is introduced into the microchannel irradiated with constant power ultraviolet light, initiating photochemical reactions in this composition with the formation of a fluorescent photo product, the time of appearance of which depends on the flow rate of the liquid bones, the time of the appearance of fluorescence of the photoproduct is recorded, and the value of the average cross-sectional flow velocity in the channel is determined by the previously constructed calibration dependence of the time of fluorescence appearance on speed.

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