A microfluidic chip-based liquid sample pH monitoring system

Abstract

This invention provides a liquid sample pH monitoring system based on a microfluidic chip. The microfluidic chip has a colorimetric region; a light emitting component emits detection light into the colorimetric region; a color sensing unit receives the colored light modulated by the colorimetric region and outputs a corresponding color signal; a temperature control unit maintains the colorimetric region within a preset temperature range; and a processing unit inputs the color signal into a pre-trained pH prediction model, ultimately outputting the pH value of the liquid sample to be tested. In this invention, the colorimetric region integrated within the microfluidic chip causes a colorimetric reaction when the liquid sample to be tested is mixed with a pH indicator; the light emitting component provides detection light, and the modulated transmitted light is received by the color sensing unit and converted into a color signal. Based on the pH prediction model, the color signal is analyzed to output the pH value of the liquid sample to be tested, achieving high-precision, continuous, and real-time quantitative pH analysis of trace flow liquid samples.

Description

Technical Field

[0001] This invention relates to the field of biomedical detection technology, and more specifically, to a liquid sample pH monitoring system based on a microfluidic chip. Background Technology

[0002] In the field of life science research and technological development, pH value is a key parameter reflecting the acid-base balance of a system. It directly affects not only the structural stability of biomolecules, enzyme reaction efficiency, cellular physiological functions, and the homeostasis of the biological microenvironment, but also provides crucial evidence for elucidating the mechanisms of life activities, optimizing experimental systems, and advancing biotechnology translation. The determination of sample pH value is not only used to quantify the acid-base properties of reaction systems, but also has applications throughout the entire chain of basic research, clinical diagnosis, and even biomanufacturing. Especially in urine analysis, pH value, as a routine detection indicator, is closely related to the body's acid-base balance, the risk of urinary tract infections, and the risk of urinary system stone formation, and has significant clinical reference value.

[0003] Microfluidic technology has been widely applied in in vitro diagnostics (IVD), cell culture, and organ-on-a-chip applications due to its advantages in microscale sample manipulation, low reagent consumption, high-throughput analysis, and high spatiotemporal resolution. In microfluidic-based applications, dynamic pH monitoring is crucial for ensuring experimental accuracy and the realism of physiological simulations. In IVD, detection systems based on enzyme-catalyzed or immunoreaction-based reactions are highly sensitive to pH. Combining microfluidic chips with high-precision pH sensors can reduce errors caused by pH drift and improve the repeatability of detections. Therefore, real-time monitoring of the system's pH value is a key step in ensuring the smooth operation of experiments.

[0004] Traditional pH measurement methods mainly include electrochemical methods and indicator-based colorimetric methods. Electrochemical methods, centered on pH meters based on the Nernst equation, are suitable for high-precision laboratory analysis when sample volumes are sufficient. Indicator-based colorimetric methods determine pH by comparing the color change of a dye with a standard color chart; for example, pH test strips are used for rapid detection, but their accuracy is relatively low. Emerging methods include absorbance measurement (suitable for batch pH analysis of clinical samples such as urine), ion-sensitive field-effect transistor (ISFET) methods (with advantages of miniaturization and integration), fluorescence methods, and surface plasmon resonance (SPR) methods (suitable for single-cell pH analysis, tumor microenvironment monitoring, etc.). However, optical detection technologies such as fluorescence methods and surface plasmon resonance (SPR) require extremely expensive optical equipment and are difficult to integrate into microfluidic systems. Although the ISFET method is suitable for microfluidic scenarios, it requires direct contact with the sample and is fragile, making long-term continuous monitoring impossible. Summary of the Invention

[0005] In view of this, the present invention proposes a liquid sample pH monitoring system based on a microfluidic chip, which aims to achieve high-precision and continuous real-time quantitative analysis of pH in trace flow samples. This invention proposes a liquid sample pH monitoring system based on a microfluidic chip, comprising: A microfluidic chip with a colorimetric region for containing a mixture of the liquid sample to be tested and a pH indicator; A light emitting component, disposed below the microfluidic chip, is used to emit detection light toward the colorimetric region; The color sensing unit, disposed above the microfluidic chip, includes an optical path receiving component and a color sensor component, used to receive colored light modulated by the color rendering region and output the corresponding color signal; The temperature control unit, thermally coupled to the microfluidic chip, is used to maintain the color display area within a preset temperature range to ensure the stability of color signal detection. The processing unit, electrically connected to the color sensing unit, is used to receive the color signal and process the color signal based on the pH prediction model, thereby outputting the pH value of the liquid sample to be tested.

[0006] Furthermore, in the above-mentioned liquid sample pH monitoring system based on microfluidic chip, the microfluidic chip is formed by hot-pressing three layers of polymethyl methacrylate plates (lower, middle, and upper layers) from bottom to top, and has a three-dimensional mixing zone inside. The three-dimensional mixing zone is composed of multiple identical circulation units connected in series. Each circulation unit includes a tortuous microchannel in a single plane and a vertical connecting section extending along the chip thickness direction and connected to the outlet of the tortuous microchannel. Adjacent circulation units are connected end to end through the vertical connecting section, so that the liquid sample to be tested and the pH indicator are disturbed in the plane and flow across the plane, thereby achieving three-dimensional mixing.

[0007] Furthermore, in the aforementioned microfluidic chip-based liquid sample pH monitoring system, the upper surface of the microfluidic chip is provided with two inlets and one outlet, with the outlet located opposite the inlets. Inside the microfluidic chip, corresponding to the two inlets, are two inlet channels that extend from top to bottom through the three-layer polymethyl methacrylate (PMMA) plate and connect to the three-dimensional mixing zone located between the lower and middle layers. The outlet of the three-dimensional mixing zone connects to the color development area located between the middle and upper layers. The color development area connects to the outlet via a discharge channel. The discharge channel extends along the area between the middle and upper layers, penetrates upwards through the upper PMMA plate, and connects to the outlet on the upper surface of the microfluidic chip.

[0008] Furthermore, in the aforementioned microfluidic chip-based liquid sample pH monitoring system, the light-emitting component includes: an LED light source, a first optical fiber, and a first lens; wherein, The emitted light from the LED light source is coupled to one end of the first optical fiber, and the other end of the first optical fiber is set as the light output end on the light incident side of the first lens, so that the LED light source, the first optical fiber and the first lens are coaxial in the optical path, so as to focus the detection light output through the first optical fiber onto the color rendering area.

[0009] Furthermore, in the aforementioned microfluidic chip-based liquid sample pH monitoring system, the temperature control unit includes: a temperature control board, a temperature sensor, a heat sink, and two Peltier thermoelectric coolers; wherein, The temperature sensor's sensing end is embedded in the heat-conducting housing containing the microfluidic chip; the heat sink has mounting holes for mounting the first lens in the light-emitting assembly; two Peltier thermoelectric coolers are symmetrically arranged on both sides of the mounting holes, with their cold ends thermally coupled to the heat-conducting housing and their hot ends thermally coupled to the heat sink; a fan is provided at the bottom of the heat sink for forced convection cooling; the temperature control board is electrically connected to the temperature sensor and the Peltier thermoelectric coolers respectively.

[0010] Furthermore, in the above-mentioned liquid sample pH monitoring system based on microfluidic chip, the bottom of the heat-conducting box is provided with a light-transmitting hole, which is aligned with the first lens and the color-developing area in the optical path, so that the detection light, after being focused by the first lens, can pass through the light-transmitting hole and illuminate the color-developing area.

[0011] Furthermore, in the above-mentioned liquid sample pH monitoring system based on microfluidic chip, an optical path receiving component is provided between the color sensing unit and the color display area, which is used to collimate the colored light modulated by the color display area and project it onto the photosensitive surface of the color sensing unit.

[0012] Furthermore, in the aforementioned liquid sample pH monitoring system based on a microfluidic chip, the inlet and outlet of the microfluidic chip are respectively equipped with fluid connectors made of polyetheretherketone (PEEK) for connecting external liquid supply pipelines and waste liquid discharge pipelines.

[0013] Furthermore, in the aforementioned microfluidic chip-based liquid sample pH monitoring system, the colorimetric region is columnar with a volume of less than or equal to 4 μL.

[0014] Furthermore, in the aforementioned microfluidic chip-based liquid sample pH monitoring system, the processing unit stores a pH prediction model, and the input feature vector of the pH prediction model is obtained by transforming the RGB three-channel intensity values ​​(R, G, B) output by the color sensing unit. Where log represents the logarithm to the natural constant e; The pH value is a stability constant; the pH prediction model is used to output the predicted pH value of the liquid sample to be tested based on the input feature vector.

[0015] The microfluidic chip-based liquid sample pH monitoring system of this invention integrates a colorimetric region within the microfluidic chip, causing a colorimetric reaction when the liquid sample to be tested is mixed with a pH indicator, generating a corresponding color. A light-emitting component located below the microfluidic chip provides detection light, which, after being modulated by the colorimetric region, is received by the upper-mounted color sensing unit and converted into a color signal. Simultaneously, a temperature control unit maintains the colorimetric region at a constant temperature to eliminate interference from ambient temperature on the pH detection results. The processing unit analyzes the color signal based on a pre-trained pH prediction model and ultimately outputs the pH value of the liquid sample to be tested. This system achieves high-precision, continuous, and real-time quantitative pH analysis of trace amounts of flowing liquid samples, effectively solving problems such as low detection accuracy, inability to dynamically monitor, and cumbersome operation in existing technologies. Attached Figure Description

[0016] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 An exploded view of the overall structure of the microfluidic chip-based liquid sample pH monitoring system provided in this embodiment of the invention; Figure 2 Another exploded view of the overall structure of the liquid sample pH monitoring system based on a microfluidic chip provided in this embodiment of the invention; Figure 3 A schematic diagram of the microfluidic chip structure in the liquid sample pH monitoring system based on a microfluidic chip provided in an embodiment of the present invention; Figure 4 for Figure 3 A magnified view of a section at point A in the middle; Figure 5 This is a schematic diagram of the liquid sample pH monitoring system based on a microfluidic chip provided in an embodiment of the present invention in the open state. Figure 6 A schematic diagram of the liquid sample pH monitoring system based on a microfluidic chip provided in an embodiment of the present invention in the closed state; Figure 7 An exploded view of the outer casing of the liquid sample pH monitoring system based on a microfluidic chip provided in an embodiment of the present invention; Figure 8 Another exploded view of the outer casing of the liquid sample pH monitoring system based on a microfluidic chip provided in an embodiment of the present invention; Figure 9 A partial structural diagram of the interior of the lower cover of the liquid sample pH monitoring system based on a microfluidic chip provided in an embodiment of the present invention; Figure 10 Another schematic diagram of the internal structure of the lower cover of the liquid sample pH monitoring system based on a microfluidic chip provided in an embodiment of the present invention; Figure 11 This is another structural diagram of the interior of the lower cover of the liquid sample pH monitoring system based on a microfluidic chip provided in an embodiment of the present invention. Figure 12 An exploded view of the optical path portion of the microfluidic chip-based liquid sample pH monitoring system provided in an embodiment of the present invention; Figure 13 The present invention provides a schematic diagram of the detection results of a microfluidic chip-based liquid sample pH monitoring system for samples with different pH values. The upper part is a standard colorimetric card of the indicator, showing the theoretical color and its RGB value corresponding to each pH. The lower part is the response curve of the calculated R / G, R / B, and G / B ratios as a function of pH, based on the actual RGB three-channel signals collected by the pH monitoring system of the present invention. Figure 14 The optical response characteristics of the microfluidic chip-based liquid sample pH monitoring system provided in this embodiment of the invention are verified under pH gradient buffer solution. Figure 15 This is a stability verification graph of the RGB ratio response under three repeated measurements in an embodiment of the present invention; Figure 16 The following are performance evaluation results of the Gradient Boosting Regression Tree (GBDT) model on an independent test set in this embodiment of the invention, including: (a) a scatter plot comparing the actual pH value and the predicted pH value; (b) a residual distribution plot; (c) a distribution plot of the absolute error; and (d) a quantile curve of the absolute error. Detailed Implementation

[0017] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] See Figures 1-12 The liquid sample pH monitoring system based on a microfluidic chip according to this invention includes: a microfluidic chip 1, a light emitting component 2, a color sensing unit 3, a temperature control unit 4, and a processing unit (not shown in the figure); wherein, the microfluidic chip 1 is provided with a color-developing region 11 for accommodating the mixture reaction of the liquid sample to be tested and a pH indicator; the light emitting component 2 is disposed below the microfluidic chip 1 for emitting detection light into the color-developing region 11; the color sensing unit 3 is disposed above the microfluidic chip 1 and includes a light path receiving component 5 and a color sensor component for receiving the colored light modulated by the color-developing region 11 and outputting a corresponding color signal; the temperature control unit 4 is thermally coupled to the microfluidic chip 1 for maintaining the color-developing region 11 within a preset temperature range to ensure the detection stability of the color signal; the processing unit (not shown in the figure) is electrically connected to the color sensing unit 3 for receiving the color signal and processing the color signal based on a pH prediction model, thereby outputting the pH value of the liquid sample to be tested.

[0019] Specifically, the liquid sample to be tested can be biological fluids such as urine or environmental liquid samples. This embodiment of the invention uses urine pH detection as the application scenario, but the pH monitoring system of this invention is also applicable to pH monitoring of other biological fluids or environmental liquid samples.

[0020] The microfluidic chip 1 is formed by hot-pressing three layers of polymethyl methacrylate plates from bottom to top. It has a three-dimensional mixing zone 12 inside, which is composed of multiple circulation units with the same structure connected in series. Each circulation unit includes a tortuous microchannel 121 in a single plane and a vertical connecting section 122 extending along the thickness direction of the chip and communicating with the outlet of the tortuous microchannel 121. Adjacent circulation units are connected end to end through the vertical connecting section 122, so that the liquid sample to be tested and the pH indicator are disturbed in the plane and flow across the plane, realizing three-dimensional mixing.

[0021] The pH indicator can be a mixture of methyl red (Mr) and bromothymol blue (BTB) or a mixture of bromothymol blue (BTB) and methyl red (Mr) and phenolphthalein (PP); preferably, it is a mixture of methyl red (Mr) and bromothymol blue (BTB).

[0022] In practice, the microfluidic chip 1 is formed by activating the surface of a colorless and transparent polymethyl methacrylate (PMMA) sheet through oxygen plasma treatment, followed by hot pressing.

[0023] The three-dimensional mixing zone 12 includes multiple circulation units connected in series. The tortuous microchannel 121 of each circulation unit is formed by continuously folded grooves of consistent depth machined on the surface of a polymethyl methacrylate (PMMA) plate. These grooves are located in the same plane, for example, in a U-shape, C-shape, or serpentine shape, to extend the liquid path and enhance turbulence within the effective space. The vertical connecting section 122 is achieved by providing through-holes or vertical connecting slots extending along the chip thickness direction at corresponding positions in the sheet. One end of the vertical connecting section connects to the outlet of the tortuous microchannel 121 of the previous circulation unit, and the other end connects to the inlet of the tortuous microchannel 121 of the next circulation unit.

[0024] like Figures 3-4 As shown, after the liquid sample to be tested and the pH indicator merge from the Y-shaped inlet, they first enter the first circulation unit and undergo turbulent flow in the tortuous microchannel 121. Then, they enter the tortuous microchannel 121 of the second circulation unit through the vertical connecting section 122 and undergo turbulent flow again. It can be seen that when the two liquids flow through each circulation unit, they alternately experience in-plane turbulence and cross-plane flow, and finally achieve an efficient three-dimensional mixing effect in a compact space.

[0025] In one specific embodiment, COMSOL simulation verification shows that under typical operating conditions (indicator inlet concentration of 1 mol / L, urine sample inlet concentration of 0 mol / L, sample flow rate of 50 μL / min, indicator flow rate of 5 μL / min), the three-dimensional mixing zone 12 of the microfluidic chip 1 can achieve thorough mixing of urine sample and indicator by using only two cascaded circulation units.

[0026] The methyl red (Mr)-bromothymol blue (BTB) mixed indicator used has an effective color development pH range of 4 to 9, covering the pH range (4.0 to 8.5) of human urine and most application scenarios in the life science field.

[0027] See Figures 13-15 When the concentration of the methyl red (Mr)-bromothymol blue (BTB) mixed indicator is 0.5~10% (volume percentage), the indicator is sensitive to pH changes, and the RGB color shows a good linear relationship with the pH value. Preferably, when the concentration of the mixed indicator is 2%, the linear slope between the RGB color parameters and the pH value is the largest, the detection sensitivity is the highest, and it can meet the quantitative analysis requirements with a resolution of 0.1 pH unit.

[0028] The microfluidic chip 1 has two liquid inlets 13 and one liquid outlet 14 on its upper surface, with the liquid outlet 14 located opposite the liquid inlets 13. Inside the microfluidic chip 1, corresponding to the two liquid inlets 13, are two liquid inlet channels 15. These two channels 15 extend from top to bottom through the three-layer polymethyl methacrylate (PMMA) plate and connect to the three-dimensional mixing zone 12 located between the lower and middle layers. The outlet of the three-dimensional mixing zone 12 connects to the color development zone 11 located between the middle and upper layers. The color development zone 11 connects to the liquid outlet 14 via a discharge channel 16. The discharge channel 16 extends along the area between the middle and upper layers, penetrates the upper PMMA plate, and connects to the liquid outlet 14 on the upper surface of the microfluidic chip 1.

[0029] Specifically, the microfluidic chip 1 has polyetheretherketone (PEEK) fluid connectors (not shown in the figure) at its inlet 13 and outlet 14, respectively, for connecting to external liquid supply lines and waste liquid discharge lines. In practice, one end of the PEEK connector is sealed to the inlet 13 and outlet 14 of the microfluidic chip 1 (e.g., using epoxy adhesive) to prevent leakage of trace amounts of urine during flow, and the other end of the PEEK connector passes through a through-hole in the side wall of the housing 7 to connect to the external liquid supply lines and waste liquid discharge lines.

[0030] The microfluidic chip 1 has two liquid inlets 13 and one liquid outlet 14 on its upper surface. The liquid outlet 14 is located on the opposite side of the two liquid inlets 13, forming a through-flow fluid passage.

[0031] In this embodiment, the microfluidic chip 1 is constructed by thermoforming upper, middle, and lower polymethyl methacrylate (PMMA) plates. Each fluid channel is formed by microgrooves or through-holes on the corresponding plates, creating a closed flow path through interlayer alignment. Internally, it has two inlet channels 15 that extend from top to bottom through the three PMMA plates, with inlets connected to two inlets 13 on the upper surface. The two inlet channels 15 extend downwards, passing through the upper and middle layers, and converge into a three-dimensional mixing zone 12 formed by the lower and middle PMMA plates. This three-dimensional mixing zone 12 ensures efficient turbulent mixing of the two fluids, guaranteeing a sufficient colorimetric reaction between the indicator and the test liquid sample. The mixed liquid flows out from the outlet of the three-dimensional mixing zone 12 and enters the colorimetric region 11 located in the middle and upper layers, where color stabilization is completed and a path for optical detection is provided. After color development, the waste liquid flows to the outlet 14 through the discharge channel. The discharge channel is formed by the microgrooves on the upper surface of the middle PMMA plate and the upper PMMA plate, and vertically penetrates the upper PMMA plate near the outlet 14, and finally connects with the outlet 14 on the upper surface, so as to realize the whole process of sample introduction, mixing, color development and waste liquid discharge.

[0032] Continue reading Figure 4The color development area 11 is columnar and its volume is less than or equal to 4 μL, for example, 1~3 μL.

[0033] In one specific embodiment, the color development area 11 is cylindrical with a diameter of 1.1 mm and a height of 2 mm, corresponding to a volume of approximately 1.9 μL.

[0034] The temperature control unit 4 includes a temperature control board 41, a temperature sensor 42, a heat sink 43, and two Peltier thermoelectric coolers 44. The temperature sensing end of the temperature sensor 42 is embedded in a heat-conducting housing 45 housing the microfluidic chip 1. The heat sink 43 has mounting holes for mounting the first lens 22 in the light-emitting assembly 2. The two Peltier thermoelectric coolers 44 are symmetrically arranged on both sides of the mounting holes, with their cold ends thermally coupled to the heat-conducting housing 45 and their hot ends thermally coupled to the heat sink 43. A fan 48 is provided at the bottom of the heat sink 43 for forced convection cooling. The temperature control board 41 is electrically connected to the temperature sensor 42 and the Peltier thermoelectric coolers 44, respectively, to receive the real-time temperature signal output by the temperature sensor 42 and generate control commands based on the difference between the signal and the set temperature to adjust the working state of the Peltier thermoelectric coolers 44, thereby achieving closed-loop temperature control of the color rendering area 11. Set the temperature to the constant temperature required for the colorimetric reaction, such as 25~28℃.

[0035] In this embodiment, the cold end of the Peltier thermoelectric cooler 44 is attached to the bottom of the heat-conducting box 45 to conduct heat from the color development area 11 in the microfluidic chip 1, thereby achieving precise temperature control. A closed-loop feedback system is formed by the temperature control board 41 and the temperature sensor 42, which automatically adjusts the working state of the Peltier thermoelectric cooler 44 according to the set temperature to ensure that the temperature distribution of the plane where the color development area 11 is located is uniform during the detection process, and the temperature difference between any two points does not exceed 0.5℃. When the cover is open, the temperature of the chip surface is stable at 25~28℃, for example, about 26.7℃, indicating that the color development area 11 is in a set constant temperature environment, which is beneficial to ensuring the stability of pH detection.

[0036] like Figure 9As shown, in practice, the heat-conducting box 45 can be a square aluminum alloy base, with a mounting groove 452 inside that matches the contour of the microfluidic chip 1. The bottom of the heat sink 43 has a downward-opening mounting cavity a. The fan mounting plate 47 is fixed to the bottom of the heat sink 43 with screws, and the lower opening of the mounting cavity a is closed, thereby forming a receiving space between the heat sink 43 and the fan mounting plate 47. A fixing block 46 is provided in the receiving space. The fixing block 46 has a mounting groove for accommodating the LED light source and is installed in the mounting cavity by a fastener. The LED light source is embedded in the mounting groove. The bottom surface of the fixing block 46 contacts the fan mounting plate 47, and the top surface contacts the bottom edge area of ​​the heat sink 43 to achieve positioning and partial heat conduction.

[0037] The bottom of the heat-conducting box 45 is provided with a light-transmitting hole 451. The light-transmitting hole 451 is aligned with the first lens 22 and the color-developing area 11 in the optical path so that the detection light, after being focused by the first lens 22, can pass through the light-transmitting hole 451 and illuminate the color-developing area 11.

[0038] In one embodiment, the light-transmitting hole 451 can be located at the center of the heat-conducting box 45, and it penetrates the bottom wall of the box along the optical axis to match the coaxial optical path layout of the LED light source and the first lens 22, so as to ensure that the light spot uniformly covers the color display area 11.

[0039] In this embodiment, the light emitting component 2 includes: an LED light source (not shown in the figure), a first optical fiber 21, and a first lens 22; wherein, the emitted light from the LED light source is coupled to one end of the first optical fiber 21, and the other end of the first optical fiber 21 is disposed on the light-incident side of the first lens 22 as a light output end, so that the LED light source, the first optical fiber 21, and the first lens 22 are coaxial in the optical path, so as to focus the detection light output through the first optical fiber 21 onto the color rendering region 11.

[0040] Specifically, the LED light source is a white LED, whose emission spectrum covers the visible light range, used to uniformly illuminate the color rendering area 11. The incident light emitted by the full-wavelength light source is absorbed at a specific wavelength after passing through the sample mixed with the indicator, thus exhibiting a color change corresponding to the pH value. The first lens 22 is fixed in the mounting hole opened on the heat sink 43.

[0041] In this embodiment, the LED light source is arranged in the area between the bottom plate of the lower cover 72 of the housing 7 and the bottom of the heat sink 43. This layout makes full use of the space at the bottom of the device. The first lens 22 is fixed in the mounting hole opened in the middle of the heat sink 43, and its optical axis is aligned with the light-transmitting hole 451 in the heat-conducting box 45 and the color display area 11 in the microfluidic chip 1.

[0042] The first optical fiber 21 is set at the emitting end of the LED light source through the optical fiber fixing head 23. The optical fiber fixing head 23 is coaxially set with the fixing block 46 embedded with the LED optical fiber to ensure that the detection light emitted by the LED light source can be efficiently coupled into the first optical fiber 21.

[0043] The detection light emitted by the LED light source is coupled into the first end of the first optical fiber 21 and then transmitted to the other end for output. The output end of the first optical fiber 21 and the first lens 22 are coaxially arranged in the optical path, so that the output excitation light is focused by the first lens 22 to form a converging beam. This converging beam conducts heat to the light-transmitting hole 451 at the bottom of the heat-conducting box 45 without obstruction and illuminates the color development area 11, so that the test liquid sample mixed with pH indicator shows a color corresponding to its acidity or alkalinity, which is convenient for subsequent analysis.

[0044] An optical path receiving component 5 is provided between the color sensing unit 3 and the color display area 11, which is used to collimate the colored light modulated by the color display area 11 and project it onto the photosensitive surface of the color sensing unit 3.

[0045] Specifically, the optical path receiving component 5 includes: a second optical fiber 51 and a second lens (not shown in the figure); wherein, the incident end of the second optical fiber 51 is aligned with the color display area 11 of the microfluidic chip 1, and its output end passes through a vertically arranged optical fiber holder 52 and is aligned with the incident end of the second lens, and the emitting end of the second lens is aligned with the photosensitive chip of the color sensing unit 3, for collimating and focusing the collected colored light onto the photosensitive surface of the photosensitive chip.

[0046] The bottom of the upper cover 71 of the outer casing 7 is provided with a mounting plate 711, on which a fixing plate 712 for guiding holes is provided. The fiber optic fixer 52 is vertically adjustable and inserted into the fixing plate 712, thereby adjusting the height and lateral position of the input end of the second fiber optic cable 52 to ensure that it is aligned with the color display area 11 of the microfluidic chip 1 below. In practice, the other end of the second fiber optic cable 51 is connected to a threaded cylinder 713, and the second lens is installed in the threaded cylinder 713. A light-shielding cylinder 714 is provided at the end of the color sensing unit near the second lens. The photosensitive chip is attached to the signal acquisition board 31 on the side of the light-shielding cylinder 714 away from the threaded cylinder. The light-shielding cylinder 714 is screwed to the threaded cylinder 713 to achieve precise alignment between the second lens and the photosensitive chip.

[0047] Preferably, the second lens is an optical fiber collimating lens, whose numerical aperture matches that of the second optical fiber 51, used to collimate and focus the collected colored light onto the photosensitive chip of the color sensing unit 3; the first lens 22 in the light emitting assembly 2 is also an optical fiber collimating lens, whose numerical aperture (e.g., 0.22) matches that of the first optical fiber 21, used to collimate the divergent light emitted by the LED into parallel light, illuminating the color rendering area 11 of the microfluidic chip 1. In this embodiment, the core diameter of the first optical fiber 21 and the second optical fiber 51 can be 0.5~1mm, preferably 0.8mm.

[0048] In this embodiment, the color sensor component uses a signal acquisition board 31, which has a built-in photosensitive chip and signal processing circuit. This board converts the received colored light signal into digital RGB values ​​and transmits them to the processing unit and display unit 6 via a serial interface. The signal acquisition board 31 can be a TCS230 signal acquisition board. In this embodiment, to eliminate ambient light interference and improve color reproduction accuracy, a mobile phone screen displaying a standard white image is used as a reference. After white balance calibration of the color sensor, verification is performed using color samples that actually develop color within a pH range of 4-9, covered with a methyl red (Mr)-bromothymol blue (BTB) mixed indicator. The verification results are as follows: Figure 13 As shown in the figure. The verification results show that the ratio of the red, green, and blue (RGB) channel detection values ​​output by the color sensor component varies significantly with pH changes, achieving the resolution required for pH quantification.

[0049] The method for white balance calibration of the color sensor component is as follows: Using the white interface of the display screen as a reference, the raw response values ​​(Rraw, Green, Braw) of the red, green, and blue (RGB) channels are collected, and the scaling factor normalized to 255 for each channel is calculated according to the following formula: R scale = Rraw / 255, G scale = Graw / 255, B scale = Braw / 255 In actual color detection, the sensor acquires the raw RGB response signals (red, green, and blue measurements) of the target sample in real time. After calibration by the aforementioned scaling factor, the calibrated RGB output values ​​are finally obtained, calculated as follows: In the formula, R calibrated G calibrated B calibrated These are the calibrated red, green, and blue channel color signal values, respectively; R measured G measured Bmeasured These are the raw measurement values ​​of the red, green, and blue channels collected by the color sensor; R scale G scale B scale These are the calibration coefficients for the red, green, and blue channels, respectively.

[0050] This algorithm significantly improves the reliability and consistency of color detection results by effectively eliminating system biases introduced by the light source and sensor itself, as well as interference caused by opaque objects in the liquid being measured.

[0051] In this embodiment, the preset standard color data refers to color reference data corresponding to different pH values ​​obtained through experimental calibration. Specifically, using several standard buffer solutions with a pH gradient of 0.1 units, under the same temperature, light, and imaging conditions as the liquid sample to be tested, the RGB color signals of its colorimetric region 11 are acquired, and a mapping relationship between pH value and color parameters (such as the original values ​​of R, G, and B or their ratios) is established. The pH value prediction model is trained based on this standard color dataset.

[0052] In this embodiment, the processing unit stores a pH prediction model, and the input feature vector of the pH prediction model is obtained by transforming the RGB three-channel intensity values ​​(R, G, B) output by the color sensing unit 3. Where log represents the logarithm to the natural constant e; The pH value is a stability constant; the pH prediction model is used to output the predicted pH value of the liquid sample to be tested based on the input feature vector.

[0053] See Figure 5 and Figure 6 In this embodiment, the device further includes: a housing 7; the housing 7 consists of an upper cover 71 and a lower cover 72, which are movably connected by a hinge. An AC power socket is provided on the outer side of the upper cover 71 of the housing 7 for connecting a 220V power supply; a power switch button is also provided on one side for controlling the power supply to and from the device. After the external power supply is input through the AC power socket, it is converted by the power management module inside the upper cover 71 into an operating voltage suitable for each functional unit.

[0054] The lower cover 72 is used to fix the microfluidic chip 1, the temperature control unit 4 and the light emitting component 2; the upper cover 71 integrates the color sensing unit 3, the light path receiving component 5, the display unit 6 and the power management module.

[0055] This embodiment of the invention also includes: a display unit 6, which is a serial port screen connected to the signal acquisition board 31 of the color sensing unit 3 via a serial interface, for real-time display of detection results.

[0056] The power management module includes an AC / DC conversion unit and a DC-DC step-down conversion unit, integrated on a circuit board inside the top cover 71. External 220V AC power is converted to 24V DC by the AC / DC conversion unit. One path powers the temperature control unit 4, while the other path is split into 3V and 5V paths by the DC-DC step-down conversion unit. The 5V path powers the serial port screen and signal acquisition board, while the 3V path powers the LED light source.

[0057] When the upper cover 71 is closed by flipping the hinge, the upper cover 71 and the lower cover 72 fit tightly together, aligning the detection optical path and the receiving optical path with the color development area 11, forming a relatively closed detection chamber, reducing environmental interference and maintaining stable ambient temperature. In use, the user can open the upper cover 71 and connect two syringes to the two PEEK connectors on the surface of the microfluidic chip 1, one containing the liquid sample to be tested and the other containing a pH indicator. Then, the two syringes are simultaneously advanced, allowing the two liquids to enter the microfluidic chip 1 through the inlet channel 15, where they are fully mixed in the three-dimensional mixing zone 12 and undergo a color development reaction. After closing the upper cover 71 and turning on the power switch, the system immediately activates the light source, temperature control unit 4, and color sensing unit 3 to complete optical detection and data processing, outputting the pH value. After detection, the waste liquid is discharged through the outlet 14 of the microfluidic chip 1 to the outer casing 7. The outer casing 7 is designed with a hinge structure for easy pipe connection, waste liquid discharge, and daily maintenance.

[0058] It is evident from the above that the microfluidic chip-based liquid sample pH monitoring system provided in this embodiment integrates a colorimetric region within the microfluidic chip, causing a colorimetric reaction when the liquid sample to be tested is mixed with a pH indicator, generating a corresponding color. Detection light is provided by a light-emitting component located below the microfluidic chip, and the transmitted light, modulated by the colorimetric region, is received by the upper-mounted color sensing unit and converted into a color signal. Simultaneously, a temperature control unit maintains the colorimetric region at a constant temperature to eliminate interference from ambient temperature on the pH detection results. The processing unit analyzes the color signal based on a pre-trained pH prediction model and ultimately outputs the pH value of the liquid sample to be tested. This achieves high-precision, continuous, and real-time quantitative pH analysis of trace amounts of flowing liquid samples, effectively solving problems such as low detection accuracy, inability to dynamically monitor, and cumbersome operation in existing technologies.

[0059] In the above embodiments, the present invention uses supervised regression to construct a pH prediction model. The dataset contains 150 clinical urine samples, and each sample records the true pH value and its corresponding RGB three-channel intensity value (0-255).

[0060] Using RGB values ​​as the input feature vector x and the true pH value as the target output y, a mapping function is learned. To achieve pH prediction, where y represents the true pH value. These are the model predictions. To obtain reliable generalization performance estimates and avoid the test set participating in model selection, the data is divided into a training set (n=120) and a test set (n=30) at a ratio of 80 / 20. The test set is completely isolated during hyperparameter tuning and model selection and is used only for the final one-time evaluation. All randomization processes use a fixed random seed (seed=42) to ensure the reproducibility of results.

[0061] To reduce the impact of exposure, brightness, and gain variations on absolute RGB intensity, this invention builds more robust features on top of the original RGB, including RGB channel normalization, logarithmic ratios, and HSV color space features.

[0062] Specifically, for a single sample, the original red, green, and blue channel intensities are measured as (R, G, B), and the following features are further calculated: First, to reduce the multiplicative changes in overall brightness and exposure, channel normalization is used to obtain the relative intensity: in, This is used to prevent stable terms with a denominator of zero.

[0063] Secondly, to further eliminate gain variations and expand the separability of weak differences, a feature of the logarithm of the ratio is constructed: Where log represents the logarithm to the natural constant e; It is still used for numerical stability, preventing zero denominators and overflow of the domain of logarithms. This transformation maps "doubling / halving" to numerically symmetrical positive and negative changes, thus making the relationship between features and target variables smoother and easier for regression models to learn.

[0064] Finally, the RGB values ​​are mapped to the HSV color space to extract the hue (H), saturation (S), and lightness (V).

[0065] Considering H For the circumferential variable (0° is equivalent to 360°), further use circumferential encoding: This circular encoding avoids the learning difficulties caused by discontinuities in hue at boundaries. Ultimately, it uses (H) sin H cos (S, V) were used as color characterization features of the sample for subsequent pH prediction model training and ablation comparison experiments.

[0066] To construct a robust pH prediction model, this invention employs Gradient Boosting Regression Tree (GBDT) as the core algorithm.

[0067] To quantify the contribution of different features to prediction accuracy, this invention conducts feature ablation experiments under the premise of fixing the GBDT model.

[0068] The results show that: based on the characteristics of the logarithm of the ratio It achieves state-of-the-art performance on the training set, with a mean absolute error (MAE) of 0.0454, a root mean square error (RMSE) of 0.0667, and a coefficient of determination R0. 2 It reached 0.9977.

[0069] Subsequently, the regression model was retrained on the entire training set and then evaluated on the reserved test set, yielding MAE = 0.0441, RMSE = 0.0675, and R² = 0.9978. These results are consistent with the performance level achieved during the training set cross-validation phase, indicating that the proposed combination of color feature representation and the GBDT model maintains stable accuracy on unknown samples, thus achieving high-precision pH estimation.

[0070] Figure 16 The results demonstrate the predictive consistency and error distribution of the GBDT model on the test set: the scatter plots of the true and predicted values ​​are generally close to the diagonal; the residuals are randomly distributed around 0, with no obvious systematic bias observed; the absolute error distribution is concentrated in a small range, and the error quantile curve further shows that the tail error is controllable, further confirming that the system of this invention has stable and high-precision pH prediction performance.

[0071] To verify the technical effectiveness of the urine pH monitoring system based on a microfluidic chip provided by this invention, it was compared with representative pH detection methods in the prior art. The results are shown in Table 1: Table 1. Comparison of key performance indicators between the present invention and existing pH detection methods. pH meter pH test strips Integrated surface field-effect transistors SPR sensor This invention Sample volume ≥1 ml ≥ 10 μL 5-50 μL 5-20 μL 1.9 μL reaction time <1 minute 10-60 s ≤ 10 s ≤ 20 s 0.2s As can be seen from the table, the microfluidic chip-based liquid sample pH monitoring system of the present invention is significantly superior to existing testing methods in terms of sample volume and reaction speed; at the same time, it has good anti-interference ability and long-term stability, and is suitable for scenarios of rapid detection of pH in portable liquid samples.

[0072] In summary, the microfluidic chip-based liquid sample pH monitoring system of this invention, by integrating an RGB sensor, a transmissive optical detection path, and a temperature control unit, can achieve high-precision quantitative pH analysis of trace liquid samples (down to 1.9 μL), with a detection resolution of up to 0.1 pH units. Its performance is comparable to some commercial pH meters and significantly superior to the pH test strip method currently used in clinical laboratories. Furthermore, thanks to the colorimetric properties of the indicator, the system exhibits strong anti-interference capability for pale yellow urine over a wide pH range (pH 4-9). Simultaneously, the non-contact colorimetric detection mechanism avoids the contamination problems of traditional electrode-type sensors. Further benefiting from the highly durable solid-state LED light source and the real-time updating of the indicator with sample flow, signal drift is effectively suppressed, resulting in a long service life and excellent long-term stability. This system is compact, easy to operate, and has broad application prospects in the life sciences field, such as microfluidic chip-based single-cell culture, organoid culture, and continuous flow microfluidic point-of-care testing (POCT) products.

[0073] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A liquid sample pH monitoring system based on a microfluidic chip, characterized in that, include: The microfluidic chip (1) has a color development area (11) for containing the liquid sample to be tested and the pH indicator, so that the two are mixed in the area and a color development reaction occurs. A light emitting component (2) is disposed below the microfluidic chip (1) and is used to emit detection light into the color display area (11); The color sensing unit (3) is disposed above the microfluidic chip (1) and includes an optical path receiving component (5) and a color sensor component, used to receive colored light modulated by the color display area (11) and output the corresponding color signal; The temperature control unit (4) is thermally coupled to the microfluidic chip (1) to maintain the color display area (11) within a preset temperature range to ensure the stability of color signal detection. The processing unit is electrically connected to the color sensing unit (3) and is used to receive the color signal and process the color signal based on the pH prediction model, thereby outputting the pH value of the liquid sample to be tested.

2. The liquid sample pH monitoring system based on a microfluidic chip according to claim 1, characterized in that, The microfluidic chip (1) is formed by hot-pressing three layers of polymethyl methacrylate plates (lower, middle and upper layers) from bottom to top, and has a three-dimensional mixing zone (12) inside. The three-dimensional mixing zone (12) is composed of multiple identical circulation units connected in series. Each circulation unit includes a tortuous microchannel (121) in a single plane and a vertical connecting section (122) extending along the chip thickness direction and connected to the outlet of the tortuous microchannel (121). Adjacent circulation units are connected end to end through the vertical connecting section (122), so that the liquid sample to be tested and the pH indicator are disturbed in the plane and flow across the plane to achieve three-dimensional mixing.

3. The liquid sample pH monitoring system based on a microfluidic chip according to claim 2, characterized in that, The microfluidic chip (1) has two inlets (13) and one outlet (14) on its upper surface. The outlet (14) is located on the opposite side of the inlets (13). The microfluidic chip (1) has two inlet channels (15) corresponding to the two inlets (13) inside. The two inlet channels (15) pass through the three-layer polymethyl methacrylate plate from top to bottom and are connected to the three-dimensional mixing zone (12) between the lower and middle layers. The outlet of the three-dimensional mixing zone (12) is connected to the color development area (11) between the middle and upper layers. The color development area (11) is connected to the outlet through the discharge channel (16). The discharge channel (16) extends along the area between the middle and upper layers and passes through the upper polymethyl methacrylate plate to the outlet (14) on the upper surface of the microfluidic chip (1).

4. The liquid sample pH monitoring system based on a microfluidic chip according to claim 1, characterized in that, The light emitting component (2) includes: an LED light source, a first optical fiber (21), and a first lens (22); wherein, The emitted light from the LED light source is coupled to one end of the first optical fiber (21), and the other end of the first optical fiber (21) is set as the light output end on the light-incident side of the first lens (22), so that the LED light source, the first optical fiber (21) and the first lens (22) are coaxial in the optical path, so as to focus the detection light output through the first optical fiber (21) onto the color rendering area (11).

5. The liquid sample pH monitoring system based on a microfluidic chip according to claim 1, characterized in that, The temperature control unit (4) includes: a temperature control board (41), a temperature sensor (42), a radiator (43), and two Peltier thermoelectric coolers (44); wherein, The temperature sensing end of the temperature sensor (42) is embedded in the heat-conducting box (45) that houses the microfluidic chip (1); The heat sink (43) has mounting holes for mounting the first lens (22) in the light emitting assembly (2). Two Peltier thermoelectric coolers (44) are symmetrically arranged on both sides of the mounting hole, with their cold ends thermally coupled to the heat-conducting box (45) and their hot ends thermally coupled to the radiator (43); a fan (48) is provided at the bottom of the radiator (43) for forced convection heat dissipation. The temperature control board (41) is electrically connected to the temperature sensor (42) and the Peltier thermoelectric cooler (44), respectively.

6. The liquid sample pH monitoring system based on a microfluidic chip according to claim 5, characterized in that, The bottom of the heat-conducting box (45) is provided with a light-transmitting hole (451). The light-transmitting hole (451) is aligned with the first lens (22) and the color-displaying area (11) in the optical path so that the detection light can pass through the light-transmitting hole (451) and illuminate the color-displaying area (11) after being focused by the first lens (22).

7. The liquid sample pH monitoring system based on a microfluidic chip according to claim 1, characterized in that, The optical path receiving component (5) includes: a second optical fiber (51) and a second lens; wherein, The incident end of the second optical fiber (51) is aligned with the color display area (11) of the microfluidic chip (1), and its output end passes through the vertically arranged optical fiber holder (52) and is aligned with the incident end of the second lens. The emitting end of the second lens is aligned with the photosensitive chip of the color sensing unit (3) to focus the colored light modulated by the color rendering area (11) onto the photosensitive surface of the photosensitive chip.

8. The liquid sample pH monitoring system based on a microfluidic chip according to claim 1, characterized in that, The microfluidic chip (1) is provided with fluid connectors made of polyetheretherketone material at the inlet (13) and outlet (14) for connecting external liquid supply pipelines and waste liquid discharge pipelines.

9. The liquid sample pH monitoring system based on a microfluidic chip according to claim 1, characterized in that, The colorimetric region (11) is columnar and its volume is less than or equal to 4 μL.

10. The liquid sample pH monitoring system based on a microfluidic chip according to claim 1, characterized in that, The processing unit stores a pH prediction model, and the input feature vector of the pH prediction model is obtained by transforming the RGB three-channel intensity values ​​(R, G, B) output by the color sensing unit (3): Where log represents the logarithm to the natural constant e; The pH value is a stability constant; the pH prediction model is used to output the predicted pH value of the liquid sample to be tested based on the input feature vector.

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