A method for rapidly detecting the concentration of Fe(II) in water, a self-correcting colorimetric gel detection chip and a preparation method thereof

Abstract

This invention develops a self-calibrated colorimetric gel detection chip for rapid detection of Fe(II) concentration in water. Using this chip, after obtaining a colorimetric image by taking a photo with a mobile phone, a Fe(II) content detection model can be established using a volume self-calibration method, achieving accurate and rapid detection of Fe(II) concentration in water. The chip is prepared from the colorimetric reagent phenanthroline (PHEN), the gel carrier polyacrylic acid (PAA), and polyvinyl alcohol (PVA). This detection chip is based on a PAA-PVA composite gel composition. Benefiting from the high swelling capacity of PAA and the high salt resistance of PVA, the PAA-PVA interpenetrating network structure not only retains the original properties of PAA and PVA but also acquires unique properties unmatched by using these two polymers alone. This results in a colorimetric sensor device prepared from the PAA-PVA gel carrier that also possesses immediate responsiveness, long-term stability, and high efficiency and accuracy.

Description

Technical Field

[0001] This invention belongs to the field of chip technology, specifically relating to a method for rapid detection of Fe(II) concentration in water, a self-calibrating colorimetric gel detection chip and its preparation method. Background Technology

[0002] Iron is one of the essential trace elements for the human body, playing an indispensable role in various physiological functions such as oxygen transport and hematopoiesis. The content of Fe(III) and Fe(II) in water directly affects water quality, and the detection of Fe(II) content in water has always been one of the important indicators for environmental water quality monitoring. Establishing a rapid, accurate, and inexpensive detection method for Fe(II) content in water samples is of great significance.

[0003] The detection of Fe(II) concentration in samples is a routine analytical procedure in many industrial sectors, including environmental and food industries. Methods based on the light absorption of colored samples to analyze sample concentration are among the most widely used in chemical composition analysis. Classical analytical procedures often employ spectrophotometry. Spectrophotometric analysis typically uses a standard curve method, which requires specialized equipment, professional operators, extensive and tedious preparation of standard solutions, and sample pretreatment steps, resulting in low efficiency. In recent years, photochromic analysis methods have emerged that can achieve excellent analytical results without the use of a specialized spectrophotometer, but still require professional personnel for accurate solution preparation and sampling.

[0004] Currently, the most common method for detecting Fe(II) content in water samples is spectrophotometry. This involves adding a colorimetric reagent to the sample to convert Fe(II) into a strongly absorbing colored ion, measuring the absorbance of the solution using a spectrophotometer, and then obtaining the Fe(II) content in the water sample using a standard curve method. This method requires specialized equipment, professional operators, a large amount of tedious standard solution preparation, and sample pretreatment steps, resulting in low efficiency. Although a dedicated rapid Fe(II) detection kit has been developed [application number 202022291370.9], accurate solution preparation and sampling by professionals are still required, which is particularly unfavorable for rapid on-site analysis. In addition, other calibration methods have been reported to accurately detect sample concentrations, such as [Andreu Vaquer, Enrique Baron, Roberto de la Rica. Wearable Analytical Platform with Enzyme-Modulated Dynamic Range for the Simultaneous Colorimetric Detection of Sweat Volume and Sweat Biomarkers[J]. ACSSensors. 2021, 6(12): 130-136.]. This paper attempts to use a colorimetric sensor composed of two filter paper strips to accurately detect lactic acid in human sweat in situ: one filter paper strip is loaded with gold nanoparticles to detect sweat volume, and the other filter paper strip is loaded with lactate oxidase to detect lactic acid. In the actual detection process, the two filter paper strips are combined with adhesive tape to obtain a sweat detector. However, this method has an unavoidable drawback, namely that the target of sweat volume detection and the target of lactic acid concentration detection are different, which makes it impossible to "truly" correct the lactic acid concentration in sweat by sweat volume (volume).

[0005] Therefore, it is of great significance to develop a detection technology that requires no precise sampling and is fast and accurate. Summary of the Invention

[0006] To achieve rapid detection of Fe(II) content in water without the need for accurate solution preparation and sampling, this patent develops a novel colorimetric gel chip for rapid Fe(II) detection. Using this detection chip, after obtaining a colorimetric image by taking a photo with a mobile phone, a Fe(II) content detection model can be established using a volume self-calibration method, enabling accurate and rapid detection of Fe(II) concentration in water.

[0007] To address the shortcomings of existing technologies, the present invention provides the following technical solution:

[0008] This invention provides a method for rapidly detecting Fe(II) concentration in water, characterized by comprising the following steps:

[0009] (1) Drop a drop of water sample of variable volume onto the self-calibrating colorimetric gel detection chip. After 1 minute, the color development is completed. Take a picture to obtain the color development photo and read the RGB value of the image.

[0010] (2) After the RGB values ​​obtained in step (1) are self-calibrated by volume, the R′G′B′ values ​​are obtained. Substitute the R′ value, G′ value, or B′ value into the standard curve to calculate the Fe(II) concentration in the water sample.

[0011] Preferably, the volume self-calibration method in step (2) specifically includes the following steps:

[0012] Fe(II) solutions of equal concentration and volumes V1, V2, and V3 were dropped onto a self-calibrating colorimetric gel detection chip. After 1 minute, color development was completed, and a colorimetric image was taken. The RGB values ​​of the image were read, and the volume-corrected R′G′B′ value was obtained using the following formula:

[0013] logR1 / logR2 = (V1 / V2) x1

[0014] logR2 / logR2=(V2 / V2) x2

[0015] logR3 / logR2 = (V3 / V2) x3

[0016] x = (x1 + x2 + x3) / 3

[0017] logR′=logR / V X ;

[0018] or

[0019] logG1 / logG2 = (V1 / V2) y1

[0020] logG2 / logG2=(V2 / V2) y2

[0021] logG3 / logG2 = (V3 / V2) y3

[0022] y = (y1 + y2 + y3) / 3

[0023] logG′=logG / V y ;

[0024] or

[0025] logB1 / logB2 = (V1 / V2) z1

[0026] logB2 / logB2=(V2 / V2) z2

[0027] logB3 / logB2 = (V3 / V2) z3

[0028] z = (z1 + z2 + z3) / 3

[0029] logB′=logB / V z ;

[0030] Wherein, R1, G1, and B1 represent the R, G, and B values ​​when the volume is V1, respectively; R2, G2, and B2 represent the R, G, and B values ​​when the volume is V2, respectively; R3, G3, and B3 represent the R, G, and B values ​​when the volume is V3, respectively; V represents the actual volume of the water sample to be tested, which is read by unfolding the reaction between the chip and the Fe(II) solution on a grid interface with a size of 2.5×2.5mm; R′, G′, and B′ represent the R, G, and B values ​​of the water sample after volume self-correction.

[0031] Preferably, the preparation of the standard curve in step (2) includes the following steps:

[0032] The concentration is 1×10 -5 -9×10 -4 A mol / L Fe(II) series standard solution was used. One drop of the standard solution was dropped onto the chip. After 1 minute of color development, the image was photographed and the RGB values ​​of the image were read. The corrected R′G′B′ values ​​were obtained through the volume self-calibration method described above. Then, fitting curves of logR′~logc(Fe(II)), logG′~logc(Fe(II)), and logB′~logc(Fe(II)) were established.

[0033] Preferably, the method can detect Fe(II) concentration in water within a range of 1 × 10⁻⁶. -5 -9×10 -4 mol / L.

[0034] The present invention also provides a method for preparing a self-calibrating colorimetric gel detection chip for rapid detection of Fe(II) concentration in water, comprising the following steps: dissolving a colorimetric agent and a gel carrier, heating to react, removing bubbles, drying, and cutting to obtain the self-calibrating colorimetric gel detection chip.

[0035] Preferably, the color developer is PHEN (o-phenanthroline), and the gel carrier is polyacrylic acid (PAA) and polyvinyl alcohol (PVA).

[0036] Preferably, the amount of PHEN added is 0.001-0.1g; the amount of PVA added is 1-10g; and the amount of PAA added is 1-5g.

[0037] Preferably, the heating reaction temperature is 90-110℃, the drying temperature is 50-80℃, the diameter of the cut is 1-10mm, and the thickness is 0.1-0.3mm.

[0038] Preferably, the diameter of the cut is 5 mm.

[0039] The present invention also provides a self-calibrating colorimetric gel detection chip prepared by the above preparation method.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] 1. This detection method is very inexpensive, as it only requires a chip with a diameter of 1-10 mm to accurately measure the Fe(II) content in a water sample.

[0042] 2. This detection chip is based on PAA-PVA composite gel. Thanks to the high swelling capacity of PAA and the high salt resistance of PVA, the PAA-PVA interpenetrating network structure not only retains the original properties of PAA and PVA, but also obtains unique properties that cannot be matched by the two polymers when used alone. This makes the colorimetric detection chip prepared by PAA-PVA gel carrier have instant response, long-term stability and accuracy.

[0043] 3. Using the novel Fe(II) concentration detection colorimetric gel chip of this invention, the concentration of Fe(II) in the solution can be quickly and accurately measured without the need for sample preparation and accurate sampling. The chip only needs to be briefly in contact with the water sample before a photographic colorimetric analysis method can be used. The use of this chip not only effectively improves the speed of analysis and detection and reduces testing costs, but also makes the relevant detection method more accessible to the general public. Attached Figure Description

[0044] Figure 1 The graph shows the relationship between the chip diameter and the volume of the Fe(II) solution.

[0045] Figure 2 The experiment aimed to observe the color development and RGB value changes of the PHEN-PAA-PVA chip after adding Fe(II) solutions of different concentrations to it.

[0046] Figure 3 To demonstrate the color development effect of different pH (1-14) solutions containing composite indicators dropped onto filter paper and PHEN-PAA-PVA chip respectively;

[0047] Figure 4 To quantitatively detect 1×10 using the PHEN-PAA-PVA chip -5 -9×10 -4 The effect of mol / L Fe(II) standard sample, where Figures a, b, and c correspond to the relationship between the R, G, and B parameters of chip color development and Fe(II) concentration before the self-calibrated RGB model is processed, respectively; Figures d, e, and f correspond to the relationship between the R, G, and B parameters of chip color development and Fe(II) concentration after the self-calibrated RGB model is processed, respectively.

[0048] Figure 5 The effects of different (a) PVA:PAA mass ratios, (b) different chip thicknesses, (c) different chip diameters on chip swelling effects; and (d) different amounts of o-phenanthroline on chip color development effects. Detailed Implementation

[0049] Example 1: 0.001g PHEN, 1.00g PAA, and 1.00g PVA were placed in freshly boiled deionized water and dissolved completely in a 105℃ oil bath using a one-pot method. The mixture was then vacuum-sealed to remove air bubbles and dried in a 60℃ oven to obtain a PHEN-PAA-PVA composite swollen film with a thickness of approximately 0.10mm (±0.01mm). PHEN-PAA-PVA composite swollen films with diameters of 1.0-5.5mm and a thickness of 0.10mm (±0.01mm) were manually prepared using a 5mm punch.

[0050] The effect of different chip diameters on chip swelling effect is shown in the figure. Figure 5 c. Small-diameter chips are more sensitive and accurate in colorimetric response to minute volumes of analytes, while large-diameter chips help to broaden the detection range of variable volumes, thereby achieving a wide-range and highly accurate detection effect.

[0051] Example 2: 0.010g PHEN, 1.00g PAA, and 5.00g PVA were placed in freshly boiled deionized water and dissolved completely in a 105℃ oil bath using a one-pot method. The mixture was then vacuum-sealed to remove air bubbles, yielding a PHEN-PAA-PVA composite swelling gel. The gel was poured into a 5.0mm mold and dried in a 60℃ oven for 14 hours to obtain a PHEN-PAA-PVA composite swelling film with a diameter of 5.0mm and a thickness of 0.05-0.30mm (±0.01mm).

[0052] The effect of different chip thicknesses on chip swelling effect is shown in the figure. Figure 5 b. Films of different thicknesses have different water absorption and swelling effects, resulting in different color development effects in the same amount of Fe(II).

[0053] Example 3: 0.001-0.10g PHEN, 5.00g PAA, and 10.00g PVA were placed in freshly boiled deionized water and dissolved completely using a one-pot method at 90°C. Air bubbles were removed under vacuum, and the solution was evenly spread on a mold and dried in a 50°C oven to obtain a PHEN-PAA-PVA swellable composite gel film. The swellable composite gel film was then cut into 10.0mm diameter pieces to obtain the PHEN-PAA-PVA swellable composite film.

[0054] from Figure 5 It can be seen that the PVA:PAA mass ratio, chip thickness, chip diameter, and o-phenanthroline dosage have a certain impact on the chip swelling effect and color development effect. However, the chips provided in the above embodiments can all achieve rapid and accurate determination of Fe(II) concentration in water.

[0055] The detection chip is used as follows:

[0056] The Fe(II) colorimetric gel chip was laid flat on a clean substrate. A drop of water sample (approximately 10-20 μL) was placed on the detection chip using a dropper. After 1 minute, color development was completed, and a colorimetric image was taken. The RGB values ​​of the image were read using Photoshop 2016. Further, based on the RGB values ​​read from the colorimetric image, a volume self-calibration method was used to obtain the volume-corrected RGB values ​​(denoted as R'G'B'). Substituting R'G'B' into the standard curve, the accurate Fe(II) content in the water sample could be obtained.

[0057] The volume self-calibration method is as follows: The reaction between the PHEN-PAA-PVA chip and Fe(II) solution is unfolded on a 2.5×2.5mm grid interface, allowing direct reading of the swelling degree of PAA-PVA. The swelling degree of the PHEN-PAA-PVA chip indirectly reflects the added volume of Fe(II) solution. Using the designed and prepared PHEN-PAA-PVA detection chip, data from Fe(II) sample solutions of different concentrations were collected. Then, 1×10⁻⁵ μL (intervals of 10 μL) were plotted. -5 -9×10 -4 Calibration curves for mol / L Fe(II) samples were used to show the effect of different Fe(II) sample volumes on the colorimetric signal of the sensor.

[0058] The volume self-calibrated colorimetric RGB model-assisted PHEN-PAA-PVA self-calibrated colorimetric detection chip can accurately measure 1×10 -5 -9×10 -4 Data processing method for mol / L Fe(II):

[0059] logR1 / logR2=(V1 / V2) x1

[0060] logR2 / logR2=(V2 / V2) x2

[0061] logR3 / logR2=(V3 / V2) x3

[0062] x=(x1+x2+x3) / 3

[0063] logR′=logR / V X

[0064] logG1 / logG2=(V1 / V2) y1

[0065] logG2 / logG2=(V2 / V2) y2

[0066] logG3 / logG2=(V3 / V2) y3

[0067] y=(y1+y2+y3) / 3

[0068] logG′=logG / V y

[0069] logB1 / logB2=(V1 / V2) z1

[0070] logB2 / logB2=(V2 / V2) z2

[0071] logB3 / logB2=(V3 / V2) z3

[0072] z=(z1+z2+z3) / 3

[0073] logB′=logB / V z

[0074] V1 refers to 5 μL, V2 refers to 15 μL, and V3 refers to 25 μL. R1, G1, and B1 are the RGB values ​​of the chip after adding 5 μL of the Fe(II) solution to be tested and developing color for 1 minute; R2, G2, and B2 are the RGB values ​​after adding 15 μL of the Fe(II) solution to be tested and developing color for 1 minute; R3, G3, and B3 are the RGB values ​​of the sensor after adding 25 μL of the Fe(II) solution to be tested and developing color for 1 minute. x1, x2, and x3 represent the correction coefficients of 5 μL, 15 μL, and 25 μL of Fe(II) to logR, respectively, where x represents the average correction coefficient of the Fe(II) addition volume to logR; y1, y2, and y3 represent the correction coefficients of 5 μL, 15 μL, and 25 μL of Fe(II) to logG, respectively, where y represents the average correction coefficient of the Fe(II) addition volume to logG; z1, z2, and z3 represent the correction coefficients of 5 μL, 15 μL, and 25 μL of Fe(II) to logB, respectively, where z represents the average correction coefficient of the Fe(II) addition volume to logB.

[0075] The standard curve is prepared as follows: Prepare a solution with a concentration of 1×10⁻⁶. -5 -9×10 -4 Fe(II) series standard solutions were used. One drop of the standard solution was dropped onto the chip. After 1 minute of color development, the image was photographed. The RGB values ​​of the image were read using Photoshop 2016. The corrected RGB values ​​(denoted as R'G'B') were obtained through the volume self-calibration method described above. Then, a fitting curve was established for logR'~logc(Fe(II)), logG'~logc(Fe(II)), and logB'~logc(Fe(II)).

[0076] This invention provides a method for rapid detection of Fe(II) in water. Even when different volumes of Fe(II) solution of unknown concentration are added, the concentration of Fe(II) at different added volumes can be accurately detected by obtaining RGB values ​​and according to the model (logR'~logc(Fe(II)),logG'~logc(Fe(II)),logB'~logc(Fe(II))).

[0077] The effectiveness of the chip described in Example 2 was verified:

[0078] This detection chip contains a component with high swelling properties (PVA-PAA composite gel). Upon contact with the water sample, the chip rapidly absorbs water and swells. The degree of swelling is directly related to the volume of the water sample added to the chip. The established volume self-calibration method can analyze the water sample volume added to the chip based on the chip's water absorption and swelling behavior. Different volumes (5-25 μL) were tested at 5 × 10⁻⁶. -4When a mol / L Fe(II) aqueous solution is dropped onto the detection chip, the chip develops color and swells, resulting in an enlarged appearance. Figure 1 As shown in the illustration, Figure 1 It also demonstrates that after the detection chip swells and expands, there is a good linear relationship between the chip diameter and the volume of the added Fe(II) solution.

[0079] This detection chip also contains the Fe(II) colorimetric reagent PHEN. Upon contact with the water sample, the chip absorbs water and swells. Simultaneously, the Fe(II) in the water sample reacts immediately with the PHEN reagent in the chip to produce a red complex, causing a color change in the chip. The degree of color change can be used to approximately estimate the Fe(II) content in the water sample (the degree of color change is also related to the sample volume). 20 μL of different concentrations (1×10⁻⁶) were added... -5 -9×10 -4 When a Fe(II) solution of mol / L is added to the detection chip, the color development intensity gradually increases with the increase of Fe(II) solution concentration. Figure 2 ).

[0080] When using PHEN as a colorimetric reagent to detect Fe(II) in water samples, the pH of the solution needs to be maintained between 3 and 8. Conventional methods typically require the addition of a buffer solution (such as HAc-NaAc buffer solution) to control the pH. The colorimetric gel component PAA used in this detection chip can itself act as a buffer, providing pH self-buffering during the detection process and avoiding the need for an additional buffer solution. Deionized water containing a composite pH indicator was adjusted to pH 1-14 using NaOH and HCl. Then, 20 μL of solutions at different pH levels were added dropwise to filter paper and the Fe(II) rapid detection chip, respectively. The color development is as follows: Figure 3 As shown, the filter paper exhibits distinctly different colors when solutions of different pH values ​​are dropped onto it. However, the colors displayed on the detection chip differ from those on the filter paper. For solutions with pH values ​​between 4 and 10, the chip's color development indicates a pH of 7 ± 1, demonstrating that the detection chip possesses a "self-buffering" effect for solutions of different pH values. Furthermore, Fe(II) samples with pH values ​​between 4 and 10 require no pretreatment and can be directly tested.

[0081] Because the color change of the chip during detection depends not only on the Fe(II) concentration in the water sample but also on the volume of water sample added, accurate solution preparation and sampling are required by professionals in routine colorimetric analysis. Figure 4As shown, the initial size of this detection chip remains consistent, allowing for precise control of the dosage of various reagents. Simultaneously, the volume of the water sample can be automatically inferred based on the degree of water absorption and swelling, providing information for further "self-correction" of color change differences caused by changes in water sample volume using a volume self-calibration model. By automatically correcting color differences caused by sample volume changes using a volume self-calibration RGB model, the detection accuracy is significantly improved.

[0082] In summary, these experiments validated our initial hypothesis: even with the addition of different Fe(II) sample volumes, our designed PAA-PVA-PHEN self-calibrating colorimetric gel microsensor can respond not only to Fe(II) concentration but also to the added volume.

[0083] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for rapid detection of Fe(II) concentration in water, characterized in that, Includes the following steps: (1) Drop a drop of water sample of variable volume onto the self-calibrating colorimetric gel detection chip. After 1 minute, the color development is completed. Take a picture to obtain the color development image and read the RGB value of the image. (2) After the RGB values ​​obtained in step (1) are self-calibrated by volume, the R', G', and B' values ​​are obtained. Substitute the R', G', or B' values ​​into the standard curve to calculate the Fe(II) concentration in the water sample. The volume self-calibration mentioned in step (2) specifically includes the following steps: Fe(II) solutions of equal concentration and volumes V1, V2, and V3 were dropped onto a self-calibrating colorimetric gel detection chip. After 1 minute, color development was completed, and a colorimetric image was taken. The RGB values ​​of the image were read, and the volume-corrected R', G', and B' values ​​were obtained using the following formula: ； or or Wherein, R1, G1, and B1 represent the R, G, and B values ​​when the volume is V1, respectively; R2, G2, and B2 represent the R, G, and B values ​​when the volume is V2, respectively; R3, G3, and B3 represent the R, G, and B values ​​when the volume is V3, respectively; V represents the actual volume of the water sample to be tested, which is read by unfolding the reaction between the chip and the Fe(II) solution on a grid interface with a size of 2.5×2.5 mm; R', G', and B' represent the R, G, and B values ​​of the water sample after volume self-correction.

2. The method according to claim 1, characterized in that, The preparation of the standard curve in step (2) includes the following steps: The concentration is 1×10 -5 -9×10 -4 A mol / L Fe(II) series standard solution was used. One drop of the standard solution was dropped onto the chip. After 1 minute of color development, the image was photographed and the RGB values ​​of the image were read. The corrected R' G'B' values ​​were obtained through the volume self-calibration method described above. Then, the fitting curves logR'~logc(Fe(II)), logG'~logc(Fe(II)), and logB'~logc(Fe(II)) were established.

3. The method according to claim 1, characterized in that, The method can detect Fe(II) concentrations in water within a range of 1 × 10⁻⁶. -5 -9×10 -4 mol / L.

4. The method according to claim 1, characterized in that, The preparation method of the self-calibrating colorimetric gel detection chip includes the following steps: dissolving the colorimetric agent and gel carrier, heating to react, removing bubbles, drying, and cutting to obtain the self-calibrating colorimetric gel detection chip.

5. The method according to claim 4, characterized in that, The colorimetric agent is PHEN (o-phenanthroline), and the gel carrier is polyacrylic acid (PAA) and polyvinyl alcohol (PVA).

6. The method according to claim 5, characterized in that, The addition amount of phenanthroline (PHEN) is 0.001-0.1g; the addition amount of polyvinyl alcohol (PVA) is 1-10g; and the addition amount of polyacrylic acid (PAA) is 1-5g.

7. The method according to claim 4, characterized in that, The heating reaction temperature is 90-110 ℃, and the drying temperature is 50-80 ℃; the diameter of the cut is 1-10 mm; and the thickness is 0.1-0.3 mm.

8. The method according to claim 7, characterized in that, The diameter of the cut is 5mm.

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