Enzyme-free colorimetric detection of uric acid on the basis of MnO2 nanosheets - mediated oxidation of 3, 3′, 5, 5′- tetramethylbenzidine
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A challenge for optofluidic absorbance detection is the high concentration limit of detection due to the short optical path length. Herein, we introduce a concept of utilizing the coiled optical nanofiber for highly sensitive and robust optofluidic absorbance detection. Investigated by measuring the absorbance of FeCl3 solutions, the sensor shows a detection limit down to 10 μM with excellent reversibility in a concentration range of 0-5 mM. The sensitivity is 10-fold higher than that of standard absorbance measurement by using a 1 cm cuvette. Also, highly sensitive chloramphenicol sensing was demonstrated by using the enzyme-linked immunosorbent assay (ELISA) method, achieving a detection limit below 0.5 ng/L. The higher sensitivity and lower detection limit are caused by the large fractional power of evanescent field outside the nanofiber and the long detection length, which can effectively improve the absorption of the evanescent field, while the excellent reversibility is caused by the support of a polydimethylsiloxane (PDMS) pillar rather than by suspending the nanofiber in the microchannel. We envision that the present work may open up new opportunities for ultrasensitive chemical and biological sensing.
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Dye-binding methods based on protein error for determining human serum albumin are classified into two methodologies via measurements of the absorbance increase under an acidic condition (absorbance increase method) and the absorbance decrease in a pH region near the neutral condition (absorbance decrease method). The color development of protein in the absorbance increase method is known to be affected by the pH, and the concentrations of dye, buffer and coexisting anions in the samples. However, the effect of coexisting anions on color development in the absorbance decrease method is unclear. In the present work, the effect of an inorganic salt on color development in the absorbance decrease method was investigated by a calculation based on the chemical equilibrium of the protein error and an experiment, and was compared with the results of the absorbance increase method. By adding an inorganic salt, the absorbance was decreased. The degree of its decrease was smaller in the absorbance decrease method than in the absorbance increase method, and differed according to the kind of inorganic salt. The experimental results agreed well with those obtained by a calculation.
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The objective of this research was to experimentally determine whether signs of water deficit stress in plants can be detected from changes in the absorbance spectra based on the relationships between absorbance spectra and physiological parameters. Absorbance of tomato leaves in the near-infrared (NIR) wavelengths (1100 nm to 2500 nm) was measured simultaneously with photosynthesis and stomatal conductance during water stress. To observe small changes in absorbance which arise from water stress, a leaf in non-stressed conditions was used as a reference for the absorbance measurements. In general, under the effects of water stress, peaks formed in the absorbance spectra at water absorbance bands near 1 440 nm and 1 940 nm, and absorbance decreased near 1 600 nm forming a valley. Although the relationship between the changes in absorbance and physiological parameters varied depending on the individual plants tested, consistent overall trends were observed, demonstrating there is potential to nondestructively detect changes in plant condition resulting from water stress by measuring NIR absorbance.
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Water Stress
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Objective:To examine the feasibility and the linear range for serum uric acid assay by integrating a kinetic uricase method with the equilibrium uricase method.Methods:Uricase reaction curves were monitored within 5.0 min by absorbance at 293 nm in 1.2 ml borate buffer(0.20 mol/L,pH 9.2) at 25℃;the absorbance at 293 nm of a reaction solution minus 5 μl uricase solution was measured as the initial absorbance,the absorbance after the addition of 5 μl solution of recombinant Bacillus fastidiosus uricase to complete the reaction was measured as the background absorbance.The difference between the initial absorbance and the background absorbance should be proportional to final levels of uric acid.By the kinetic uricase method,the background absorbance was predicted by kinetic analysis of uricase reaction curve rather than being determined by experimentation.The threshold of a uric acid level for changing from the equilibrium uricase method to the kinetic uricase method was estimated by simulation analysis.The threshold and the linear range of the integration strategy were examined by experimentation.Results:The threshold was 5.0 μmol/L uric acid in reaction solutions by simulation at 40 U/L uricase,and was supported by experimentation.The equilibrium uricase method determined 1.0 to 6.0 μmol/L uric acid.The integration strategy determined uric acid from 1.5 to 60 μmol/L with resistance to final 30 μmol/L xanthine;CV was below 10% for uric acid below 5.0 μmol/L and was lower than 5% for uric acid over 5.0 μmol/L.Conclusion:The integration strategy for uric acid assay had wider linear range,lower cost and practical analysis efficiency.
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Urate Oxidase
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Abstract A method is presented for the direct determination of iron in the HCl soluble fraction of carbonate rocks. Use is made of the absorbance‐difference technique as developed by Glasner and Avinur, whereby the chloroferrate absorbance of the solution is measured at two wavelengths and the difference of absorbance between them is made the basis of the determination. Determination of iron by the chloroferrate absorbance when measured at only one wavelength was found to be impeded by the variation of the absorbance with the following factors: the ratio of chloride salt to free HCl; the nature of the chloride salt (Ca or Mg); slight changes in the total chloride concentration; and temperature. All these difficulties were largely overcome by the application of the absorbance‐difference technique.
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Fraction (chemistry)
Iron(III) chloride
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LPCVD and PECVD techniques were used to deposit SiN_x and SiC thin films. The IR absorbance spectra of the films were acquired by using a Nicolet Magna 750 FTIR. The experiment results show that the LPCVD SiN_x had an absorbance peak in the range of 8～14 μm, and PECVD SiN_x and SiC had two absorbance peaks, which is in the range of 3～5 μm and 8～14 μm respectively. The IR absorbance of the films increased as the films thickness increase. The peak absorbance of SiN_x film of 1 μm thick can reach 0.92. Ion implantation technology was also utilized to change the IR absorbance of the materials.
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In the absorbance measurement of a sample that scatters light significantly, it is necessary to consider the effect of the attenuation of incident light due to scattering on the measured absorbance. Since the usual absorbance measurement with an integrating sphere (IS) cannot remove the influence of backscattering, we performed the absorbance measurement considering the light scattered to almost all solid angles by placing the sample inside the IS. Ni(NO3)2 and Co(NO3)2 aqueous solutions were used as non-scattering samples, and Ni(NO3)2 solutions mixed with submicrometer polystyrene spheres as scatterers were used as scattering samples. The sample-concentration dependence of the measured absorbance was investigated for the cell containing the sample placed at the entrance of or inside the IS. It was found that even inside the IS, the measured absorbance does not match the true absorbance because light is partially multiply transmitted through the sample or detected without being transmitted through the sample. Due to the latter reason, the saturated absorbance inside the IS was lower than that at the entrance. We derived the formula with three fitting parameters relating the measured and true absorbance taking these factors into account, which quantitatively reproduced the concentration dependence of the absorbance in the non-scattering sample. When the scattering samples were placed at the entrance and inside of the IS, the measured absorbance increased and decreased, respectively, compared to those without scatterers. This decrease in absorbance for the scattering samples inside the IS was also explained by the proposed formula slightly modified.
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Integrating sphere
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This paper researched the linear relationship between UV absorbance and concentrations of nitrobenzene. It used the UV-1700 UV/VIS spectroscopy to get the absorbance diagram and analyze it. Then it calculated the absorbance of maximum absorption peak and the absorbance integration in a wavelength interval. There is a linear relationship between absorbance and concentration, the correlation coefficient is 0.981 of the maximum absorption peaks and the concentrations, and the largest correlation coefficient between concentrations and the integration of absorbance is 0.995 with the wavelength interval of 235-245 nm, which is between the two absorption peaks of 210 nm and 270 nm. Therefore, it’s a good way to use integration of absorbance in the middle of two absorption peaks to measure the concentration of nitrobenzene, which is more accurate and reliable.
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Nitrobenzene
Molar absorptivity
Linear correlation
Linear relationship
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