An optical material for the detection of trace S2O3 2− in milk based on a copper complex
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In this study, a novel method for the fast, sensitive and selective detection of Cu2+ using gold nanoparticles (AuNPs) was developed and used in immunoassays. In the presence of L-cysteine, L-cysteine can bind to the surface of citrate-stabilized AuNPs through Au-S bonds. As a result, aggregation of AuNPs occurs through electrostatic interactions between the cysteine-bound AuNPs. In contrast, in the presence of Cu2+, Cu2+ can catalyze O2 oxidation of cysteine, leading to the quick formation of disulfide cystine. An increase in the concentration of Cu2+ decreased L-cysteine-induced AuNPs aggregation by decreasing the number of free cysteine thiol groups, and the solution color changed from purple to red. Therefore, the concentration of Cu2+ can be detected with the naked eye or with ultraviolet–visible spectroscopy, and the detection limits of Cu2+ were 20 nM and 10 nM, respectively. This sensitivity was approximately three orders of magnitude higher than that of traditional AuNPs-based colorimetric Cu2+ detection methods. Because of the high sensitivity of the proposed method, we further used it with a labeled antibody in colorimetric immunoassays. The detection limit of the cancer biomarker α-fetoprotein was 2 ng ml−1, which is comparable to the detection limit of the enzyme-linked immunosorbent assay method. Huang-Hao Yang and co-workers at Fuzhou University have devised an ultra-sensitive method to detect copper ions (Cu2+), whose accumulation in the body has been linked to several diseases. The researchers' method relies on gold nanoparticles, popular in colourimetric sensing because they turn a solution from red to purple on aggregation. Here, however, instead of triggering the aggregation directly, the copper ions catalyse a 'supporting reaction' – the oxidation of a monomeric amino acid (cysteine) into a dimeric one (cystine). Only cysteine triggers the aggregation of the nanoparticles, which means the presence or absence of copper results in a red or purple solution, respectively. The method's sensitivity is very high because only catalytic quantities of copper are needed. The researchers further used this rapid, convenient, sensitive method in an immunoassay for a human protein. A novel method based on the AuNPs for fast, sensitive and selective detection of Cu2+ was developed and applied in immunoassays.
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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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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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A simple, rapid, and convenient colorimetric chemosensor of a specific target toward the end user is still required for on-site detection and real-time monitoring applications. In this study, we developed a rapid in situ colorimetric assay for cobalt detection using the naked eye. Interestingly, a yellow to light orange visual color transition was observed within 3 s when a Chrysoidine G (CG) chemosensor was exposed to cobalt. Surprisingly, the CG chemosensor had great selectivity toward cobalt without any interference of other metal ions. Under optimized conditions, a lower detection limit of 0.1 ppm via a spectrophotometer and a visual detection limit of 2 ppm with a linear range from 0.4 to 1 ppm (R² = 0.97) were determined. Moreover, the CG chemosensor is reversible and maintains its functionality after treatment with chelating agents. In conclusion, we show the superior capabilities of the CG chemosensor, which has the potential to provide extremely facile handling, high sensitivity, and a fast response time for applications of on-site detection to real-time cobalt monitoring for the general public.
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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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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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