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Nanobiosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
Chen et al. (2008) described a colorimetric sensing approach for the determination of ATP in urine samples (Figure 9.20). A colorimetric sensor measures the concentration of a known constituent of a solution by comparison with spectroscopic or visual standards. What is the principle behind this approach? In the absence of ATP, the color of the Apt-AuNP solution changed from wine-red to purple via self-induced aggregation. In the presence of ATP, binding of the analytes to the Apt-AuNPs induced folding of the aptamers on the AuNP surfaces into four-stranded quadruplex or tetraplex (fourfold) structures (G-quartet) and/or an increase in charge density. Consequently, the Apt-AuNP solution was wine-red in color when the analyte was present. G-quartets are atypical nucleic acid structures, consisting of a planar arrangement where each guanine is hydrogen bonded by Hoogsteen pairing to another guanine in the quartet. (a) Synthesis of aptamer-Au nanoparticles. (b) Sensing mechanism of Apt-AuNPs for the colorimetric determination of ATP: the solution containing no ATP changes color from wine-red to purple due to aggregation, whereas the one containing ATP retains its original red-wine color. (Chen, S.-J. et al., Biosens. Bioelectron., 23, 1749, 2008.)
Basic concepts in photometry, radiometry, and colorimetry
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
The perception of color is a psychophysical phenomenon, and the measurement of color must be defined in such a way that the results correlate accurately with what the visual sensation of color is to a normal human observer. Colorimetry is the measurement science used to quantify and describe physically the human color perception. The basis of colorimetry was established by CIE in 1931 based on a number of visual experiments that defined a set of three spectral weighting functions [39]. These functions, shown in Figure 8.11, are called the CIE 1931 XYZ color matching functions denoted as x¯(λ),y¯(λ),z¯(λ). These functions were derived from a linear transformation of the original set of color matching functions in such a way that y¯(λ) is equal to V(λ).
Analytical Chemistry
Published in W. M. Haynes, David R. Lide, Thomas J. Bruno, CRC Handbook of Chemistry and Physics, 2016
W. M. Haynes, David R. Lide, Thomas J. Bruno
Colorimetry, Spot Tests, Presumptive Tests: Rapid, simple tests based on color change are frequently used as the basis of preliminary conclusions or approximate concentration measurement. Colorimetric methods use simple comparative instruments to determine the concentration of colored compounds in solution. These devices, called colorimeters, can be manual or automatic, and use filtered light in the visible region (between 400 nm and 700 nm). In both cases, the operation depends upon having multiple solutions, including a blank, for comparison with a solution of unknown concentration. Manual colorimeters function by measuring the variable light path through the unknown solution as compared to a known solution until a match is achieved visually. The product of concentration and path length matches when the concentrations are the same, so an unknown concentration may be obtained by a proportion. Automated devices function similarly but with photocells. Colorimetric tests are usually done following four basic protocols: (1) an unknown can be treated/ reacted with a reagent to form a new compound which is colored, (2) a chelate complex is formed having a different color than the starting compound, (3) a colored compound is oxidized or
Characterization of the piezoelectric lead zirconate titanate catalyzed degradation of rhodamine B and methylene blue dyes by smartphone-based colorimetry
Published in Instrumentation Science & Technology, 2021
Vishvendra Pratap Singh, Ankit Susaniya, S. C. Jain, Rahul Vaish
A colorimetry method is usually based on a change in the absorbance value of a specific solution for a specific wavelength range. The RGB (red, green, blue) values of the color shifts may be collected by cellphones. Any smartphone with a moderate camera may capture the image that may be characterized using various RGB analysis programs accessible on various internet application stores. The photographs were captured on a Redmi Y3 (Xiaomi) smartphone and the RGB data analyzed using the RGB color picker application. The degradation of MB and RhB was quantified using this method. In addition, a spectrophotometer (Shimadzu UV-2600) was used to verify the measurements. The wavelength of the spectrophotometer is fixed between 400 nm and 800 nm. The peak absorption was recorded at 663 nm and 568 nm for MB and RhB, respectively.
Aptamer based tools for environmental and therapeutic monitoring: A review of developments, applications, future perspectives
Published in Critical Reviews in Environmental Science and Technology, 2020
Błażej Kudłak, Monika Wieczerzak
Colorimetric tests are easy to perform, and their results can be measured and determined with uncomplicated equipment and in some cases, by the naked eye (Lu et al., 2013). Most colorimetric aptamer based tests are based on the principle that the visible color of AuNP suspensions change depending on the dispersion and aggregation in the solution. For example, if aptamers are immobilized on AuNPs stabilized in highly concentrated salts (e.g. NaCl), they are dispersed in the solution and prevent nanoparticle aggregation. This would turn the sample solution red. As soon as an aptamer recognized analyte appears in the solution, the aptamer is separated from the AuNPs, which then aggregate and cause the solution to turn blue (Figure 7d). Change and color intensity provide qualitative and quantitative information about the presence and concentration sample analyte, and the blue shift range is quantified as the ratio of absorbance from 620 nm to 520 nm (∼A620/A520 nm) (Akki & Werth, 2018).
Gelation-based visual detection of analytes
Published in Soft Materials, 2019
Wangkhem Paikhomba Singh, Rajkumar Sunil Singh
Detection of target analytes in a given sample with high specificity and sensitivity is important in many scientific and technological disciplines. Frequently, detection is performed by using different instrumental techniques based on absorbance, fluorescence, chemiluminescence, electrochemical, surface plasmon resonance, circular dichroism, and others (18–20). Most of these detection techniques, however, entail the use of expensive and sophisticated instrumentations and need highly trained personnel for their operation. Therefore, there is a great deal of interest in developing inexpensive, simple, and rapid methods for the identification of analytes preferably without the aid of instruments. Colorimetry is one such attractive technique due to its low cost, simplicity, and use of basic instrumentation. Visual detection of analytes with naked eyes is possible with colorimetric technique. But this does not work well with colored samples. Gelation-based visual detection technique is another example which is equally simple, convenient, cost-effective, and instrument-free. This is the focus of the present review article.