PubMed · 3594867
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P J Parks, S N Thibodeau. 1987. A modified method for quantifying urinary vanillylmandelic acid.. https://pubmed.ncbi.nlm.nih.gov/3594867/
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The development of colorimetric methods based on directly inhibiting nanozyme activity for pesticide detection has attracted considerable attention. In this study, we report a novel colorimetric sensing strategy utilizing BiO2-x/Bi2O2.75 nanosheets (BiO2-x/Bi2O2.75 NSs) with haloperoxidase (HPO)-like activity for the rapid and sensitive detection of carbosulfan (CBS) in foods. Oxygen-vacancy-rich BiO2-x/Bi2O2.75 NSs with HPO-like activity were rationally constructed. Kinetic studies revealed a remarkable Michaelis-Menten constant (Km) of 0.014 mM for I-, indicating a higher affinity for iodide ions than other reported HPO-like nanozymes, as evidenced by its lower Km. Under acidic conditions, CBS tends to be hydrolyzed to produce reductive sulfide species, which directly inhibit the iodoperoxidase-like activity of BiO2-x/Bi2O2.75 NSs, enabling selective detection with a limit of detection (LOD) of 0.18 μg/mL and a linear range of 0.20-100 μg/mL. When the concentration of interfering pesticides and substances was 5 times that of CBS, the sensor remained unaffected, exhibiting excellent stability and specificity. This work contributes to the detection of CBS in complex food matrices, bridging the application gap of HPO-like nanozymes in pesticide detection and providing a promising method for food safety detection.
A new, rapid methodology for trace analysis using solid-phase extraction is described. The two-step methodology is based on the concentration of an analyte onto a membrane disk and on the determination by diffuse reflectance spectroscopy of the amount of analyte extracted on the disk surface. This method, which is adaptable to a wide range of analytes, has been used for monitoring ppm levels of iodine and iodide in spacecraft water. Iodine is used as a biocide in spacecraft water. For these determinations, a water sample is passed through a membrane disk by means of a 10-mL syringe that is attached to a disk holder assembly. The disk, which is a polystyrene-divinylbenzene composite, is impregnated with poly(vinylpyrrolidone) (PVP), which exhaustively concentrates iodine as a yellow iodine-PVP complex. The amount of concentrated iodine is then determined in only 2 s by using a hand-held diffuse reflectance spectrometer by comparing the result with a calibration curve based on the Kubelka-Munk function. The same general procedure can be used to determine iodide levels after its facile and exhaustive oxidation to iodine by peroxymonosulfate (i.e., Oxone reagent). For samples containing both analytes, a two-step procedure can be used in which the iodide concentration is calculated from the difference in iodine levels before and after treatment of the sample with peroxymonosulfate. With this methodology, iodine and iodide levels in the 0.1-5.0 ppm range can be determined with a total workup time of approximately 60 s with a RSD of approximately 6%.
The MIDITECH colorimetric susceptibility test with automated reading is a modification of the standard broth microdilution method that uses a 3-(4,5-dimetylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) dye for detecting viable bacteria. The method can be applied to non-fastidious aerobic Gram-negative bacteria, staphylococci and Enterococcus faecalis. To assess the reliability of this method, we compared susceptibility data obtained by this test with standard NCCLS microdilution assay results. For this purpose, 15 antibiotics and a well characterized set of 527 Gram-negative and Gram-positive bacterial isolates collected and stored at the Division of Infectious Diseases and Chemotherapy (Vienna General Hospital, Austria), yielding 5751 organism-antibiotic combinations, were analysed in duplicate. The overall essential agreement (+/-1 log(2) dilution) between the MIDITECH and NCCLS methods was 96.18 +/- 0.67%. The colorimetric assay compared with the reference method produced MICs < or = 2 log(2) dilutions and > or = 2 log(2) dilutions in 2.34% and 1.48% comparisons, respectively. For 326 Gram-negative bacteria, the absolute interpretative agreement of both methods ranged from 87.12% for ampicillin-sulbactam to 99.85% for meropenem (mean 94.86%); 417 (4.92%) minor, three (0.05%) major and 15 (0.63%) very major errors were found. For 127 staphylococci and 74 E. faecalis isolates, the absolute interpretative agreement ranged from 90.80% for ciprofloxacin to 100% for vancomycin and linezolid (mean 96.96%); 81 (2.77%) minor, three (0.15%) major and eight (0.83%) very major errors were found. For most of the clinically important aerobically growing pathogens, the MIDITECH colorimetric test provided reliable quantitative susceptibility data. The main advantage of this method is simple performance, automated reading and data processing without expensive investments.