• Bulletin of the Korean Chemical Society
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• 제34권1호
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• pp.287-290
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• 2013

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.958-962
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• 2012

In single-molecule fluorescence experiment, the oxygen scavenging system is indispensable for avoiding photo-bleaching of fluorescent dyes. Here we report that the gloxy-based oxygen scavenging system commonly used in single molecule fluorescence experiments can disturb the solution pH considerably. To track in situ pH change, we utilized the pH-sensitive conformational transition of i-motif and examined the transition with ensemble and single-molecule FRET measurements. Based on our results, we also suggested several practical remedies for the stability of the solution pH.

• Journal of Industrial and Engineering Chemistry
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• 제67권
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• pp.461-468
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• 2018

A highly sensitive, selective and rapid method for the determination of lead based on the reaction of lead (II) with 5-(4'-chlorophenylazo)-6-hydroxypyrimidine-2,4-dione (CPAHPD) and the solid phase extraction of the Pb(II)-CPAHPD complex with Amberlite XAD-2000 was developed, in the presence of pH 5.6 buffer solution and Triton X-114 medium. CPAHPD reacts with lead to form a violet complex with a molar ratio of 2:1 (CPAHPD to lead). This complex was enriched by the solid phase extraction with Amberlite XAD-2000. An enrichment factor of 500 was obtained by elution of the complex from the resin with a minimal amount of isopentyl alcohol(0.2 mL). In isopentyl alcohol medium,the molar absorptivity of the complex is $1.13{\times}10^6L\;mol^{-1}cm^{-1}$ at 647 nm. Beer's law is obeyed in the range of $5.0-160ng\;mL^{-1}$ in the measured solution. The relative standard deviation for 10 replicate samples of $50ng\;mL^{-1}$ level is 1.26%. The detection and quantification limits reaches 1.5 and $4.7ng\;mL^{-1}$ in the original samples. The presented procedure was successfully applied for determination of lead content in real samples such as vegetables, waters, biological and soil samples with satisfactory results.

• 센서학회지
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• 제29권2호
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• pp.93-99
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• 2020

A colorimetric paper sensor was used to detect volatile nitrogen-containing compounds emitted from spoiled salmon filets to determine their freshness. The sensing mechanism was based on acid-base reactions between acidic pH-indicating dyes and basic volatile ammonia and amines. A sensing layer was simply fabricated by drop-casting a dye solution of bromocresol green (BCG) on a polyvinylidene fluoride substrate, and its color-change response was enhanced by optimizing the amounts of additive chemicals, such as polyethylene glycol, p-toluene sulfonic acid, and graphene oxide in the dye solution. To avoid the adverse effects of water vapor, both faces of the sensing layer were enclosed by using a polyethylene terephthalate film and a gas-permeable microporous polytetrafluoroethylene sheet, respectively. When exposed to basic gas analytes, the paper-like sensor distinctly exhibited a color change from initially yellow, then to green, and finally to blue due to the deprotonation of BCG via the Brønsted acid-base reaction. The use of ammonia analyte as a test gas confirmed that the sensing performance of the optimized sensor was reversible and excellent (detection time of < 15 min, sensitive naked-eye detection at 0.25 ppm, good selectivity to common volatile organic gases, and good stability against thermal stress). Finally, the coloration intensity of the sensor was quantified as a function of the storage time of the salmon filet at 28℃ to evaluate its usefulness in monitoring of the food freshness with the measurement of the total viable count (TVC) of microorganisms in the food. The TVC value increased from 3.2 × 10⁵ to 3.1 × 10⁹ cfu/g in 28 h and then became stable, whereas the sensor response abruptly changed in the first 8 h and slightly increased thereafter. This result suggests that the colorimetric response could be used as an indicator for evaluating the degree of decay of salmon induced by microorganisms.