Direct laser photo-induced fluorescence determination of bisphenol A

Aptamer-Adjusted Carbon Dot Catalysis-Silver Nanosol SERS Spectrometry for Bisphenol A Detection

Carbon dots (CDs) can be prepared from various organic (abundant) compounds that are rich in surfaces with –OH, –COOH, and –NH₂ groups. Therefore, CDs exhibit good biocompatibility and electron transfer ability, allowing flexible surface modification and accelerated electron transfer during catalysis. Herein, CDs were prepared using a hydrothermal method with fructose, saccharose, and citric acid as C sources and urea as an N dopant. The as-prepared CDs were used to catalyze AgNO₃–trisodium citrate (TSC) to produce Ag nanoparticles (AgNPs). The surface-enhanced Raman scattering (SERS) intensity increased with the increasing CDs concentration with Victoria blue B (VBB) as a signal molecule. The CDs exhibited a strong catalytic activity, with the highest activity shown by fructose-based CDs. After N doping, catalytic performance improved; with the passivation of a wrapped aptamer, the electron transfer was effectively disrupted (retarded). This resulted in the inhibition of the reaction and a decrease in the SERS intensity. When bisphenol A (BPA) was added, it specifically bound to the aptamer and CDs were released, recovering catalytical activity. The SERS intensity increased with BPA over the concentration range of 0.33–66.67 nmol/L. Thus, the aptamer-adjusted nanocatalytic SERS method can be applied for BPA detection.

Development of an on-site early warning water quality monitoring system for pesticide detection by absorption and photo-induced fluorescence

This paper describes prototypes of an on-site early warning water quality monitoring system (EWWQMS) for pesticide quantification in natural waters by fluorescence and absorbance. As many pesticides are not naturally fluorescent, this EWWQMS uses UV irradiation to transform these compounds into highly fluorescent photoproducts and obtain sufficient sensitivity. To obtain a better specificity, the system uses four UV LEDs at different wavelengths to excite the fluorescent photoproducts. For pesticides that are not sensitive to photoconversion, the EWWQMS prototypes also use UV absorption for their quantification, thus offering a wider application range. A first system uses a diode array spectrometer for detection. A second system uses a higher resolution spectrometer and an intensified CCD camera detection to increase sensitivity. Analytical applications were conducted for the determination of fipronil, acetamipride, cyprodinil, trifluraline and pendimethaline in water using both the EWWQMS prototypes. The analytical performances of these new systems are good compared with other photo-induced fluorescence methods already published. Limits of detection without pre-concentration are in the range of 0.2 to 3 ng mL^-1 and the recovery values range from 95 to 108%. These results show that the EWWQMS prototypes can be used as an alert system to protect industrial plants from pesticide contaminations that exceed the capabilities of their cleaning processes.