Chinese rice wine is abundant in amino acids. The possibility of quantitative detection of 16 free amino acids (aspartic acid, threonine, serine, glutamic acid, proline, glycine, alanine, valine, methionine, isoleucine, leucine, tyrosine, phenylalanine, lysine, histidine, and arginine) in Chinese rice wine by Fourier transform near-infrared (NIR) spectroscopy was investigated for the first time in this study. A total of 98 samples from vintage 2007 rice wines with different aging times were analyzed by NIR spectroscopy in transmission mode. Calibration models were developed using partial least-squares regression (PLSR) with high-performance liquid chromatography (HPLC) by postcolumn derivatization and diode array detection as a reference method. To validate the calibration models, full cross (leave-one-out) validation was employed. The results showed that the calibration statistics were good (rcal>0.94) for all amino acids except proline, histidine, and arginine. The correlation coefficient in cross validation (rcv) was >0.81 for 12 amino acids. The residual predictive deviation (RPD) value obtained was >1.5 in all amino acids except proline and arginine, and it was >2.0 in 6 amino acids. The results obtained in this study indicated that NIR spectroscopy could be used as an easy, rapid, and novel tool to quantitatively predict free amino acids in Chinese rice wine without sophisticated methods.

Fluorescence sensing of specific biological molecules by artificial chemosensors is a versatile technique. In the present work, a switch-on fluorescence sensor for rapid, sensitive, and selective sensing of glutathione (GSH) in food samples was developed. This method was based on the g-CNQDs-Hg(2+) system, in which the initial fluorescence from g-CNQDs was quenched by Hg(2+) with an electron transfer process. In the presence of GSH, the fluorescence sensor was switched to the "on" state, which was attributed to a competitive affinity of Hg(2+) to GSH and the functional groups on the surface of g-CNQDs. Under the optimal conditions, the limit of detection (LOD) of 37 nM for GSH was achieved with a wide range of 0.16-16 μM. The repeatability was better than 5.3% for GSH in both standard and food samples (n = 3). Finally, this fluorescence sensor was successfully employed for the determination of GSH in various kinds of food samples with excellent recoveries. Furthermore, this application may pave a new way for fluorescence sensing of other substances in food samples.

Covalent organic frameworks (COFs), as one of the most significant members of the porous organic frameworks, have been well used in the photocatalysis owing to their outspread π-conjugated framework, high crystallinity and regular pore structure. Herein, after reducing the labile imine-linked COF-300 to the more stable aminelinked COF-300-AR, we for the first time demonstrated that COF-300-AR was the light-responsive oxidase mimic. COF-300-AR exhibited excellent oxidase-mimicking activity under purple light stimulation (λ = 400 nm), which can catalyze the oxidation of classical substrates such as 3,3′,5,5′-tetramethylbenzydine (TMB) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) by the formation of • OH and O 2•− free radicals in the presence of dissolved oxygen. The COF-300-AR oxidase mimic has outstanding advantages of easy light control, high stability, good reusability, and highly catalytic oxidation capacity and has been applied to detect glutathione (GSH) levels in HL60 cells with good selectivity and high sensitivity. This study will broaden the sensing applications of COFs and offer a promising build block for the construction of artificial enzymes.

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