Metal-assisted core-shell plasmonic nanoparticles for small molecule biothiol analysis and enantioselective recognition.

Cysteine (Cys) enantiomorphs, important small-molecule biothiols, participate in various antioxidative, flavoring, and poison-removing processes in the food industry. Current cysteine enantiomorph analysis methods require effective strategies for distinguishing them due to their similar structures and reactivity. Herein, we present a metal ion-assisted enantiomorph-selective surface-enhanced Raman scattering (SERS) biosensor based on an amphiphilic polymer matrix (APM), which can promote cysteine enantiomorph (L/D-Cys) identification. The highly selective molecular orientation is perhaps caused by the intermolecular hydrogen bonding with chiral isomers (metal centers). The experimental results show that the SERS biosensor has a sensitivity-distincting factor toward L-Cys and D-Cys. The linear range is from 1 mmol L-1 to 1 nmol L-1, along with a low limit of detection of 0.77 pmol L-1. Moreover, the fabricated Cu-APM biosensor exhibits remarkable stability and high repeatability, with an RSD of 3.7%. Real food cysteine enantiomorph detection was performed with L-Cys-containing samples of onion, cauliflower, garlic, and apple, and D-Cys-containing samples of vinegar, black garlic, cheese, and beer. The results show that the Cu-APM biosensor can be utilized as a powerful tool for real-time determination of Cys enantiomorphs in different food samples. Thus, the metal-ion-assisted enantiomorph-selective SERS biosensor has potential as an adaptable tool for enantiomorph detection and food sample analysis.

[Determination of fatty alkyl dimethyl tertiary amines by gas chromatography in the synthesis of cationic surfactants].

A method to determine fatty alkyl dimethyl tertiary amines by gas chromatography (GC) was set up using HP-INNOWax capillary column, hydrogen flame ionization detector (FID) and temperature programming. The linearities were all excellent in the range of 0.005-1.0 g/L with the correlation coefficients being above 0.9996. The limits of detection (LODs, S/N=3) of the method were between 0.001 g/L and 0.002 g/L, and the limits of quantification (LOQs, S/N=10) were between 0.003 g/L and 0.005 g/L. The recoveries ranged between 90% and 130% with relative standard deviations of 1.3%-6.9% (n=6). The proposed method has the advantages of wide linear range, higher recovery, and selectivity, which was suitable for the quantitative analysis of fatty alkyl dimethyl tertiary amines and monitoring process control in industrial production. The method was faster and more accurate than titration, and also precluded the need for pre-column derivatization and determination by liquid chromatography-tandem mass spectrometry.