Surface-Enhanced Raman Scattering Enantioselective Detection of Gastric Cancer-Related d-Amino Acids in Saliva Based on Enzyme-Mediated Cascade Reaction

Abstract

The unusual D-amino acids (D-AAs), as the counter enantiomer of usual L-amino acids (L-AAs), have evoked increasing attention because of their potential relevance with diseases. Accordingly, it is essential to establish sensitive and selective detection methods for D-AAs without the interferences from L-AAs. The surface-enhanced Raman scattering (SERS) technique is efficacious for the detection of molecules but routinely ineffective in enantiomeric differentiation. D-Proline (D-Pro) and D-alanine (D-Ala) are regarded as biomarkers of gastric cancer. Herein, Ramanactive boronate modified SERS chips are constructed to develop a Damino acid oxidase (DAAO)-mediated cascade reaction-based SERS enantioselective assay for D-Pro and D-Ala. The principle is that DAAO selectively catalyzes the deamination of D-Pro and D-Ala, and the produced H 2 O 2 oxidizes boronate to present a new SERS peak at 883 cm −1 for quantitative analysis in a ratiometric way. A linear range from 20 to 400 μmol/L and a limit of detection down to 14.8 μmol/L are reached. In addition, interferences from L-AAs and many other possible species coexisting in biofluids with the detection of D-Pro and D-Ala are ignorable. Enzyme-mediated cascade reaction-based SERS chips are further utilized for saliva sample analysis, and the total levels of D-Pro and D-Ala in salivary samples from gastric cancer patients are much higher than those of healthy persons. This work provides a solution for SERS enantioselective analysis and noninvasive screening chiral biomolecules for disease diagnosis.

Enantiomer-Specific Colorimetric Tandem Assays for Salivary d-Alanine Associated with Gastric Cancer

“…However, this route is unable to distinguish between d -Ala and d -Pro and only obtains the total concentration of d -Ala and d -Pro (denoted by c ( d -Ala and d -Pro)). In addition, peroxidase enzyme or synthetic nanomaterials are required to detect H 2 O 2 , which have some disadvantages including storage instability of enzymes, tedious synthesis procedures, expensive raw materials, and employment of high-temperature/pressure equipment. − ,− …”