Gold nanoparticles in situ generated on carbon dots grafted paper: application in enantioselective fluorescence sensing of D-alanine

The integration of paper-based devices with fluorescent nanomaterials as recognition elements has offered novel opportunities for biosensing with enhanced sensitivity and selectivity, as well as stable signals. This work innovatively designed a fluorescent paper-based device for enantioselective sensing of D-alanine (D-Ala), where carbon dots (CDs) grafted cellulose paper (PCD) was used as the fluorophore and the in situ generated gold nanoparticles (AuNPs) were used as quenchers. D-α-Amino acid oxidase (DAAO) stereo-selectively catalyzed D-Ala to produce hydrogen peroxide (H2O2), which mediated the in situ formation of PCD/AuNPs composites and quenched the fluorescence of PCD based on fluorescence resonance energy transfer (FRET). Under optimal conditions, the designed PCD/AuNPs demonstrated a reliable quenching response to D-Ala in the range of 1–100 μM and the limit of detection was 0.55 μM. Moreover, the platform was applied to detect D-Ala in serum, simulated gastric fluid samples, and was further employed to determine D-Ala in BGC-823 gastric cancer cells with satisfactory results. Ultimately, the PCD/AuNPs platform provided a novel strategy for the development of reliable and sensitive assays based on paper-based devices. It has great potential to be utilized in enantioselective sensing and clinical early diagnosis.