Using bimetallic Au/Cu nanoplatelets for construction of facile and label-free inner filter effect-based...

Herein, we report a facile and label-free method for sensitive and specific determination of prostate cancer biomarker sarcosine via using photoluminescent bimetallic Au/Cu nanoplatelets (AuCu NPs) to construct an inner filter effect (IFE)-based photoluminescence (PL) sensing platform. The AuCu NPs were formed by the cysteine-induced co-reduction reaction, which displayed bright PL with an emission peak at 560 nm. Meanwhile, the Cu(I) doping caused a maximum 25-fold enhancement of quantum yield (QY), compared with the native Au(I) complexes, i.e., from 0.85 to 21.5%. By integrating the AuCu NPs with p-phenylenediamine (PPD) oxidation reaction, an IFE-based sensor for sarcosine detection was constructed. In this method, sarcosine is oxidized under the catalysis of sarcosine oxidase (SOx) to yield H₂O₂. The latter further oxidizes PPD to form 2,5-diamino-N,N'-bis(p-aminophenyl)-l,4-benzoquinone di-imine (PPDox) in the presence of horseradish peroxidase (HRP). The UV-vis absorption spectrum of the PPDox can overlap well with the excitation and emission spectra of the AuCu NPs, resulting in the efficient quenching of the AuCu NPs via the IFE effect. Therefore, this IFE-based AuCu NPs/SOx/PPD/HRP sensing platform can be used for highly sensitive and specific sensing of sarcosine. The sensing platform showed two linear regions of the PL intensity of the AuCu NPs versus the concentration of sarcosine in the range of 0.5-5 μM and 5-100 μM with a detection limit (LOD) of 0.12 μM (S/N = 3). Furthermore, this IFE-based sensing platform could be developed into a paper-based biosensor for simple, instrument-free, and visual detection of sarcosine.