Near-Infrared Fluorescent Silica Nanoparticles Based on Gold-Silver Alloy Nanoclusters for Clinical Diagnosis

In clinical diagnosis, fluorescent particles are applied to detect analytes in biofluids, such as blood and saliva. However, current fluorescence detection methods have not been optimized to account for the overlapping autofluorescence peaks of biological substances. Gold and silver nanoclusters are known to the novel fluorescent materials and their emission wavelengths depend on cluster size. In this study, we developed fluorescent silica nanoparticles using gold-silver alloy nanoclusters and chitosan (CS) (NH₂-SiO₂@Au@CS@AuAg) by the layer-by-layer method. Under UV-light irradiation at 365 nm, the emission wavelength of NH₂-SiO₂@Au@CS@AuAg reached 750 nm in the near-IR region. Scanning electron microscopy images revealed that the shape of NH₂-SiO₂@Au@CS@AuAg was uniform and spherical. The fluorescence spectrum of horse blood obtained in the presence of NH₂-SiO₂@Au@CS@AuAg contained a specific fluorescence peak attributed to NH₂-SiO₂@Au@CS@AuAg, which was distinguishable from the autofluorescence peaks. These results showed that NH₂-SiO₂@Au@CS@AuAg has advantageous fluorescence properties for clinical diagnostic applications.