A novel dual-emission fluorescent nanohybrid containing silica nanoparticles and gold nanoclusters for ratiometric determination of cysteine based on turn-on fluorescence strategy

Abstract

In the present study, we developed a novel ratiometric fluorescent sensor for the detection of cysteine (Cys) by linking the recognition indicators glutathione-capped gold nanoclusters (GSH–AuNCs) onto the surface of amino-modified SiO₂NPs@SiO₂ spheres. The as-prepared nanohybrid (SiO₂NPs/AuNCs) exhibited dual-emission fluorescence peaking at 425 and 605 nm under single excitation of 360 nm. Furthermore, its morphology, composition, surface chemical features and optical properties have been fully characterized through transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-vis absorption spectroscopy, and fluorescence spectroscopy. For Cys detection, the red fluorescence intensity of AuNCs of the nanohybrid could be selectively and effectively enhanced by Cys due to specific interaction between the indicator and the target, whereas the reference signal of blue-emitting SiO₂NPs@SiO₂ spheres remained constant as SiO₂NPs were entirely encapsulated by the silica shell. Thus, the variation in the intensity ratio (I₆₀₅/I₄₂₅) of the nanohybrid could be used to determine Cys based on the ratiometric method. The I₆₀₅/I₄₂₅ against the concentration of Cys demonstrated a good linear relationship from 0 to 20 μM, and the detection limit reached as low as 0.35 μM. Moreover, this ratiometric system has been applied to determine Cys in serum samples with satisfactory results.