Fine-tunable fluorescence quenching properties of core-satellite assemblies of gold nanorod-nanosphere: Application in sensitive detection of Hg²⁺

In this work, we developed a simple, effective fluorescence method to detect Hg²⁺ by inhibiting core-satellite assemblies of gold nanorods (AuNRs) and gold nanospheres (AuNPs). The fluorescence of Rhodamine 6G (Rh6G), which was simply mixed with the nanoassemblies, was efficiently quenched by the inner filter effect (IFE). When the heterogenous core-satellite nanostructures were assembled, the corresponding local surface plasmon resonance (LSPR) absorption shifts and broadens which results in the increase of the spectral overlap between the emission peak and the absorption band and more efficient energy transfer from Rh6G to nanoparticles. Fluorescence quenching efficiency is related to the size and number density of satellite nanoparticles. It is interesting that the AuNR-AuNP assemblies with the moderate size and high density of AuNPs have the best fluorescence quenching efficiency. In the presence of Hg²⁺, p-aminothiophenol (p-ATP) breaks away from the surface of AuNRs and competitively bounds to Hg²⁺, resulting in a low yield of the AuNR-AuNP assemblies, which further leads to the decrease of fluorescence quenching efficiency. Under the optimum conditions, the limit of detection (LOD) for Hg²⁺ was 0.18 nM, with an excellent linear response from 0.6 to 800 nM. Interference experiment and real samples detection indicate that these nanosensors endowed with higher sensitivity and selectivity for the detection of Hg²⁺ in the real samples. Compared with the conventional Hg²⁺ detection techniques, this method based on Hg²⁺ induced inhibition of core-satellite AuNR-AuNP assemblies has better performance and is suitable for the detection of Hg²⁺.