The fluorescence quenching and aggregation induced emission behaviour of silver nanoclusters labelled on poly(acrylic acid-co-maleic acid)

Abstract

In this study, we examined the spectroscopic properties of silver nanoclusters (AgNCs) labelled on poly(acrylic acid-co-maleic acid), (P(AA-co-MA)). The results suggested that the optimized labeling conditions for the AgNCs on P(AA-co-MA) are pH = 5.9, temperature = 30 °C and [COO⁻]/[Ag⁺] = 10. The AgNCs revealed the highest intensity at pH = 4.5, and the fluorescence quantum yields of the P(AA-co-MA) AgNCs excited at 500 nm and 600 nm were estimated to be 5.9% and 2.3%, respectively. Upon 500 nm excitation, the P(AA-co-MA) AgNCs showed clear emission dependent fluorescence decay dynamics, and this phenomenon disappeared when the excitation wavelength was shifted to 635 nm. The result suggested that the emission wavelength dependent fluorescence decay dynamics of the P(AA-co-MA) AgNCs is associated with the co-excitation of multiple emissive species. In addition, we further demonstrated that the fluorescence of the P(AA-co-MA) AgNCs would be significantly quenched by glutathione. The fluorescence quenching is caused by the interaction between glutathione and Ag⁺ ions, and the removal of Ag⁺ ions from the AgNCs causes the formation of large non-emissive silver nanoparticles. Moreover, we also reported aggregation induced emission of the P(AA-co-MA) AgNCs in DMSO solution. The fluorescence quenching and time-resolved fluorescence measurements confirmed that the aggregation induced emission of the P(AA-co-MA) AgNCs in DMSO solution was caused by the formation of a layer of carbonyl clusters on the AgNCs, which could effectively suppress the non-radiative processes of the P(AA-co-MA) AgNCs.