Fluorescent ovalbumin-functionalized gold nanocluster as a highly sensitive and selective sensor for relay detection of salicylaldehyde, Hg(II) and folic acid.

A sensitive and selective relay-based scheme for the detection of salicylaldehyde, Hg2+, and folic acid (FA) has been demonstrated using fluorescent ovalbumin functionalized gold nanoclusters (OVA-AuNCs, λem = 655 nm) in this article. The OVA-AuNCs were conjugated to salicylaldehyde via an imine linkage to form Salic_OVA-AuNCs conjugate. The molecular docking study reveals that multiple functional groups and amino acid residues are involved in the interaction between salicylaldehyde and the OVA-AuNCs. The coupling of salicylaldehyde with OVA-AuNCs results in fluorescence quenching at 655 nm and concomitant formation of an emission band at 500 nm, which have leveraged to detect salicylaldehyde down to 2.02 µM. Following that, the Salic_OVA-AuNCs has been used for the detection of Hg2+ and FA. Several processes, such as internal charge transfer (ICT), photoinduced electron transfer (PET) and metallophilic interactions, are involved between the Salic_OVA-AuNCs nanoprobe and the analytes, which allowed to detect Hg2+ and FA down to 0.13 nM and 0.11 nM, respectively. The Salic_OVA-AuNCs nanoprobe has an additional naked-eye utility when applied to paper-strip sensing strategy for Hg2+ and FA detection.

Tuning Zn(â ¡) selectivity by conjugating vitamin B6 cofactors over bovine serum albumin stabilized red-emitting silver nanoclusters.

The red-emitting bovine serum albumin stabilized silver nanoclusters (BSA-AgNCs) were conjugated with the vitamin B6 cofactors pyridoxal 5'-phosphate (PLP) and pyridoxal (PL). The deconvoluted bands in XPS revealed that the conjugation occurred due to the formation of imine-linkage between the vitamin B6 cofactors and the BSA functionalized over BSA-AgNCs. The TEM images supported the formation of pseudo-spherical shaped nano-aggregates upon conjugating vitamin B6 cofactor PLP over BSA-AgNCs. An emission band appeared at 532 nm after the conjugation of PLP or PL over the surface of BSA-AgNCs. The in situ formed nano-assembly PLP_BSA-AgNCs and PL_BSA-AgNCs showed a significant fluorescent enhancement, respectively, at 490 nm and 481 nm in the presence of Zn2+. The complexation-induced fluorescence enhancement from PLP_BSA-AgNCs and PL_BSA-AgNCs was reversed by adding a strong chelating agent EDTA. In addition, the fluorescence of PL_BSA-AgNCs was irreversibly quenched with the appearance of an emission band at 423 nm in the presence of Hg2+. The analytical performance and sensing mechanism of the developed nanoprobes PLP_BSA-AgNCs and PL_BSA-AgNCs were discussed, and the highly selective and sensitive nanoprobe PLP_BSA-AgNCs was applied for the quantification of Zn2+ in real samples.