Vitamin B Cofactor Pyridoxal 5'-phosphate Conjugated Papain-Stabilized Fluorescent Gold Nanoclusters for Switch-on Detection of Zinc(II).

In this study, fluorescent gold nanoclusters (AuNCs) conjugated with pyridoxal-5-phosphate (PLP) were synthesized, characterized, and used for Zn fluorescence turn-on sensing. PLP was conjugated over the surface of papain-stabilized fluorescent gold nanoclusters (pap-AuNCs; λ = 380 nm, λ = 670 nm) by forming imine linkage. Due to this modification, the red color emitting pap-AuNCs changed to orange color emitting nanoclusters PLP_pap-AuNCs. The nano-assembly PLP_pap-AuNCs detect Zn selectively by showing a notable fluorescence enhancement at 477 nm. Zn detection with PLP_pap-AuNCs was quick and easy, with an estimated detection limit of 0.14 µM. Further, paper strips and cotton buds coated with PLP_pap-AuNCs were developed for affordable on-site visual detection of Zn. Finally, the detection of Zn in actual environmental water samples served as validation of the usefulness of PLP_pap-AuNCs.