Rapid Detection of Ag (I) via Size Induced Photoluminescence Quenching of Biocompatible Green Emitting L-Tryptophan Scaffolded Copper Nanocluster

Atomically precise metal nanoclusters capped with small molecules like amino acids are highly favoured due to their specific interactions and easy incorporation into biological systems. However, they are rarely explored due to the challenge in surface functionalization of nanocluster with small molecules. Herein, we report the synthesis of green emitting (λ_ex = 380 nm, λ_em = 500 nm) single amino acid (L-tryptophan) scaffolded copper nanocluster (Trp-Cu NC) via one-pot route under mild reaction conditions. The synthesized nanocluster can be used for the rapid detection of heavy metal (Ag(I)) in the nanomolar concentration range in real environmental and biological samples. The strong green photoluminescence intensity of the nanocluster quenched significantly upon addition of Ag(I) due to the formation of bigger nanoparticles, thereby losing its energy quantization. A notable colour change from light yellow to reddish brown can also be observed in the presence of Ag(I) allowing its visual colorimetric detection. Portable paper strips fabricated with Cu-Trp NC can be reliably used for on-site visual detection of Ag(I) in the micromolar concentration range. The Trp-Cu NC possesses excellent biocompatibility making them suitable nanoprobe for cell imaging, thus can act as an in-vivo biomarker. The nanocluster showed a significant spectral overlap with an anticancer drug doxorubicin, thus can be used as an effective FRET pair. FRET results can reveal important information regarding the attachment of the drug to the nanocluster and hence, its role as a potential drug carrier for targeted drug delivery within human body.