Albumin-stabilized fluorescent metal nanoclusters: fabrication, physico-chemical properties and cytotoxicity

Abstract

Fluorophores with a wide excitation range and the possibility of multicolor fluorescence are required for different applications such as sensing or multiplex analysis. Here we report about fluorescent Au, Cd and bimetallic Au-Cd nanoclusters (NCs) with sizes less than 1.6 nm fabricated and stabilized with bovine serum albumin (BSA). Based on mass spectrometry (MS) and energy-dispersive X-ray spectroscopy (EDX) data the average number of metal atoms per each BSA molecule was estimated to be 15 for BSA-Au NCs; 40 for BSA-Cd NCs; 9 atoms of Au and 26 of Cd for bi-metallic Au-Cd NCs. The NCs demonstrated large Stokes shifts of more than 130 nm. Fluorescence emission maxima for Au NCs at excitation wavelength of 325 nm were at 410 nm and 650 nm; for Cd NCs excitation at 370 nm resulted in the maximal emission at 500 nm, whereas for mixed Au-Cd NCs two peaks of emission were observed at 440 and 640 nm after excitation at 365–380 nm. For human cell lines HEp-2 and L41 both Au and Cd NCs in complex with BSA were less toxic compared to highly toxic original CdCl2 and HAuCl4 solutions. Protein nanoparticles (NPs) fabricated from BSA with metal NCs retained fluorescent properties.