BSA capped bi-functional fluorescent Cu nanoclusters as pH sensor and selective detection of dopamine

Abstract

In this study, a facile and environment-friendly method for the preparation of bovine serum albumin (BSA) capped fluorescent Cu nanoclusters (BSA-CuNCs) was adopted. The as-prepared BSA-CuNCs were characterized by ultraviolet-visible spectroscopy (UV-Vis), fluorescent spectroscopy, Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM). The fluorescence excitation and emission wavelength of BSA-CuNCs appeared at 325 and 406 nm, respectively. The as-synthesized BSA-CuNCs can be utilized as a bi-functional nanomaterial for pH sensing and dopamine (DA) detection with good performance. The fluorescence intensity decreased linearly with decrease in pH from 12 to 5 and increased linearly with increase in DA concentration from 0.5 to 50 μM. TEM measurements proved that the decrease in the pH value resulted in the aggregation of BSA-CuNCs, leading to color change and the quenching of fluorescence. The FT-IR spectra, fluorescent spectra, UV-Vis spectra and zeta potential measurements demonstrated that DA can be combined with Cu²⁺ and the Cu²⁺ would be removed from the surface of BSA-CuNCs. As a result, the fluorescence was recovered owing to the formation of the highly stable compound CuH₂(DA)₂. The pH value of five water samples was determined by the proposed method with relative errors of less than 0.91%. Furthermore, DA in human urine samples was also analyzed by BSA-CuNCs with good recoveries ranging from 90.4% to 104.7% using the standard addition method. It is believed that the bi-functional BSA-CuNCs will show great potential in bio-systems.