Bovine serum albumin-protected copper nanoclusters as a label-free biosensor for the discrimination of bacterial strains.

The development of biosensors for infectious diseases is crucial, especially in the post pandemic era. Point-of-care (POC) devices are highly needed in developing countries to provide quick and cost-effective results. Nanoparticles with enzymatic-like activity, also known as nanozymes, show great promise for diagnostic applications and have recently gained significant attention. In this study, bovine serum albumin (BSA)-protected copper nanoclusters (Cu NCs) with enzymatic-like characteristics were created and analysed for their intrinsic enzymatic-like activity, physicochemical properties, and colloidal stability. The Cu NCs were synthesized via the use of BSA as a capping and reducing agent to ensure their biocompatibility and colloidal stability. Various techniques, such as UV‒Vis spectroscopy, photoluminescence (PL), dynamic light scattering (DLS), elemental analysis, and transmission electron microscopy (TEM), have been used to characterize the prepared Cu NCs. The Cu NCs demonstrated oxidase- and peroxidase-like activity by catalyzing the oxidation of o-phenylenediamine (OPD) into 2,3-diaminophenazine (DAP), the oxOPD product. Showing higher oxidase-like activity by 1.6x compared to the peroxidase-like activity at the same substrate concentration. Their catalytic properties were utilized to detect two common bacteria, gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus), demonstrating a differential label-free detection of different strains at concentrations higher than 105 CFU mL- 1. This study introduces a promising and affordable application for a label-free biosensor used in detecting infectious diseases.