Luminescent silver nanoclusters for probing immunoglobulins and serum albumins in protein mixtures†
The concentrations of total immunoglobulins (Ig) and human serum albumin (HSA) and their relative levels are important characteristics of the health state. Significant increase of the [Ig]/[HSA] ratio may be indicative of some blood diseases, such as multiple myeloma. We employed silver nanoclusters (AgNCs) as luminescent labels for the detection of HSA and Ig in their mixtures in a single experiment. The luminescent complexes of AgNCs with HSA, IgG, and pentaglobin (IgG + IgA + IgM) and their mixtures were prepared by mixing silver nitrate with the proteins followed by reduction of silver ions using borohydride. Each type of complex demonstrated characteristic luminescence spectra and quantum yields allowing us to apply AgNCs to detect HSA and Ig selectively in their mixtures. We have obtained calibration curves indicating the dependence of the luminescence intensity and position of its spectral maximum on the Ig concentration. The calibration curves reveal linear dependences in a wide range of [Ig]/[HSA] ratios, extending beyond their physiological levels. The obtained results demonstrate that the application of AgNCs as a luminescent probe allows quantitative determination of the [Ig]/[HSA] ratio in mixtures without any sample pre-treatment and avoiding expensive immunochemical approaches. The described approach could be applied in the determination of the levels of albumin and immunoglobulins in physiological liquids.