Luminescent silver nanoclusters in probing immunoglobulins and serum albumins in protein mixtures
The concentrations of total immunoglobulins (Ig), human serum albumin (HSA) and their relative level are important characteristics of health state. Significant increase of [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, 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 to apply AgNCs to detect HSA and Ig selectively in their mixtures. We have obtained calibration curves indicating dependence of the luminescence intensity and position of its spectral maximum on Ig concentration. The calibration curves reveal linear dependences in a wide range of [Ig]/[HSA] ratio, extending beyond its physiological levels. The obtained results demonstrate that application of the AgNCs as a luminiscent probe allows quantitative determination of the [Ig]/[HSA] ratio in the mixtures without any sample pre-treatment and avoiding expensive immunochemical approaches. The described approach could be applied in determination of the levels of albumin and immunoglobulins in physiological liquids.