Design and Fabrication of a Silver Nanocluster-Based Aptasensor for Lysozyme Detection

Lysozyme is a universal part of the innate immune system and is present in various bodily fluids. It is also vastly studied as a biomarker for a variety of diseases and is used in the food industry as a preservative. However, due to lack of a universal and precise detection method, new techniques are highly sought after for this purpose. Here, we introduce a silver nanocluster-based aptasensor to detect lysozyme with high sensitivity. The sensor consists of an RNA aptamer and a complementary DNA sequence with a silver nanocluster template. Silver nanoclusters were synthesized by reduction of silver nitrate in the presence of complementary DNA sequence and characterized by transmission electron microscopy, UV-Visible, fluorescence, and circular dichroism spectroscopy. Emission of the silver nanoclusters switched between low and high intensity based on the quenching ability of the aptamer for DNA-silver nanoclusters and the binding affinity of the aptamer for lysozyme. In the presence of the aptamer, DNA-silver nanoclusters show low fluorescence due to the hybridization of the aptamer, and hence disruption in the formation of DNA-silver nanoclusters. Upon addition of lysozyme, aptamer binding to the DNA-templated silver nanoclusters will be inhibited due to the stronger interaction between the aptamer and lysozyme. Presence of the free DNA template leads to a restored fluorescence signal of DNA-silver nanoclusters which is dependent upon the lysozyme concentration. By utilizing this strategy, the complementary DNA-templated silver nanoclusters sensor can detect concentrations of lysozyme lower than 10 nM via a signal in the visible spectral region. The proposed sensor presents valuable features such as low-cost, high sensitivity, easy fabrication, and convenient operation for detection of lysozyme.