Ultrasensitive Detection of Lysozyme upon Conformational Change of DNA Duplex

Abstract

We report a simple, cost-effective, and ultrasensitive approach for colorimetric detection of lysozyme based on target-induced conformational change of DNA duplex. The detection method utilizes the interaction between DNA aptamer and its target leading to the dissociation of DNA aptamer from the DNA duplex and forms a structured complex. The complementary DNA that detached from the DNA duplex adsorbed on the AuNPs surface protects the nanoparticles against salt-induced aggregation, resulting in maintaining the red dispersed state of AuNPs. Such an approach allowed the femtomolar detection of lysozyme with a wide linear scale ranging from 0.1 to 200 pM by simple spectroscopic analysis with detection time of ~40 min. In case of naked eye detection, the detection limit of nanoaptasensor corresponds to ~0.5 pM. The nanoaptasensor demonstrated high specificity with regard to lysozyme in the presence of a variety of nonspecific proteins. In case of lysozyme detection in simulated saliva samples, the average recoveries were in the range of 90.47 to 105.90%, with the relative standard deviations (RSD) of 3.45-4.89% that suggests a good reproducibility. The results clearly indicated the reliability and applicability of the proposed assay for the simple and rapid detection of lysozyme in real samples. Compared with existing diagnostic assays, the proposed nanoaptasensor showed many advantages regarding simplicity, versatility, cost, and time for analysis. This approach demonstrated a great potential for ultrasensitive and on-site analysis of a wide range of protein biomarkers using plasmonic nanoparticles.