Click chemistry-assisted self-assembly of DNA aptamer on gold nanoparticles-modified screen-printed carbon electrodes for label-free electrochemical aptasensor

A highly sensitive and label-free electrochemical aptasensor was developed by employing click chemistry-assisted self-assembly of DNA aptamers on gold nanoparticles (GNPs)-modified screen-printed carbon electrodes (SPCEs). Lysozyme, a ubiquitous protein in mammals that is known as the “bodyʹs own antibiotic”, was chosen as the target protein and hexaammineruthenium(III) ([Ru(NH3)6]3+) was used as the electrochemical indicator. GNPs were first electrodeposited onto SPCEs and used as a platform for the immobilization of the aptamers. The aptasensor was fabricated by the self-assembly of 10-azidoundecan-1-thiol on GNPs-modified SPCE surfaces, followed by covalent attachment of anti-lysozyme binding aptamer (LBA) modified with alkynyl groups via click chemistry. The measurement was based on the displacement of [Ru(NH3)6]3+ from the LBA on the electrode in the presence of lysozyme and the decrease of square wave voltammetric response of surface-bound [Ru(NH3)6]3+. The decrease in the peak current was linear with the logarithm of the concentration of lysozyme in the range from 1.0 pg mL−1 to 50.0 pg mL−1 with a detection limit of 0.3 pg mL−1. The aptasensor was successfully applied to the analysis of lysozyme in egg white samples. This work provides a promising immobilization strategy for the fabrication of biosensors and offers an alternative and sensitive method for protein detection.