Ultrasensitive SERS detection of lysozyme by a target-triggering multiple cycle amplification strategy based on a...

An ultrasensitive surface enhanced Raman scattering (SERS) method has been designed to selectively and sensitively detect lysozyme. The gold chip as the detection substrate, the aptamer-based target-triggering cascade multiple cycle amplification, and gold nanoparticles (AuNPs) bio-barcode Raman probe enhancement on the gold substrate are employed to enhance the SERS signals. The cascade amplification process consists of the nicking enzyme signaling amplification (NESA), the strand displacement amplification (SDA), and the circular-hairpin-assisted exponential amplification reaction (HA-EXPAR). With the involvement of an aptamer-based probe, two amplification reaction templates, and a Raman probe, the whole circle amplification process is triggered by the target recognition of lysozyme. The products of the upstream cycle (NESA) could act as the "DNA trigger" of the downstream cycle (SDA and circular HA-EXPAR) to generate further signal amplification, resulting in the immobility of abundant AuNPs Raman probes on the gold substrate. "Hot spots" are produced between the Raman probe and the gold film, leading to significant SERS enhancement. This detection method exhibits excellent specificity and sensitivity towards lysozyme with a detection limit of 1.0×10(-15)  M. Moreover, the practical determination of lysozyme in human serum demonstrates the feasibility of this SERS approach in the analysis of a variety of biological specimens.