Ultrasensitive Detection of Microrna-21 in Human Serum Based on the Confinement Effect Enhanced Chemical Etching of Gold Nanorods

Natural enzymes, such as horseradish peroxidase (HRP), are a class of important biocatalysts with the high specificity, but their catalytic efficiency is usually unsatisfactory. Thus, the higher catalytic efficiency induced by the confinement effect is promising in optical sensing systems. In this work, a dark-field light scattering sensing platform was fabricated by the confinement effect of HRP from hybridization chain reaction (HCR) and then released to solution by the toehold-mediated strand displacement reaction (TSDR). Then, HRP catalyzed the 3,3′,5,5′-tetramethylbenzidine (TMB) to TMB2+ with the assistance of hydrogen peroxide, which etched the gold nanorods (AuNRs) with weakened light scattering. The single-particle assay was established based on the decreased light scattering intensity of AuNRs under dark-field microscope. The proposed assay revealed excellent analytical performance within a linear range from 25 pmol/L to 600 pmol/L, and a low limit of detection of 3.12 pmol/L. Additionally, it also manifested satisfactory recovery of miRNA-21 in human serum samples. The high sensitivity, excellent specificity, and universal applicability make this sensing platform promising for disease diagnosis.