Plasmonic biosensor for the highly sensitive detection of microRNA-21 via the chemical etching of gold nanorods under a dark-field microscope

MicroRNAs involved in tumor-related tissues at abnormal expression level present tremendous potential in the early diagnosis of cancers. However, their intrinsic shortcomings, for instance, low abundance and high sequence homology, make it challengeable to quantify them with high sensitivity and selectivity. Herein, a highly sensitive platform with great specificity was developed for microRNA-21 based on the produced-I2 triggered chemical etching of gold nanorods to a smaller size, resulting in a significant blue shift and a great intensity decrease in the localized surface plasmon resonance (LSPR) scattering. The synergism of strand displacement and enzymatic reaction enabled the proposed strategy with a high sensitivity and selectivity toward microRNA-21 in a dynamic range from 0.1 to 10,000 pM and a low limit of detection of 71.22 fM (3σ/k) by dark-field microscope. Additionally, the remarkable discrimination of single nucleotide difference suggested the superior selectivity towards microRNA-21, which presented a satisfactory recovery in human serum samples. The proposed plasmon platform could also serve as a universal and sensitive detection of cancer biomarkers, presenting the amusing application prospects in the early diagnosis of various cancers by adapting the corresponding nucleic acid sequences.