In situ template generation of silver nanoparticles as amplification tags for ultrasensitive surface plasmon resonance biosensing of microRNA

Surface plasmon resonance (SPR) biosensing strategies have drawn substantial attention due to their advantages of label free, real time, and high performance, but complicated modification procedures and strict reaction conditions of amplification tags associated with current SPR biosensors hinder their potential utilizations. Herein, an in situ prepared AgNPs-based SPR biosensor for MicroRNA (miRNA) sensitive detection was developed based on hybridization chain reaction (HCR) without the biomodification on amplification tags. The target miRNA initiated the HCR of the hairpin probes to generate long double strand DNA (dsDNA) chains that were immobilized on SPR disk. Thus, with Ag+ intercalating into dsDNA chains, large numbers of AgNPs generated after NaBH4 reduction, resulting in the significantly elevated SPR angle. Further, the SPR angle is positively proportional to target miRNA concentrations. As a result, the in situ generated AgNPs-based SPR biosensor realized exceptional let-7a detection with linear range of 0.001-0.1 pM and detection limit (LOD) of 0.35 fM, lower than that of other SPR biosensors that used modifiable amplification tags. Featured with the modification-free characteristic and excellent performance, the proposed strategy provides new way for ultrasensitive detection of miRNA, and allows to detect other biomarkers by simply verifying the target responsive substances, and thus has a great potential for health and early disease diagnosis.