Switchable Target-Responsive 3D DNA Hydrogels As a Signal Amplification Strategy Combining with SERS Technique for Ultrasensitive Detection of miRNA 155.

Usually, SERS technology requires labeling of the Raman reporter to obtain characteristic spectra for detection of biological samples. However, the number of labeled Raman reporters is often limited, resulting in the restricted improvement for sensitivity of SERS biosensor. In this work, switchable target-responsive 3D DNA hydrogels were introduced to precisely control trapping and release of Raman reporter toluidine blue (TB), which not only avoid labeling signal molecule but also improve the sensitivity of miRNA detection due to immobilization of abundant TB. In the absence of target miRNA, the DNA hydrogel presented a weak Raman signal because TB was far away from SERS substrates with an "OFF" status. However, the DNA hydrogel can be opened by the target miRNA to release TB producing strong Raman signal with an "ON" status. On the basis of this sensitive strategy, this switchable DNA hydrogel-based SERS platform can achieve quantitative detection of miRNA 155. Simultaneously, flexible SERS substrate (leaf@nafion@Ag) and target miRNA-induced duplex-specific nuclease signal amplification strategy were employed to significantly improve the sensitivity of the SERS platform. As a result, the as-proposed SERS platform can sensitively and selectively detect miRNA 155 with a wide linear range of 0.1 fM to 100 pM and low detection limit of 0.083 fM, which indicated that the platform has great potential to be applied in miRNA-related clinical diagnostics and biochemical researches.