Glass Nanopipette-Based Plasmonic SERS Platform for Single-Cell MicroRNA-21 Sensing during Apoptosis

As one of the most widely distributed microRNAs, microRNA-21 (miRNA-21) significantly regulates target genes' expression levels and participates in many cellular and intercellular activities, and its abnormal expression is always related to some diseases, especially cancer. Hence, detecting miRNA-21, as a biomarker, at the single-cell level helps us to reveal cell heterogeneity and expression level variation during the state change of cells. In this study, we constructed a gold nanoparticles nanomembrane (AuNPs-NM)-modified plasmonic glass nanopipette (P-nanopipette) surface-enhanced Raman scattering (SERS) sensing platform to sensitively detect content variation of the intracellular miRNA-21 during the electrostimulus (ES)-induced apoptosis process. The cytoplasm-located miRNA-21 was first extracted by using the extraction DNA (HP1)-modified P-nanopipette through a hybridization chain reaction (HCR). The nanopipette was then incubated with a labeling DNA (HP2) and reporter 4-MBA-modified Raman tag. The Raman signal (collected from the tip area near the orifice within 1 μm) showed a good response to the content variation of intracellular miRNA-21 under ES, and the proposed single-cell SERS detection platform provides a simple way to study intracellular substance change and evaluate cancer treatment outcomes.