Self-referencing nanopipette based on photoelectrochemistry for single-cell analysis of breast cancer biomarker miRNA-21

Breast cancer (BC) is the most common malignancy in women and ranks second among all cancer types worldwide. The escalating demand for early and precise diagnosis has intensified the quest for ultrasensitive and highly specific biosensors. Here we present a self-referencing photoelectrochemical (PEC) strategy based on a nanopipette that enables the direct quantification of the BC biomarker miRNA-21 in single living cells. The nanopipette's ultrafine tip minimizes membrane disruption, while an integrated self-referencing electrode cancels out trans-membrane potential fluctuations, yielding a linear dynamic range of 1–7 nM and a detection limit of 0.328 nM without cell lysis or amplification. The platform markedly enhances the accuracy of single-cell heterogeneity analyses and offers a new paradigm for intracellular trace-nucleic-acid quantification. Moreover, the modular self-referencing architecture creates a methodological foundation for extending nanopipette-based sensors to broader single-cell omics applications.