A novel hybrid biosensor for miRNA detection based on peptide nucleic acids and molecularly imprinted polymers

The detection of miRNAs serving as key biomarkers in cancer diagnostics is challenging due to their small size, low abundance, and high sequence similarity, which complicates their sensitive and selective detection. Here, we report a biosensor that combines molecularly imprinted polymers (MIPs) with peptide nucleic acids (PNAs) to achieve a sensitive and highly selective miRNA detection in RNA isolates of cancer cells. MIPs were synthesized by electropolymerization utilizing PNA-supported and pre-oriented miR-21 templates molecules, which serve as both a linker for improved template orientation and an assistive recognition element for miRNA binding. Electrochemical impedance spectroscopy (EIS) was used to detect miR-21 after optimization of the sensor architecture and the experimental parameters. The sensor exhibited excellent sensitivity and selectivity toward miR-21 even when compared to the single mismatched sequence, with a linear response of 0.5–5000 pM and a limit of detection (LoD) of 0.11 ± 0.04 pM without any amplification steps. The sensor was used to quantify miR-21 in artificial serum and in RNA isolates of cancer cells to discriminate between MCF-7 and Hela cells. This approach opens new avenues for the application of MIPs as synthetic antibodies in miRNA research and emphasizes the importance of the synergistic integration of PNA.