In₂O₃ Nanoribbon-Based Field-Effect Transistor Biosensors for Ultrasensitive Detection of Exosomal Circulating microRNA with Peptide Nucleic Acid Probes

The expression of distinct microRNA (miRNA) species is associated with many major diseases, and thus, stable and reliable detection at low concentrations is crucial for early diagnosis and treatment. Field-effect transistor (FET)-based biosensors have shown significant progress in miRNA detection, but detection at ultralow concentrations remains challenging due to weak signal generation from small, low-charge miRNA molecules. Here, we report an In2O3 nanoribbon-based FET biosensor platform capable of detecting miRNAs at attomolar (aM) concentrations. Conventional surface functionalization approaches for metal-oxide-based FETs often involve complex, multistep protocols that are time-consuming and limit reproducibility. Here, we introduce a simplified one-step surface chemistry strategy with a 10-(maleimidyl)decylphosphonic acid (MalC10PA) linker molecule that addresses this limitation. We first demonstrated the detection of biotin-labeled miRNAs. Subsequently, we have further demonstrated a label-free miRNA sensing technique by employing an uncharged peptide nucleic acid (PNA) probe/target RNA/secondary DNA-biotin sandwich structure, followed by the introduction of streptavidin and biotin-urease. The urease-induced pH changes amplify the detection of charge changes in the In2O3 channel region, significantly improving the biosensor's sensitivity. The electrolyte-gated In2O3-FET biosensors achieved an ultralow detection limit of 0.72 aM in buffer and high selectivity over miRNAs with two and three base-pair mismatches. Furthermore, the detection of miRNAs from patient plasma exhibited consistent signal compared to the detection in buffer. The detection of specific miRNA species is of recognized importance in early cancer detection and evaluation, and our described method demonstrates great potential for highly multiplexed detection technology with ultrahigh sensitivity.