A PEG-based strategy to improve detection of clinical microRNA 155 by bio-Field Effect Transistor in high ionic strength environment

microRNAs are small oligonucleotides involved in post-transcriptional gene regulation whose alteration is found in several diseases, including cancer, and therefore their detection is crucial for diagnosis, prognosis, and treatment purposes. Field-Effect Transistor-based biosensors (bioFETs) represent a promising technology for the clinical detection of microRNAs. However, one of the main challenges associated with this technology is the Debye screening, becoming significant at the high ionic strengths required for effective hybridization. We aimed at detecting oncogenic microRNA-155 by using a bioFET system using as capture element a complementary RNA probe (antimiR-155) combined with the introduction of PEG molecules (20 kDa, PEG20), at an ionic strength of 300 mM. We optimized the co-immobilization ratio between antimiR-155 and PEG20 and assessed its impact on the interactions between the oligonucleotides. The kinetics can be well described by the Langmuir-Freundlich isotherm with an affinity constant within the range typical of nucleic acid interactions. The introduction of PEG20 significantly enhanced the detection sensitivity of miR-155 by reaching a level of less than 200 pM, together with excellent discrimination against other clinically relevant microRNAs. Our findings demonstrate that the incorporation of PEG20 constitutes an effective strategy to mitigate the Debye screening effects and facilitates bioFET-based clinical applications at physiological ionic strengths.