Measurement of microRNA-106b as a gastric cancer biomarker based on Zn-BTC MOF label-free genosensor

Due to the late detection of stomach cancer, this cancer usually causes high mortality. The development of an electrochemical genosensor to measure microRNA 106b (miR-106b), as a gastric cancer biomarker, is the aim of this effort. In this regard, first, 1,3,5-benzenetricarboxylate (BTC) metal-organic frameworks (Zn-BTC MOF) were self-assembled on the glassy carbon electrode and then the probe (ssDNA) was immobilized on it. The morphology Zn-BTC MOF was characterized by SEM, FT-IR, Raman and X-Ray techniques. Zn-BTC MOF as a biosensor substrate has strong interaction with ssDNA. Quantitative measurement of miR-106b was performed by electrochemical impedance spectroscopy (EIS). To perform this measurement, the difference of the charge transfer resistances (ΔRct) of Nyquist plots of the ssDNA probe modified electrode before and after hybridization with miR-106b was obtained and used as an analytical signal. Using the suggested genosensor, it is possible to measure miR-106b in the concentration range of 1.0 fM to 1.0 μM with a detection limit of 0.65 fM under optimal conditions. Moreover, at the genosensor surface, miR-106b can be detected from a non-complementary and a single base mismatch sequence. Also, the genosensor was used to assess miR-106b in a human serum sample and obtained satisfactory results.

Highly selective sensing and measurement of microRNA-541 based on its sequence-specific digestion by the restriction enzyme Hinf1

In this study, a genosensor is introduced to detect microRNA-541 through an enzymatic digestion method and using a restriction enzyme (RE). Hinf1 is a type of RE which can cut the double helix DNA at specific sequences. The hybridization event and the corresponding enzymatic reactions are studied through guanine signal tracing on a pencil graphite electrode modified with graphene quantum dots (GQDs/PGE). The stages of fabricating the electrode are monitored by atomic force microscopy, and its electrochemical behavior is studied by cyclic voltammetry. The results indicate that the guanine current response of a 25-mer oligonucleotide of 7-guanine immobilized on the electrode surface decreases after hybridization despite an increase in the number of the guanine bases. Also, after enzyme treatment, the current decreases further due to the separation of a number of guanine bases from ds-DNA. A comparison of the analytical parameters of the proposed method with those of the conventional guanine oxidation method indicates that the linear concentration range in the proposed method, i.e. 1.0 fM to 1.0 nM, is lower than that in the conventional method, i.e. 10.0 pM-1.0 μM. On the basis of these findings, it is concluded that the use of Hinf1 enzyme makes it possible to measure microRNA at a femtomolar level. The selectivity of the designed biosensor has been proved using a non-complementary sequence with a one-base mismatch in the recognition site, rather than a complementary sequence. Finally, the proposed genosensor can be satisfactorily applied to measure microRNA-541 in human plasma samples.