Aim: A new type of surface modification of SOI-FET sensors with ultrathin sensor-probe transition layer and uncharged probes for highly specific detection of short RNA (saRNA) was suggested. Materials & methods: Carbonyldiimidazole (CDI) or glycidoxypropyltrimethoxysilane were used as precursors of sensor-probe interface layers, together with peptide nucleic acids and new NA analogues – phosphoryl guanidine oligo(2′-OMe)ribonucleotides (PGO) as probes for RNA hybridization. RNA sequences corresponding to mRNA NELFA (NM_005663) and microRNA-29a (cancer markers) were used as saRNA targets. Real-time saRNA detection by SOI-FET sensors and fluorescence analysis were applied. Results: Highly specific response with femtomolar sensitivity to saRNA was demonstrated for CDI-PGO-modified sensors fabricated by optical lithography. Conclusion: The proposed CDI–PGO protocol of modification of Si sensor surface is a promising procedure for biomedical applications.

Nanowire (NW) detection is one of the fast and highly sensitive methods. An NW biosensor based on silicon-on-insulator (SOI) structures are used in the reported study for real-time label-free biospecific detection of the NFATc1 (D-NFATc1) cancer marker. For this purpose, the SOI NWs are functionalized with NFATc1 aptamers used as macromolecular probes. It is demonstrated that such a biosensor can ensure a detection limits up to 10⁻¹⁵ M, which is comparable with the sensitivity ensured by an NW biosensor with immobilized antibodies used as macromolecular probes. The results of this study demonstrate that such approaches to the development of sensor elements for highly sensitive diagnostics of diseases are really promising.

A method of nanostructuring of silicon-on-insulator (SOI) layers on the basis of gas etching in XeF₂ or SF₆:CFCl₃ is developed for the purpose of obtaining SOI nanowire structures. SOI nanowire transistors (SOI NWTs) with free channels, used as sensors in electron detectors, are fabricated and tested. The results of experiments show that the method used to fabricate nanowires requires no high-temperature operations for elimination of defects after nanostructuring of SOI layers. The sensitivity of SOI NWTs to test molecules of bovine serum albumin is 10⁻¹⁵ mole/liter, which is one of the best results for nanowire biosensors.

Nanowire or nanobelt sensors based on silicon-on-insulator field-effect transistors (SOI-FETs) are one of the leading directions of label-free biosensors. An essential issue in this device construction type is obtaining reproducible results from electrochemical measurements. It is affected by many factors, including the measuring solution and the design parameters of the sensor. The biosensor surface should be charged minimally for the highest sensitivity and maximum effect from interaction with other charged molecules. Therefore, the pH value should be chosen so that the surface has a minimum charge. Here, we studied the SOI-FET sensor containing 12 nanobelt elements concatenated on a single substrate. Two types of sensing elements of similar design and different widths (0.2 or 3 μm) were located in the chips. The drain-gate measurements of wires with a width of 3 µm are sufficiently reproducible for the entire chip to obtain measurement statistics in air and deionized water. For the pH values from 3 to 12, we found significant changes in source-drain characteristics of nanobelts, which reach the plateau at pH values of 7 and higher. High pH sensitivity (ca. 1500 and 970 mV/pH) was observed in sensors of 3 μm and 0.2 μm in width in the range of pH values from 3 to 7. We found a higher “on” current to “off” current ratio for wide wires. At all studied pH values, I_on/I_off was up to 4600 and 30,800 for 0.2 and 3 μm wires, respectively. In the scheme on the source-drain current measurements at fixed gate voltages, the highest sensitivity to the pH changes reaches a gate voltage of 13 and 19 V for 0.2 μm and 3 μm sensors, respectively. In summary, the most suitable is 3 μm nanobelt sensing elements for the reliable analysis of biomolecules and measurements at pH over 7.