Electrical Characterization of Biological Molecules Deposition in MOS Capacitors

The aim of this work was the electrical characterization of biological molecules covalently immobilized on the dielectric of a MOS-like structure. The experimental protocol to bond the biological molecules on SiO₂ lies in: oxide activation, silanization, linker molecule deposition, biological molecule bonding. Both an enzyme, the glucose oxidase (GOx), and single-stranded oligonucleotides (ssDNA) were selected as biological molecules. The effectiveness of the immobilization procedure was tested by X-ray Photoelectron spectroscopy. The electrical characterization was carried out on reference and fully processed samples as a function of the electrolyte pH, from 3 to 8, and of measurement time, up to 200 s. The oxide does not experience any aging during the measurement sets for voltages up to ±3 V. GOx deposition produces a shift of about −0.7 ± 0.04 V in the V_FB, suggesting the molecule has a positive charge when anchored to the oxide layer. On the other hand, ssDNA deposition causes a positive shift, below 0.3 V, as expected due to the DNA negative charge in solution. The hybridization process causes a further shift in the V_FB above 0.4 V, well above the experimental errors, confirming the sensitivity of this device to monitor the hybridization. Our preliminary data show a potential for the development of MOS-based biosensors.