Silicon nitride surfaces as active substrate for electrical DNAbiosensors

tMiniaturization and integration are fundamental steps to fabricate smart and easy-to-use DNA biosensorsto be massively exploited. Among the several materials, silicon nitride, extensively used as passivationlayer in the microelectronics industry, is a good candidate for the development of biosensors employingelectrical transduction. We report an exhaustive study on chemical grafting of DNA oligonucleotides onSi3N4surfaces and electrical testing for DNA detection. In particular, we developed an optimised graftingprotocol on Si3N4surfaces characterised by contact angle, ellipsometry, Atomic Force Microscopy, andTransmission Electron Microscopy. A comparison with thermally grown SiO2surfaces chemically treatedwith the same immobilization protocol was also carried out. DNA size electrical detection was carriedout by immobilizing oligonucleotide probes on MIS (Metal Insulator Semiconductor)-like capacitors andmeasuring the characteristic capacitance voltage (C-V) curves upon hybridization with both oligo-perfectmatch (DNA PM) and PCR product targets. The correlation between DNA size and C-V shift has beenevaluated. The analytical performances at various PM target concentrations showed a sensitivity valueof 0.048 V/nM with a LoD (Limit of Detection) of about bout 2.0 nM and LoQ (Limit of Quantification)of 6.5 nM. For PCR product target, the measured sensitivity was 0.043 V/ng ml-1with a LoD of about2.7 ng/l and LoQ of 8.8 ng/l.