Approaches to label-free flexible DNA biosensors using low-temperature solution-processed InZnO thin-film transistors

• For practical use of solution-processed In–Zn–O (IZO) thin film transistor (TFT) as a biosensor, achieving remarkable sensitivity and feasibility of flexible devices is strongly desired.
• Here we report low-temperature solution-processed IZO TFTs with a construction temperature of only 280°C, which is a decisive factor in flexible devices being able to compensate for the aforementioned limitations for the first time.
• These findings can enhance the applicability of IZO TFTs as a next generation biosensor.

Low-temperature solution-processed In–Zn–O (IZO) thin-film transistors (TFTs) exhibiting a favorable microenvironment for electron transfer by adsorbed artificial deoxyribonucleic acid (DNA) have extraordinary potential for emerging flexible biosensor applications. Superb sensing ability to differentiate even 0.5 μL of 50 nM DNA target solution was achieved through using IZO TFTs fabricated at 280 °C. Our IZO TFT had a turn-on voltage (Von) of −0.8 V, on/off ratio of 6.94×105, and on-current (Ion) value of 2.32×10−6 A in pristine condition. A dry-wet method was applied to immobilize two dimensional double crossover tile based DNA nanostructures on the IZO surface, after which we observed a negative shift of the transfer curve accompanied by a significant increase in the Ion and degradation of the Von and on/off ratio. As the concentration of DNA target solution increased, variances in these parameters became increasingly apparent. The sensing mechanism based on the current evolution was attributed to the oxidation of DNA, in which the guanine nucleobase plays a key role. The sensing behavior obtained from flexible biosensors on a polymeric substrate fabricated under the identical conditions was exactly analogous. These results compare favorably with the conventional field-effect transistor based DNA sensors by demonstrating remarkable sensitivity and feasibility of flexible devices that arose from a different sensing mechanism and a low-temperature process, respectively.