Passivation Strategies for Enhancing Solution-Gated Carbon Nanotube Field-Effect Transistor Biosensing Performance and Stability in Ionic Solutions

Interest in point-of-care diagnostics has led to increasing demand for the development of nanomaterial-based electronic biosensors such as biosensor field-effect transistors (BioFETs) due to their inherent simplicity, sensitivity, and scalability. The utility of BioFETs, which use electrical transduction to detect biological signals, is directly dependent upon their electrical stability in detection-relevant environments. However, BioFET device structures vary substantially, especially in electrode passivation modalities. Improper passivation of electronic components in ionic solutions can lead to excessive leakage currents and signal drift, thus presenting a hinderance to signal detectability. Here, we harness the sensitivity of nanomaterials to study the effects of various passivation strategies on the performance and stability of a biosensing platform based on aerosol-jet-printed carbon nanotube thin-film transistors. Specifically, nonpassivated devices were compared to devices passivated with photoresist (SU-8), dielectric (HfO2), or photoresist + dielectric (SU-8 followed by HfO2) and were evaluated primarily by initial performance metrics, large-scale device yield, and stability throughout long-duration cycling in phosphate buffered saline. We find that all three passivation conditions result in improved device performance compared to nonpassivated devices, with the photoresist + dielectric strategy providing the lowest average leakage current in solution (∼2 nA). Notably, the photoresist + dielectric strategy also results in the greatest yield of BioFET devices meeting our selected performance criteria on a wafer scale (∼90%), the highest long-term stability in solution (<0.01% change in on-current), and the best average on/off-current ratio (∼104), hysteresis (∼32 mV), and subthreshold swing (∼192 mV/decade). This passivation schema has the potential to pave the path toward a truly high-yield, stable, and robust electrical biosensing platform.