Zwitterionic polymer-modified silicon nanowire field-effect transistor biosensor for interleukin-6 detection in saliva.

As a key inflammatory cytokine biomarker, interleukin-6 (IL-6) plays an essential role in the early diagnosis of inflammatory diseases. Nevertheless, long-term, continuous biosensing monitoring of ultralow-level IL-6 remains great challenges owing to severe nonspecific adsorption effects in complex biological media such as saliva. In this study, a silicon nanowire (SiNW) field-effect transistor (FET) functionalized with the zwitterionic polymer sulfobetaine methacrylate (SBMA) on the SiNW surface has been developed for IL-6 detection in saliva. After aptamer functionalization, the SBMA-modified FET biosensor exhibits high sensitivity for IL-6 detection in artificial saliva over a concentration range of 7-250 pg/mL. It also displays high stability, retaining ∼96.0% of its initial sensitivity after 2 h of immersion in saliva. The high stability and sensitivity of the biosensor can be attributed to the electrically neutral hydration layer induced by SBMA, which weakens the electrical double-layer screening effect by reducing nonspecific adsorption and counterion adsorption in complex biological fluids. The enhancement in sensitivity of the SBMA-modified SiNW FET was also evaluated by extracting the effective electric-field interaction length. This method offers an effective strategy for SiNW FET biosensing to achieve reliable, long-term monitoring of ultralow-concentration biomarkers in saliva samples.