Label-free and real-time detection of ferritin using a horn-like polycrystalline-silicon nanowire field-effect transistor biosensor

In this paper, we used the horn-like polycrystalline-silicon nanowire field-effect transistor (poly-Si NW FET) biosensors to detect ferritin. It employs the trapezoidal-shape dummy gate structure fabricated at the spacer wire process to form the shape of horn-like nanowires. The horn-like poly-Si NW FET using a channel length of 2 μm exhibited better electrical characteristics, such as a smaller threshold voltage of 1.1 V and a higher I_on/I_off of 3.47 × 10⁵, compared to other channel lengths. In addition, the horn-like poly-Si NW FET sensor exhibited a high sensitivity of 133.47 mV/pH exceeding the Nernst limit. This result is attributed to the higher capacitive-coupling ratio (top-gate capacitance to bottom-gate capacitance). Moreover, we used a horn-like poly-Si NW FET biosensor to detect the ferritin in buffer solution due to its label-free, real-time, and high-sensitive. We modified 3-aminopropyltriethoxysilane on the SiO₂/Si₃N₄/SiO₂ stacked surface followed by glutaraldehyde functionalized, and the ferritin antibodies were immobilized on the aldehyde terminal. While the serum ferritin antigen was prepared in the buffer, the results indicated that the sensor could detect serum ferritin below 50 pg/mL in a micro-fluidic channel.