Sarcosine Prostate Cancer Biomarker Detection by Controlling Oxygen in NiO x Membrane on Vertical Silicon Nanowires in Electrolyte-Insulator-Nanowire Structure.

Sarcosine prostate cancer biomarker with the low concentration of 1 pM has been detected by controlling oxygen from 1 to 15 sccm in a NiO _x membrane on chemically etched vertical Si nanowires (SiNWs) in an electrolyte-insulator-nanowire (EIN) structure. The vertical Si nanowires with approximately 17 μm length and polycrystalline NiO _x membrane are observed by both field-emission scanning electron microscope (FE-SEM) and high-resolution transmission electron microscope (HRTEM) images, respectively. The optimized NiO _x membrane with oxygen content of 4 sccm on planar SiO _x /Si substrate shows good pH sensitivity of approximately 50 mV/pH, low hysteresis of 3.4 mV, and low drift rate of 2.4 mV/h as compared to other oxygen content membranes of 1, 10, and 15 sccm. Further, uric acid with the concentration of 0.1 μM is detected directly by using the optimized NiO _x membrane. In addition, repeatable H ₂ O ₂ sensing with the low concentration of 10 pM as well as prostate cancer biomarker is detected, which is owing to the reduction-oxidation phenomena of the NiO _x membranes. The sensing mechanism is owing to the Ni ²⁺ /Ni ³⁺ oxidation states of the NiO _x membrane, which is confirmed by X-ray photoelectron spectroscopy. The optimized NiO _x membrane on vertical Si nanowire in the EIN structure shows a good drift rate of 3.84 mV/h and sarcosine detection with improvement of approximately 1000 times as compared to the planar Si in an electrolyte-insulator-semiconductor (EIS) structure. This sensor paves a way to detect early-stage diagnosis of prostate cancer rapidly in the near future.