Now-a-days different kinds of bio-analytes sensing like creatinine [1], dopamine, uric acid [2], H₂O₂ [3] and so on using different methods like metal-insulator-metal structure, amperometric, cyclic voltammetry [2], colorimetric, capacitor-voltage [3] method has huge demand in bio-chemical industry. Sarcosine is also one type of bio-analyte that remains in human urine. Sreekumar et al. [4] have marked sarcosine as prostate cancer bio-marker. A lower range of 50 pM sarcosine is reported by Samanta et al. and Z. Heger et al. with GeO_x and paramagnetic nanoparticles respectively [5-6]. In presence of sarcosine oxidase (SOx) enzyme, sarcosine produces formaldehyde (HCHO), glycine and H₂O₂ [5-6]. Sarcosine sensing is realized by detecting this product H₂O₂. We have detected sarcosine as a prostate cancer bio-marker by fabricating silicon nanowire based sensors in electrolyte-insulator-semiconductor structure (EIS). The silicon nanowires (SiNWs) are etched in chemical etching method (Fig. 1) as it has low cost, quick and easier process among the well known SiNWs growth processes like CVD, laser ablation, MBE [7], and so on. Etching was performed on n-type Si wafer in 0.02 M AgNO₃ and 5 M aqueous HF solution. A 10-nm thick SiO₂ layer was grown in thermal oxidation method and 300-nm thick back sides Al contact was performed by thermal evaporator. Then, a 2 nm-thick NiO_x layer was deposited on it by RF sputtering. Finally, the device was patterned in photolithography and attached to printed circuit board. The SiNWs based sensors with NiO_x layer show improvement in sensitivity (̴ 49 mV/pH), linearity (̴ 99.78%), drift (̴ 3.4 mV/hr) and hysteresis (̴ 3.4 mV) characteristics due to increase in surface sites. The NiO_x sensing membrane shows novel nature on SiNWs as well as the chemically etched NWs are rough on surface. These results enhance the catalytic activity of the NiO_x membrane. In practice planar SiO₂ based sensors cannot show H₂O₂ sensing due to its stoichiometric structure. But the SiNWs sensor is capable of 1 nM H₂O₂ sensing because the Ni²⁺oxidation state changes to Ni³⁺. This sensor is also able to sense sarcosine as a prostate cancer biomarker. In presence of 25 units SOx it has detected 1 nM sarcosine with a higher shift towards negative direction (Fig. 2) because of NiO_x work function changes. This novel sensor paves a way to detect prostate cancer at early state of a patient in near future.

Acknowledgement: This work was supported by Ministry of Science and Technology (MOST), Taiwan under contract number: 105-2221-E-182-002.

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