Silicon nanodevice biosensors have been attracted a lot of attention due to its advantages of label-free, real-time and very high sensitive detection. This study employs self-assembly monolayer (SAM) of methoxy-poly(ethyleneglycol) silane (MPEG-sil) as passivation on Si nanodevices. Ablation of SAM by Joule heating (JH) was performed at n- region of a nanobelt device, where the linker molecules, biotin were modified subsequently. Detection of Alexa dye-labeled Streptavidin (SA) showed that the fluorescence intensity at n - region increased with each 50-μl SA injection and saturated after the 4th injection. A difference of fluorescence intensity between SAM-ablated device and without passivation is 4.9 fold. Threshold voltage (Vth) shifted ca. 35 mV after the 4th injection for SAM-ablated device and as-fabricated device exhibited only a 10-mV V th shift. The results indicated that SAM-ablated device possess potential in reduction of sensing time and in increase of sensitivity for low concentration detection.