In this paper, we demonstrate an electrical detection technique based on solution processed zinc oxide nanosphere for ultra-low level detection of bovine serum albumin (BSA). Our sensor device works on the basis of the variation of conductance of the ZnO nanosphere with different concentration of BSA. The morphological and structural characterizations of ZnO nanosphere were carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Circular dichroism (CD) spectroscopy was performed to investigate the chemical interaction between the BSA and zinc oxide nanosphere. Optical detection was performed using absorbance and Fourier transform infrared spectroscopy (FTIR) studies. Our device exhibits sensitivity 0.126 nA/pM, lower limit of detection (LOD) 10 pM and the fast response time around 5 s, confirming the highest sensitivity for BSA detection achieved so far. Sensing mechanism is governed on the basis of the charge transfer phenomenon between BSA and ZnO. All measurements were carried out at 1 V bias for low power operation.