Because of detection characteristics in traditional capacitive-based biomolecular sensing technologies, it is important to have a uniform and defect-free interface layers. However, efforts to achieve the interface layer are tedious and labor intensive. To conquer this problem and enhance the sensing characteristics of capacitive-based biomolecular sensing device, in our report, we use co-planar electrode with nano-gap structure and placed the sensing element on the gap surface, which is different from traditional capacitive putting antigen/antibody on the electrode surface. This arrangement leads to gap-surface charge changes as molecular binding occurring. And the altered gap-surface charges modulate the electric double layer (EDL) of electrode sidewalls and result in the change of nano-gap capacitance. Utilizing surface modification with amine-terminated and aldehyde-terminated groups, we demonstrates the proposed electrode sidewall EDL contraction phenomena induced by gap-surface ion redistribution. Based on our experimental results of surface modifications, the capacitance variance of 1 µm and 100 nm gap width are 8% and 17%, respectively. In addition, we show that both gap width and detection environment play important roles in sensitivity and detection limit of the developed nano-gap device. With a demonstration of cTnT detection, a demonstrated detection dynamic range of the proposed method is from 10 pg/ml to 1 µg/ml, which is around 100 fold higher than that of traditional capacitive biosensors. The limit of detection is 10 pg/ml, which is the cut-off level in clinical examinations.