Microcantilever-based biosensors have emerged as promising technologies for point-of-care sensing systems. However, since they are typically utilized as a single piezoresistor in a quarter Wheatstone bridge configuration, they suffer from output asymmetry and require rigorous calibration to eliminate their common-mode interference. In this study, we propose a novel piezoresistive double-clamped beam structure in a half-Wheatstone bridge configuration, which offers a highly accurate biosensing approach for measuring the levels of free valproic acid (fVPA) in biological samples. The sensor design incorporates two active piezoresistors, resulting in improved measurement accuracy by providing balanced recordings. This balanced configuration allows for automatic compensation of environmental parameters and enhances the robustness of recordings against common signal interferences such as temperature variations. In addition, this new biosensing mechanism offers a lower limit of detection, enabling precise measurements within the entire therapeutic range of fVPA. To assess the sensor efficacy under various experiment conditions, in-silico simulations were conducted. The simulation results demonstrated the remarkable potential of the new sensor for use in point-of-care settings.