Highly sensitive detection of cancer cells using a voltage-tuned terahertz chemical microscope

Terahertz chemical microscopy (TCM) is a promising label-free technique for detecting biochemical interactions by monitoring changes in terahertz (THz) wave emission from semiconductor sensing plates. However, quantitative biological detection has been hindered by large plate-to-plate variations originating from uncontrolled depletion-layer electric fields formed during fabrication. These variations shift the response curve of THz amplitude and reduce reproducibility and sensitivity. Here, we introduce a voltage-tuned sensing plate that allows direct control of the depletion-layer electric field by applying a bias voltage to the Si layer of the sensing plate. This enables deliberate adjustment of surface potential and alignment of the THz response curve to the region of highest gain. Using lung adenocarcinoma cells (PC9) captured via AE1/AE3 antibodies targeting specific cell-surface antigens, we demonstrate that voltage tuning enhances detection sensitivity by up to 50-fold and restores linearity between THz amplitude and the logarithm of cell concentration, even in plates with negligible response at 0 V. These findings establish voltage control as a simple, universally applicable strategy to stabilize TCM performance, reduce fabrication-induced variability, and improve analytical sensitivity for biosensing and materials-analysis applications.