An Unpatterned and Cost-Effective Terahertz Sensing Platform for Thin Film Detection

Field-confining techniques represented by metamaterials have been widely employed in terahertz (THz) biosensing. Although such sensors can achieve remarkable sensitivity by enhancing the interaction efficiency between THz waves and samples, they typically rely on complex microfabrication processes and finely resolved spectra obtained from expensive THz spectrometers. These factors substantially increase the device and system costs, limiting their widespread applications. In this work, we address these challenges by introducing an unpatterned sensing platform based on a conductive-film antireflection architecture. Doped PEDOT:PSS thin films spin-coated on the substrate function simultaneously as an impedance-matching layer and as an analyte-interaction interface, whose conductivity is sensitively modulated upon sample attachment. The dual roles significantly amplify the signal variation induced by analytes. Experimental measurements on bovine serum albumin (BSA) samples with varying quantities confirm the excellent sensitivity and linearity of the proposed sensor, achieving a limit of detection (LOD) of 8.67 nm, corresponding to 5.767 × 104 times smaller than the operating wavelength. The resonance-free design enables an ultra-broadband response, ensuring compatibility with most types of THz systems, including those based on continuous-wave sources and incoherent detectors. This novel mechanism establishes a new paradigm for low-cost, scalable, and highly reproducible THz sensing applications.