Selective breath biomarker sensing of trimethylamine using Cu-doped Janus Al₂SeTe monolayers: a DFT investigation

Noninvasive detection of breath biomarkers offers a powerful approach for early diagnosis of respiratory and metabolic disorders. Trimethylamine (TMA) is a key biomarker associated with trimethylaminuria and hepatic dysfunction; however, achieving high selectivity among structurally diverse yet clinically overlapping biomarkers remains challenging. In this work, first-principles density functional theory (DFT) simulations are employed to systematically investigate the adsorption behavior of TMA and eleven competing gases through adsorption energy, charge transfer, adsorption distance, electronic band structure, density of states (DOS), and recovery time. Pristine Al₂SeTe exhibits mild sensitivity to TMA but strong responses to NO and NO₂. In contrast, Cu doping markedly enhances selectivity toward TMA while suppressing interference from NO _x species, driven by bandgap reduction from 2.14 eV to 0.816 eV at 2.77% doping. Tunable sensitivity is achieved through controlled Cu concentrations (2.77-11.11%). Mixed-gas simulations under breath-like conditions confirm that TMA produces a dominant electronic signature on the Cu-doped surface. Rapid desorption and favorable recovery times indicate good reusability. Overall, Cu-doped Janus Al₂SeTe emerges as a promising 2D sensing platform for potential selective breath-based TMA detection and early disease diagnosis.