Detecting ammonia (NH₃) in human breath is vitally important for early warning and disease detection. Polymer composite nanomaterials, which serve as high-performance NH₃ gas sensors, have become a prominent research focus in this field. In this study, polypyrrole (PPy) and various gallium nitride (GaN) nanostructures were selected for synthesis. PPy/GaN gas sensors were successfully fabricated by employing the precisely controllable metal-organic chemical vapor deposition (MOCVD) process in conjunction with in situ oxidative polymerization methods. The gas sensing performance of the sensors was systematically analyzed. The PPy/GaN-1 sensor demonstrated an ultra-wide detection range for NH₃ (100 ppb–1000 ppm) at room temperature, along with exceptional moisture resistance and long-term stability. This can be attributed to the excellent uniformity of the film distribution, which enabled optimal synergy between GaN and PPy. Furthermore, an experiment detecting human exhaled breath was carried out using a sensor array to validate its high sensitivity. With the assistance of machine learning algorithms, high-precision prediction of gases within the low-concentration range was achieved (with an error of 1.17 ppm). Overall, this study offers valuable insights into the development of early warning systems for chronic kidney disease (CKD).

Poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)-based organic electrochemical transistors (OECTs) are widely utilized to construct highly sensitive biosensors. However, the PSS phase exhibits insulation, weak acidity, and aqueous instability. In this work, we fabricated PEDOT OECT by alternating current electrodeposition in protic ionic liquids. The steady-state characteristics were demonstrated to be stable in long-term tests. In detail, the maximum transconductance, the on/off current ratio, and the hysteresis were stable at 2.79 mS, 504, and 0.12 V, respectively. Though the transient behavior was also stable, the time constant could reach 218.6 ms. Thus, the trade-off between switching speed and stability needs to be considered in applications that require a rapid response.