We are in the evolution of continuous monitoring of neural activity with non-invasive wearable EEGs. The development of hydrogel electrodes technology is important for home-use systems for long-term EEG monitoring and diagnostics of disease.

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Previous studies have shown that breath ammonia (breath-NH3) concentration is associated with blood urea nitrogen (BUN) levels. However, interindividual variations in breath-NH3 concentrations were observed. Thus, the present study aimed to assess the effect of oral cavity conditions on breath-NH3 concentration and to validate whether the measurement of breath-NH3 concentration is feasible in clinical settings. A total of 125 individuals, including patients with stage 3 to 5 chronic kidney disease (CKD3–5), those on dialysis, and healthy participants, were recruited. A nanostructured sensor was used to detect breath-NH3 concentrations. Pre- and post-gargling as well as pre- and post-hemodialysis (HD) breath-NH3, salivary pH, and salivary urea levels were measured. Breath-NH3, salivary urea, salivary pH, and BUN levels were positively correlated to each other. Breath-NH3 concentrations were associated with BUN levels (r = 0.43, p < 0.001) and were significantly higher in CKD3–5 (p < 0.005) and dialysis patients (p < 0.001) than in healthy participants. Higher correlation coefficients were noted between breath-NH3 concentrations and BUN levels during follow-up (r = 0.59–0.94, p < 0.05). When the cutoff value of breath-NH3 was set at 523.65 ppb, its sensitivity and specificity in predicting CKD (BUN level >24 mg dl−1) were 87.6% and 80.9%, respectively. Breath-NH3 concentrations decreased after HD (p < 0.001) and immediately after gargling (p < 0.01). Breath-NH3 concentration, which was affected by gargling, was correlated to BUN level. The measurement of breath-NH3 concentration using the nanostructured device may be used as a tool for CKD detection and personalized point-of-care for CKD and dialysis patients. The current study had a small sample size. Thus, further studies with a larger cohort must be conducted to validate the effect of oral factors on breath-NH3 concentration and to validate the benefit of breath-NH3 measurement.

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Organic semiconductor (OSC) gas sensors have grown into a widely discussed technology because of the presence of nanoscale fabrication processes. Thanks to the rapid development of nanotechnology, the performance of the OSC gas sensor has been pushed to the peak of its own and now can be used for numerous biomedical and environmental monitoring purposes that require high-precision sensing capability. However, the sophisticated and nonstandard fabrication process of most of these sensors has become the major impediment on the way of commercialization. Here, we demonstrate a micrometer-scale structure with a coupling layer using the current spreading effect to further enhance the sensing performance. The high-conductivity material poly(3,4ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS PH1000) was used as the coupling layer to increase the device operational current. The sensor exhibits a remarkably enhanced operational current of the microampere level without sacrificing the ammonia sensing capability. The issues of the structural profile are discussed carefully, and the sensor was tested with human breath samples to demonstrate a promising result. With the most common micrometer-scale fabrication technology, a ppb-regime sensing capability has been achieved, and the result of this work gives us a cut-in point regarding the high-sensitivity OSC gas sensors.

With the low-cost hygroscopic polymers as the sensing layer of the nano-porous devices, the “Nano Sponge sensors” enable efficient and reversible ammonia gas absorption to realize highly sensitive and stable ammonia detection.