The study of plant electrophysiology offers promising techniques to track plant health and stress in vivo for both agricultural and environmental monitoring applications. Use of superficial electrodes on the plant body to record surface potentials may provide new phenotyping insights. Bacterial nanocellulose (BNC) is a flexible, optically translucent, and water-vapor-permeable material with low manufacturing costs, making it an ideal substrate for non-invasive and non-destructive plant electrodes. This work presents BNC electrodes with screen-printed carbon (graphite) ink-based conductive traces and pads. It investigates the potential of these electrodes for plant surface electrophysiology measurements in comparison to commercially available standard wet gel and needle electrodes. The electrochemically active surface area and impedance of the BNC electrodes varied based on the annealing temperature and time over the ranges of 50 °C to 90 °C and 5 to 60 min, respectively. The water vapor transfer rate and optical transmittance of the BNC substrate were measured to estimate the level of occlusion caused by these surface electrodes on the plant tissue. The total reduction in chlorophyll content under the electrodes was measured after the electrodes were placed on maize leaves for up to 300 h, showing that the BNC caused only a 16% reduction. Maize leaf transpiration was reduced by only 20% under the BNC electrodes after 72 h compared to a 60% reduction under wet gel electrodes in 48 h. On three different model plants, BNC–carbon ink surface electrodes and standard invasive needle electrodes were shown to have a comparable signal quality, with a correlation coefficient of >0.9, when measuring surface biopotentials induced by acute environmental stressors. These are strong indications of the superior performance of the BNC substrate with screen-printed graphite ink as an electrode material for plant surface biopotential recordings.

Auscultation - the practice of listening to sounds emanating from the heart, lungs, and other organs - has been a mainstay of noninvasive physiological monitoring and diagnosis since at least the 17 ^th century BCE. Coincident with the contemporary push towards population health, telemedicine, and longitudinal outpatient monitoring, advances in both wearable electronics and data analytics have enabled new wearable sensors and systems targeting mechanoacoustic biosignals. These signals are an attractive option for health monitoring as they are passively transduced, low frequency, and can directly identify mechanical abnormalities which lack an associated bioelectrical signal change (e.g., a heart murmur that does not appear on an electrocardiogram). This work explores the viability of wearable mechanoacoustic sensors and their potential future role in precision medicine, examining their historical context, fundamental theory of operation, and the relevance of specific techniques to various pathologies. Finally, the advantages and limitations of various transduction schemes are reviewed, along with relevant areas of active research and potential future research directions.