ABSTRACT
Plant-available nitrogen, often in the form of nitrate, is an essential nutrient for plant growth. However, excessive nitrate in the environment and watershed has harmful impacts on natural ecosystems and consequently human health. A distributed network of nitrate sensors could help to quantify and monitor nitrogen in agriculture and the environment. Here, we have developed fully printed potentiometric nitrate sensors and characterized their sensitivity and selectivity to nitrate. Each sensor comprises an ion-selective electrode and a reference electrode that are functionalized with polymeric membranes. The sensitivity of the printed ion-selective electrodes was characterized by measuring their potential with respect to a commercial silver/silver chloride reference electrode in varying concentrations of nitrate solutions. The sensitivity of the printed reference electrodes to nitrate was minimized with a membrane containing polyvinyl butyral (PVB), sodium chloride, and sodium nitrate. Selectivity studies with sulphate, chloride, phosphate, nitrite, ammonium, calcium, potassium, and magnesium showed that high concentrations of calcium can influence sensor behavior. The printed ion-selective and reference electrodes were combined to form a fully printed sensor with sensitivity of -48.0 ± 3.3 mV/dec between 0.62 and 6200 ppm nitrate in solution and -47 ± 4.1 mV/dec in peat soil.
Subject(s)
Nitrates , Soil , Calcium/analysis , Ecosystem , Humans , Ion-Selective Electrodes , NitrogenABSTRACT
Human skin perceives external mechanical stimuli by sensing the variation in the membrane potential of skin sensory cells. Many scientists have attempted to recreate skin functions and develop electronic skins (e-skins) based on active and passive sensing mechanisms. Inspired by the skin sensory behavior, we investigated materials and electronic devices that allow us to encode mechanical stimuli into potential differences measured between two electrodes, resulting in a potentiometric mechanotransduction mechanism. We present here a potentiometric mechanotransducer that is fabricated through an all-solution processing approach. This mechanotransducer shows ultralow-power consumption, highly tunable sensing behavior, and capability to detect both static and low-frequency dynamic mechanical stimuli. Furthermore, we developed two novel classes of sensing devices, including strain-insensitive sensors and single-electrode-mode e-skins, which are challenging to achieve using the existing methods. This mechanotransduction mechanism has broad impact on robotics, prosthetics, and health care by providing a much improved human-machine interface.
ABSTRACT
This work reports the process of sensor development, optimization, and characterization before the transition to on-body measurements can be made. Sensors using lactate oxidase as a sensing mechanism and tetrathiafulvalene as a mediator were optimized for sporting applications. Optimized sensors show linear range up to 24 mM lactate and sensitivity of 4.8 µA/mM which normalizes to 68 µA*cm-2/mM when accounting for surface area of the sensor. The optimized sensors were characterized 3 different ways: using commercially available reference and counter electrodes, using printed reference and counter electrodes, and using a printed reference electrode with no counter electrode. Sensors intended for measuring sweat must be selective in the presence of sweat constituents. Thus, in addition to traditional characterization in pH 7.0 buffer, we characterized sensor performance in solutions intended to approximate sweat. Sensor performance in pH 7.0 buffer solution was not reflective of sensor performance in artificial sweat, indicating that further characterization is necessary between sensor measurement in pH 7.0 buffer and on-body measurements. Furthermore, we performed enzyme activity measurements and sensor measurements concurrently in five different salts individually, finding that while NH4Cl and MgCl2 do not affect enzyme activity or sensor performance in physiologically relevant ranges of salt concentration, NaCl concentration or KCl concentration decreases enzyme activity and sensor current. On the other hand, CaCl2 induced a nonlinear change in sensor performance and enzyme activity with increasing salt concentration.
ABSTRACT
The title charge-transfer (CT) complex, C10H2O6·C14H8S4, composed of donor dibenzo-tetra-thia-fulvalene (DBTTF) and acceptor pyromellitic dianhydride (PMDA), forms a mixed stacking pattern along the [-110] direction. The constituent mol-ecules occupy crystallographic inversion centers. They are nearly parallel and lie ca.3.41â Å from each other. The crystals exhibit a high degree of donor/acceptor overlap [88.20â (4)%] in the long direction of the DBTTF and PMDA mol-ecules as compared with 51.27â (5)% in the shortest direction of the mol-ecules.
