Chemicals are ubiquitous, from the food we eat to the composition of our own bodies. Different chemicals can give us information about ourselves or our surroundings. For example, chemicals in the body can give information about the state of a person’s health, while chemicals in the atmosphere can give information about pollution. Chemical sensors are necessary to gain this information. Electrochemical sensors can use electrical signal output to indicate the presence and amount of chemicals. This is done two ways: amperometric sensors output current, and potentiometric sensors output potential. The magnitude of the signal indicates the amount of chemical present. Printing is useful for fabricating these sensors in flexible form factors and for disposable uses.

This thesis discusses the development of several different printed electrochemical sensors. An overview is first given of the developments in printed electrochemical sensors which enabled this work. Printed amperometric sensors for determination of lactate in sweat are optimized for sensing the transition from aerobic to anaerobic metabolism. These sensors are printed to accommodate form factors closely matching that of skin. These sensors have a sensitivity of 4.8 µA/mM and a linear range up to 25 mM lactate. However, an investigation into the selectivity of these sensors determines they are susceptible to interference from the salt present in sweat, making them less useful as sensors and more useful as indicators. Potentiometric sensors are proposed as an alternative for sensing metabolites in sweat, due to their selectivity in sweat. Potentiometric sensors cannot be made for sensing lactate, but ammonium sensors are demonstrated instead for determining levels of carbohydrates and metabolic condition. Potentiometric ammonium sensors show a near-Nernstian response of 57.5 mV/decade ± 0.3 mV/decade. Sweat is not the only application for printed sensors. Printed potentiometric sensors for nitrate in soil are also demonstrated, where printing enables the use of degradable materials. The nitrate sensors have near-Nernstian sensitivity of -53.3 mV/decade ± 1.1 mV/decade, and the printed reference developed shows relative insensitivity to nitrate in solution. The work discussed here indicates a step toward distributed networks of sensors.




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