UC San Diego

In marine studies, the current sensors technologies have limitations such as time-consuming batch sample analysis, size-weight-power restrictions, and complex encapsulation, which impedes real-time in-situ measurements. In this thesis, we develop printed integrated ocean sensor designs that address the challenges through novel device configurations and soft materials selection and processing and integration strategies. My novel device configuration of dual-gate organic electrochemical transistors (OECTs) extended the operating potential window over 2 V with remarkable stability, allowing high potential redox reactions to occur. Detailed analysis of the operating principle has been derived by introducing two capacitance ratios to describe the mechanism of modulating the channel conductance. The printed dual-gate OECTs achieves a detection limit of 0.3 ppm dissolved oxygen concentration in seawater, with a sensitivity of 222 µA cm−2 ppm−1 for concentrations below 5 ppm. My second approach to enhance the sensitivity of the printed integrated ocean sensor is through the use of a compact microfluidics design. This design allows for the in-situ detection of target anions that are generally interfered with by the high background of chloride, especially under seawater. The tandem microfluidics structure comprises a flow feeding unit, two desalination electrochemical cells, channel extensions to reduce signals cross talk, and downstream detection through a solid-state ion-selective membrane (ISM) sensor. The integration of these components was achieved through digital cutting, stencil-printing, and lamination. This printed microfluidics platform has demonstrated a detection limit of 0.5 mM nitrate with a sensitivity of 11.3 mV/dec under a continuous seawater flow, with a response time within 8 minutes. The integration of electronic components into printed ocean sensors has been demonstrated, allowing for the simultaneous detection of multiple signals, including dissolved oxygen, salinity, and curvature changes, using customized integrated multiplexer (MUXs) systems. The printed integrated ocean sensor was constructed by patterning conductive carbon paste/graphite foils onto a flexible plastic substrate. The active devices were fabricated through electrodeposition in different configurations, including electrochemical cells and transistor structures. This integrated ocean sensor demonstrated the feasibility of detecting oyster gape down to sub-mm levels, with a measurement range of dissolved oxygen between 0.5-6 ppm and salinity between 4-40 g kg-1. In addition, I also contributed to the development of an organic retinomorphic sensor for infrared spectrum. The sensor achieved a noise-equivalent power of 0.24 nW over 0.09 cm2 detector area. Leveraging the technique of intensity-modulated photovoltage spectroscopy from the photovoltaic community, my study probed the detector operation mechanism and in turn enhanced the sensor detectivity by interfacial modifications. The improved sensor is compatible with the aforementioned ocean sensors and has the potential to serve as a high-performance motion detector in ocean environments.