Aerosol Jet Printed Devices and Logic Gates for Biosensing Applications

Abstract

Flexible electronics in recent years have gained attention due to their application in the medical and biosensing industries. The biosensor market in particular has been expanding significantly, with its market value expected to double by 2028 [1]. Electronic sensors have been widely used as biosensors due to their easy compatibility and interfaceability with electronic measurement and display systems. With the development of flexible electronics, wearable electronics have been demonstrated in the literature as well as sold commercially [2, 3]. This work focuses on building flexible electronic devices using a 3D printing technique known as aerosol jet printing. Both passive and active sensors are demonstrated. The active sensors are based on organic electrochemical transistor (OECT) devices, which are the main electronic devices in this work. Due to the inclusion of an organic semiconductor as part of their structure, these devices are able to be aerosol jet printed, enabling rapid changes to their geometry and characteristics. OECTs also operate at low voltages, compatible with aqueous environments, and are built using biocompatible materials, making them ideal for biosensing applications. First, a passive temperature sensor is fabricated using a combination of aerosol jet printing and drop-casting techniques. The electrodes as well as a polyimide well to contain the drop-casted sensing material for the sensors are 3D printed. A nanocomposite dispersion of multi-walled carbon nanotubes and a thermoplastic is used as the sensing material. The sensor was found to have a maximum sensitivity of 237 Ω/°C, with a negative temperature coefficient of -0.00134 K-1, while also displaying extremely high linearity in the range of 20 to 55°C. The device was also tested on skin to verify correct operation as a biosensor. Development of logic gate sensors is outlined as well as individual characterization of high-performance PEDOT:PSS-based OECTs. Devices are found to be extremely sensitive with a maximum transconductance value of 117 mS, currently the highest reported value for a planar OECT at the time of writing. Ion sensing, glucose sensing, and the effect of hydrogel treatment on device performance are also explored. The maximum sensitivity reported is 570 mV/dec when sensing NaCl concentration in the range of 1-10 mM, a value nearly 10x higher than the theoretical Nernst limit. Finally, complimentary logic gates are fabricated using a combination of PEDOT:PSS and gNDI-Br2 as channel materials. Individual characterizations of each device are outlined as well as the logical operation of the completed NOT gate. In summary, all devices were fabricated using aerosol jet 3D printing, which was verified as an effective and, in some cases, preferred method of fabrication for specific applications. The devices shown are suitable for sensing temperature, ions, and glucose in a variety of different media such as skin, sweat, saliva, and blood measurements. The fabrication method has also shown to be capable of printing digital logic circuits that may allow for interfacing of the various biosensors outlined in this work.