Custom Inks and Printing Processes for Electronic Biosensing Devices

As the cost of medical care increases, people are relying increasingly on internet diagnosis and community care rather than the expertise of medical professionals. Technological and medical advances have facilitated a partial answer through the increase in handheld sensing apparatuses. Yet even with these developments, significant further advancements are required to further drive down fabrication requirements (both in terms of cost and environmental impact) and facilitate fully-integrated and easy to use sensors. Printing electronics could be a powerful tool to accomplish this as printing allows for low-cost fabrication of high-area electronics. The vast majority of printed electronics reports focus on utilization of already developed commercial inks to create devices with new functionalities. This significantly limits development because current inks both necessitate damaging post processing—which precludes the use of delicate substrates, making skin-integration impossible—and many inks require bespoke printing processes, which increases fabrication complexity and thus cost. Further, with the proliferation of single-use medical testing, consideration must be made towards environmental compatibility. Therefore, innovations in electronic ink formulation and printing geared towards addressing the post-processing and environmental impact concerns are needed to enable continued progress towards printed POC sensors. The work contained in this dissertation centers around the development of inks intended to advance electronic biosensing applications. Focus is on using aerosol jet printing to enable the printing of nanomaterials and utilizes the unique properties of these nanomaterials—such as functionality immediately after printing, recyclability, and compatibility with deposition directly on biological surfaces (i.e., human skin)—to develop technologies intended to democratize healthcare. Notably, low temperature printable silver nanowire (AgNW) inks for the creation of biologically integrated electronics are demonstrated. Electrically conductive inks are created that are capable of achieving high conductivities when directly deposited onto living tissue at temperatures compatible with life (20 °C). The conductive lines yielded high resistance to degradation from bending strain, with a mere 8% decrease in conductivity when the plastic film on which they were printed was folded in half. As a demonstration, the AgNW ink was printed onto a human finger and used to illuminate a small light that remained illuminated even when the finger was bent. These results pave the way towards patient-specific medical diagnostics that are comfortable to wear, easy to use, and designed towards the needs of each individual patient. Next, a printing method to deposit biological sensing proteins for biomedical assays is investigated. Traditional techniques require extended time and the use of large quantities of immensely expensive proteins to make biosensors. Herein, a decade-old belief that aerosol jet printing is incompatible with the deposition of proteins is overturned, and, in doing so, highly sensitive biosensors for carcinoembryonic antigen (CEA) that compare favorably the mainstay fabrication technique that is known to impart no damage to the printed biological inks is demonstrated. Finally, the co-printing of a bio-recognition element with the previously mentioned electrically conductive AgNW ink demonstrate the potential for the future investigation of a fully aerosol-jet printed electronic biosensor. To address the environmental waste accumulation concern that plagues the advancement of ubiquitous patient-guided sensing, inks that facilitate the creation of fully-printed, all-carbon recyclable electronics (ACRE) are investigated. The combination of nanocrystalline cellulose, graphene and semiconducting carbon nanotubes enable the first fully recyclable transistor device. The ACRE transistors maintain high stability for over 10 months, display among the best performance of any printed transistor (Ion/Ioff: 104 and Ion 65 µA µm-1) and can be entirely deconstructed for recapture and reuse of the constituent CNT and graphene inks with near 100% nanomaterial retention and the biodegradation of the cellulose-based components. ACRE-based lactate sensors are used as an illustration of utility to show the versatility of the platform. Finally, as a culminating demonstration, a fully-printed chip for the handheld measurement of blood clot time (prothrombin time) was developed. Printing the entirety of the device allows for the creation of a low-cost chip for the simple, fast, and robust measurement of human blood clot times. In addition, a custom-designed, handheld control system with a 3D-printed case was developed to create a fully integrated point-of-care measurement platform towards simplifying medicine dosing strategies. The work described herein marks a significant leap in the development of printed inks to enable custom biological sensing applications. Once fully realized, these applications will mark a watershed, ushering in an era of individualized medicine with ubiquitous sensing to actively track disease progression in real-time. We are at the dawn of a new era in medicine that focuses more on prevention and control as opposed to reaction. One future direction for this work is promoting directly printed and reusable on-skin theragnostics for bespoke patient care such as the delivery and monitoring of pain medication that allows for better oversite over use and misuse.