Inkjet-printed electrochemical devices for bioelectronics

In recent years, inkjet printing has received increasing attention from academic and industrial communities as a rapid prototyping and cost-effective tool for manufacturing a wide variety of electronic devices. The printed electronic field has great application in biosensors since printed sensors are cheap, small, portable and flexible. Therefore, substantial efforts have been devoted to the improvement of this powerful technology to render it suitable for microscale fabrication with the prospect of practical applications. The purpose of this research is to create a new alternative platform for developing diagnostic tools with high sensitivity and low cost. In this dissertation, I propose an alternative approach for sensitive detection of disease biomarkers and cardiac action potential using printed technology. This alternative approach is based on three main elements (i) controlled bioreceptor immobilization using photonic immobilization technique, (ii) signal amplification using electrochemical redox cycling, (iii) novel printing methodology. The first is achieved by combining a rapid and simple printing scheme with the photonic immobilization technique for site-specific immobilization of antibodies. Pho-tonic immobilization, which is easy and fast to perform, is presented on printed chips for the first time, achieving a higher sensitivity and better limit of detection compared to the conventional immobilization approaches. In the first application, I targeted the determination of C-reactive protein (CRP) in the presence of human serum. The second element, which is signal amplification using electrochemical redox cycling, is realized by repetitive cycling of redox probes between two adjacent electrodes. The sensitivity of a redox cycling sensor depends on the distance between the two electrodes. In other words, a short distance between the electrodes in the micro- or even nanometer regime is required to achieve an effective redox cycling amplification. Therefore, I developed a new scheme for fabricating micro-gap electrodes with in-plane displacement, as well as porous nano-gap electrodes with out-of-plane displacement, using inkjet printing and without prior surface patterning. As a proof of concept, I demonstrated the use of micro-gap redox cycling sensors for the detection of single-stranded DNA (ssDNA) using peptide nucleic acids (PNAs) immobilized on the carbon microelectrodes. The developed genosensors were then applied to the detection of human immunodeficiency virus-1 (HIV-1) marker sequence encoding of HIV-1 nef gene. The third element, namely the development of novel printing methodology for high-resolution printing, is accomplished by exploring the different physical, chemical and hydro-dynamical properties of an ink droplet that interacts with the substrate surface. I provide the first demonstration for fabricating microelectrode arrays (MEA) in a rapid prototyping approach based on inkjet printing. The printed MEAs on flexible substrates resulted in a high-resolution outcome with good electrical and outstanding electrochemical characteristics, suitable for cellular recording and stimulation. I cultured Hl-1 cells on MEAs printed using gold and carbon inks on flexible substrates. Using the MEAs, the propagating action potentials were recorded across the cellular network with high signal-to-noise ratios. The benefits of having a transparent and flexible printed MEA are well appreciated when it comes to in-vivo applications, such as neuronal implants. With such an application in mind, I printed high resolution MEAs on soft materials such as PDMS, agarose, and gelatin-based substrates including gummy bears. A series of in-vitro extracellular recordings of action potentials were recorded from cardiac HL-1 cells and the results demonstrate that inkjet printing can be used for fabricating functional cell-device interfaces on soft materials in a rapid prototyping approach. Hereafter, this dissertation contributes significantly to the vision I have for providing healthcare system with sensitive biosensors and soft MEA platforms that avoid expensive fabrication utilities, towards rapid prototyping of ultra-low-cost medical devices