Low-Power/High-Gain Flexible Complementary Circuits Based on Printed Organic Electrochemical Transistors

The ability to accurately extract low-amplitude voltage signals is crucial in several fields, ranging from single-use diagnostics and medical technology to robotics and the Internet of Things (IoT). The organic electrochemical transistor (OECT), which features large transconductance values at low operating voltages, is ideal for monitoring small signals. Here, low-power and high-gain flexible circuits based on printed complementary OECTs are reported. This work leverages the low threshold voltage of both p-type and n-type enhancement-mode OECTs to develop complementary voltage amplifiers that can sense voltages as low as 100 \ub5V, with gains of 30.4\ua0dB and at a power consumption of 0.1–2.7 \ub5W (single-stage amplifier). At the optimal operating conditions, the voltage gain normalized to power consumption reaches 169\ua0dB \ub5W−1, which is >50\ua0times larger than state-of-the-art OECT-based amplifiers. In a monolithically integrated two-stage configuration, these complementary voltage amplifiers reach voltage gains of 193\ua0V/V, which are among the highest for emerging complementary metal-oxide-semiconductor-like technologies operating at supply voltages below 1 V. These flexible complementary circuits based on printed OECTs define a new power-efficient platform for sensing and amplifying low-amplitude voltage signals in several emerging beyond-silicon applications

Design, characterization, and interrogation of surface-based electrochemical biosensors

Many modern technologies rely on the the use of sensors, or devices that translate subtle differences in the chemical or biological composition of sample into a measurable response. The most widely recognizable sensor, the glucose meter, serves as just one example of the impact that a reliable diagnostic device can have on the quality of life of people affected by life-threatening health conditions. As exemplified with the glucose meter, the capacity of analytical devices to perform a given task may be greatly enhanced by incorporating biointerfaces, or surfaces populated with biological recognition molecules, into the sensor design. Sensors that implement biological probes to engineer \u27\u27smart\u27\u27 surfaces for target recognition are commonly referred to as biosensors. This dissertation describes the design and development of electrochemical biosensors that rely on the ability of biological recognition probes to selectively bind to their respective targets with high affinity. Biological probe molecules are constructed for compatibility with electrochemical interrogation by conjugating a thiolated linker at the probe terminus that facilitates tethering to a gold electrode. At the other end, the probe is modified with an electrochemical reporter molecule that can be monitored using a variety of electrochemical methods. Binding of the target to a surface-anchored probe leads to changes in probe flexibility or conformation in proportion to target concentration. Consequently, the presence of the target in a sample has a strong influence on the electrochemical signal arising from the reporter molecule. The development of two electrochemical biosensors that rely on the recognition of two distinct probe-target couples, is described herein. The first system utilizes a short antigenic peptide probe to capture its target antibody while the second system relies on the binding of a structure-switching DNA aptamer to a small molecule target. Sensor figures of merit for both systems are determined using cyclic and alternating current voltammetry. The structural and functional properties of aptamer-modified biointerfaces are additionally investigated using combinatorial spectroscopic ellipsometry and quartz crystal microbalance

Development of an Electrochemical Insulin Sensor Based on a High Affinity DNA Sequence Found in the Insulin-linked Polymorphic Region

The detection of pertinent biomarkers has the potential provide an early indication of disease progression before considerable damage has been incurred. A decrease in an individual’s sensitivity to insulin, which may be quantified as the ratio of insulin to glucose in the blood after a glucose pulse, has recently been reported as an early predictor of insulin-dependent diabetes mellitus. Routine measurement of insulin levels is therefore desirable in the care of diabetes-prone individuals. A rapid, simple, and reagentless method for insulin detection would allow for wide-spread screenings that provide earlier signs of diabetes onset. The aim of this thesis is to develop a folding-base electrochemical sensor for the detection of insulin. The sensor described herein consists of a DNA probe immobilized on a gold disc electrode via an alkanethiol linker and embedded in an alkanethiol self-assembled monolayer. The probe is labeled with a redox reporter, which readily transfers electrons to the gold electrode in the absence of insulin. In the presence of insulin, electron transfer is inhibited, presumably due to a binding-induced conformational or dynamic change in the DNA probe that significantly alters the electron-tunneling pathway. A 28-base segment of the insulin-linked polymorphic region that has been reported to bind insulin with high affinity serves as the capture element of the DNA probe. Three probe constructs that vary in their secondary structure and position of the redox label are evaluated for their utility as insulin-sensing elements on the electrochemical platform. The effects of probe modification on secondary structure are also evaluated using circular dichroism spectroscopy

Combined optical and acoustical method for determination of thickness and porosity of transparent organic layers below the ultra-thin film limit

Analysis techniques are needed to determine the quantity and structure of materials composing an organic layer that is below an ultra-thin film limit and in a liquid environment. Neither optical nor acoustical techniques can independently distinguish between thickness and porosity of ultra-thin films due to parameter correlation. A combined optical and acoustical approach yields sufficient information to determine both thickness and porosity. We describe application of the combinatorial approach to measure single or multiple organic layers when the total layer thickness is small compared to the wavelength of the probing light. The instrumental setup allows for simultaneous in situ spectroscopic ellipsometry and quartz crystal microbalance dynamic measurements, and it is combined with a multiple-inlet fluid control system for different liquid solutions to be introduced during experiments. A virtual separation approach is implemented into our analysis scheme, differentiated by whether or not the organic adsorbate and liquid ambient densities are equal. The analysis scheme requires that the film be assumed transparent and rigid (non-viscoelastic). We present and discuss applications of our approach to studies of organic surfactant adsorption, self-assembled monolayer chemisorption, and multiple-layer target DNA sensor preparation and performance testing

High-Density Noncovalent Functionalization of DNA by Electrostatic Interactions

Preserving DNA hybridization in organic solvents could someday serve to significantly extend the applicability of DNA-based technologies. Here, we present a method that can be used to solubilize double-stranded DNA at high concentrations in organic media. This method requires first precipitating a DNA molecule from the aqueous environment with an anilinium derivative and subsequently exchanging this moiety with an amine-containing surfactant in organic solvent. We demonstrate that this method yields complete exchange of the surfactant and allows for the modification of DNA with hydrophobic primary, secondary, and tertiary alkylamines and ordered functional π-systems. Using this approach, we fabricate a multichromophoric light harvesting system that would be unattainable by traditional methods. Additionally, this method makes it possible to use small, hydrophilic molecules to solubilize DNA in organic solvents, which reduces the shielding around the DNA and makes the macromolecule more accessible for further chemical modification. We believe that this approach will prove tremendously beneficial in expanding the scope of DNA-based nano- and biotechnologies

Nucleic Acid Chemistry in the Organic Phase: From Functionalized Oligonucleotides to DNA Side Chain Polymers

DNA-incorporating hydrophobic moieties can be synthesized by either solid-phase or solution-phase coupling. On a solid support the DNA is protected, and hydrophobic units are usually attached employing phosphoramidite chemistry involving a DNA synthesizer. On the other hand, solution coupling in aqueous medium results in low yields due to the solvent incompatibility of DNA and hydrophobic compounds. Hence, the development of a general coupling method for producing amphiphilic DNA conjugates with high yield in solution remains a major challenge. Here, we report an organic-phase coupling strategy for nucleic acid modification and polymerization by introducing a hydrophobic DNA–surfactant complex as a reactive scaffold. A remarkable range of amphiphile–DNA structures (DNA–pyrene, DNA–triphenylphosphine, DNA–hydrocarbon, and DNA block copolymers) and a series of new brush-type DNA side-chain homopolymers with high DNA grafting density are produced efficiently. We believe that this method is an important breakthrough in developing a generalized approach to synthesizing functional DNA molecules for self-assembly and related technological applications

Enzymatically Polymerized Organic Conductors on Model Lipid Membranes

Seamless integration between biological systems and electrical components is essential for enabling a twinned biochemical-electrical recording and therapy approach to understand and combat neurological disorders. Employing bioelectronic systems made up of conjugated polymers, which have an innate ability to transport both electronic and ionic charges, provides the possibility of such integration. In particular, translating enzymatically polymerized conductive wires, recently demonstrated in plants and simple organism systems, into mammalian models, is of particular interest for the development of next-generation devices that can monitor and modulate neural signals. As a first step toward achieving this goal, enzyme-mediated polymerization of two thiophene-based monomers is demonstrated on a synthetic lipid bilayer supported on a Au surface. Microgravimetric studies of conducting films polymerized in situ provide insights into their interactions with a lipid bilayer model that mimics the cell membrane. Moreover, the resulting electrical and viscoelastic properties of these self-organizing conducting polymers suggest their potential as materials to form the basis for novel approaches to in vivo neural therapeutics

Controlling the volatility of the written optical state in electrochromic DNA liquid crystals

Liquid crystals are widely used in displays for portable electronic information display. To broaden their scope for other applications like smart windows and tags, new material properties such as polarizer-free operation and tunable memory of a written state become important. Here, we describe an anhydrous nanoDNA-surfactant thermotropic liquid crystal system, which exhibits distinctive electrically controlled optical absorption, and temperature-dependent memory. In the liquid crystal isotropic phase, electric field-induced colouration and bleaching have a switching time of seconds. Upon transition to the smectic liquid crystal phase, optical memory of the written state is observed for many hours without applied voltage. The reorientation of the DNA-surfactant lamellar layers plays an important role in preventing colour decay. Thereby, the volatility of optoelectronic state can be controlled simply by changing the phase of the material. This research may pave the way for developing a new generation of DNA-based, phase-modulated, photoelectronic devices

Metabolite-induced in vivo fabrication of substrate-free organic bioelectronics

Interfacing electronics with neural tissue is crucial for understanding complex biological functions, but conventional bioelectronics consist of rigid electrodes fundamentally incompatible with living systems. The difference between static solid-state electronics and dynamic biological matter makes seamless integration of the two challenging. To address this incompatibility, we developed a method to dynamically create soft substrate-free conducting materials within the biological environment. We demonstrate in vivo electrode formation in zebrafish and leech models, using endogenous metabolites to trigger enzymatic polymerization of organic precursors within an injectable gel, thereby forming conducting polymer gels with long-range conductivity. This approach can be used to target specific biological substructures and is suitable for nerve stimulation, paving the way for fully integrated, in vivo-fabricated electronics within the nervous system