Reconfiguration of organic electrochemical transistors for high-accuracy potentiometric sensing.

Organic electrochemical transistors have emerged as a promising alternative to traditional 2/3 electrode setups for sensing applications, offering in-situ transduction, electrochemical amplification, and noise reduction. Several of these devices are designed to detect potentiometric-derived signals. However, potentiometric sensing should be performed under open circuit potential conditions, allowing the system to reach thermodynamic equilibrium.

Eutectogels as a Semisolid Electrolyte for Organic Electrochemical Transistors.

Organic electrochemical transistors (OECTs) are signal transducers offering high amplification, which makes them particularly advantageous for detecting weak biological signals. While OECTs typically operate with aqueous electrolytes, those employing solid-like gels as the dielectric layer can be excellent candidates for constructing wearable electrophysiology probes. Despite their potential, the impact of the gel electrolyte type and composition on the operation of the OECT and the associated device design considerations for optimal performance with a chosen electrolyte have remained ambiguous.

Polarization of disk electrodes in high-conductivity electrolyte solutions.

We investigate the polarization of disk electrodes immersed in an electrolyte solution and subjected to a small external AC voltage over a wide range of frequencies. A mathematical model is developed based on the Debye-Falkenhagen approximation to the coupled Poisson-Nernst-Planck equations. Analytical techniques are used for predicting the spatial distribution of the electric potential and the complex impedance of the system.

SpyDirect: A Novel Biofunctionalization Method for High Stability and Longevity of Electronic Biosensors.

Electronic immunosensors are indispensable tools for diagnostics, particularly in scenarios demanding immediate results. Conventionally, these sensors rely on the chemical immobilization of antibodies onto electrodes. However, globular proteins tend to adsorb and unfold on these surfaces.

A single n-type semiconducting polymer-based photo-electrochemical transistor.

Conjugated polymer films, which can conduct both ionic and electronic charges, are central to building soft electronic sensors and actuators. Despite the possible interplay between light absorption and the mixed conductivity of these materials in aqueous biological media, no single polymer film has been utilized to create a solar-switchable organic bioelectronic circuit that relies on a fully reversible and redox reaction-free potentiometric photodetection and current modulation. Here we demonstrate that the absorption of light by an electron and cation-transporting polymer film reversibly modulates its electrochemical potential and conductivity in an aqueous electrolyte, which is harnessed to design an n-type photo-electrochemical transistor (n-OPECT).

Convection Driven Ultrarapid Protein Detection via Nanobody-Functionalized Organic Electrochemical Transistors.

Conventional biosensors rely on the diffusion-dominated transport of the target analyte to the sensor surface. Consequently, they require an incubation step that may take several hours to allow for the capture of analyte molecules by sensor biorecognition sites. This incubation step is a primary cause of long sample-to-result times.

Organic Bioelectronic Devices for Metabolite Sensing.

Electrochemical detection of metabolites is essential for early diagnosis and continuous monitoring of a variety of health conditions. This review focuses on organic electronic material-based metabolite sensors and highlights their potential to tackle critical challenges associated with metabolite detection. We provide an overview of the distinct classes of organic electronic materials and biorecognition units used in metabolite sensors, explain the different detection strategies developed to date, and identify the advantages and drawbacks of each technology.

Rapid single-molecule detection of COVID-19 and MERS antigens via nanobody-functionalized organic electrochemical transistors.

The coronavirus disease 2019 (COVID-19) pandemic has highlighted the need for rapid and sensitive protein detection and quantification in simple and robust formats for widespread point-of-care applications. Here, we report on nanobody-functionalized organic electrochemical transistors with a modular architecture for the rapid quantification of single-molecule-to-nanomolar levels of specific antigens in complex bodily fluids. The sensors combine a solution-processable conjugated polymer in the transistor channel and high-density and orientation-controlled bioconjugation of nanobody-SpyCatcher fusion proteins on disposable gate electrodes.

Microfluidic Integrated Organic Electrochemical Transistor with a Nanoporous Membrane for Amyloid-β Detection.

Alzheimer's disease (AD) is a neurodegenerative disorder associated with a severe loss in thinking, learning, and memory functions of the brain. To date, no specific treatment has been proven to cure AD, with the early diagnosis being vital for mitigating symptoms. A common pathological change found in AD-affected brains is the accumulation of a protein named amyloid-β (Aβ) into plaques.

Rapid and Sensitive Detection of Nanomolecules by an AC Electrothermal Flow Facilitated Impedance Immunosensor.

Conventional immunosensors typically rely on passive diffusion dominated transport of analytes for binding reaction and hence, it is limited by low sensitivity and long detection times. We report a simple and efficient impedance sensing method that can be utilized to overcome both sensitivity and diffusion limitations of immunosensors. This method incorporates the structural advantage of nanorod-covered interdigitated electrodes and the microstirring effect of AC electrothermal flow (ACET) with impedance spectroscopy.

Characterization of Temperature Rise in Alternating Current Electrothermal Flow Using Thermoreflectance Method.

Alternating current electrothermal flow (ACET) induced by Joule heating is utilized to transport biologically relevant liquids in microchannels using simple electrode designs. However, Joule heating may cause significant temperature rises, which can degrade biological species, and hence, ACET may become impractical for biomicrofluidic sensors and other possible applications. In this study, the temperature rise at the electrode/electrolyte interface during ACET flow is measured using a high-resolution, noninvasive, thermoreflectance imaging method, which is generally utilized in microelectronics thermal imaging applications.

Self-Similar Response of Electrode Polarization for Binary Electrolytes in Parallel Plate Capacitor Systems.

Classical electrochemistry problem of polarization of an electrode immersed in a symmetric binary electrolyte and subjected to a small external ac voltage is revisited. The Nernst-Planck equations are simplified to the Debye-Falkenhagen equation, which is solved together with the Poisson equation, leading to analytical formulas for the space charge density and impedance of the system for two parallel plate electrodes. We then define a limit of thin electrical double layer and illustrate the emergence of the characteristic time scale, τ = λ/, a function of the Debye length, λ, the electrode separation distance, , and the ionic diffusion coefficient .

Atomic Scale Interfacial Transport at an Extended Evaporating Meniscus.

Recent developments in fabrication techniques have enabled the production of nano- and Ångström-scale conduits. While scientists are able to conduct experimental studies to demonstrate extreme evaporation rates from these capillaries, theoretical modeling of evaporation from a few nanometers or sub-nanometer meniscus interfaces, where the adsorbed film, the transition film, and the intrinsic region are intertwined, is absent in the literature. Using the computational setup constructed, we first identified the detailed profile of a nanoscale evaporating interface and then discovered the existence of lateral momentum transport within and associated net evaporation from adsorbed liquid layers, which are long believed to be at the equilibrium established between equal rates of evaporation and condensation.

Quantification of Cell Death Using an Impedance-Based Microfluidic Device.

Dielectric spectroscopy is a nondestructive method to characterize dielectric properties by measuring impedance data over a frequency spectrum. This method has been widely used for various applications such as counting, sizing, and monitoring biological cells and particles. Recently, utilization of this method has been suggested in various stages of the drug discovery process due to low sample consumption and fast analysis time.

Gold nanostructure microelectrode arrays for in vitro recording and stimulation from neuronal networks.

An ideal microelectrode array (MEA) design should include materials and structures which exhibit biocompatibility, low electrode polarization, low impedance/noise, and structural durability. Here, the fabrication of MEAs with indium tin oxide (ITO) electrodes deposited with self-similar gold nanostructures (GNS) is described. We show that fern leaf fractal-like GNS deposited on ITO electrodes are conducive for neural cell attachment and viability while reducing the interfacial impedance more than two orders of magnitude at low frequencies (100-1000 Hz) versus bare ITO.

Self-Similar Interfacial Impedance of Electrodes in High Conductivity Media: II. Disk Electrodes.

Electrode polarization effects were investigated using impedance spectroscopy measurements for planar and nanorod-structured gold disk electrodes at 100 Hz to 1 MHz frequency range and in 0.25 S/m to 1.5 S/m conductivity KCl solutions.

Electrical Impedance Measurements of Biological Cells in Response to External Stimuli.

Dielectric spectroscopy (DS) is a noninvasive technique for real-time measurements of the impedance spectra of biological cells. DS enables characterization of cellular dielectric properties such as membrane capacitance and cytoplasmic conductivity. We have developed a lab-on-a-chip device that uses an electro-activated microwells array for capturing, DS measurements, and unloading of biological cells.

Self-Similar Interfacial Impedance of Electrodes in High Conductivity Media.

Electrode polarization (EP) happening due to accumulation of ions at the electrode/electrolyte interface is an inevitable phenomenon while measuring impedance spectrum in high conductivity buffers and at low RF spectrum. Well-characterized time scales elucidating the EP effect are important for the rational design of microfluidic devices and impedance sensors. In this Article, interfacial impedance at the electrode/electrolyte interface is investigated considering channel height and Debye length effects on characteristic time scale in a binary electrolyte solution using parallel plate electrode configuration.

Dielectrophoresis assisted loading and unloading of microwells for impedance spectroscopy.

Dielectric spectroscopy (DS) is a noninvasive, label-free, fast, and promising technique for measuring dielectric properties of biological cells in real time. We demonstrate a microchip that consists of electro-activated microwell arrays for positive dielectrophoresis assisted cell capture, DS measurements, and negative dielectrophoresis driven cell unloading; thus, providing a high-throughput cell analysis platform. To the best of our knowledge, this is the first microfluidic chip that combines electro-activated microwells and DS to analyze biological cells.

Enhancement of dielectrophoresis using fractal gold nanostructured electrodes.

Dielectrophoretic motions of Saccharomyces cerevisiae (yeast) cells and colloidal gold are investigated using electrochemically modified electrodes exhibiting fractal topology. Electrodeposition of gold on electrodes generated repeated patterns with a fern-leaf type self-similarity. A particle tracking algorithm is used to extract dielectrophoretic particle velocities using fractal and planar electrodes in two different medium conductivities.

Rough Gold Electrodes for Decreasing Impedance at the Electrolyte/Electrode Interface.

Electrode polarization at the electrolyte/electrode interface is often undesirable for bio-sensing applications, where charge accumulated over an electrode at constant potential causes large potential drop at the interface and low measurement sensitivity. In this study, novel rough electrodes were developed for decreasing electrical impedance at the interface. The electrodes were fabricated using electrochemical deposition of gold and sintering of gold nanoparticles.

Platinum black electrodeposited thread based electrodes for dielectrophoretic assembly of microparticles.

We report dielectrophoretic (DEP) assembly of biological cells and microparticles using platinum-black electrodeposited conductive textile fiber. The three-dimensional conductive structures with high aspect ratios were found to facilitate high electric field regions, as revealed by scanning electron microscope characterization. The effective conducting area (Aeff) and its stability of thread electrodes were estimated using electrochemical methods.

Electrothermal flow on electrodes arrays at physiological conductivities.

AC electrothermal (ET) flow is inevitable for microfluidic systems dissipating electric energy in a conducting medium. Therefore, many practical applications of biomicrofluidics are prone to ET flow. Here, a series of observations are reported on ET flow in a microfluidic chamber that houses three electrode pairs.