Electronic control of H+ current in a bioprotonic device with carbon nanotube porins

Proton Logic Gate Based on a Gramicidin-ATP Synthase Integrated Biotransducer

Ion channels are membrane proteins that allow ionic signals to pass through channel pores for biofunctional modulations. However, biodevices that integrate bidirectional biological signal transmission between a device and biological converter through supported lipid bilayers (SLBs) while simultaneously controlling the process are lacking. Therefore, in this study, we aimed to develop a hybrid biotransducer composed of ATP synthase and proton channel gramicidin A (gA), controlled by a sulfonated polyaniline (SPA) conducting polymer layer deposited on a microelectrode, and to simulate a model circuit for this system. We controlled proton transport across the gA channel using both electrical and chemical input signals by applying voltage to the SPA or introducing calcium ions (inhibitor) and ethylenediaminetetraacetic acid molecules (inhibitor remover). The insertion of gA and ATP synthase into SLBs on microelectrodes resulted in an integrated biotransducer, in which the proton current was controlled by the flux of adenosine diphosphate molecules and calcium ions. Lastly, we created an XOR logic gate as an enzymatic logic system where the output proton current was controlled by Input A (ATP synthase) and Input B (calcium ions), making use of the unidirectional and bidirectional transmission of protons in ATP synthase and gA, respectively. We combined gA, ATP synthase, and SPA as a hybrid bioiontronics system to control bidirectional or unidirectional ion transport across SLBs in biotransducers. Thus, our findings are potentially relevant for a range of advanced biological and medical applications.

Integrated bioelectronic proton-gated logic elements utilizing nanoscale patterned Nafion

A central endeavour in bioelectronics is the development of logic elements to transduce and process ionic to electronic signals. Motivated by this challenge, we report fully monolithic, nanoscale logic elements featuring n- and p-type nanowires as electronic channels that are proton-gated by electron-beam patterned Nafion. We demonstrate inverter circuits with state-of-the-art ion-to-electron transduction performance giving DC gain exceeding 5 and frequency response up to 2 kHz. A key innovation facilitating the logic integration is a new electron-beam process for patterning Nafion with linewidths down to 125 nm. This process delivers feature sizes compatible with low voltage, fast switching elements. This expands the scope for Nafion as a versatile patternable high-proton-conductivity element for bioelectronics and other applications requiring nanoengineered protonic membranes and electrodes.

Nanoparticle-Mediated Visualization and Control of Cellular Membrane Potential: Strategies, Progress, and Remaining Issues

The interfacing of nanoparticle (NP) materials with cells, tissues, and organisms for a range of applications including imaging, sensing, and drug delivery continues at a rampant pace. An emerging theme in this area is the use of NPs and nanostructured surfaces for the imaging and/or control of cellular membrane potential (MP). Given the important role that MP plays in cellular biology, both in normal physiology and in disease, new materials and methods are continually being developed to probe the activity of electrically excitable cells such as neurons and muscle cells. In this Review, we highlight the current state of the art for both the visualization and control of MP using traditional materials and techniques, discuss the advantageous features of NPs for performing these functions, and present recent examples from the literature of how NP materials have been implemented for the visualization and control of the activity of electrically excitable cells. We conclude with a forward-looking perspective of how we expect to see this field progress in the near term and further into the future.

A Microfluidic Ion Sensor Array

A balanced concentration of ions is essential for biological processes to occur. For example, [H⁺ ] gradients power adenosine triphosphate synthesis, dynamic changes in [K⁺ ] and [Na⁺ ] create action potentials in neuronal communication, and [Cl^- ] contributes to maintaining appropriate cell membrane voltage. Sensing ionic concentration is thus important for monitoring and regulating many biological processes. This work demonstrates an ion-selective microelectrode array that simultaneously and independently senses [K⁺ ], [Na⁺ ], and [Cl^- ] in electrolyte solutions. To obtain ion specificity, the required ion-selective membranes are patterned using microfluidics. As a proof of concept, the change in ionic concentration is monitored during cell proliferation in a cell culture medium. This microelectrode array can easily be integrated in lab-on-a-chip approaches to physiology and biological research and applications.