A Multienzyme Logic H+ and Na+ Biotransducer.

Sodium ions and protons regulate various fundamental processes at the cell and tissue levels across all biological kingdoms. It is therefore pivotal for bioelectronic devices, such as biosensors and biotransducers, to control the transport of these ions through biological membranes. Our study explores the regulation of proton and sodium concentrations by integrating an Na+-type ATP synthase, a glucose dehydrogenase (GDH), and a urease into a multienzyme logic system. This system is designed to operate using various chemical control input signals, while the output current corresponds to the local change in proton or sodium concentrations. Therein, a H+ and Na+ biotransducer was integrated to fulfill the roles of signal transducers for the monitoring and simultaneous control of Na+ and H+ levels, respectively. To increase the proton concentration at the output, we utilized GDH driven by the inputs of glucose and nicotinamide adenine dinucleotide (NAD+), while recorded the signal change from the biotransducer, together acting as an AND enzyme logic gate. On the contrary, we introduced urease enzyme which hydrolyzed urea to control the decrease in proton concentration, serving as a NOT gate and reset. By integrating these two enzyme logic gates we formed a simple multienzyme logic system for the control of proton concentrations. Furthermore, we also demonstrate a more complex, Na+-type ATP synthase-urease multienzyme logic system, controlled by the two different inputs of ADP and urea. By monitoring the voltage of the peak current as the output signal, this logic system acts as an AND enzyme logic gate. This study explores how multienzyme logic systems can modulate biologically important ion concentrations, opening the door toward advanced biological on-demand control of a variety of bioelectronic enzyme-based devices, such as biosensors and biotransducers.

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.

pH modulation in adhesive cells with a protonic biotransducer.

Protons (H+) are essential for most physiological functions in organelles and cells. In this study, we have demonstrated a sulfonated polyaniline (SPA) biotransducer that can modulate the intracellular pH in C6 cells with an applied potential, which is directly coupled with H+ to facilitate engineering interactions with physiological processes in the cells. To modulate the pH in the intracellular fluid, we improved the performance of SPA biotransducer by coating of a carbon nanotube (CNT) supportive layer that provides high H+ selectivity in the solution and also high H+ capacity in the hybrid SPA electrode. The intracellular pH modulation was succeeded by applying a potential difference of less than ±0.6 V. pH modulation in the cells is effected by using the biotransducer, which drives the activity of plasma membrane potential and the flow of molecules through the permeable membrane between cells and culture medium, whereas the poly (3,4-ethylenedioxythiophene) (PEDOT)-based biotransducer, which does not have H+ selectivity, was insufficient for modulation. Furthermore, the protonic biotransducer can control the increase/decrease in mitochondria membrane potential, reactive oxygen species and intracellular Ca2+ concentration. Therefore, the protonic biotransducer provides a new perspective to transfer a H+ signal into the cells for modulating the functions.