Optical Communication among Oscillatory Reactions and Photo-Excitable Systems: UV and Visible Radiation Can Synchronize Artificial Neuron Models

Neuromorphic engineering promises to have a revolutionary impact in our societies. A strategy to develop artificial neurons (ANs) is to use oscillatory and excitable chemical systems. Herein, we use UV and visible radiation as both excitatory and inhibitory signals for the communication among oscillatory reactions, such as the Belousov–Zhabotinsky and the chemiluminescent Orban transformations, and photo-excitable photochromic and fluorescent species. We present the experimental results and the simulations regarding pairs of ANs communicating by either one or two optical signals, and triads of ANs arranged in both feed-forward and recurrent networks. We find that the ANs, powered chemically and/or by the energy of electromagnetic radiation, can give rise to the emergent properties of in-phase, out-of-phase, anti-phase synchronizations and phase-locking, dynamically mimicking the communication among real neurons.     

Canard explosion and internal signal stochastic bi-resonance in the CO oxidation on platinum surface

Canard explosion means a dramatic change fromsmall amplitude quasi-harmonic oscillation to largeamplitude relaxation oscillation, accompanied by anexponential increase of period, of a limit cycle withina very narrow interval of a control parameter. Thisphenomenon was first found in the Van Der Pol equa-tions[1], and later has been found also in chemical[2]and biological[3] systems. Generally speaking, it is theresult of multi-time scales in the system, and can bedealt with singular perturbati…     

Micropatterning chemical oscillations: waves, autofocusing, and symmetry breaking

Arrays of chemical oscillators are micropatterned by Wet Stamping. The technique is used to demonstrate that chemical waves can be initiated and controlled in oscillatory systems and that such waves can give rise to phenomena not observed in excitable media. Interoscillator coupling and synchronization, kinetic autofocusing, and twist-symmetry breaking are a consequence of the dependence of the oscillation phase on the local concentrations of reagents and on systems' geometry. Conditions under which a generic oscillatory system would exhibit such behaviors are determined.     

Stoichiometric network analysis of the photochemical processes in the mesopause region

The mechanism of photochemistry in the mesopause region entails a chemical oscillator forced by solar short-wave radiation. A model with periodic forcing between day and night conditions produces nonlinear dynamics including period-doubling bifurcations and chaos. The photochemical mechanism represents a network involving positive and negative feedbacks that can be examined by methods of stoichiometric network analysis. We use these methods to decompose the network into irreducible subnetworks and then apply linear stability analysis to find all possible sources of oscillatory instabilities in the mesopause chemistry. These oscillators are classified according to topological features in their reaction networks and phase shifts of oscillating species. We subsequently compare phase shifts indicated by the network analysis with those from direct simulations to identify a specific subnetwork in the mechanism underlying the complex oscillatory dynamics observed in earlier simulations.     

Oscillatory interaction between two like‐charged nanoparticles induced by polyelectrolyte brush–solvent interface

We use two‐dimensional (2D) self‐consistent field theory to study the effective interactions between two like‐charged cylindrical nanoparticles mediated by an oppositely weakly charged polyelectrolyte brush in a solvent solution. In a poor solvent, where a sharp brush–solvent interface forms, an oscillatory interaction is observed when two nanoparticles are both located at the brush–solvent interface. This oscillatory interaction depends on the penetration depths of the particles and their geometric orientations with respect to the substrate. When the particles are both immersed in the brush and/or the particles are oriented vertically or diagonally with large angles to the substrate, the oscillatory behavior disappears. We interpret our findings by analyzing in detail the contributions to the free energy from electrostatic interaction, nonelectrostatic interaction, and entropies, separately. Briefly, the deformations of the interface and the ion layers formed in the vicinity of the interface are responsible for this oscillatory behavior. In a good solvent, where the narrow brush–solvent interface vanishes, the effective particle–particle interactions behave like that for both particles immersed into the brush with poor solvent. They are found to be repulsive. The influences of the particle size, grafting density, and amount of charges and ions are also briefly discussed. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1458–1468     

New substrates in the ferroin-catalyzed bromate system in aqueous-organic mixed media

A large number of substrates have hitherto been employed in the Belousov-Zhabotinsky (B-Z) oscillatory system in pure aqueous medium. A systematic study of aromatic bromate oscillators is limited by solubility problem relating to the compounds and the brominated derivatives. The use of aqueous-organic mixed media for the oscillatory study is found to be highly useful for the study of water insoluble substances. A comparative study of the oscillatory behavior of gallic acid as substrate in pure aqueous as well as in a number of mixed media have been made in order to ascertain the suitability of mixed media in oscillatory systems. The alteration of oscillatory characteristics in the presence of organic solvent can be understood in terms of the Field-Koros-Noyes (FKN) mechanism. The oscillatory behavior of seventeen new substrates in the ferroin-catalyzed bromate system in 20% (v) acetonitrile is also presented and discussed in this communication. The reactivity of structurally related substrates has been correlated to the structure in terms of the relevant oscillatory parameters. The use of aqueous-organic mixed media in oscillatory systems would enable the investigation of new classes of substrates since getting them into the solution phase would no longer be a limitation. © 1993 John Wiley & Sons, Inc.     

Pt nanoparticles modified Au nanowire array for amperometric and potentiometric detection of glucose

A new glucose biosensor, based on the modification of highly ordered Au nanowire arrays (ANs) with Pt nanoparticles (PtNPs) and subsequent surface adsorption of glucose oxidase (GOx), is described. Morphologies of ANs and ANs/PtNPs were observed by scanning electron microscope. The electrochemical properties of ANs, ANs/GOx, ANs/PtNPs, and ANs/PtNPs/GOx electrodes were compared by cyclic voltammetry. Results obtained from comparison of the cyclic voltammograms show that PtNPs modification enhances electrochemical catalytic activity of ANs to H₂O₂. Hence, ANs/PtNPs/GOx biosensor exhibits much better sensing to glucose than ANs/GOx. Optimum deposition time of ANs/PtNPs/GOx biosensor for both amperometric and potentiometric detection of glucose was achieved to be 150 s at deposition current of 1?×?10^?6 A. A sensitivity of 0.365 μA/mM with a linear range from 0.1 to 7 mM was achieved for amperometric detection; while for potentiometric detection the sensitivity is 33.4 mV/decade with a linear range from 0.1 to 7 mM.     

A Reversible DNA Logic Gate Platform Operated by One‐ and Two‐Photon Excitations

We demonstrate the use of two different wavelength ranges of excitation light as inputs to remotely trigger the responses of the self‐assembled DNA devices (D‐OR). As an important feature of this device, the dependence of the readout fluorescent signals on the two external inputs, UV excitation for 1 min and/or near infrared irradiation (NIR) at 800 nm fs laser pulses, can mimic function of signal communication in OR logic gates. Their operations could be reset easily to its initial state. Furthermore, these DNA devices exhibit efficient cellular uptake, low cytotoxicity, and high bio‐stability in different cell lines. They are considered as the first example of a photo‐responsive DNA logic gate system, as well as a biocompatible, multi‐wavelength excited system in response to UV and NIR. This is an important step to explore the concept of photo‐responsive DNA‐based systems as versatile tools in DNA computing, display devices, optical communication, and biology.     

In–out asymmetry and interference effects in plasmon excitation by swift charged particles traversing a surface

We investigate the excitation of plasmons by a fast charged particle moving in the vicinity or traversing the surface of a solid along an arbitrary trajectory. We use both quantum‐mechanical and semiclassical dielectric formulations to study how the particle couples with the bulk and surface excitations. We pay special attention to the differences and similarities between incoming and outgoing trajectories, finding some novel oscillatory structures that can be ascribed to an interference effect between direct and reflected plasmon excitations. Copyright © 2013 John Wiley & Sons, Ltd.     

Strobes: Pyrotechnic Compositions That Show a Curious Oscillatory Combustion

Strobes are pyrotechnic compositions which show an oscillatory combustion; a dark phase and a flash phase alternate periodically. The strobe effect has applications in various fields, most notably in the fireworks industry and in the military area. All strobe compositions mentioned in the literature were discovered by trial and error methods and the mechanisms involved remain unclear. Many oscillatory systems such as Belousov–Zhabotinsky reactions, cool flames, self‐propagating high‐temperature synthesis have been observed and theories developed to elucidate their unstable behavior based on chemical interactions or based on physical processes. These systems are compared to experimental observations made on strobe mixtures.     

Model study of synchronization and other phenomena in light perturbation of the Briggs–Rauscher reaction

Calculations are performed to model several phenomena observed when a photosensitive oscillating chemical reaction, the Briggs–Rauscher (BR) reaction, is subject to irradiation in a continuous-flow stirred-tank reactor. The BR mechanism proposed earlier by De Kepper and Epstein is supplemented by additional steps involving the photogeneration and subsequent reaction of iodine atoms. The calculations show qualitative agreement with the following experimentally observed phenomena: (a) change in the period and amplitude of oscillation as a function of the intensity of constant illumination, (b) synchronization between periodically varying illumination and the period of chemical oscillation, (c) phase shifts induced by single light pulses, and (d) dark steady states which are excitable by single light pulses and become oscillatory at appropriate levels of constant illumination.     

A SERS Optophysiological Probe for the Real‐Time Mapping and Simultaneous Determination of the Carbonate Concentration and pH Value in a Live Mouse Brain

To have a profound understanding of the physiological and pathological processes in a brain, both chemical and electrical signals need to be recorded, but this is still very challenging. Herein, micrometer‐ to nanometer‐sized SERS optophysiological probes were created to determine both the CO₃^2? concentration and the pH in live brains and neurons because both species play important roles in regulating the acid–base balance in the brain. A ratiometric SERS microarray of eight microprobes with tip sizes of 5 μm was established and used for the first time for real‐time mapping and simultaneous quantification of CO₃^2? and pH in a live brain. We found that both the CO₃^2? concentration and the pH value dramatically decreased under ischemic conditions. The present SERS technique can be combined with electrophysiology without cross‐talk to record both electrical and chemical signals in brains. To deepen our understanding of the mechanism of ischemia on the single‐cell level, a SERS nanoprobe with a tip size of 200 nm was developed for use in a single neuron.     

Referenced Dual Pressure‐ and Temperature‐Sensitive Paint for Digital Color Camera Read Out

The first fluorescent material for the referenced simultaneous RGB (red green blue) imaging of barometric pressure (oxygen partial pressure) and temperature is presented. This sensitive coating consists of two platinum(II) complexes as indicators and a reference dye, each of which is incorporated in appropriate polymer nanoparticles. These particles are dispersed in a polyurethane hydrogel and spread onto a solid support. The emission of the (oxygen) pressure indicator, PtTFPP, matches the red channel of a RGB color camera, whilst the emission of the temperature indicator [Pt^II(Br‐thq)(acac)] matches the green channel. The reference dye, 9,10‐diphenylanthracene, emits in the blue channel. In contrast to other dual‐sensitive materials, this new coating allows for the simultaneous imaging of both indicator signals, as well as the reference signal, in one RGB color picture without having to separate the signals with additional optical filters. All of these dyes are excitable with a 405 nm light‐emitting diode (LED). With this new composite material, barometric pressure can be determined with a resolution of 22 mbar; the temperature can be determined with a resolution of 4.3 °C.     

Excitability in chemical and biochemical pH-autocatalytic systems

Using two different kinds of pH systems--the papain catalyzed hydrolysis of N-benzoyl-L-arginine ethyl ester in a membrane reactor and the bromate-sulfite-ferrocyanide (BSF) reaction in the CSTR--we study the relation among excitability, oscillations and bistability, and the ability of the system to respond to external periodic perturbations. Excitable properties of dynamical systems are examined in terms of a threshold set which is used to characterise dynamics in the reactor subject to external periodic stimuli. A precise definition and a method of calculating the threshold set are formulated. Two kinds of excitability distinguished by either direct or indirect initiation of the activatory process are found in both pH systems. Periodic pulsed perturbations of the BSF system display a nontrivial dependence of an excitation number on the forcing period. We examined this system also in oscillatory mode by looking at the phase shifts caused by single-pulse perturbations and constructing the phase transition curves (PTCs).     

Spatial bistability in a pH autocatalytic system: from long to short range activation

The acid-auto-activated chlorite-tetrathionate reaction is studied in a one-side-fed spatial reactor. It was previously shown that in these conditions the unstirred reaction-diffusion system can generate oscillatory and excitable states even though under well-stirred nonequilibrium conditions only steady-state bistability is observed. Numerical simulations suggest that these temporal reaction-diffusion instabilities result from long-range activation by rapidly diffusing protons. We study here experimentally and numerically the effect of introducing into this reaction-diffusion system macromolecular carboxylate species that reduce the effective diffusivity of protons. Consistent with the original assumption, the introduction of such slow mobility proton-binding species quenches both oscillatory and excitability dynamics. Within the bistability domain the direction of the propagation of an interface between the two steady states depends on control parameter value. We elaborate on the fact that beyond a low critical concentration of macromolecular carboxylate species, the stability limit of the "thermodynamic" branch of spatial steady state does not depend on this concentration. Despite the relative simplicity of the kinetic model used in the numerical simulations, the results are in quasi-quantitative agreement with the experimental observations.     

Disodium[hydroxotetranitronitrosyl]ruthenate(II), a Photochromic Substance with Long‐lived Metastable States: Structure at 110 K,Spectroscopic and Thermal Properties

Disodium[hydroxotetranitronitrosyl]ruthenate(II) is a photochromic compound excitable with blue‐green light which exhibits at least one unusually long‐lived metastable state at low temperature. At 298 K, the compound crystallises in the space group C2/m. A reversible phase transition occurs at 240 K upon cooling, as detected by Differential Scanning Calorimetry and X‐ray powder diffraction which causes a lowering of the crystal symmetry to the space group P2₁/n. Synchrotron X‐ray single crystal diffraction and FT‐IR spectroscopy data obtained on the ground and the excited states of the title compound low temperature phase are presented.     

Long‐Lasting Oscillations in the Electro‐Oxidation of Formic Acid on PtSn Intermetallic Surfaces

Even when in contact with virtually infinite reservoirs, natural and manmade oscillators typically drift in phase space on a time‐scale considerably slower than that of the intrinsic oscillator. A ubiquitous example is the inexorable aging process experienced by all living systems. Typical electrocatalytic reactions under oscillatory conditions oscillate for only a few dozen stable cycles due to slow surface poisoning that ultimately results in destruction of the limit cycle. We report the observation of unprecedented long‐lasting temporal oscillations in the electro‐oxidation of formic acid on an ordered intermetallic PtSn phase. The introduction of Sn substantially increases the catalytic activity and retards the irreversible surface oxidation, which results in the stabilization of more than 2200 oscillatory cycles in about 40 h; a 30–40‐fold stabilization with respect to the behavior of pure Pt surfaces. The dynamics were modeled and numerical simulations point to the surface processes underlying the high stability.     

Oscillatory Dynamics of CO Oxidation on Platinum-Group Metal Catalysts

Rate oscillations are theoretically studied for the CO + O₂ reaction proceeding according to a modified Langmuir-Hinshelwood mechanism on a platinum-group metal catalyst. A new hierarchical system of consistent mathematical models is suggested for the identification of oscillatory regimes in the stochastic model. This system includes the stochastic model based on the Monte Carlo method and a point deterministic model in the medium field approximation. Three fundamentally different types of oscillatory behavior of the stochastic model are revealed and studied. These are kinetic oscillations corresponding to autooscillations of the point model, fluctuation-induced oscillations occurring in an excitable medium in the region of the unique stable stationary solution of the point model, and fluctuation-induced random phase transitions between stable stationary solutions of the point model in the bistability region. The effect of internal fluctuations (which are inherent in stochastic models) on the oscillatory dynamics of the reaction is studied.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 485–496.Original Russian Text Copyright © 2005 by Kurkina, Semendyaeva.     

Highly Sensitive Dopamine Detection Using a Bespoke Functionalised Carbon Nanotube Microelectrode Array

Understanding how the brain works requires developing advanced tools that allow measurement of bioelectrical and biochemical signals, including how they propagate between neurons. The introduction of nanomaterials as electrode materials has improved the impedance and sensitivity of microelectrode arrays (MEAs), allowing high quality recordings of single cells in situ using electrode diameters of ≤20 μm. MEAs also have the potential to measure electroactive biological molecules in situ, such as dopamine, a neurotransmitter in the nervous system. Thus, this work focused on fabricating a functionalised carbon nanotube (CNT)‐based MEA to demonstrate its potential for future measurement of small signals generated from excitable cells. To this end, the functionalised CNT MEA has recorded one of the lowest electrochemical interfacial impedances available in the literature, 2.8±0.2 kΩ, for an electrode of its geometric surface area. Electrochemical detection of dopamine revealed again one of the best sensitivity values per area available in the literature, 9.48 μA μM⁻¹ mm⁻². Additionally, a limit of detection of 7 nM was recorded for dopamine using the functionalised CNT MEA, with selectivity against common electrochemical interferents such as ascorbic acid. These results indicate improvement beyond currently available MEAs, along with the feasibility of using these devices for multi‐site detection of physiologically relevant electroactive biomolecules.