The current demands of sustainable green methodologies have increased the use of enzymatic technology in industrial processes. Employment of enzyme as biocatalysts offers the benefits of mild reaction conditions, biodegradability and catalytic efficiency. The harsh conditions of industrial processes, however, increase propensity of enzyme destabilization, shortening their industrial lifespan. Consequently, the technology of enzyme immobilization provides an effective means to circumvent these concerns by enhancing enzyme catalytic properties and also simplify downstream processing and improve operational stability. There are several techniques used to immobilize the enzymes onto supports which range from reversible physical adsorption and ionic linkages, to the irreversible stable covalent bonds. Such techniques produce immobilized enzymes of varying stability due to changes in the surface microenvironment and degree of multipoint attachment. Hence, it is mandatory to obtain information about the structure of the enzyme protein following interaction with the support surface as well as interactions of the enzymes with other proteins. Characterization technologies at the nanoscale level to study enzymes immobilized on surfaces are crucial to obtain valuable qualitative and quantitative information, including morphological visualization of the immobilized enzymes. These technologies are pertinent to assess efficacy of an immobilization technique and development of future enzyme immobilization strategies.

https://www.tandfonline.com/doi/pdf/10.1080/13102818.2015.1008192

An overview of technologies for immobilization of enzymes and surface analysis techniques for immobilized enzymes

Probing liquid/solid interfaces at the molecular level.

The electrocatalytic properties of nanoparticles depend on their size, shape and composition1,2. These properties are typically probed by measuring the total electrocatalytic reaction current of a large number of nanoparticles, but this approach is time-consuming and can only measure the average catalytic activity of the nanoparticles under study. However, the identification of new catalysts requires the ability to rapidly measure the properties of nanoparticles synthesized under various conditions and, ideally, to measure the electrocatalytic activity of individual nanoparticles. Here, we show that a plasmonic-based electrochemical current-imaging technique3 can simultaneously image and quantify the electrocatalytic reactions of an array of 1.6 × 105 platinum nanoparticles printed on an electrode surface, which could facilitate high-throughput screening of the catalytic activities of nanoparticles. We also show that the approach can be used to image the electrocatalytic reaction current and measure the cyclic voltammograms of single nanoparticles. A plasmonic-based electrochemical current imaging technique can be used to study the electrocatalytic properties of individual platinum nanoparticles.

Imaging the electrocatalytic activity of single nanoparticles.

In living systems, ion conduction plays a major role in numerous cellular processes and can be controlled by biological ion channels in response to specific environmental stimuli. This article describes biomimetic ionic gates for ion conduction based on sodium and potassium activated nanochannels. The Na+ activated ionic gate and K+ activated ionic gate were developed by immobilizing the alkali metal cation-responsive functional molecules, 4′-aminobenzo-15-crown-5 and 4′-aminobenzo-18-crown-6, respectively, onto the conical polyimide nanochannels. When the ionic gate was in the presence of the specific alkali metal cation, positively charged complexes formed between the crown ether and the alkali metal cation. On the basis of the resulting changes in surface charge, wettability and effective pore size, the nanochannel can achieve reversible switching. The switching behaviors of the two complexes differed due to the differences in binding strength between the two complexes. The Na+ activated ionic gate is ...

Engineered Ionic Gates for Ion Conduction Based on Sodium and Potassium Activated Nanochannels

Scanning electrochemical microscopy (SECM), is a recent analytical technique in electrochemistry, which was developed in the 1990s and uses microelectrodes to probe various surfaces. Even with the well-known disc microelectrodes, the system geometry is not as simple as in regular electrochemistry. As a consequence even the simplest experiments, the so-called positive and negative feedback approach curves, cannot be described with exact analytical expressions. This review gathers all the analytical expressions available in the SECM literature in steady-state feedback experiments. Some of them are claimed as general expressions, other are presented as approximate. Their validity is discussed in the light of the current understanding and computer facilities.

Analytical Expressions for Quantitative Scanning Electrochemical Microscopy (SECM)

Review: Recent applications of scanning electrochemical microscopy to the study of charge transfer kinetics.

Self-assembled monolayers (SAMs) of thiol-derivatized tetraphenylporphyrin (SH-TPP) and cobalt tetraphenylporphyrin (SH-CoTPP) have been prepared to examine the structure and direct electron transfer (ET) on a gold electrode in an aqueous solution. The cyclic voltammetry peaks of the porphyrin were obviously observed in aqueous solution. An interesting phenomenon was that direct ET cannot occur in phosphate-buffered solutions when a highly oriented and tightly packed monolayer is in existence, but the relatively low-density SH-TPP SAMs exhibited good electrochemical response. The electron transfer rate constants were obtained from the impedance spectra (Cole−Cole plot), upon application of different biasing potentials to the modified electrode. We propose a new kinetic model of the ET processes of SAMs of thiol-derivatized porphyrin and apply the density functional theory (DFT) to study the ET of porphyrin molecules on Au surfaces.

Direct Electron Transfer of Thiol-Derivatized Tetraphenylporphyrin Assembled on Gold Electrodes in an Aqueous Solution

Ion transport is especially crucial in normal body function, which is regulated by specialized ion channels. In this report, the simple hydrophilic alumina nanochannel is constructed at liquid/liquid (L/L) interface to simulate veritably and compactly complex cross-channel ion transfer processes of living systems in a similar physiological saline environment. The selectivity and regulation that are known for being two important characteristics of ion channels were achieved due to controllable electrosurface properties of alumina nanochannel. This channel shows good selectivity for ion with low electronegativity. The regulatory role of ion channel in confined space was achieved by varying diameters of nanochannel and lengths of ions travel path. In addition, a new theory based on the Randles-Sevcik equation is proposed for evaluation of cross-channel ion transfer in this article for the first time. The ingenious design strategy is demonstrated to be a useful means for investigating the complex cross-channe...

Ion Transport Traversing Bioinspired Ion Channels at Bionic Interface

The density functional theory was employed to investigate the mechanism for the cyclopropanation reactions of samarium carbenoid with an allylic alcohol. Seven competitive reaction pathways were investigated. Analysis of the calculated results shows that the models 4 and 6 have relatively low reaction barriers which suggested that the deprotonation of allylic alcohol promoted by CH 3 SmCH 2 I plays a significant important role in the cyclopropanation reaction via a samarium carbenoid. The methylene transfer and carbometalation pathways are involved in both intermolecular and intramolecular reaction pathways. On the basis of the energetics of the reaction pathways, the methylene transfer pathway is favored over the carbometalation pathway in the whole reactions. Our computational results are in good agreement with the experimental results performed by G.A. Molander and L.S. Harring.

Theoretical studies of samarium carbenoid promoted cyclopropanation reaction with allylic alcohol on the reaction pathways

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Review: Recent applications of scanning electrochemical microscopy to the study of charge transfer kinetics.

Direct Electron Transfer of Thiol-Derivatized Tetraphenylporphyrin Assembled on Gold Electrodes in an Aqueous Solution

Ion Transport Traversing Bioinspired Ion Channels at Bionic Interface

Theoretical studies of samarium carbenoid promoted cyclopropanation reaction with allylic alcohol on the reaction pathways