Electrochemistry of Cytochrome c Immobilized on Colloidal Gold Modified Carbon Paste Electrodes and Its Electrocatalytic Activity

The enhanced electrocatalytic performance of nanoscopic Cu6Pd12Fe12 heterometallic molecular box encaged cytochrome c

Designing molecular cages for atomic/molecular scale guests is a special art used by material chemists to harvest the virtues of the otherwise vile idea known as "the cage". In recent years, there has been a notable surge in research investigations focused on the exploration and utilization of the distinct advantages offered by this art in the advancement of efficient and stable bio-electrocatalysts. This usually is achieved through encapsulation of biologically accessible redox proteins within specifically designed molecular cages and matrices. Herein, we present the first successful method for encaging cytochrome c (Cyt-c), a clinically significant enzyme system, inside coordination-driven self-assembled Cu6Pd12Fe12 heterometallic hexagonal molecular boxes (Cu-HMHMB), in order to create a Cyt-c@Cu-HMHMB composite. 1H NMR, FTIR, and UV-Vis spectroscopy, ICP-MS, TGA and voltammetric investigations carried out on the so-crafted Cyt-c@Cu-HMHMB bio-inorganic composite imply that the presented strategy ensures encaging of Cyt-c in a catalytically active, electrochemically stable and redox-accessible state inside the Cu-HMHMB. Cyt-c@Cu-HMHMB is demonstrated to exhibit excellent stability and electrocatalytic activity toward very selective, sensitive electrochemical sensing of nitrite exhibiting a limit of detection as low as 32 nanomolar and a sensitivity of 7.28 μA μM-1 cm-2. Importantly, Cyt-c@Cu-HMHMB is demonstrated to exhibit an excellent electrocatalytic performance toward the 4ē pathway oxygen reduction reaction (ORR) with an onset potential of 0.322 V (vs. RHE) and a Tafel slope of 266 mV dec-1. Our findings demonstrate that Cu-HMHMB is an excellent matrix for Cyt-c encapsulation. We anticipate that the entrapment-based technique described here will be applicable to other enzyme systems and Cyt-c for various electrochemical and other applications.

Behind the Optimization of the Sensor Film: Bioconjugation of Triangular Gold Nanoparticles with Hemoproteins for Sensitivity Enhancement of Enzymatic Biosensors

Electrochemical biosensors are widely used in a multitude of applications, such as medical, nutrition, research, among other fields. These sensors have been historically used and have not undergone many changes in terms of the involved electrochemical processes. In this work, we propose a new approach on the immobilization and enhancement of the electrochemical properties of the sensing layers through the control and bioconjugation of hemoproteins (hemoglobin, myoglobin, and cytochrome C) on anisotropic gold nanoparticles (gold nanotriangles (AuNTs)). The hemeproteins and the AuNTs are mixed in a solution, resulting in stable bioconjugates that are deposited onto the electrode surface to obtain the biosensors. All the systems proposed herein exhibited direct well-defined redox responses, highlighting the key role of the AuNTs acting as mediators of such electron transfers. Several protein layers surrounding the AuNTs are electroactive, as demonstrated from the charge measured by cyclic voltammetry. The retention of the stability of the hemeproteins once they are part of the bioconjugates is evidenced towards the electrocatalytic reduction of hydrogen peroxide, oxygen, and nitrite. The parameters obtained for the proposed biosensors are similar or even lower than those previously reported for similar systems based on nanomaterials, and they exhibit attractive properties that make them potential candidates for the latest developments in the field of sensing devices.

Molecularly imprinted electrochemical sensor for the ultrasensitive detection of cytochrome c

Cytochrome c (Cyt c) is an important biomarker for the early stage of apoptosis that plays a role in the diagnosis and therapy of several diseases including cancer. Here, an electrochemical sensor based on molecularly imprinted polymer (MIP) for the ultrasensitive detection of Cyt c is studied. It is prepared by electropolymerization of o-phenylenediamine in the presence of Cyt c as template, followed by solvent extraction, resulting in the formation of Cyt c recognition sites. The MIP is characterised by cyclic voltammetry and differential pulse voltammetry, using ferrocenecarboxylic acid as redox probe. Voltammetric data indicates that the MIP-sensor behaves as an electrode with partially blocked surface. The partition isotherm obtained fits the Langmuir model, indicating a high affinity for Cyt c, with an association constant K_a = 5 × 10 ¹¹ M^-1. DPV measurements allow to achieve extremely high analytical sensitivity and low detection limit, in the femtomolar range, with negligible unspecific adsorption. Satisfactory analytical recovery tests performed in the presence of possible interfering proteins and in diluted human serum confirmed the selectivity of the MIP-sensor as well as its potential applicability for real samples analysis.

Enhancement of direct electron transfer in graphene bioelectrodes containing novel cytochrome c553 variants with optimized heme orientation

The highly efficient bioelectrodes based on single layer graphene (SLG) functionalized with pyrene self-assembled monolayer and novel cytochromec₅₅₃(cytc₅₅₃)peptide linker variants were rationally designed to optimize the direct electron transfer (DET) between SLG and the heme group of cyt. Through a combination of photoelectrochemical and quantum mechanical (QM/MM) approaches we show that the specific amino acid sequence of a short peptide genetically inserted between the cytc₅₅₃holoprotein and thesurface anchoring C-terminal His₆-tag plays a crucial role in ensuring the optimal orientation and distance of the heme group with respect to the SLG surface. Consequently, efficient DET occurring between graphene and cyt c₅₅₃ leads to a 20-fold enhancement of the cathodic photocurrent output compared to the previously reported devices of a similar type. The QM/MM modeling implies that a perpendicular or parallel orientation of the heme group with respect to the SLG surface is detrimental to DET, whereas the tilted orientation favors the cathodic photocurrent generation. Our work confirms the possibility of fine-tuning the electronic communication within complex bio-organic nanoarchitectures and interfaces due to optimization of the tilt angle of the heme group, its distance from the SLG surface and optimal HOMO/LUMO levels of the interacting redox centers.

Metal-based Nanoparticles as Conductive Mediators in Electrochemical Sensors: A Mini Review

Background:

Modified electrodes are a new approach to improving the characteristics of the electrochemical sensors. The high conductivity and low charge transfer resistance are the major properties of new mediators for improving electrochemical sensors. Metal-based nanoparticles showed good electrical conductivity and can be selected as the suitbale mediator for modified electrodes.

Objective:

Recently, metal-based nanoparticles, such as Au nanoparticle, TiO2 nanoparticle, Fe3O4 nanoparticle and etc. were suggested as the suitable mediator for modification of solid electrodes. The high surface area and low charge transfer resistance of metal-based nanoparticles, suggested the exceptional intermediate in the electrochemical sensors. Here, we tried to consider these exceptional effects through reviewing some of the recently published works.

The influence of pH and divalent/monovalent cations on the internal electron transfer (IET), enzymatic activity, and structure of fructose dehydrogenase

We report on the influence of pH and monovalent/divalent cations on the catalytic current response, internal electron transfer (IET), and structure of fructose dehydrogenase (FDH) by using amperometry, spectrophotometry, and circular dichroism (CD). Amperometric measurements were performed on graphite electrodes, onto which FDH was adsorbed and the effect on the response current to fructose was investigated when varying the pH and the concentrations of divalent/monovalent cations in the contacting buffer. In the presence of 10 mM CaCl₂, a current increase of up to ≈ 240% was observed, probably due to an intra-complexation reaction between Ca²⁺ and the aspartate/glutamate residues found at the interface between the dehydrogenase domain and the cytochrome domain of FDH. Contrary to CaCl₂, addition of MgCl₂ did not show any particular influence, whereas addition of monovalent cations (Na⁺ or K⁺) led to a slight linear increase in the maximum response current. To complement the amperometric investigations, spectrophotometric assays were carried out under homogeneous conditions in the presence of a 1-electron non-proton-acceptor, cytochrome c, or a 2-electron-proton acceptor, 2,6-dichloroindophenol (DCIP), respectively. In the case of cytochrome c, it was possible to observe a remarkable increase in the absorbance up to 200% when 10 mM CaCl₂ was added. However, by further increasing the concentration of CaCl₂ up to 50 mM and 100 mM, a decrease in the absorbance with a slight inhibition effect was observed for the highest CaCl₂ concentration. Addition of MgCl₂ or of the monovalent cations shows, surprisingly, no effect on the electron transfer to the electron acceptor. Contrary to the case of cytochrome c, with DCIP none of the cations tested seem to affect the rate of catalysis. In order to correlate the results obtained by amperometric and spectrophotometric measurements, CD experiments have been performed showing a great structural change of FDH when increasing the concentration CaCl₂ up to 50 mM, at which the enzyme molecules start to agglomerate, hindering the substrate access to the active site probably due to a chelation reaction occurring at the enzyme surface with the glutamate/aspartate residues.

Graphical Abstract

An iron hydroxyl phosphate microoctahedron catalyst as an efficient peroxidase mimic for sensitive and colorimetric quantification of H2O2 and glucose

An iron hydroxyl phosphate that possesses high peroxidase activity is synthesized via a one-step hydrothermal method and used for colorimetric glucose detection in human serum.

Electrochemical reactive oxygen species detection by cytochrome c immobilized with vertically aligned and electrochemically reduced graphene oxide on a glassy carbon electrode

Selective detection of hydrogen peroxide and superoxide based on a cytochrome c modified glassy carbon electrode.

Mesoporous CuO–ZnO p–n heterojunction based nanocomposites with high specific surface area for enhanced photocatalysis and electrochemical sensing

Mesoporous and core–shell like (p)CuO–(n)ZnO nanocomposites were prepared using microstructural refinement and solid state reactions, which showed enhanced photochemical and electrochemical performances.

Screen-printed graphite macroelectrodes for the direct electron transfer of cytochrome c: a deeper study of the effect of pH on the conformational states, immobilization and peroxidase activity

The direct electron transfer of cytochrome c has been studied at screen-printed graphite macroelectrodes without recourse to mediators or the need for any electrode pre-treatment as is commonly employed within the literature. A wide range of pH values from 2.0 to 11.0 have been explored upon the electrochemical response of cytochrome c and different voltammetric signatures have been observed. The direct electron transfer of the alkaline transition of cytochrome c was found impeded within alkaline media leading to either an irreversible redox process or even no voltammetric responses. In acidic aqueous media the electrochemical process is observed to undergo a mixed diffusion and adsorption controlled process rather than a purely diffusional process of the native conformation as observed at pH 7.0. Interestingly, at pH 3.5 a new conformational state is revealed in cooperation with the native conformation. The immobilization of the protein was satisfactorily obtained using a simple method by cycling the protein at specific solution pH values allowing amperometric responses to be obtained and gives rise to useful pseudo-peroxidase activity for sensing H2O2. Apparent Michaelis-Menten constant values (Km) were calculated via the Lineweaver-Burk method with deduced values of 25 ± 4, 98 ± 12 and 230 ± 30 mM, respectively for pH values of 2.0, 3.0 and 7.0. Such work is important for those utilising cytochrome c in bio-electrochemical and related applications.

Trends in protein-based biosensor assemblies for drug screening and pharmaceutical kinetic studies

The selection of natural and chemical compounds for potential applications in new pharmaceutical formulations constitutes a time-consuming procedure in drug screening. To overcome this issue, new devices called biosensors, have already demonstrated their versatility and capacity for routine clinical diagnosis. Designed to perform analytical analysis for the detection of a particular analyte, biosensors based on the coupling of proteins to amperometric and optical devices have shown the appropriate selectivity, sensibility and accuracy. During the last years, the exponential demand for pharmacokinetic studies in the early phases of drug development, along with the need of lower molecular weight detection, have led to new biosensor structure materials with innovative immobilization strategies. The result has been the development of smaller, more reproducible biosensors with lower detection limits, and with a drastic reduction in the required sample volumes. Therefore in order to describe the main achievements in biosensor fields, the present review has the main aim of summarizing the essential strategies used to generate these specific devices, that can provide, under physiological conditions, a credible molecule profile and assess specific pharmacokinetic parameters.

Nickel oxide thin film from electrodeposited nickel sulfide thin film: peroxide sensing and photo-decomposition of phenol

Porous NiO thin film: a peroxide sensor and effective catalyst for phenol decomposition.

Direct electrochemistry of cytochrome c immobilized on a graphene oxide–carbon nanotube composite for picomolar detection of hydrogen peroxide

A new bionanocomposite electrode based on cytochrome c immobilized graphene oxide-multiwalled carbon nanotube is used to fabricate a highly selective and sensitive amperometric biosensor for the picomolar level detection of hydrogen peroxide which may find application in bioimaging and healthcare

Facile synthesis of ultrathin worm-like Au nanowires for highly active SERS substrates

Ultrathin worm-like Au nanowires were facilely synthesized and used for the fabrication of porous Au films as highly active SERS substrates.

Peroxide-dependent analyte conversion by the heme prosthetic group, the heme Peptide "microperoxidase-11" and cytochrome C on chitosan capped gold nanoparticles modified electrodes

In view of the role ascribed to the peroxidatic activity of degradation products of cytochrome c (cyt c) in the processes of apoptosis, we investigate the catalytic potential of heme and of the cyt c derived heme peptide MP-11 to catalyse the cathodic reduction of hydrogen peroxide and to oxidize aromatic compounds. In order to check whether cyt c has an enzymatic activity in the native state where the protein matrix should suppress the inherent peroxidatic activity of its heme prosthetic group, we applied a biocompatible immobilization matrix and very low concentrations of the co-substrate H₂O₂. The biocatalysts were entrapped on the surface of a glassy carbon electrode in a biocompatible chitosan layer which contained gold nanoparticles. The electrochemical signal for the peroxide reduction is generated by the redox conversion of the heme group, whilst a reaction product of the substrate oxidation is cathodically reduced in the substrate indication. The catalytic efficiency of microperoxidase-11 is sufficient for sensors indicating HRP substrates, e.g., p-aminophenol, paracetamol and catechol, but also the hydroxylation of aniline and dehalogenation of 4-fluoroaniline. The lower limit of detection for p-aminophenol is comparable to previously published papers with different enzyme systems. The peroxidatic activity of cyt c immobilized in the chitosan layer for catechol was found to be below 1 per mill and for p-aminophenol about 3% as compared with that of heme or MP-11.

Low-potential synthesis of "clean" Au nanodendrites and their high performance toward ethanol oxidation

The shape control of Au nanocrystals is crucial to their catalytic applications and optical properties. Well-defined Au nanodendrites (NDs) have been prepared on a glassy carbon electrode using low-potential synthesis, assisted by ethylenediamine (EDA). The effects of applied potential, deposition time, and HAuCl(4) (or EDA) concentrations on the morphology of the Au deposits are discussed in our work. The growth mechanism can be explained by a two-staged growth of dendrites: initial branching and subsequent dendritic growth. The Au NDs exhibits superior catalytic performance toward ethanol oxidation, in comparison with the polycrystalline Au nanoparticles. The simple and facile synthetic technique can be applied to the construction of other metals with complex hierarchical structures on a large-scale.