Clay–chitosan–gold nanoparticle nanohybrid: Preparation and application for assembly and direct electrochemistry of myoglobin

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.

Carbon Nitride Nanosheet and Myoglobin Modified Electrode for Electrochemical Sensing Investigations

Background:

Carbon-based nanomaterials, especially carbon nitride (C3N4) has attracted tremendous interest in biosensor applications. Meanwhile, the mechanism of redox protein sensing and related electrocatalytic reactions can provide a valid basis for understanding the process of biological redox reaction.

Objective:

The aim of this paper is to construct a new electrochemical enzyme sensor to achieve direct electron transfer of myoglobin (Mb) on CILE surface and display electrocatalytic reduction activity to catalyze trichloroacetic acid (TCA) and H2O2.

Methods:

The working electrode was fabricated based on ionic liquid modified Carbon Paste Electrode (CILE) and C3N4 nanosheets were modified on the CILE surface, then Mb solution was fixed on C3N4/CILE surface and immobilized by using Nafion film. The as-prepared biosensor displayed satisfactory electrocatalytic ability towards the reduction of TCA and H2O2 in an optimum pH 7.0 buffer solution.

Results:

The results indicated that C3N4 modified electrode retained the activity of the enzyme and displayed quasi-reversible redox behavior in an optimum pH 7.0 buffer solution. The electrochemical parameters of the immobilized Mb on the electrode surface were further calculated with the results of the electron transfer number (n) as 1.27, the charge transfer coefficient (α) as 0.53 and the electrontransfer rate constant (ks) as 3.32 s-1, respectively. The Nafion/Mb/C3N4/CILE displayed outstanding electrocatalytic reduction activity to catalyze trichloroacetic acid and H2O2.

Conclusion:

The Nafion/Mb/C3N4/CILE displayed outstanding electrocatalytic reduction, which demonstrated the promising applications of C3N4 nanosheet in the field electrochemical biosensing.

Enzyme-Based Ultrasensitive Electrochemical Biosensors for Rapid Assessment of Nitrite Toxicity: Recent Advances and Perspectives

In the present era of rapid international globalization and industrialization, intensive use of nitrite as a fertilizing agent in agriculture, preservative, dyeing agent, food additive and as corrosion inhibitor in industrial sectors is adversely effecting environment, natural habitats and human health. The issue of toxicity and carcinogenicity due to excessive ingestion of nitrites via the dietary intake has led to an imminent need for its efficient real-time monitoring in situ. Nitrite detection employing electrochemical biosensors has been gaining high credibility in the field of clinical research. Nitrite biosensors have emerged as an outstanding choice for portable point of care testing of nitrite quantification owing to the excellent properties, such as rapidity, miniaturization, ultra-low limits of detection, multiplexing and enhanced detection sensitivity. The article is enclosed with an interesting outlook on latest emerging trends in the development of nitrite biosensors utilizing nanomaterials, such as metal nanoparticles, carbon nanotubes, metal oxide nanoparticles, nanocomposites, polymers and biomaterials. The present review embarks on the highlights relevant to the nitrite quantification in real samples, then proceeds with a meticulous description of the most pertinent electrochemical nitrite biosensors, which have been proposed by adopting diverse materials and strategies of fabrication and finally end with the achievements and future outlook signifying the application of these nanoengineered biosensors for environmental surveillance and human safety.

Biomedical Applications of Multifunctional Gold-Based Nanocomposites

Active application of gold nanoparticles for various diagnostic and therapeutic purposes started in recent decades due to the emergence of new data on their unique optical and physicochemical properties. In addition to colloidal gold conjugates, growth in the number of publications devoted to the synthesis and application of multifunctional nanocomposites has occurred in recent years. This review considers the application in biomedicine of multifunctional nanoparticles that can be produced in three different ways. The first method involves design of composite nanostructures with various components intended for either diagnostic or therapeutic functions. The second approach uses new bioconjugation techniques that allow functionalization of gold nanoparticles with various molecules, thus combining diagnostic and therapeutic functions in one medical procedure. Finally, the third method for production of multifunctional nanoparticles combines the first two approaches, in which a composite nanoparticle is additionally functionalized by molecules having different properties.

Multifunctional gold-based nanocomposites for theranostics

Although Au-particle potential in nanobiotechnology has been recognized for the last 15 years, new insights into the unique properties of multifunctional nanostructures have just recently started to emerge. Multifunctional gold-based nanocomposites combine multiple modalities to improve the efficacy of the therapeutic and diagnostic treatment of cancer and other socially significant diseases. This review is focused on multifunctional gold-based theranostic nanocomposites, which can be fabricated by three main routes. The first route is to create composite (or hybrid) nanoparticles, whose components enable diagnostic and therapeutic functions. The second route is based on smart bioconjugation techniques to functionalize gold nanoparticles with a set of different molecules, enabling them to perform targeting, diagnostic, and therapeutic functions in a single treatment procedure. Finally, the third route for multifunctionalized composite nanoparticles is a combination of the first two and involves additional functionalization of hybrid nanoparticles with several molecules possessing different theranostic modalities. This last class of multifunctionalized composites also includes fluorescent atomic clusters with multiple functionalities.

Emergent Properties and Toxicological Considerations for Nanohybrid Materials in Aquatic Systems

Conjugation of multiple nanomaterials has become the focus of recent materials development. This new material class is commonly known as nanohybrids or "horizon nanomaterials". Conjugation of metal/metal oxides with carbonaceous nanomaterials and overcoating or doping of one metal with another have been pursued to enhance material performance and/or incorporate multifunctionality into nano-enabled devices and processes. Nanohybrids are already at use in commercialized energy, electronics and medical products, which warrant immediate attention for their safety evaluation. These conjugated ensembles likely present a new set of physicochemical properties that are unique to their individual component attributes, hence increasing uncertainty in their risk evaluation. Established toxicological testing strategies and enumerated underlying mechanisms will thus need to be re-evaluated for the assessment of these horizon materials. This review will present a critical discussion on the altered physicochemical properties of nanohybrids and analyze the validity of existing nanotoxicology data against these unique properties. The article will also propose strategies to evaluate the conjugate materials' safety to help undertake future toxicological research on the nanohybrid material class.

Direct electrochemistry and electrocatalysis of myoglobin-based nanocomposite membrane electrode

The direct electron transfer of myoglobin (Mb) was achieved based on the immobilization of Mb/Silver nanoparticles (AgNPs) on glassy carbon electrode by multi-wall carbon nanotubes (MWNTs)-chitosan(Chit) film. The immobilized Mb displayed a pair of well-defined and reversible redox peaks with a formal potential (E(θ')) of -24 mV (vs. Ag/AgCl) in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k(s)) of Mb confined to Chit-MWNTs film was evaluated as 5.47 s(-1) according to Laviron's equation. The surface concentration (Γ(*)) of the electroactive Mb in the Chit-MWNTs film was estimated to be (4.16±0.35)×10(-9) mol cm(-2). Meanwhile, the catalytic ability of Mb toward the reduction of H(2)O(2) was studied. Its apparent Michaelis-Menten constant for H(2)O(2) was 0.024 mM, showing a good affinity. The linear range for H(2)O(2) determination was from 2.5×10(-5) M to 2.0×10(-4) M with a detection limit of 1.02×10(-6) M (S/N=3). Moreover, the biosensor displays rapid response to H(2)O(2) and good stability and reproducibility.

Nitrite biosensing via selective enzymes--a long but promising route

The last decades have witnessed a steady increase of the social and political awareness for the need of monitoring and controlling environmental and industrial processes. In the case of nitrite ion, due to its potential toxicity for human health, the European Union has recently implemented a number of rules to restrict its level in drinking waters and food products. Although several analytical protocols have been proposed for nitrite quantification, none of them enable a reliable and quick analysis of complex samples. An alternative approach relies on the construction of biosensing devices using stable enzymes, with both high activity and specificity for nitrite. In this paper we review the current state-of-the-art in the field of electrochemical and optical biosensors using nitrite reducing enzymes as biorecognition elements and discuss the opportunities and challenges in this emerging market.

Iron phosphate nanostructures synthesized by microwave method and their applications in biosensing

A fast, simple microwave heating method has been developed for synthesizing iron phosphate (FePO(4)) nanostructures. The nanostructures were characterized and confirmed by transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), x-ray powder diffraction (XRD), Fourier transform infrared (FT-IR), and UV-vis spectroscopy. The morphology and the size of the nanomaterials are significantly influenced by the concentration of the precursors and the kinds of surfactants. The nanostructures have been employed as an electrode substrate to immobilize myoglobin (Mb) and to facilitate the direct electron transfer (DET) reaction of the protein. After being immobilized on the nanomaterials, Mb can keep its natural structure and undergo effective DET reaction with a pair of well-defined redox peaks at - (330 ± 3.0) mV (pH 6.8) and an apparent electron transfer rate constant of 5.54 s(-1). The Mb-FePO(4)/GC electrode displays good features in the electrocatalytic reduction of H(2)O(2), and thus can be used as a biosensor for detecting substrates with a low detection limit (5 ± 1 µM), a wide linear range (0.01-2.5 mM), a high sensitivity (ca. 85 ± 3 µA mM(-1) cm(-2)), as well as good stability and reproducibility. Therefore, FePO(4) nanomaterials can become a simple and effective biosensing platform for the integration of proteins/enzymes and electrodes, which can provide analytical access to a large group of enzymes for a wide range of bioelectrochemical applications.

Simple synthesis of clay-gold nanocomposites with tunable color

Clay-based nanocomposites have been studied for several decades, mainly focusing on clay-polymer nanocomposites. Here, we report on a simple wet chemical method to synthesize clay-APTES-Au (CAAu) nanocomposites, where 3-aminopropyltriethoxysilane (APTES) acts as the linkage. The silane terminal of APTES formed bonds with the clay surface, while the other -NH(2) terminal bonds to gold nanoparticles. The color of clay changed when these CAAu nanocomposites were formed. By changing the size of the gold nanoparticles, the color of CAAu could be adjusted, simply by changing process parameters. TEM characterization of the synthesized nanocomposites showed an even distribution of gold nanoparticles on the clay surfaces. The nanocomposites were stable in strong acid and high concentration of salt conditions, while strong basic solution like NaOH could slightly influence the status of the gold nanoparticles due to the rupture of the Si-O-Si bonds between APTES and clay. To demonstrate the potential for label free sensing application of CAAu nanocomposites, we made hybrids of clay-APTES-Au-HD-Au (CAAuHAu), where hexamethylene diamine (HD) served as links between CAAu nanocomposites and the gold nanoparticles. The color of the composites changed from red to blue, when the hybrids were formed. Moreover, hemoglobin was loaded on the CAAu nanocomposites, which can potentially be used as a biosensor. These synthesized nanocomposites may combine the catalytic properties of clay and the well-known excellent properties of gold nanoparticles, such as the ability to anchor biological and chemical molecules. Furthermore, the color change of CAAu, when the CAAuHAu hybrids were observed, suggests the applications of these nanocomposites in biochemical and chemical sensing.

Direct electrochemistry and bioelectrocatalysis of horseradish peroxidase based on gold nano-seeds dotted TiO2 nanocomposite

Gold nano-seeds (GNSs) (capital EF, Cyrillic=2-5 nm) were dotted in TiO(2) colloids and the horseradish peroxidase (HRP) was successfully immobilized on the as-made GNSs-TiO(2) nanocomposite by a convenient and effective method. The matrix integrates the merits of both GNSs and TiO(2), which provides a favorable microenvironment for the immobilization of HRP. The cyclic votammetric results demonstrated that the entrapped HRP achieves direct electron transfer at glassy carbon electrode (GCE). A pair of stable and quasi-reversible redox peaks with a small peak-to-peak separation of 43 mV was observed in phosphate buffer solution. The GNSs stabilized by TiO(2) colloids acted sufficiently as the conducting tunnel to promote the electron transfer. As a result, the electrochemical behaviors were improved in virtue of the synergic effect of TiO(2) and GNSs. The Nafion/HRP-GNSs-TiO(2)/GCE displayed an excellent and rapid electrocatalytic response to the reduction of H(2)O(2). The proposed biosensor exhibited a good linear response in the range from 4.1 x 10(-5) to 6.3 x 10(-4) mol L(-1), with a detection limit of 5.9 x 10(-6) mol L(-1) (at the ration of signal to noise, S/N=3). The apparent Michaelis-Menten constant was estimated to be 0.63 mmol L(-1). Furthermore, the biosensor possesses satisfactory stability and good reproducibility.

Biosensing applications of clay-modified electrodes: a review

Two-dimensional layered inorganic solids, such as cationic clays and layered double hydroxides (LDHs), also defined as anionic clays, have open structures which are favourable for interactions with enzymes and which intercalate redox mediators. This review aims to show the interest in clays and LDHs as suitable host matrices likely to immobilize enzymes onto electrode surfaces for biosensing applications. It is meant to provide an overview of the various types of electrochemical biosensors that have been developed with these 2D layered materials, along with significant advances over the last several years. The different biosensor configurations and their specific transduction procedures are discussed.

Direct electron transfer and enhanced electrocatalytic activity of hemoglobin at iron-rich clay modified electrodes

The possible role of structural iron in clays to promote direct electron transfer of hemoglobin (Hb) was investigated. Clays containing different amounts of iron situated in octahedral or tetrahedral sites have been used to modify glassy carbon electrodes: nontronite, synthetic montmorillonite, and saponite. A synthetic montmorillonite containing non-iron impurities was used as a reference. Interactions between Hb and these clays were studied with the establishment of adsorption isotherms and by the analysis of X-ray diffraction patterns, FTIR, and UV-vis spectra of the Hb-clay samples. The electrochemical behavior of clay modified electrodes (CME) was characterized by cyclic voltammetry in the presence of Hb in solution or adsorbed within the clays. Nontronite, which contains the highest amount of structural iron, enhanced significantly direct electron transfer of Hb. Finally, the electrocatalytic behavior of Hb-Nontronite CME in the presence of hydrogen peroxide was also studied, and the H(2)O(2) calibration curve was recorded under amperometric conditions for different bioelectrode configurations.