Electrode surface confinement of self-assembled enzyme aggregates using magnetic nanoparticles and its application in bioelectrocatalysis

Efficient magnetic recycling of covalently attached enzymes on carbon-coated metallic nanomagnets

In the pursuit of robust and reusable biocatalysts for industrial synthetic chemistry, nanobiotechnology is currently taking a significant part. Recently, enzymes have been immobilized on different nanoscaffold supports. Carbon coated metallic nanoparticles were found to be a practically useful support for enzyme immobilization due to their large surface area, high magnetic saturation, and manipulatable surface chemistry. In this study carbon coated cobalt nanoparticles were chemically functionalized (diazonium chemistry), activated for bioconjugation (N,N-disuccinimidyl carbonate), and subsequently used in enzyme immobilization. Three enzymes, β-glucosidase, α-chymotrypsin, and lipase B were successfully covalently immobilized on the magnetic nonsupport. The enzyme-particle conjugates formed retained their activity and stability after immobilization and were efficiently recycled from milliliter to liter scales in short recycle times.

Heterogeneous reconstitution of the PQQ-dependent glucose dehydrogenase immobilized on an electrode: a sensitive strategy for PQQ detection down to picomolar levels

A highly sensitive electroanalytical method for determination of PQQ in solution down to subpicomolar concentrations is proposed. It is based on the heterogeneous reconstitution of the PQQ-dependent glucose dehydrogenase (PQQ-GDH) through the specific binding of its pyrroloquinoline quinone (PQQ) cofactor to the apoenzyme anchored on an electrode surface. It is shown from kinetics analysis of both the enzyme catalytic responses and enzyme surface-reconstitution process (achieved by cyclic voltammetry under redox-mediated catalysis) that the selected immobilization strategy (i.e., through an avidin/biotin linkage) is well-suited to immobilize a nearly saturated apoenzyme monolayer on the electrode surface with an almost fully preserved PQQ binding properties and catalytic activity. From measurement of the overall rate constants controlling the steady-state catalytic current responses of the surface-reconstituted PQQ-GDH and determination of the PQQ equilibrium binding (Kb = 2.4 × 10(10) M(-1)) and association rate (kon = 2 × 10(6) M(-1) s(-1)) constants with the immobilized apoenzyme, the analytical performances of the method could be rationally evaluated, and the signal amplification for PQQ detection down to the picomolar levels is well-predicted. These performances outperform by several orders of magnitude the direct electrochemical detection of PQQ in solution and by 1 to 2 orders the detection limits previously achieved by UV-vis spectroscopic detection of the homogeneous PQQ-GDH reconstitution.

Developing nanotechnological strategies for green industrial processes

Nanotechnology and green chemistry can have much in common from the point of view of processes, considering the possibilities of improving efficiency and quality, achieving a better economy of atoms and energy, promoting catalysis under mild and sustainable conditions, and facilitating online monitoring of production lines and environment. Some of these aspects are dealt with in this paper, focusing on selected examples of application of functionalized nanoparticles and -materials in chemistry and industry.

Magnetic loading of tyrosinase-Fe3O4/mesoporous silica core/shell microspheres for high sensitive electrochemical biosensing

A new protocol is proposed for magnetic loading and sensitive electrochemical detection of phenol via the tyrosinase cross-linked mesoporous magnetic core/shell microspheres. The mesoporous magnetic microspheres, characterized by transmission electron microscopy, N(2) adsorption/desorption isotherms, and magnetic curve displays high capacity for enzyme immobilization and strong magnetism to adhere to the magnetic electrode surface without any additional adhesive reagent. The biosensor exhibits a wide linear response to phenol ranging from 1.0×10(-9) to 1.0×10(-5) M, a high sensitivity of 78 μA mM(-1), a low detection limit of 1 nM, and a fast response rate (less than 5s). The proposed method is simple, rapid, inexpensive and convenient in electrode renewal, which is recommended as a promising experimental platform for wider applications in biosensing.

Label-free detection of antibody-antigen interactions on (R)-lipo-diaza-18-crown-6 self-assembled monolayer modified gold electrodes

Novel (R)-diaza-18-crown-6 has been prepared by a simple two-step synthetic method and characterized for its ability to form a uniform self-assembled monolayer (SAM) on gold as well as to immobilize proteins using atomic force microscopy, quartz crystal microbalance, and electrochemical impedance spectroscopy (EIS) experiments. The (R)-lipo-diaza-18-crown-6 was shown to form a well-defined SAM on gold, which subsequently captures the antibody (Ab) molecules that in turn capture the antigen (Ag) molecules. The Ab molecules studied include antibody C-reactive protein (Ab-CRP) and antibody ferritin (Ab-ferritin) along with their Ag's, i.e., CRP and ferritin. Quantitative detection of the Ab-Ag interactions was accomplished by EIS experiments with a Fe(CN)6(3-/4-) redox probe present. The ratios of the charge-transfer resistances for the redox probe on the SAM-antibody-covered electrode to those with the antigen molecules attached show an excellent linearity for log[Ag] with lower detection limits than those of other SAMs for the electrochemical sensing of proteins.

Bifunctional Nanostructure of Magnetic Core Luminescent Shell and Its Application as Solid-State Electrochemiluminescence Sensor Material

Bifunctional nanoarchitecture has been developed by combining the magnetic iron oxide and the luminescent Ru(bpy)32+ encapsulated in silica. First, the iron oxide nanoparticles were synthesized and coated with silica, which was used to isolate the magnetic nanoparticles from the outer-shell encapsulated Ru(bpy)32+ to prevent luminescence quenching. Then onto this core an outer shell of silica containing encapsulated Ru(bpy)32+ was grown through the Stöber method. Highly luminescent Ru(bpy)32+ serves as a luminescent marker, while magnetic Fe3O4 nanoparticles allow external manipulation by a magnetic field. Since Ru(bpy)32+ is a typical electrochemiluminescence (ECL) reagent and it could still maintain such property when encapsulated in the bifunctional nanoparticle, we explored the feasibility of applying the as-prepared nanostructure to fabricating an ECL sensor; such method is simple and effective. We applied the prepared ECL sensor not only to the typical Ru(bpy)32+ co-reactant tripropylamine (TPA), but also to the practically important polyamines. Consequently, the ECL sensor shows a wide linear range, high sensitivity, and good stability.