Nature of immobilized antibody layers linked to thioctic acid treated gold surfaces

Nanoporous Gold for Enzyme Immobilization

Nanoporous gold (NPG) is a material of emerging interest for immobilization of biomolecules, especially enzymes. The material provides a high surface area form of gold that is suitable for physisorption or for covalent modification by self-assembled monolayers. The material can be used as a high surface area electrode and with immobilized enzymes can be used for amperometric detection schemes. NPG can be prepared in a variety of formats from alloys containing between 20 and 50 % atomic composition of gold and less noble element(s) by dealloying procedures. Materials resembling NPG can be prepared by hydrothermal and electrodeposition methods. Related high surface area gold structures have been prepared using templating approaches. Covalent enzyme immobilization can be achieved by first forming a self-assembled monolayer on NPG bearing a terminal reactive functional group followed by conjugation to the enzyme through amide linkages to lysine residues. Enzymes can also be entrapped by physisorption or immobilized by electrostatic interactions.

Surface modifications of microprojection arrays for improved biomarker capture in the skin of live mice

New technologies are needed to translate biomarker discovery research into simple, inexpensive, and effective molecular diagnostic assays for use by clinicians or patients to guide and monitor treatment. Microprojection arrays were recently introduced as tools which, when applied to the skin, penetrate into the dermal tissue, and capture specific circulating biomarkers. In our initial work on Microprojection arrays, carbodiimide chemistry was used to immobilize biomarker-specific probes for affinity capture in vivo using a mouse model. However, as the observed capture efficiencies were relatively low, with significant variation across the surface, here we investigated the surface modifications to (a) determine the source of the variability and (b) find ways of improving capture efficiency. We found the protein immobilization step accounted for almost all of the variability in surface uniformity. Varying the protein immobilization conditions following a standard carbodiimide activation process resulted in a reduction in overall variation 14-fold and an increase in captured biomarker amount ∼18-fold. In conclusion, we found that investigating and optimizing the surface chemistry of microprojection array devices led to drastic improvements in capturing biomarkers from skin fluid.

Nanoporous gold for enzyme immobilization

Nanoporous gold (NPG) is a material of emerging interest for immobilization of biomolecules and -especially enzymes. NPG materials provide a high gold surface area onto which biomolecules can either be directly physisorbed or covalently linked after first modifying the NPG with a self-assembled monolayer. The material can be used as a high surface area electrode and with immobilized enzymes can be used for amperometric detection schemes. NPG can be prepared in a variety of formats from alloys containing less than 50 atomic% gold by dealloying procedures. Related high surface area gold structures have been prepared using templating approaches. Covalent enzyme immobilization can be achieved by first forming a self-assembled monolayer on NPG bearing a terminal reactive functional group followed by conjugation to the enzyme through amide linkages to lysine residues.

Gold-coated magnetic particles for solid-phase immunoassays: enhancing immobilized antibody binding efficiency and analytical performance

The preparation and characterization of gold-coated magnetic particles are described for use as more efficient solid-phase materials in immunoassay development. A thin gold coating on commercial tosylated magnetic polystyrene particles (4.5 microm) is achieved via an electroless plating method involving initial reaction of the particles with Sn(II), followed by redox deposition of Ag0, that serves as a catalytic site for the subsequent reduction of Na3Au(SO3)2 in the presence of formaldehyde to yield the adhered gold layer. Scanning electron microscopy, energy-dispersive X-ray analysis, and X-ray photoelectron spectroscopy indicate the presence of the desired Au0 outer layer. To characterize the improved yield of antibody binding sites on such gold-coated phases, the modified particles are reacted with the free thiols of Fab' fragments of an anti-alkaline phosphatase (ALP) antibody to orient all the antigenic binding sites in a favorable direction. After equilibration with ALP, the amount of ALP bound to the surface of such particles is nearly 2.5-fold greater than on non-gold-coated particles possessing the same amount of immobilized anti-ALP Fab', but oriented randomly on the surface. The new gold-coated magnetic particles are further used as a solid phase for developing a sandwich-type enzyme immunoassay to detect C-reactive protein (CRP) using horseradish peroxidase as the enzyme label. The gold-coated magnetic particles with anti-CRP monoclonal Fab' reagents provide assays with enhanced assay slope (1.8-fold), lower nonspecific adsorption, and a detection limit improvement of nearly 10-fold (0.14 vs 1.9 ng/mL) compared to the same Fab' anti-CRP immobilized on the initial tosylated polystyrene magnetic particles. The improved assay performance is attributed to the more favorable binding orientation of the self-assembled monolayer of Fab' fragments on the gold-coated particles compared to the random orientation on the non-gold-coated surfaces.

Determination of monoenzyme- and bienzyme-stimulated precipitation by a cuvette-based surface plasmon resonance instrument

This paper describes the use of a cuvette-based surface plasmon resonance (SPR) instrument to measure biocatalyzed precipitation reactions. Enzyme-modified SPR sensor disk forms the base of a cuvette, in which the substrate solution is added with stirring. The determination of the substrate concentration relies on the measurement of SPR angle shift (Deltatheta(SPR)) induced by the deposition of the insoluble products without involving in any electrochemical reactions. As examples, horseradish peroxidase (HRP)-modified monoenzyme SPR sensor and HRP-glucose oxidase bienzyme-layered sensor are created to determine hydrogen peroxide and glucose via the catalyzed oxidation of 4-chloro-1-naphthol (4-CN). The deposition of the oxidized 4-CN-insoluble products leads to SPR angle shifts, which are linear to H(2)O(2) and glucose in the concentration ranges of 0.067-7.24 x 10(-5) and 0.7-8.3 x 10(-4) mM, respectively. The SPR sensitivities are greater than those of nonelectrochemical quartz crystal microbalance (QCM) (the parallel results in this study) and compare favorable with those of electrochemical QCM and electrochemical SPR methods. This study opens the field for enhanced SPR measurements by using biocatalyzed precipitation as a signal amplification method.