Reversible surface thiol immobilization of carboxyl group containing haptens to a BIAcore biosensor chip enabling repeated usage of a single sensor surface

Biophysical and biochemical approach to locating an inhibitor binding site on cholesteryl ester transfer protein

Cholesteryl ester transfer protein (CETP) transfers neutral lipids between different types of plasma lipoprotein. Inhibitors of CETP elevate the fraction of plasma cholesterol associated with high-density lipoproteins and are being developed as new agents for the prevention and treatment of cardiovascular disease. The molecular basis of their function is not yet fully understood. To aid in the study of inhibitor interactions with CETP, a torcetrapib-related compound was coupled to different biotin-terminated spacer groups, and the binding of CETP to the streptavidin-bound conjugates was monitored on agarose beads and in a surface plasmon resonance biosensor. CETP binding was poor with a 2.0 nm spacer arm, but efficient with polyethyleneglycol spacers of 3.5 or 4.6 nm. The conjugate based on a 4.6 nm spacer was used for further biosensor experiments. Soluble inhibitor blocked the binding of CETP to the immobilized drug, as did preincubation with a disulfide-containing covalent inhibitor. To provide a first estimate of the binding site for torcetrapib-like inhibitors, CETP was modified with a disulfide-containing agent that modifies Cys-13 of CETP. Mass spectrometry of the modified protein indicated that a single half-molecule of the disulfide was covalently bound to CETP, and peptide mapping after digestion with pepsin confirmed previous reports based on mutagenesis that Cys-13 was the site of modification. Modified CETP was unable to bind to the biosensor-mounted torcetrapib analog, indicating that the binding site on CETP for torcetrapib is in the lipid-binding pocket near the N-terminus of the protein. The crystal structure of CETP shows that the sulfhydryl group of Cys-13 resides at the bottom of this pocket.

Detection of carbohydrate-binding proteins by oligosaccharide-modified polypyrrole interfaces using electrochemical surface plasmon resonance

This paper reports on the use of electrochemical surface plasmon resonance (E-SPR) for the detection of carbohydrate-binding proteins. The generation of an SPR sensor specific to lectins Arachis hypogaea (PNA) and Maackia amurensis (MAA) is based on the electrochemical polymerization of oligosaccharide derivatives functionalized by pyrrole groups. The resulting thin conducting polymer films were characterized using E-SPR and atomic force microscopy (AFM). The specific binding of PNA to polypyrrole-lactosyl and of MAA to polypyrrole-3'-sialyllactosyl films was investigated using SPR. The detection limit was 41 nM for PNA and 83 nM for MAA. Through Scatchard analysis and linear transformation of the SPR sensorgram data, association (k(ass)) and dissociation rate constants (k(diss)) could be determined.

Multichannel SPR biosensor for detection of endocrine-disrupting compounds

A surface plasmon resonance (SPR) biosensor for simultaneous detection of multiple organic pollutants exhibiting endocrine-disrupting activity, namely atrazine, benzo[a]pyrene, 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-nonylphenol, is reported. The biosensor utilizes a multichannel SPR sensor based on wavelength modulation of SPR and wavelength division multiplexing (WDM) of sensing channels, antibodies as biorecognition element and a competitive immunoassay detection format. An analysis time of 45 min (including 30-min incubation of the sample with antibodies) and limits of detection as low as 0.05, 0.07, 0.16 and 0.26 ng mL(-1) are demonstrated for benzo[a]pyrene, atrazine, 2,4-D and 4-nonylphenol, respectively. The biosensor is also shown to be regenerable and suitable for repeated use.

Stability of the gold/silica thin film interface: electrochemical and surface plasmon resonance studies

This article reports chemical stability studies of a gold film electrode coated with thin silicon oxide (SiOx) layers using electrochemical, surface plasmon resonance (SPR) and atomic force microscopy (AFM) techniques. Silica films with different thicknesses (d = 6.4, 9.7, 14.5, and 18.5 nm) were deposited using a plasma-enhanced chemical vapor deposition technique (PECVD). For SiOx films with d >/= 18.5 nm, the electrochemical behavior is characteristic of a highly efficient barrier for a redox probe. SiOx films with thicknesses between 9.5 and 14.5 nm were found to be less efficient barriers for electron transfer. The Au/SiOx interface with 6.4 nm of SiOx, however, showed an enhanced steady-state current compared to that of the other films. The stability of this interface in solutions of different pH was investigated. Whereas a strongly basic solution led to a continuous dissolution of the SiOx interface, acidic treatment produced a more reticulated SiOx film and improved electrochemical behavior. The electrochemical results were corroborated by SPR measurements in real time and AFM studies.

Point mutation detection with the sandwich method employing hydrogel nanospheres by the surface plasmon resonance imaging technique

We propose a surface modification procedure to construct DNA arrays for use in surface plasmon resonance (SPR) imaging studies for the highly sensitive detection of a K-ras point mutation, enhanced with hydrogel nanospheres. A homobifunctional alkane dithiol was adsorbed on Au film to obtain the thiol surface, and ethyleneglycol diglycidylether (EGDE) was reacted to insert the ethyleneglycol moiety, which can suppress nonspecific adsorption during SPR analysis. Then streptavidin (SA) was immobilized on EGDE using tosyl chloride activation. Biotinylated DNA ligands were bound to the SA surface via biotin-SA interaction to fabricate DNA arrays. In SPR analysis, the DNA analyte was exposed on the DNA array and hybridized with the immobilized DNA probes. Subsequently, the hydrogel nanospheres conjugated with DNA probes were bound to the DNA analytes in a sandwich configuration. The DNA-carrying nanospheres led to SPR signal enhancement and enabled us to discriminate a K-ras point mutation in the SPR difference image. The application of DNA-carrying hydrogel nanospheres for SPR imaging assays was a promising technique for high throughput and precise detection of point mutations.

A survey of the year 2002 commercial optical biosensor literature

We have compiled 819 articles published in the year 2002 that involved commercial optical biosensor technology. The literature demonstrates that the technology's application continues to increase as biosensors are contributing to diverse scientific fields and are used to examine interactions ranging in size from small molecules to whole cells. Also, the variety of available commercial biosensor platforms is increasing and the expertise of users is improving. In this review, we use the literature to focus on the basic types of biosensor experiments, including kinetics, equilibrium analysis, solution competition, active concentration determination and screening. In addition, using examples of particularly well-performed analyses, we illustrate the high information content available in the primary response data and emphasize the impact of including figures in publications to support the results of biosensor analyses.