A novel biosensing interfacial design based on the assembled multilayers of the oppositely charged polyelectrolytes

Construction of supported lipid membrane modified piezoelectric biosensor for sensitive assay of cholera toxin based on surface-agglutination of ganglioside-bearing liposomes

A novel piezoelelctric biosensor has been developed for cholera toxin (CT) detection based on the analyte-mediated surface-agglutination of ganglioside (GM1)-functionalized liposomes. To achieve a CT-specific agglutination at the surface, the gold electrode is modified by a GM1-functionalized supported lipid membrane via spontaneous spread of the liposomes on a self-assembled monolayer of a long-chain alkanethiol. In the presence of CT, the GM1-incorporated liposomes in assay medium will rapidly specifically agglutinate at the electrode surface through the binding of CT to GM1 on the electrode surface and the liposome interface. This results in an enormous mass loading on the piezoelelctric crystal as well as a significant increase of density and viscosity at the interface, thereby generating a decrease in frequency of the piezoelelctric crystal. The combination of mass loading with interfacial change in the surface-agglutination reaction allows the developed piezoelelctric biosensor to show substantial signal amplification in response to the analyte CT. The detection limit can be achieved as low as 25 ng mL(-1) CT. This is the first demonstration on CT detection based on specific surface-agglutination of GM1-modified liposomes. The supported lipid layer based sensing interface can be prepared readily and renewably, making the developed technique especially useful for simple, reusable and sensitive determination of proteins.

Aspects of recent development of immunosensors

This chapter focuses on the recent developments in the field of immunosensors. Immunosensors incorporate the specific immunochemical reaction with the modern transducers including electrochemical (potentiometric, conductometric, capacitative, impedance, amperometric), optical (fluorescence, luminescence, refractive index), and microgravimetric transducers. These immunosensor devices with dramatic improvements in the sensitivity and selectivity possess the abilities to investigate the reaction dynamics of antibody–antigen binding and the potential to revolutionize conventional immunoassay techniques. With the rapid development of immunological reagents and detection equipments, immunosensors have allowed an increasing range of analytes to be identified and quantified and in particular, simple-to-use, inexpensive, and reliable immunosensing systems have been developed for areas such as outpatient monitoring, large screening programs, and remote environmental surveillance. Immunosensors with lowered detection limits and increased sensitivities have been developed in various fields, particularly in clinical analysis. A noticeable development trend is also observed in the development of immunosensors combining with other techniques such as flow injection analysis (FIA) or capillary electrophoretic (CE) analysis, which complement and improve the present immunoassay methods. Belov et al. have proposed a novel immunophenotyping method for leukemias which uses a cluster of differentiation antibody microarray, and a microarray of enzyme-linked immunosorbent assay has been developed for autoimmune diagnosis of systematic rheumatic disease. Development of microfluidic immunosensor systems for proteomics and drug discovery have also been reported in recent years where the microfluidic system integrates multiple processes in a single device to improve analytical performance by reducing the reagent consumption and the analysis time, and increasing reliability and sensitivity through automation.

Electrogenerated Chemiluminescence in Polyelectrolyte Multilayers: Efficiency and Mechanism

The presence of an ultrathin film of polyelectrolyte complex, formed by the multilayering method, on an electrode was shown to enhance the intensity of electrogenerated chemiluminescence (ECL) from the tris(2,2')bipyridylruthenium(II)/tripropylamine system. Platinum electrodes coated with up to 17 layers of poly(diallyldimethylammonium chloride) or poly(vinylmethylpyridine), alternately layered with poly(styrenesulfonate), revealed significant differences in enhancement of ECL, depending on the identity of the multilayer. ECL following deposition of each layer showed an oscillating intensity of light emission, which alludes to the importance of surface and bulk charge. This effect, along with others, such as increased output with increasing tripropylamine concentration, was used to suggest a mechanism for enhanced ECL intensity at multilayer-coated electrodes.

Mucin-chitosan complexes at the solid-liquid interface: multilayer formation and stability in surfactant solutions

The adsorption of a biologically important glycoprotein, mucin, and mucin-chitosan complex layer formation on negatively charged surfaces, silica and mica, have been investigated employing ellipsometry, the interferometric surface apparatus, and atomic force microscopy techniques. Particular attention has been paid to the effect of an anionic surfactant sodium, dodecyl sulfate (SDS), with respect to the stability of the adsorption layers. It has been shown that mucin adsorbs on negatively charged surfaces to form highly hydrated layers. Such mucin layers readily associate with surfactants and are easily removed from the surfaces by rinsing with solutions of SDS at concentrations > or =0.2 cmc (1 cmc SDS in 30 mM NaCl is equal to 3.3 mM). The mucin adsorption layer is negatively charged, and we show how a positively charged polyelectrolyte, chitosan, associates with the preadsorbed mucin to form mucin-chitosan complexes that resist desorption by SDS even at SDS concentrations as high as 1 cmc. Thus, a method of mucin layer protection against removal by surfactants is offered. Further, we show how mucin-chitosan multilayers can be formed.

Real-time QCM-D immunoassay through oriented antibody immobilization using cross-linked hydrogel biointerfaces

This report presents the development of pre-cross-linked and in situ cross-linked polyethyleneimine-carboxymethylcellulose antibody immobilization platforms for real-time QCM-D immunoassay of sepsis-related biomarkers. These platforms differ significantly from recent trends in QCM-based assays, a rapidly expanding field given the affordability and sensitivity of the transduction system, by providing ultrafast biointerface deposition through cross-linking of polysaccharides. Using rhIL-1ra (17 kDa), a known sepsis biomarker, for development, various immunoassay modifications to increase sensitivity were investigated, including the use of Protein A, Protein G, and anti-IgG Fc specific antibody capture ligands for oriented antibody immobilization, higher-frequency QCM-D crystals, and amplification using secondary antibodies. The optimized assay employs Protein A oriented immobilization on pre-cross-linked polymer and secondary antibodies to achieve a detection limit of 25 ng/mL on 5 MHz crystals. Assay repeatability using the optimized chemistry is robust, with no loss in 100 ng/mL antigen detection over 20 cycles of the 10 min sandwich assay. Nonspecific adsorption of human serum albumin, as characterized by ToF-SIMS, is minimal and negligible for the pre-cross-linked and in situ cross-linked compositions, respectively.