Enhanced performance of an affinity biosensor interface based on mixed self-assembled monolayers of thiols on gold

An affinity biosensor interface of a biosensor is the interface between the sample and the transducer surface and is therefore of the utmost importance for the general performance of a biosensor. For immunosensor applications the affinity biosensor interface consists of antibodies, which are preferably covalently attached to the transducer surface. In this paper the properties and the enhanced performance of an affinity biosensor interface based on mixed self-assembled monolayers (SAMs) on gold are discussed. Mixed SAMs consist of two different functionalities, which allow attachment of bioreceptor molecules and avoid nonspecific adsorption. In this work, mixed SAMs of thiols with carboxylic and hydroxyl or poly(ethylene glycol) groups are characterized with contact angle measurements, cyclic voltammetry, and grazing-angle Fourier transform infrared spectroscopy. It is found that the various mixed SAMs exhibit acceptable coverage and structural properties. Most importantly, surface plasmon resonance measurements clearly show the enhanced performance of these mixed SAMs with regard to sensitivity, stability, and selectivity compared to commercially available affinity biosensor interfaces. This superiority is experimentally demonstrated by evaluating the amount of immobilized antibodies, the recognition of antigens by the immobilized antibody, and the nonspecific adsorption of IgG molecules on the antibody-coated surfaces.status: publishe

Biosensing based on light absorption of nanoscaled gold and silver particles

The absorption spectrum of noble metal spherical nanoparticles is known to be strongly influenced by the dielectric constant of the surrounding material, and as such, these particles are well suited for biosensing applications. To perform biosensing using nanoparticles on a substrate, the metal particles are covalently attached onto quartz using an organic adhesion layer of mercaptosilanes. The particles in solution are characterized by UV-vis spectroscopy and transmission electron microscopy, while those attached to the quartz are characterized with UV-vis spectroscopy and atomic force microscopy. Antibodies are attached to the metal nanoparticles, and the antigen recognition is monitored via the change of light absorption when this binding event occurs. Not only is the absorbance originating from plasmon resonances of the particles influenced by the dielectric properties of molecules attached to the nanospheres but also the interband absorption of the particles changes, which will be demonstrated in this report. A light absorption change is detected when a molecular recognition occurs between the bioreceptor molecules attached to the nanoparticle and a biomolecular counterpart. This change in absorption can be very large when adhered molecules are at resonance (interband transitions). In addition, the presented type of biosensing can be a cost-effective and easy to use alternative to conventional biosensing techniques.status: publishe

Human immunoglobulin adsorption investigated by means of quartz crystal microbalance dissipation, atomic force microscopy, surface acoustic wave, and surface plasmon resonance techniques

Time-resolved adsorption behavior of a human immunoglobin G (hIgG) protein on a hydrophobized gold surface is investigated using multitechniques: quartz crystal microbalance/dissipation (QCM-D) technique; combined surface plasmon resonance (SPR) and Love mode surface acoustic wave (SAW) technique; combined QCM-D and atomic force microscopy (AFM) technique. The adsorbed hIgG forms interfacial structures varying in organization from a submonolayer to a multilayer. An "end-on" IgG orientation in the monolayer film, associated with the surface coverage results, does not corroborate with the effective protein thickness determined from SPR/SAW measurements. This inconsistence is interpreted by a deformation effect induced by conformation change. This conformation change is confirmed by QCM-D measurement. Combined SPR/SAW measurements suggest that the adsorbed protein barely contains water after extended contact with the hydrophobic surface. This limited interfacial hydration also contributed to a continuous conformation change in the adsorbed protein layer. The viscoelastic variation associated with interfacial conformation changes induces about 1.5 times overestimation of the mass uptake in the QCM-D measurements. The merit of combined multitechnique measurements is demonstrated

Nanoscaled interdigitated electrode arrays for biochemical sensors

Nanoscaled interdigitated electrode arrays were made with deep UV lithography. Electrode widths and spacings from 500 down to 250 nm were achieved on large active areas (0.5 x 1 mm). These electrodes allow for the detection of affinity binding of biomolecular structures (e.g. antigens, DNA) by impedimetric measurements. Such a sensor with Pd electrodes on SiO2 is developed and theoretically analysed. It was experimentally characterised in KCl solutions demonstrating its bulk-insensitive behaviour and the immobilisation of glucose oxidase (GOD) could be monitored by measuring the double layer impedance. (C) 1998 Elsevier Science S.A. All rights reserved