Surface affinity biosensors

Figure 7. Concept of affinity biosensor based on surface plasmon resonance.

Immunosensors are affinity biosensors and are defined as analytical devices that detect the binding of an antigen to its specific antibody by coupling the immunochemical reaction to the surface of a device... 

Mitsui K, Handa Y, Kajikawa K (2004) Optical fiber affinity biosensor based on localized surface plasmon resonance. Appl Phys Lett 85 4231 233... 

Figure 15. Construction and proposed operational principle for the affinity biosensor based on the avidm-biotin interaction on a gold electrode surface. (Right) Molecular models of the chemicals used for electrode construction and affinity biosensing. (Adapted from Ref. [172]).

Figure 17. Schematic representation of the affinity biosensor construction and the proposed operational principle and voltammetric traces for affinity sensor signalling a biotin-functionalized surface before (A) and after (B) target protein (antibiotin IgG-HRP) association and precipitation reaction steps. Voltammetric measurements were performed in 0.1 M phosphate buffer (pH 7.0),containing 0.1 mM ferrocene methanol as a signal tracer. Inset charge coupled device (CCD) camera images of a sensor surface upon signalling reactions (Adapted from Refs. [176] [177]).

In Chap. 1 by J. Homola of this volume [1] surface plasmons were introduced as modes of dielectric/metal planar waveguides and their properties were estabhshed. It was demonstrated that the propagation constant of a surface plasmon is sensitive to variations in the refractive index at the surface of a metal film supporting the surface plasmon. In this chapter, it is shown how this phenomenon can be used to create a sensing device. The concept of optical sensors based on surface plasmons, commonly referred as to surface plasmon resonance (SPR) sensors, is described and the main approaches to SPR sensing are presented. In addition, the concept of affinity biosensors is introduced and the main performance characteristics of SPR biosensors are defined. 

Fig. 3 Principle of surface plasmon resonance affinity biosensor...

SPR sensors directly measure refractive index. In conjunction with appropriate biorecognition elements, they can be used as affinity biosensors allowing detection of the capture of analyte molecules by biorecognition elements immobibzed on the sensor surface. The abihty of SPR sensors to perform measurements is described by the performance characteristics, of which the most important are the sensitivity, resolution, accuracy, reproducibihty, and hmit of detection. The sensitivity and resolution are primarily determined by the properties of the optical system of the SPR sensor and can be linked to specific design parameters. 

Conversely, the development of affinity biosensors constitutes a field of application where monolayer-modified electrodes are of great importance, as testified by the abundant literature [135-142]. Antibodies, aptamers, and strands of nucleic acids are the most common biological recognition elements used for the selective detection of the target analyte. These biomolecules require to be stably grafted oti the electrode surface through a monolayer without losing their activity [143]. 

Mixed monolayers have been widely employed in affinity biosensors, in order to prevent non-specific adsorption of dissolved species on the electrode surface, to reduce the steric hindrance between biological receptors, and to increase the degree of order of the bio-receptors on the electrode surface (Fig. 5.18). 

In general, affinity biosensors may be constructed in such a way that one counterpart of the above-mentioned couple (affinity ligand or affinant) is immobilzed on the surface of a membrane sensor (or on the bed of a reactor sensor) and the second counterpart (in this case the analyte) may be determined in a complex sample. 

The range of biosensors for the analysis of vitamins that use enzymes as the biorecognition elements is rather restricted. However, affinity biosensors have opened a new horizon in the field of vitamin analysis with surface plasmon resonance (SPR) biosensors at the forefront. Commercialization of optical SPR... 

---