Biosensors surface modification

Fig.1 Different platforms for biomolecule immobilization or biosensor surface modifications a reactive ester-terminated SAM on gold b substrate-supported lipid bilayer on glass (structure of 1.2-dimyristoyl-sM-glycero-3-phosphatidylcholine, DMPC) c substrate-immobilized lipid vesicle d spin-coated thin film of a reactive homopolymer, such as poly(JV)-hydroxysuccinimidyl methacrylate (PNHSMA with tunable thickness dfiim the reactive groups are located in a region near the surface with depth the reactant molecules and reactive moieties in the film are schematically depicted as bars and dots, respectively)...

A wide variety of parameters can directly affect the chemical and physical characteristics of a plasma, which in turn affect the surface chemistry obtained by the plasma modification. Some of the more important parameters include electrode geometry, gas type, radio frequency (0-10 ° Hz), pressure, gas flow rate, power, substrate temperature, and treatment time. The materials and plasmas used for specific biomedical applications are beyond the scope of this text, but the applications include surface modification for cardiovascular, ophthalmological, orthopedic, pharmaceutical, tissue culturing, biosensor, bioseparation, and dental applications. 

Since none of the liposomal immunoassay approaches described in the scientific literature thus far took advantage of surface immobilization techniques, one could envision a double-amplification biosensor in which surface modification plays an important role [35]. For example, consider a dehydrogenase enzyme marker system which requires an electroactive cofactor such as NAD+. In the enzymatic reaction scheme ... 

With the help of surface modification, the catalytic activity and selectivity could be manipulated by tailoring the structure of the electrodes. The rapid development of nanotechnology and bioscience has been witnessed by a large number of recent literatures on novel electrodes such as BDD, nanoelectrodes, and biosensors. This trend is likely to remain so for the next decade when the hot research topics for electrochemistry will be in advanced materials, biochemical-related application, and environmental analysis and protection. 

Hemoproteins are a broad class of redox-proteins that act as cofactors, e.g. cytochrome c, or as biocatalysts, e.g. peroxidases. Direct ET between peroxidases such as horseradish peroxidase, lactoperoxidase," or chloropcroxidasc"" and electrode surfaces, mainly carbonaceous materials, were extensively studied. The mechanistic aspects related with the immobilized peroxidases on electrode surfaces and their utilization in developing biosensor devices were reviewed in detail. The direct electrical contact of peroxidases with electrodes was attributed to the location of the heme site at the exterior of the protein that yields close contact with the electrode surface even though the biocatalyst is randomly deposited on the electrode. For example, it was reported " that non-oriented randomly deposited horseradish peroxidase on a graphite electrode resulted in 40-50% of the adsorbed biocatalyst in an electrically contacted configuration. For other hemoproteins such as cytochrome c it was found that the surface modification of the electrodes with promoter units such as pyridine units induced the binding of the hemoproteins in an orientation that facilitated direct electron transfer. By this method, the promoter sites induce a binding-ET process-desorption mechanism at the modified electrode. Alternatively, the site-specific covalent attachment of hemoproteins such as cytochrome c resulted in the orientation of the protein on the electrode surfaces and direct ET communication. ... 

Key words Biosensor, Bacteriophage, Surface modification, Electrochemical impedance, Electrode. 

The range of surface modification techniques available for sensors is quite large and continues to grow. While some of these approaches are well established for the modification of the surfaces of sensors others are only beginning to find application as ideas and approaches from the related fields of molecular electronics, self-assembly, and surface electrochemistry find their way into sensor and biosensor applications. 

An amperometric biosensor for OPC pesticides based on a CNT-modified transducer and an OPH biocatalyst is described. A bilayer approach with the OPH layer on top of the CNT film was used for preparing the CNT/OPH biosensor. The CNT layer leads to a greatly improved anodic detection of the enzymatically generated p-nitrophenol product, including higher sensitivity and stability. The sensor performance was optimized with respect to the surface modification and operating conditions. Under the optimal conditions the biosensor was used to measure as low as... 

Lin, C. H., Lee, G. B., Fu, L. M., and Chen, S. H., Integrated optical-fiber capillary electrophoresis microchips with novel spin-on-glass surface modification. Biosensors and Bioelectronics 20, 83-90, 2004. 

The surface of any material governs its interactions with the environment. Knowledge over and control of these interaction is especially important when a material is in contact with the biosystem, for example, when applied as transplant, in tissue engineering, in cell cultures, and in blood contact, as weU as in biosensors in medicinal diagnosis, fluids analysis, environmental moititoring, and many other areas. Whereas, on the one hand, the bulk properties of the material are essential for its successful application, for example, as a catheter or a heart valve, special attention has to be paid to render to the surface suitable biocompatible or bioactive properties, no matter of the chemical composition of the bulk material. This is usually achieved by any surface modification process by low molar mass or polymeric compounds. An essential feature of such a modification procedure is the need for a permanent and bioresistant surface finish [87]. 

In addition, as a hydrophilic and ftmctionalizable polymer, dextrans are used extensively for surface modification in biosensor fabrication. Dextran layers on sensor chips can effectively minimize nonspecific adsorption of analyte and facilitate surface immobilization of ligand, subsequently increasing the sensitivity of biosensors. 

Polyaniline is an attractive electropolymerizable polymer for surface modifications due to its unique redox properties, high electrical conductance, and ease of preparation. In addition, polyaniline-modified surfaces retain a large specific surface area and can remain conductive facilitating subsequent electron transfer. Feng and coworkers [8] constructed a DNA impedance biosensor based on gold nanoparticle/pol5 niline nanotube membranes formed in the presence of chitosan as shown in Fig. 14.1. Chitosan was used... 

This chapter focuses on the use of nanotechnology in the development of cellulose and chitin nanoctystals and their novel biomedical applications. It consists of four main sections. The first section is a brief introduction. The second section focuses on cellulose nanocrystals (CNCs) and their preparation procedure, physical properties, and surface modifications. Cationic modification of CNCs is also presented to produce positively charged CNCs. Various bioapplications of CNCs in bionanocomposites, drug delivery, and biosensors are discussed as well. The third section focuses on chitin nanoctystals (CHNCs). Except for a short introduction on chitin and its structure, the methods of isolation and characterization of chitin are discussed and the surface modifications and properties of CHNCs are summarized. The applications of CHNCs as reinforcing fillers in nanocomposites and several biomedical applications are discussed. The fourth section is a summary and perspective highlighting the future directions on the application of these natural nanoctystals in various key industries related to biomedicine. 

Mammalian cell immobilization to electrode surfaces is vitally important for the construction of cell-based biosensors which hold out the promise for the development of practical methods for the screening of drugs for possible toxic side effects and for the monitoring of the effects of biochemical warfare agents. Surface modification of the substrate could effectively enhance the... 

Electrode surface modification has been done by different DNA adsorption immobilization procedures, electrostatic adsorption or evaporation, with the formation of a monolayer or a multilayer DNA film. A very important factor for the optimal construction of a DNA-electrochemical biosensor is the immobilization of the DNA probe on the electrode surface [2-6]. 

Considerable effort has been dedicated to die investigation of different surface modification processes of metal and carbon electrodes in the construction of electrochemical enzyme biosensors with separate redox mediator and enzyme layers, see Fig. 6.4. 

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