Biosensors proteins/enzymes

Biomaterials such as proteins/enzymes or DNA display highly selective catalytic and recognition properties. Au nanoparticles or nanorods show electronic, photonic and catalytic properties. The convergence of both types of materials gives rise to Au NP-biomolecule hybrids that represent a very active research area. The combination of properties leads to the appearance of biosensors due to the optical or electrical transduction of biological phenomena. Moreover, multifunctional Au NP-peptide hybrids can be used for targeting nuclear cells where genetic information is stored and could be useful for biomedical applications [146]. 

The universal character of the LbL method has catalyzed the introduction of the method for a wide range of bioapplications. Proteins (enzymes) [30-33], polypeptides [34], polysaccharides [35], lipids [36, 37], nucleic acids [38-42], viruses [43], inorganic particles, and crystals [44] have been embedded in the films. Use of these compounds makes the films attractive for biorelated applications such as biosensors, drug delivery, tissue engineering, and biocoatings. Biological [45, 46] and nonbio-logical [21, 47 19] applications of LbL films are reviewed in the literature. 

Among the analytes detectable with biosensors are carbohydrates, organic acids, alcohols, phenols. amines, heterocyclic compounds, proteins, enzymes, cofactors, inorganic ions, hormones, vitamins. peptides, drugs, xenobiotics. microorganisms, gases, and pesticides. Analyte concentrations... 

Since the report of carbon nanotubes (CNT) in 1991, much attention has been focused on their unique electrical and mechanical properties. The integration of bioactive molecules (enzymes, proteins, antigens, antibodies, DNA, etc.) with CNT enables the use of the hybrid systems as biosensor devices (enzyme electrodes, immunosensors, or DNA sensors), but the hydrophobicity of the CNT limits their application in biology. Thus, the functionalization of CNT with biopolymers promises to be one of the most successful methods to improve the hydrophilicity of CNT. These biopolymers can bring a hydrophilic surface of the CNT for covalent, absorptive, or ionic bindings with bioactive molecules. 

Enzymes are biocatalysts with an extremely high selectivity. Their molecules are protein molecules with a molecular mass between 10 to 10 Da. Enzymes work under mild conditions, i.e. at room temperature or slightly above and at near-neutral pH. Biosensors with enzymes generally contain a layer of enzyme molecules immobilized at the sensor surface. This layer is able to catalyse just one reaction with a definite biologically active substance. The latter is recognized and determined specifically in this way. 

Mesoporous materials with controlled porosity and functionality have been used to immobilize biomolecules, e.g., proteins. Enzymes of small or medium size such as cytochromes, oxidases, peroxidases, lipases or proteases, can be immobilized via physical adsorption, encapsulation, or chemical binding. Such immobilization was found to maintain some activity of the biomolecule, with applications in the biosensor field. Recently, some developments have been reported in the immobilization of redox proteins in mesoporous transparent electrodes for... 

Chitosan films can also be readily functionalized with proteins, enzymes, antibodies, and DNA, for selective coatings for biosensors. Different methods have been demonstrated for chitosan modification physical interaction (eg, surface absorption, entrapment), chemical bonding, or covalent crosslink with each other (Koev et al., 2010). 

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