Adsorbed biomolecules

In surface sensing, the adsorbed biomolecules onto the inner wall of a microtube will change the wave vector of a supported mode from A 0 to k and the electric field from E0 to ). These unperturbed (L0) and perturbed (E ) electric fields still satisfied wave equation ... 

Thus the value of the dielectric constant at the sample/metal interface determines the shift of the resonance. When adsorption of molecules at the metal surface results in the change of the refractive index or of the local value of the dielectric constant, the change of reflectivity is observed. This phenomenon has been used as the mechanism for detection of gases (Fig. 9.18a) and of adsorbed biomolecules (Fig. 9.18b). The depth of penetration of the surface plasmon is comparable to that of the evanescent field, that is, 100-500 nm for the visible-near infrared range. 

The interaction of nanoparticles with the proteins is governed from the same type of interactions described for carbon nanotubes. Since NPs carry charges, they can electrostatically adsorb biomolecules with different charges, which depend on the pH that the immobilization takes place and the pi of the protein [3,191]. Moreover, hydrophobic interactions, hydrogen bonds and non-specific absorption can play a role for enzyme non-covalent adsorption onto the surface of nanoparticles. 

Fig. 7 Coupled water mass per adsorbed biomolecule mass, (p, versus time for streptavidin...

Another advantage of the SERS spectroscopy is to obtain vibrational spectroscopic informations in electrolyte solution under conditions close to the real biological situation. The continuous development of laser sources with new excitation wavelength lines renders it possible to expand the study of adsorbed biomolecules on different metal surfaces which can also be chemically or electrically modified to adjust specific adsorption properties. Such a crucial event in medical applications as the behaviour of implants in contact with blood can be thus envisaged by the study of the adsorption of blood proteins and its physiological consequences. The possibility to monitor the interfacial electric field of the electrode surface can also be used to... 

BiomateriaiS. Biomaterials find important application as medical implants and tissue engineering substrates. In each case, clinical or scientific effectiveness strongly depends on the behavior of interfacial biomolecules. Other articles in this encyclopedia discuss various aspects of biomaterials. In this section, important aspects dealing with adsorbed biomolecules are briefly presented. 

Owing to the difficulties inherent to in vivo studies, the surface modifications of materials placed in biological environments are often examined in vitro. Besides the adsorption of biomacromolecules, which inevitably occms when materials are placed in contact with biological solutions, some authors have examined the effect of such solutions and of cells on the surface chemistry of the material itself. This approach is made rather difficult owing to the necessity to separate the effect of adsorbed biomolecules from that of the substrate alteration. The protocols used... 

In the studies presented in this section so far, the concern was the integrity of the material after implantation, and efforts were made to avoid the interference of adsorbed biomolecules in the XPS data. 

With the extremely high enhancement of the Raman scattering signals in the immediate vicinity of the charged metal-surface (electrode, Ag colloidal particles, activated nano-TLC plates) it is possible to identify the adsorbed parts of the methylated guanine derivatives and to study their configuration at very low concentrations. These results demonstrate new possibilities of Raman-spectroscopy to obtain high resolution vibrational spectra of adsorbed biomolecules. 

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