Evidences For Charge Transfer-Induced Conformational Changes In Carbon Nanostructure-Protein Corona.

The binding of proteins to a nanostructure often alters protein secondary and tertiary structures. However, the main physical mechanisms that elicit protein conformational changes in the presence of the nanostructure have not yet been fully established. Here we performed a comprehensive spectroscopic study to probe the interactions between bovine serum albumin (BSA) and carbon-based nanostructures of graphene and single-walled carbon nanotubes (SWNTs). Our results showed that the BSA "corona" acted as a weak acceptor to facilitate charge transfer from the carbon nanostructures. Notably, we observed that charge transfer occurred only in the case of SWNTs but not in graphene, resulting from the sharp and discrete electronic density of states of the former. Furthermore, the relaxation of external α-helices in BSA secondary structure increased concomitantly with the charge transfer. These results may help guide controlled nanostructure-biomolecular interactions and prove beneficial for developing novel drug delivery systems, biomedical devices and engineering of safe nanomaterials.

Effects of surface functional groups on the formation of nanoparticle-protein corona.

Herein, we examined the dependence of protein adsorption on the nanoparticle surface in the presence of functional groups. Our UV-visible spectrophotometry, transmission electron microscopy, infrared spectroscopy, and dynamic light scattering measurements evidently suggested that the functional groups play an important role in the formation of nanoparticle-protein corona. We found that uncoated and surfactant-free silver nanoparticles derived from a laser ablation process promoted a maximum protein (bovine serum albumin) coating due to increased changes in entropy. On the other hand, bovine serum albumin displayed a relatively lower affinity for electrostatically stabilized nanoparticles due to the constrained entropy changes.

Image enhancement in near-field scanning optical microscopy with laser-trapped metallic particles.

A trapped-particle near-field scanning optical microscope is constructed by use of submicrometer- or micrometer-sized metallic particles (gold and silver) to increase scattering efficiency. The image contrast of the evanescent-wave interference pattern on the surface of a prism upon total internal reflection, obtained with trapped gold particles of diameter 0.1 and 2microm , is improved by a factor of approximately 2 and 1.5, respectively, compared with that obtained with trapped polystyrene particles of similar size. The use of a 2-microm gold particle leads to image contrast that is approximately three times as great as that obtained with a 0.1-microm gold particle, and interference patterns of a subwavelength period are obtained in both cases.

Characterization of trapping force on metallic mie particles.

Transverse trapping force on three types of metallic Mie particles (gold, nickel, and silver) is measured for different values of the numerical aperture of an objective used for trapping. The experimental results are compared with those calculated with a modified ray-optics model. It is found that, unlike the situation for a trapped dielectric particle, the maximum transverse trapping efficiency for a trapped metallic particle is increased with the numerical aperture of the trapping objective. After consideration of radiometric force, which is caused by the heating effect, and spherical aberration, which is induced by the refractive-index mismatch, the measured results agree well with the theoretical prediction. The magnitude of the radiometric force is approximately ten times stronger than the maximum transverse trapping force.