Gold nanoparticle plasmonic field effect on the primary step of the other photosynthetic system in nature, bacteriorhodopsin

Nanohybrid Structures Based on Plasmonic or Fluorescent Nanoparticles and Retinal-Containing Proteins

Rhodopsins are light-sensitive membrane proteins enabling transmembrane charge separation (proton pump) on absorption of a light quantum. Bacteriorhodopsin (BR) is a transmembrane protein from halophilic bacteria that belongs to the rhodopsin family. Potential applications of BR are considered so promising that the number of studies devoted to the use of BR itself, its mutant variants, as well as hybrid materials containing BR in various areas grows steadily. Formation of hybrid structures combining BR with nanoparticles is an essential step in promotion of BR-based devices. However, rapid progress, continuous emergence of new data, as well as challenges of analyzing the entire data require regular reviews of the achievements in this area. This review is devoted to the issues of formation of materials based on hybrids of BR with fluorescent semiconductor nanocrystals (quantum dots) and with noble metal (silver, gold) plasmonic nanoparticles. Recent data on formation of thin (mono-) and thick (multi-) layers from materials containing BR and BR/nanoparticle hybrids are presented.

Thin films and assemblies of photosensitive membrane proteins and colloidal nanocrystals for engineering of hybrid materials with advanced properties

The development and study of nano-bio hybrid materials engineered from membrane proteins (the key functional elements of various biomembranes) and nanoheterostructures (inorganic colloidal nanoparticles, transparent electrodes, and films) is a rapidly growing field at the interface of materials and life sciences. The mainspring of the development of bioinspired materials and devices is the fact that biological evolution has solved many problems similar to those that humans are attempting to solve in the field of light-harvesting and energy-transferring inorganic compounds. Along this way, bioelectronics and biophotonics have shown considerable promise. A number of proteins have been explored in terms of bioelectronic device applications, but bacteriorhodopsin (bR, a photosensitive membrane protein from purple membranes of the bacterium Halobacterium salinarum) and bacterial photosynthetic reaction centres have received the most attention. The energy harvesting in plants has a maximum efficiency of 5%, whereas bR, in the absence of a specific light-harvesting system, allows bacteria to utilize only 0.1-0.5% of the solar light. Recent nano-bioengineering approaches employing colloidal semiconductor and metal nanoparticles conjugated with biosystems permit the enhancement of the light-harvesting capacity of photosensitive proteins, thus providing a strong impetus to protein-based device optimisation. Fabrication of ultrathin and highly oriented films from biological membranes and photosensitive proteins is the key task for prospective bioelectronic and biophotonic applications. In this review, the main advances in techniques of preparation of such films are analyzed. Comparison of the techniques for obtaining thin films leads to the conclusion that the homogeneity and orientation of biomembrane fragments or proteins in these films depend on the method of their fabrication and increase in the following order: electrophoretic sedimentation < Langmuir-Blodgett and Langmuir-Schaefer methods < self-assembly and layer-by-layer methods. The key advances in the techniques of preparation of the assemblies or complexes of colloidal nanocrystals with bR, purple membranes, or photosynthetic reaction centres are also reviewed. Approaches to the fabrication of the prototype photosensitive nano-bio hybrid materials with advanced photovoltaic, energy transfer, and optical switching properties and future prospects in this field are analyzed in the concluding part of the review.

Protein-based ultrafast photonic switching

Several inorganic and organic materials have been suggested for utilization as nonlinear optical material performing light-controlled active functions in integrated optical circuits, however, none of them is considered to be the optimal solution. Here we present the first demonstration of a subpicosecond photonic switch by an alternative approach, where the active role is performed by a material of biological origin: the chromoprotein bacteriorhodopsin, via its ultrafast BR->K and BR->I transitions. The results may serve as a basis for the future realization of protein-based integrated optical devices that can eventually lead to a conceptual revolution in the development of telecommunications technologies.

Gold nanorods: from synthesis and properties to biological and biomedical applications

Noble metal nanoparticles are capable of confining resonant photons in such a manner as to induce coherent surface plasmon oscillation of their conduction band electrons, a phenomenon leading to two important properties. Firstly, the confinement of the photon to the nanoparticle's dimensions leads to a large increase in its electromagnetic field and consequently great enhancement of all the nanoparticle's radiative properties, such as absorption and scattering. Moreover, by confining the photon's wavelength to the nanoparticle's small dimensions, there exists enhanced imaging resolving powers, which extend well below the diffraction limit, a property of considerable importance in potential device applications. Secondly, the strongly absorbed light by the nanoparticles is followed by a rapid dephasing of the coherent electron motion in tandem with an equally rapid energy transfer to the lattice, a process integral to the technologically relevant photothermal properties of plasmonic nanoparticles. Of all the possible nanoparticle shapes, gold nanorods are especially intriguing as they offer strong plasmonic fields while exhibiting excellent tunability and biocompatibility. We begin this review of gold nanorods by summarizing their radiative and nonradiative properties. Their various synthetic methods are then outlined with an emphasis on the seed-mediated chemical growth. In particular, we describe nanorod spontaneous self-assembly, chemically driven assembly, and polymer-based alignment. The final section details current studies aimed at applications in the biological and biomedical fields.

The dependence of the plasmon field induced nonradiative electronic relaxation mechanisms on the gold shell thickness in vertically aligned CdTe-Au core-shell nanorods

The dependence of the plasmon field enhancement of the nonradiative relaxation rate of the band gap electrons in vertically aligned CdTe-Au core-shell nanorods on the plasmonic gold nanoshell thickness is examined. Increasing the thickness of the gold nanoshell from 15 to 26 nm is found to change the decay curve from being nonexponential and anisotropic to one that is fully exponential and isotropic (i.e., independent of the nanorod orientation with respect to the exciting light polarization direction). Analysis of the kinetics of the possible electronic relaxation enhancement mechanisms is carried out, and DDA simulated properties of the induced plasmonic field of the thin and thick gold nanoshells are determined. On the basis of the conclusions of these treatments and the experimental results, it is concluded that by increasing the nanoshell thickness the relaxation processes evolve from multiple enhancement mechanisms, dominated by highly anisotropic Auger processes, to mechanism(s) involving first-order excited electron ejection process(es). The former is shown to give rise to nonexponential anisotropic decays in the dipolar plasmon field of the thin nanoshell, while the latter exhibits an exponential isotropic decay in the unpolarized plasmonic field of the thick nanoshell.

Gold nanoparticles surface plasmon field effects on the proton pump process of the bacteriorhodopsin photosynthesis

The rate of the proton pump of bacteriorhodopsin photosynthetic system is examined in the presence of a gold nanorod plasmon field. It is found that while the rate of the proton dissociation from the protonated Schiff base is not affected, the rate of its reprotonation increases. These results are qualitatively discussed in terms of several possible mechanisms.

Exciton lifetime tuning by changing the plasmon field orientation with respect to the exciton transition moment direction: CdTe-Au core-shell nanorods

We studied the anisotropy of the influence of plasmonic fields, arising from the optical excitation of a gold nanoshell plasmon absorption at 770 nm, on the lifetime of the bandgap state of the CdTe core in vertically aligned CdTe-Au core-shell nanorods. The previously observed decrease in the lifetime was studied as a function of the tilt angle between the long axis of the nanorod and the electric field polarization direction of the plasmon inducing exciting light. It is observed that the strongest enhancement to the exciton relaxation rate occurs when the two axes are parallel to one another. These results are discussed in terms of the coupling between the exciton transition moment of the CdTe rod and the electric field polarization direction of the gold nanoshell plasmon at 770 nm, which was determined from theoretical modeling based on the discrete dipole approximation.

Metallic Nanostructures as Localized Plasmon Resonance Enhanced Scattering Probes for Multiplex Dark Field Targeted Imaging of Cancer Cells

In this paper, we report the use of bioconjugated gold nanorods and silver nanoparticles as targeted localized surface plasmon resonance enhanced scattering probes for dark field multiplex and transmission electron microscopy (TEM) imaging of pancreatic cancer cells. We take advantage of the spectrally widely separated localized plasmon resonance of the gold nanorods and silver nanoparticles which produce wavelength selective plasmon resonance scattering to allow multiplex imaging with high contrast. By functionalizing the surfaces, aqueous dispersions of bioconjugated gold nanorods and silver nanoparticles are prepared. We demonstrate receptor-mediated delivery of bioconjugated gold nanorods and silver nanoparticles simultaneously into pancreatic cancer cells, using multiplexed dark field microscopy technique. We also show that the bioconjugated metallic nanostructures can be used for high contrast TEM imaging as well.

Plasmon field effects on the nonradiative relaxation of hot electrons in an electronically quantized system: CdTe-Au core-shell nanowires

The intense electromagnetic fields of plasmonic nanoparticles, resulting from the excitation of their localized surface plasmon oscillations, are known to enhance radiative processes. Their effect on the nonradiative electronic processes, however, is not as well-documented. Here, we report on the enhancement of the nonradiative electronic relaxation rates in CdTe nanowires upon the addition of a thin gold nanoshell, especially at excitation energies overlapping with those of the surface plasmon oscillations. Some possible mechanisms by which localized surface plasmon fields can enhance nonradiative relaxation processes of any quantized electronic excitations are proposed.