Our calculations show that a nonchiral nanocrystal is able to dramatically change the circular dichroism (CD) of a chiral molecule when the nanocrystal and molecule form a complex and couple via dipole and multipole Coulomb interactions. Plasmon resonances of metal nanocrystals in the nanocrystal-molecule complex result in both the resonant enhancement of CD signals of molecules and the appearance of new spectral structures. Two mechanisms, in which a nanocrystal can influence the CD effect, have been identified. The first mechanism is the plasmon-induced change in the electromagnetic field inside the chiral molecule. The second is the optical absorption of the nanocrystal-molecule complex due to the chiral currents inside the metal nanocrystal induced by the dipole of the chiral molecule. The first mechanism creates a change in the angle between the effective electric and magnetic dipoles of the molecule. This mechanism can lead to symmetry breaking and to a plasmon-induced CD signal of the nonchiral molecule. Both mechanisms create interesting Fano-like shapes in the CD spectra. Importantly, the second mechanism gives the main contribution to the CD signal at the plasmon frequency when the absorption band of the chiral molecule is far from the plasmon resonance. This may happen in many cases since many biomolecules are optically active in the UV range, whereas plasmon resonances in commonly used nanometals are found at longer wavelengths. As concrete examples, the paper describes alpha-helix and calixarene ligand molecules coupled with metal nanocrystals. The above results are also applied to complexes incorporating semiconductor nanocrystals. The results obtained here can be used to design a variety of hybrid nanostructures with enhanced and tailored optical chirality in the visible wavelength range.

We perform a set of experiments on photo-heating in a water droplet containing gold nanoparticles (NPs). Using photo-calorimetric methods, we determine efficiency of light-to-heat conversion (η) which turns out to be remarkable close to 1, (0.97< η <1.03). Detailed studies reveal a complex character of heat transfer in an optically-stimulated droplet. The main mechanism of equilibration is due to convectional flow. Theoretical modeling is performed to describe thermal effects at both nano- and millimeter-scales. Theory shows that the collective photo-heating is the main mechanism. For a large concentration of NPs and small laser intensity, an averaged temperature increase (at the millimeter-scale) is significant (~ 7 °C) whereas, on the nanometer scale, the temperature increase at the surface of a single NP is small (0.02 °C). In the opposite regime, a small NP concentration and intense laser irradiation, we find an opposite pictures: a temperature increase at the millimeter-scale is small (0.1 °C) but a local, nanoscale temperature has strong local spikes at the surfaces of NPs (3 °C). These studies are crucial for the understanding of photo-thermal effects in NPs and for their potential and current applications in nano-and bio -technologies.

Electronic interactions at the nanoscale represent one of the fundamental problems of nanotechnology. Excitons and plasmons are the two most typical excited states of nanostructures, which have been shown to produce coupled electronic systems. Here, we explore these interactions for the case of nanowires with mobile excitons and nanoparticles with localized plasmons and describe the theoretical formalism, its experimental validation and the potential practical applications of such nanoscale systems. Theory predicts that emission of coupled excitations in nanowires with variable electronic confinement is stronger, shorter and blue-shifted. These predictions were confirmed with a high degree of accuracy in molecular spring assemblies of CdTe nanowires and Au nanoparticles, where we can reversibly change the distance between the exciton and the plasmon. The prepared systems were made protein-sensitive by incorporating antibodies in the molecular springs. Modulation of exciton-plasmon interactions can serve as a wavelength-based biodetection tool, which can resolve difficulties in the quantification of luminescence intensity for complex media and optical pathways.

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