Joanna Olesiak-Banska

DNA as scaffolding for nanophotonic structures

Deoxyribonucleic acid (DNA) chains can be engineered for diverse nanophotonics applications by the insertion of molecular groups in different spatial configurations. DNA chains can be assembled into wire-like structures, origami structures, photonic crystal-like assemblies, liquid-crystal phases, and thin films. These structures can be made to serve as scaffolds for the organization of various organic molecules and nanoparticles. The properties of nanostructures can be modified by the use of DNA and DNA modified by the surfactants.

Revealing spectral features in two-photon absorption spectrum of Hoechst 33342: a combined experimental and quantum-chemical study.

We present the results of wide spectral range Z-scan measurements of the two-photon absorption (2PA) spectrum of the Hoechst 33342 dye. The strongest 2PA of the dye in aqueous solution is found at 575 nm, and the associated two-photon absorption cross section is 245 GM. A weak but clearly visible 2PA band at ∼850 nm is also observed, a feature that could not be anticipated from the one-photon absorption spectrum. On the basis of the results of hybrid quantum mechanics/molecular mechanics calculations, we put forward a notion that the long-wavelength feature observed in the two-photon absorption spectrum of Hoechst 33342 is due to the formation of dye aggregates.

Remarkable effect of iridium cyclometalation on the nonlinear absorption properties of a quadrupolar imine ligand.

A new type of dinuclear iridium complex, based on a quadrupolar Schiff base ligand, is synthesized and its structure fully characterized. Its linear and nonlinear spectroscopic properties are investigated, evidencing a strong contribution of the metal-to-ligand transitions not only to the linear absorption but also to the two- and three-photon absorption properties.

Liquid crystal phases of DNA: Evaluation of DNA organization by two-photon fluorescence microscopy and polarization analysis†

We report on the investigation of the structure of DNA liquid crystal (LC) phases by means of polarization sensitive two-photon microscopy (PSTPM). DNA was stained with fluorescent dyes, an intercalator propidium iodide, or a groove binder Hoechst 3342, and the angular dependence of the intensity of two-photon excited fluorescence emitted by the dye was collected. The local orientation of DNA molecules in cholesteric and columnar LC phases was established on the basis of the relative angle between the transition dipole of the dye and the long axis of DNA helix. Three-dimensional images of the cholesteric phase were obtained making use of the intrinsic 3D resolving ability of two-photon microscopy. We also discuss the influence of dyes on the parameters of DNA LC phases and comment on advantages and limitations of the PSTPM technique in comparison with other LC characterization techniques.

Photochromic switching of the DNA helicity induced by azobenzene derivatives

The photochromic properties of azobenzene, involving conformational changes occurring upon interaction with light, provide an excellent tool to establish new ways of selective regulation applied to biosystems. We report here on the binding of two water-soluble 4-(phenylazo)benzoic acid derivatives (Azo-2N and Azo-3N) with double stranded DNA and demonstrate that the photoisomerization of Azo-3N leads to changes in DNA structure. In particular, we show that stabilization and destabilization of the B-DNA secondary structure can be photochemically induced in situ by light. This photo-triggered process is fully reversible and could be an alternative pathway to control a broad range of biological processes. Moreover, we found that the bicationic Azo-3N exhibited a higher DNA-binding constant than the monocationic Azo-2N pointing out that the number of positive charges along the photosensitive polyamines chain plays a pivotal role in stabilizing the photochrome-DNA complex.

Interactions of Isophorone Derivatives with DNA: Spectroscopic Studies

Interactions of three new isophorone derivatives, Isoa Isob and Isoc with salmon testes DNA have been investigated using UV-Vis, fluorescence and circular dichroism spectroscopic methods. All the studied compounds interact with DNA through intercalative binding mode. The stoichiometry of the isophorone/DNA adducts was found to be 1:1. The fluorescence quenching data revealed a binding interaction with the base pairs of DNA. The CD data indicate that all the investigated isophorones induce DNA modifications.

Shell-thickness-dependent nonlinear optical properties of colloidal gold nanoshells

Third-order nonlinear optical properties of gold nanoshells of different thickness were investigated over a broad wavelength range (530–1200 nm) by the Z-scan technique using femtosecond laser pulses. Nonlinear absorption of the nanoshells is dominated by strong absorption saturation phenomena. The reciprocals of the relevant saturation intensities are the highest at the maxima of one-photon absorption (1 PA) bands for all the studied nanoshells but the scaling with the one-photon extinction coefficients within the relevant absorption bands is rather approximate. The reciprocals of the saturation intensities scaled by the values of the extinction coefficients are also found to decrease with the increase of the shell thickness. This can be attributed mostly to the increase of the contribution of the scattering of NIR light to the total extinction of the solutions. The two-photon absorption (2 PA) behavior is found to be dominant only within the shortest wavelength range studied for the gold nanoshells with the thinnest shells which exhibit high 2 PA cross-section values, with σ2 reaching 5.1 × 1010 GM.

A closer look at two-photon absorption, absorption saturation and nonlinear refraction in gold nanoclusters

The optical properties of atomically-precise gold nanoclusters differ significantly from those of plasmonic gold nanoparticles, in both linear and nonlinear regimes. Here, we present a systematic study on the third-order nonlinear optical (NLO) properties of thiol-protected gold clusters in a wide range of wavelengths. We applied the Z-scan technique to evaluate the wavelength dispersion of two-photon absorption (2PA) and nonlinear refraction of the nanoclusters in water. The results are discussed with reference to 2PA of plasmonic gold nanoparticles and literature data on NLO properties of gold nanoclusters.

One- and Two-Photon Absorption of a Spiropyran–Merocyanine System: Experimental and Theoretical Studies

We report on the nonlinear optical properties measurements and quantum-chemical calculations of a well-known photochromic system consisting of spiropyran and the merocyanine photoproduct. The study of nonlinear absorption and refraction properties of the molecules dissolved in chloroform were performed with the Z-scan technique, using femtosecond pulses in a wide range of wavelengths. Maxima in the two-photon absorption spectrum at 700 and 1050 nm were found for the merocyanine form, and the corresponding two-photon absorption cross section is 80 GM and 20 GM, respectively. The latter feature does not vanish completely in the nonlinear spectrum of the spiropyran form, possibly because of the existence of some photoconversion caused by the laser beam during the measurements. A nonlinear absorption peak at 900 nm is found in the spiropyran form with an effective cross section of about 20 GM; it is likely due to three-photon absorption or to absorption by some intermediate species. The experimental data are supported by calculations performed with the use of a hybrid quantum mechanics-molecular mechanics approach.

A 5-(difluorenyl)-1,10-phenanthroline-based Ru(II) complex as a coating agent for potential multifunctional gold nanoparticles

The synthesis and photophysical properties of small gold nanoparticles (NPs, AuNP-[Ru-PFF]) surface functionalized by 5-substituted-1,10-phenanthroline-ligand based Ru(II) complexes are described. Luminescence of the grafted and confined Ru(II) complexes is totally quenched on the gold surface. Nonlinear optical properties were determined via Z-scan measurements in the range 600-1300 nm for both the free Ru(II) complex and the related NPs. In the short wavelength range (around 600 nm) the behaviour switches from that of two-photon absorption (2PA) for the complex to saturable absorption for the NPs. 2PA applications such as optical power limiting or two-photon dioxygen sensitization can be anticipated for these nanoplatforms.