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We analyze surface texturing induced by femtosecond laser irradiation of a silicon target at high repetition rates. The features of the produced surface structures in ablative conditions, i.e. at fluences larger than the ablation threshold, are investigated as a function of number of pulses and pulse energy, for various repetition rates, in the range 10 Hz–200 kHz. Our experimental findings highlight a significant influence of the pulse repetition rate on both surface texture and crater size produced by irradiation with a fixed sequence of N laser pulses. This effect is ascribed to plume shielding occurring at repetition rates larger than ≈10 kHz.

A novel technique was demonstrated that overcome important drawbacks to crosslink cells by irradiation with ultrashort UV laser pulses (L-crosslinking). To use this technique coupled to Chromatin ImmunoPrecipitation (ChIP) in a high throughput context, a pre-screening fast method needs to be implemented to set up suitable irradiation conditions of the cell sample for efficient L-crosslinking with no final and long ChIP analysis. Here a fast method is reported where living human cells have been first transfected with a vector coding for Estrogen Receptor {\alpha} (ER{\alpha}), linked to Green Florescent protein (ER{\alpha}-GFP), so that the well-known interaction between the Estrogen Receptor Elements (ERE) region of the cell DNA and the ER{\alpha} protein can be detected by studying the fluorometric response of the irradiated cells. The damage induced to cells by UV irradiation is characterized by looking at DNA integrity, proteins stability and cellular viability. A second novel approach is presented to analyze or re-visit DNA and RNA sequences and their molecular configurations. This approach is based on methods derived from Chern-Simons super-gravity adapted to describe mutations in DNA/RNA strings, as well as interactions between nucleic acids. As a preliminary case we analyze the KRAS human gene sequence and some of its mutations. Interestingly, our model shows how the Chern-Simons current are capable to characterize the mutations within a sequence, in particular giving a quantitative indication of the mutation likelihood., Comment: 33 pages, 5 figures

Interactions of novel bi-dimensional nanomaterials and live matter such as bacteria and viruses represent an extremely hot topic due to the unique properties of the innovative nanomaterials, capable in some cases to exhibit bactericide and antiviral actions. The interactions between bacteria and viruses and two dimensional nanosheets are here investigated. We extensively studied the interaction between a gram-negative bacterium, Escherichia coli, and a gram-positive bacterium, Staphylococcus aureus, with two different types of 2D nanoflakes such as MoS2, belonging to the Transition Metal Dichalcogenides family, and Graphene Oxide. The same two types of nanomaterials were employed to study their antiviral action toward the Herpes simplex virus type-1, (HSV-1). The experimental results showed different bactericide impacts as well as different antiviral power between the two nanomaterials. The experimental findings were interpreted in bacteria on the base of the Derjaguin–Landau–Verwey–Overbeek theory. A simple kinetic model of bacterial growth in the presence of the interacting nanosheets is also elaborated, to explain the observed results. The experimental results in viruses are really novel and somewhat surprising, evidencing a stronger antiviral action of Graphene Oxide as compared to MoS2. Results in viruses are complicated to quantitatively interpret due to the complexity of the system under study, constituted by virus/host cell and nanoflake, and due to the lack of a well assessed theoretical context to refer to. Thus, these results are interpreted in terms of qualitative arguments based on the chemical properties of the interactors in the given solvent medium.

The influence of the pulse repetition rate on laser irradiation of silicon, in air, with femtosecond laser pulses is experimentally investigated in the range 10 Hz – 200 kHz. The features of the produced crater and the laser-induced periodic surface structures generated on its surface are characterized by exploiting surface profilometry and scanning electron microscopy. The experimental characterization evidences an interesting influence of the pulse repetition rate on the crater size qualitatively addressing a progressive reduction of the material removal efficiency at higher repetition rates. Moreover, also the surface structures produced by an irradiation sequence with a fixed number of laser pulses (namely N = 100) shows a clear dependence on the repetition rate. The observed effects are rationalized by considering the possible influence of plume shielding and heat accumulation effects typically observed during laser processing with high repetition rate laser systems.

We present a detailed study of the excited state properties of 5-benzyluracil (5BU) in the gas phase and in implicit solvent using different electronic structure approaches ranging from time-dependent density functional theory in the linear response regime (LR-TDDFT) to a set of different wave-function-based methods for excited states, namely perturbed coupled cluster (CC2), algebraic diagrammatic construction method to second order (ADC(2)), and perturbed configuration interaction (CIS(D)). 5BU has been used to investigate DNA base-amino acid interactions. In particular, it served as a model of protein-DNA photoinduced cross-linking. While LR-TDDFT is computationally the most efficient first-principles approach for static and dynamic simulations of this bichromophoric system, its accuracy is difficult to assess due to the presence of excited states with charge transfer character. In this work, the performance of different exchange correlation functionals is compared against accurate benchmarks obtained either from high level wave-function-based methods or directly from experimental absorption spectra. Our investigation shows that accurate results for the excitation energies can be obtained using the hybrid meta-GGA functional M06. In view of dynamical studies of the relaxation of 5BU after photoexcitation, we also show that the PBE functional, while failing in the Franck-Condon region, provides qualitatively good results for the characterisation of a possible photocyclization path.