The Effect of Femtosecond Laser Irradiation and Plasmon Field on the Degree of Conversion of a UDMA-TEGDMA Copolymer Nanocomposite Doped with Gold Nanorods.

In this work, the effects of femtosecond laser irradiation and doping with plasmonic gold nanorods on the degree of conversion (DC) of a urethane dimethacrylate (UDMA)-triethylene glycol dimethacrylate (TEGDMA) nanocomposite were investigated. The UDMA-TEGDMA photopolymer was prepared in a 3:1 weight ratio and doped with dodecanethiol- (DDT) capped gold nanorods of 25 × 75 or 25 × 85 nm nominal diameter and length. It was found that the presence of the gold nanorods alone (without direct plasmonic excitation) can increase the DC of the photopolymer by 6-15%. This increase was found to be similar to what could be achieved with a control heat treatment of 30 min at 180 °C. It was also shown that femtosecond laser impulses (795 nm, 5 mJ pulse energy, 50 fs pulse length, 2.83 Jcm-2 fluence), applied after the photopolymerization under a standard dental curing lamp, can cause a 2-7% increase in the DC of undoped samples, even after thermal pre-treatment. The best DC values (12-15% increase) were obtained with combined nanorod doping and subsequent laser irradiation close to the plasmon resonance peak of the nanorods (760-800 nm), which proves that the excited plasmon field can directly facilitate double bond breakage (without thermoplasmonic effects due to the short pulse length) and increase the crosslink density independently from the initial photopolymerization process.

Crater formation and deuterium production in laser irradiation of polymers with implanted nano-antennas.

Recent validation experiments on laser irradiation of polymer foils with and without implanted golden nanoparticles are discussed. First we analyze characteristics of craters, formed in the target after its interaction with the laser beam. Preliminary experimental results show significant production of deuterons when both the energy of laser pulse and concentration of nanoparticles are high enough. We consider the deuteron production via the nuclear transmutation reactions p+C→d+X where protons are accelerated by the Coulomb field generated in the target plasma. We argue that maximal proton energy can be above threshold values for these reactions and the deuteron yield may noticeably increase due to presence of nanoparticles.

Binding of alkaloids into the S1 specificity pocket of α-chymotrypsin: evidence from induced circular dichroism spectra.

Non-covalent binding of planar aromatic molecules into the S1 specificity pocket of the serine protease α-chymotrypsin (αCHT) can be detected by measuring induced circular dichroism (CD) spectroscopic signals. Utilizing this phenomenon, αCHT association of proflavine (PRF), the well known serine protease inhibitor has been investigated together with plant-derived compounds including isoquinoline, pyridocarbazole and indoloquinoline alkaloids, of which αCHT binding has never been reported. Non-degenerate exciton coupling between π-π* transitions of the ligand molecules and two tryptophan residues (Trp172 and Trp215) near to the binding site is proposed to be responsible for the induced CD activity. The association constants calculated from CD titration data indicated strong αCHT association of sanguninarine, ellipticine, desmethyl-isocryptolepine and isoneocryptolepine (K(a) ≈ 10(5) M(-1)) while berberine, coptisine and chelerythrine bind to the enzyme with lower, PRF-like affinity (K(a) ≈ 10(4) M(-1)). PRF-trypsin and ellipticine-trypsin binding interactions have also been demonstrated. The binding of the alkaloids into the S1 pocket of αCHT has been confirmed by CD competition experiments. Molecular docking calculations showed the inclusion of PRF as well as the alkaloid molecules in the S1 cavity where they are stabilized by hydrophobic and H-bonding interactions. These novel nonpeptidic scaffolds can be used for developing selective inhibitors of serine proteases having chymotrypsin-like folds. Furthermore, the results provide a novel, CD spectroscopic based approach for probing the ligand binding of αCHT and related proteases.

Towards more reliable AFM force-curve evaluation: A method for spring constant selection, adaptive lever sensitivity calibration and fitting boundary identification.

This work discusses key issues regarding the atomic force microscopy (AFM) force-curve evaluation practice, which can affect the determined Young's modulus of the investigated sample. These issues are 1) the proper calibration of lever sensitivity and the effect of its variation between the measurements; 2) the selection of proper cantilever spring constant for the investigated sample; and 3) the selection of the fitting boundaries for the contact mechanics model-based force-curve evaluation. A method is proposed, which solves the above mentioned issues, namely, categorizes the obtained force-curves based on the relation between the elastic properties of the sample and the spring constant of the cantilever, and thus helps in the selection of the proper spring constant for the given surface; helps in the identification of the optimal model-fitting boundaries, and also, provides a way of adaptive lever sensitivity calibration. The method is demonstrated on PDMS (polydimethylsiloxane) samples, which were irradiated with various fluences of ion beams to control their elastic properties in the 4 MPa - 22 GPa range. Our proposed method, if applied correctly can significantly increase the reliability of AFM force-curve evaluation.

Spring constant and sensitivity calibration of FluidFM micropipette cantilevers for force spectroscopy measurements.

The fluidic force microscope (FluidFM) can be considered as the nanofluidic extension of the atomic force microscope (AFM). This novel instrument facilitates the experimental procedure and data acquisition of force spectroscopy (FS) and is also used for the determination of single-cell adhesion forces (SCFS) and elasticity. FluidFM uses special probes with an integrated nanochannel inside the cantilevers supported by parallel rows of pillars. However, little is known about how the properties of these hollow cantilevers affect the most important parameters which directly scale the obtained spectroscopic data: the inverse optical lever sensitivity (InvOLS) and the spring constant (k). The precise determination of these parameters during calibration is essential in order to gain reliable, comparable and consistent results with SCFS. Demonstrated by our literature survey, the standard error of previously published SCFS results obtained with FluidFM ranges from 11.8% to 50%. The question arises whether this can be accounted for biological diversity or may be the consequence of improper calibration. Thus the aim of our work was to investigate the calibration accuracy of these parameters and their dependence on: (1) the aperture size (2, 4 and 8 µm) of the hollow micropipette type cantilever; (2) the position of the laser spot on the back of the cantilever; (3) the substrate used for calibration (silicon or polystyrene). It was found that both the obtained InvOLS and spring constant values depend significantly on the position of the laser spot. Apart from the theoretically expectable monotonous increase in InvOLS (from the tip to the base of the cantilever, as functions of the laser spot's position), we discerned a well-defined and reproducible fluctuation, which can be as high as ±30%, regardless of the used aperture size or substrate. The calibration of spring constant also showed an error in the range of -13/+20%, measured at the first 40 µm of the cantilever. Based on our results a calibration strategy is proposed and the optimal laser position which yields the most reliable spring constant values was determined and found to be on the first pair of pillars. Our proposed method helps in reducing the error introduced via improper calibration and thus increases the reliability of subsequent cell adhesion force or elasticity measurements with FluidFM.

Publisher Correction: Spring constant and sensitivity calibration of FluidFM micropipette cantilevers for force spectroscopy measurements.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.