Modulating Electronic Properties of Dinitrosoarene Polymers

We present a comprehensive analysis on how the electronic structure and the optical properties of an organic polymer can be modulated, based on the example of the dinitrosobenzene polymer (1). Using a combination of computational and experimental tools, we explore the effects of solid-state packing, backbone torsion, surface adsorption, the conjugation in the aromatic core, and substituents. The band gap (Eg) and optical spectrum of 1 are calculated using both GW-BSE with zero-gap renormalization (ZGR) and hybrid TD-DFT, with the former method predicting a value (2.41 eV) in excellent agreement with our diffuse reflectance spectroscopy measurements (2.39 eV). Using GW-BSE-ZGR, changes occurring upon solidstate packing are separated into a contribution arising from (i) the change in the torsional angle and (ii) the change in the screened Coulombic interaction, which strongly effects the exciton binding energies. Comprehensive hybrid TD-DFT calculations find that the effects of substituents on Eg and on transport properties can mostly be explained through changes in the torsional angle, and predict a linear dependence between it and Eg. Extending the conjugation in the aromatic core is found to enhance transport properties and narrow Eg, identifying future synthetic targets. Atomic force microscopy and spectroscopic ellipsometry are used to study 1 adsorbed to a (111) gold surface (1@Au), with the latter method showing a significant narrowing of the band gap to 0.68 eV, in good agreement with TD-DFT predictions.

New Insights on Plasmin Long Term Stability and the Mechanism of Its Activity Inhibition Analyzed by Quartz Crystal Microbalance

We used the research quartz crystal microbalance (RQCM) to monitor regulatory effects of plasmin and trypsin in the presence of their inhibitor α2-antiplasmin. The gold surface of quartz crystals was modified with a β-casein layer that served as a substrate for protease digestion. The addition of plasmin or trypsin as well as their mixtures with α2-antiplasmin resulted in an increase of resonant frequency, f, and in a decrease of motional resistance, Rm, depending on the molar ratio of protease: antiplasmin. At equimolar concentrations of protease and α2-antiplasmin (5 nM:5 nM) full inhibition of protease activity took place. Monitoring of plasmin activity on an hourly and daily basis revealed a prominent effect of autolysis and decrease of plasmin activity in freshly activated samples. The degree of inhibition as well as plasmin half-life (t1/2 = 2.48 ± 0.28 days) connected with its degradation was determined.

Conformational heterogeneity of molecules physisorbed on a gold surface at room temperature

A quantitative single-molecule tip-enhanced Raman spectroscopy (TERS) study at room temperature remained a challenge due to the rapid structural dynamics of molecules exposed to air. Here, we demonstrate the hyperspectral TERS imaging of single or a few brilliant cresyl blue (BCB) molecules at room temperature, along with quantitative spectral analyses. Robust chemical imaging is enabled by the freeze-frame approach using a thin Al2O3 capping layer, which suppresses spectral diffusions and inhibits chemical reactions and contaminations in air. For the molecules resolved spatially in the TERS image, a clear Raman peak variation up to 7.5 cm-1 is observed, which cannot be found in molecular ensembles. From density functional theory-based quantitative analyses of the varied TERS peaks, we reveal the conformational heterogeneity at the single-molecule level. This work provides a facile way to investigate the single-molecule properties in interacting media, expanding the scope of single-molecule vibrational spectroscopy studies.

Anti-Colonization Effect of Au Surfaces with Self-Assembled Molecular Monolayers Functionalized with Antimicrobial Peptides on S. epidermidis

Medical devices with an effective anti-colonization surface are important tools for combatting healthcare-associated infections. Here, we investigated the anti-colonization efficacy of antimicrobial peptides covalently attached to a gold model surface. The gold surface was modified by a self-assembled polyethylene glycol monolayer with an acetylene terminus. The peptides were covalently connected to the surface through a copper-catalyzed [3 + 2] azide-acetylene coupling (CuAAC). The anti-colonization efficacy of the surfaces varied as a function of the antimicrobial activity of the peptides, and very effective surfaces could be prepared with a 6 log unit reduction in bacterial colonization.

Developing a Novel Method of Analysis for Thiols in Sauvignon blanc

<p>New Zealand wine had an export value of $1.21 billion in 2013. Of the total 170million litres of wine exported thatyear, Sauvignon blanc madeup 84.5%. Sauvignon blanc wines have specific flavours and aromas that consumers detect and enjoy including grapefruit, passion fruit,and citrus characters that are due to the presence of sulfur containing thiols. Unfortunately, thiols are also responsible for aromas such as cat’s urine, grass, and gasoline, which taint the flavour of a wine. Careful analysis of these compounds could lead to wines tailored to specific palates and a reduction of taint aromas and flavours, therefore further increasing the market potential for New Zealand Sauvignon blanc. The aim of this project was to further develop an SPME-based technique for thiol analysis of wine that is more reproducible, more accessible, and less toxic than the current method that concentrates the thiols using organomercury columns. To do this, gold nanoparticles were synthesised and coated onto SPME fibres in an attempt to selectively extract thiols from wine samples. Initial results showed an inconsistency between analyses and led to the need for a more comprehensive analysis ofthe gold surface,the gold-sulfur bond, and its RED-OX chemistry. Techniques employed for analysis of the gold surface included scanning electron microscopy, transmission electron microscopy,zeta-sizing and UV-VisSpectrophotometry. To examine the interactions between gold and sulfur, Surface-Enhanced Raman Spectroscopy and computational chemistry were used. The RED-OX chemistry was initially assessed in terms of the carrier gas in the gas chromatographs but was later changed to reductive and oxidative dips. It was found that an H2O2 dip in between samples oxidised the bound thiolates to a series of dimers that were easier to remove from the gold. While not yet completely resolving the hysteresis observed in previous attempts, this method of cleaning the fibres will lead to future experimentation and development in this area.</p>

Developing a Novel Method of Analysis for Thiols in Sauvignon blanc

<p>New Zealand wine had an export value of $1.21 billion in 2013. Of the total 170million litres of wine exported thatyear, Sauvignon blanc madeup 84.5%. Sauvignon blanc wines have specific flavours and aromas that consumers detect and enjoy including grapefruit, passion fruit,and citrus characters that are due to the presence of sulfur containing thiols. Unfortunately, thiols are also responsible for aromas such as cat’s urine, grass, and gasoline, which taint the flavour of a wine. Careful analysis of these compounds could lead to wines tailored to specific palates and a reduction of taint aromas and flavours, therefore further increasing the market potential for New Zealand Sauvignon blanc. The aim of this project was to further develop an SPME-based technique for thiol analysis of wine that is more reproducible, more accessible, and less toxic than the current method that concentrates the thiols using organomercury columns. To do this, gold nanoparticles were synthesised and coated onto SPME fibres in an attempt to selectively extract thiols from wine samples. Initial results showed an inconsistency between analyses and led to the need for a more comprehensive analysis ofthe gold surface,the gold-sulfur bond, and its RED-OX chemistry. Techniques employed for analysis of the gold surface included scanning electron microscopy, transmission electron microscopy,zeta-sizing and UV-VisSpectrophotometry. To examine the interactions between gold and sulfur, Surface-Enhanced Raman Spectroscopy and computational chemistry were used. The RED-OX chemistry was initially assessed in terms of the carrier gas in the gas chromatographs but was later changed to reductive and oxidative dips. It was found that an H2O2 dip in between samples oxidised the bound thiolates to a series of dimers that were easier to remove from the gold. While not yet completely resolving the hysteresis observed in previous attempts, this method of cleaning the fibres will lead to future experimentation and development in this area.</p>

Optical control of the interface between gold surface and blood cell samples

The optical properties of blood (spectra of the extinction coefficient, k, refractive index, n, etc.) carry important diagnostic information and are usually monitored using bulk samples. In this work, attention is drawn to the interface between the blood volume and the surface of glass or thin gold films on it, where the refractive index may differ from the bulk one. We draw attention to the relationship between two effects – SPR and TIR. It is shown that if the named effects are measured for two different external media 0 and 1 with different refractive indices, then the values of the angles SPR and TIR will be linearly related by the empirical formula SPR1=SPR0+TIR1- TIR0)*K, where the coefficient K depends on the thickness of the transition layer di between the surface and the volume of the liquid medium (suspension). Numerical calculation of K (di) for gold films shows that K = 1.6 at di = 0 and monotonically decreases to 0.01 with an increase in di to 300 nm (and further to 0). Measurement of the angular dependences of reflection, R(), on (1) 100% hematocrit blood samples, (2) hemolyzed samples and (3) washed erythrocytes with dilutions with a buffer solution. It was shown that all samples exhibit a minimum SPR, but the TIR angle can be measured only for blood samples with destroyed membranes (hemolyzed), buffer solution and plasma. The n-value for hemolyzed blood is 1.3505, which is indicative of a low hemoglobin content in the sample. At the same time, di for a sample of 100% hematocrit was 60-105 nm, which indicates a strong deformation of erythrocytes in the form of polyhedrocytes and their dense packing after centrifugation. Washing the cells with a buffer increases di to 280 nm and more and practically eliminates blood cells from the SPR sensitivity region. The reason for this may be that in the blood of 100% hematocrit, erythrocytes are in the form of polyhedrocytes tightly adhering to the gold surface, while as a result of washing and diluting with a buffer solution, the cells relax back into discocytes. As a result, the containing hemoglobin erythrocyte cytoplasm moves away from the surface at a distance di> 300 nm into the suspension volume and leaves the area of the enhanced plasmon-polariton field.

Synthesis of 5,15-A2BC-Type Porphyrins to Modify a Field-Effect Transistor for Detection of Gram-Negative Bacteria

Current biological sensing technologies of bacteria are time consuming, labor intensive and thus expensive. Furthermore, their accuracy and reproducibility could be improved. Conventional electrical measurement methods might combine high sensitive sensing systems with biological requirements. A promising approach is the trapping of bacteria on the surface of the gate-electrode of a modified field-effect transistor (FET) using porphyin based self-assembled monolayers (SAMs). 5,15-A2BC-type porphyrins were synthesized originating from a 5,15-diphenylporphyrin with the functionality to connect to a gold surface. The SAM formation on the surface of the gold electrode was proven by well-established analytical methods. In this work a synthesis route is presented for a linker which is attached to a peptide or cysteine group for trapping of Gram-negative bacteria. Fluorescence lifetime imaging microscopy (FLIM) measurements of porphyrin-stained bacteria were performed to verify the linkage ability.