Dynamic Gate Control of Aryldiazonium Chemistry on Graphene Field-Effect Transistors.

As graphene field-effect transistors (GFETs) are becoming increasingly valued for sensor applications, efficiency and control of their surface functionalization become critical. Here, we introduce an innovative method using a gate electrode to precisely modulate aryldiazonium functionalization directly on graphene devices. Although this covalent chemistry is well-known, we show that its spontaneous reaction on GFETs is highly heterogeneous with a low overall yield. By dynamically tuning the gate voltage in the presence of the reactant, we can quickly enable or suppress the reaction, resulting in a high degree of homogeneity between devices. We are also able to monitor and control functionalization kinetics in real time. The mechanism for our approach is based on electron transfer availability, analogous to chemical, substrate-based, or electrochemical doping, but has the practical advantage of being fully implementable on devices or chips. This work illustrates how powerful the FET platforms are to study surface reactions on nanomaterials in real time.

Graphene field-effect transistors as bioanalytical sensors: design, operation and performance.

Graphene field-effect transistors (GFETs) are emerging as bioanalytical sensors, in which their responsive electrical conductance is used to perform quantitative analyses of biologically-relevant molecules such as DNA, proteins, ions and small molecules. This review provides a detailed evaluation of reported approaches in the design, operation and performance assessment of GFET biosensors. We first dissect key design elements of these devices, along with most common approaches for their fabrication. We compare possible modes of operation of GFETs as sensors, including transfer curves, output curves and time series as well as their integration in real-time or a posteriori protocols. Finally, we review performance metrics reported for the detection and quantification of bioanalytes, and discuss limitations and best practices to optimize the use of GFETs as bioanalytical sensors.

Ultrafast decoherence dynamics govern photocarrier generation efficiencies in polymer solar cells.

All-organic-based photovoltaic solar cells have attracted considerable attention because of their low-cost processing and short energy payback time. In such systems the primary dissociation of an optical excitation into a pair of photocarriers has been recently shown to be extremely rapid and efficient, but the physical reason for this remains unclear. Here, two-dimensional photocurrent excitation spectroscopy, a novel non-linear optical spectroscopy, is used to probe the ultrafast coherent decay of photoexcitations into charge-producing states in a polymer:fullerene based solar cell. The two-dimensional photocurrent spectra are interpreted by introducing a theoretical model for the description of the coupling of the electronic states of the system to an external environment and to the applied laser fields. The experimental data show no cross-peaks in the twodimensional photocurrent spectra, as predicted by the model for coherence times between the exciton and the photocurrent producing states of 20 fs or less.

Oxidative stress and antimicrobial activity of chromium(III) and ruthenium(II) complexes on Staphylococcus aureus and Escherichia coli.

The prevalence of antibiotic resistance has resulted in the need for new approaches to be developed to combat previously easily treatable infections. The main aim of this work was to establish the potential of the synthetic α-diimine chromium(III) and ruthenium(II) complexes (where the α-diimine ligands are bpy = 2,2-bipyridine, phen = 1,10-phenanthroline, and dppz = dipyrido[3,2-a:2',3'-c]-phenazine) like [Cr(phen)3](3+), [Cr(phen)2(dppz)](3+), [Ru(phen)3](2+), and [Ru(bpy)3](2+) as antibacterial agents by generating oxidative stress. The [Cr(phen)3](3+) and [Cr(phen)2(dppz)](3+) complexes showed activity against Gram positive and Gram negative bacteria with minimum inhibitory concentrations (MICs) ranging from 0.125 µg/mL to 1 µg/mL, while [Ru(phen)3](2+) and [Ru(bpy)3](2+) do not exhibit antimicrobial activity against the two bacterial genera studied at the concentration range used. When ciprofloxacin was combined with [Cr(phen)3](3+) for the inhibition of Staphylococcus aureus and Escherichia coli, an important synergistic effect was observed, FIC 0.066 for S. aureus and FIC 0.064 for E. coli. The work described here shows that chromium(III) complexes are bactericidal for S. aureus and E. coli. Our results indicate that α -diimine chromium(III) complexes may be interesting to open new paths for metallodrug chemotherapy against different bacterial genera since some of these complexes have been found to exhibit remarkable antibacterial activities.

Interaction of α-diimine-chromium(III) complexes with non-ionic surfactant Triton X-100.

Using either luminescence intensity or lifetime measurements, we have studied the binding interactions of Cr(NN)(3)(3+) (NN=α-diimine ligands) with non-ionic solutions of surfactant p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol), Triton X-100 (TX-100). The titration curves consisted of two curved regions with different slopes. This biphasic behavior of lifetime-TX-100 concentration data revealed the presence of premicellar aggregates at low TX-100 concentration and the formation of normal micelles at high surfactant concentration. The results were analyzed with a model that includes binding of Cr(NN)(3)(3+) (probe) to small premicellar aggregates and to micelles. There is a good correlation between the hydrophobicity of the ligands of Cr(III) complex and the strength of the binding of the complexes to the micelles. A comparison with the binding of Cr(NN)(3)(3+) to sodium dodecylsulfate (SDS) is discussed.

Screening of Argentinian plants for pesticide activity.

Aerial parts of 27 plant species native to Argentina were tested in anti-insect, germination inhibition and bactericide bio-assays. In antifeedant assays on Epilachna paenulata larvae, 11 species showed strong feeding deterrent effects (higher than 90% at 200 microg/cm(2)). Twelve plants strongly inhibited the germination of Avena sativa seeds, but only six inhibited Raphanus sativum germination at 10 mg/ml. Four plants showed complete growth inhibition of Escherichia coli at a concentration of 2 mg/ml.