Jonathan Hobley

Graphene Liquid Marbles as Photothermal Miniature Reactors for Reaction Kinetics Modulation

We demonstrate the fabrication of graphene liquid marbles as photothermal miniature reactors with precise temperature control for reaction kinetics modulation. Graphene liquid marbles show rapid and highly reproducible photothermal behavior while maintaining their excellent mechanical robustness. By tuning the applied laser power, swift regulation of graphene liquid marbles surface temperature between 21-135 °C and its encapsulated water temperature between 21-74 °C are demonstrated. The temperature regulation modulates the reaction kinetics in our graphene liquid marble, achieving a 12-fold superior reaction rate constant for methylene blue degradation than at room temperature.

Wide-field single metal nanoparticle spectroscopy for high throughput localized surface plasmon resonance sensing

Noble metal nanoparticles (mNPs) have a distinct extinction spectrum arising from their ability to support Localized Surface Plasmon Resonance (LSPR). Single-particle biosensing with LSPR is label free and offers a number of advantages, including single molecular sensitivity, multiplex detection, and in vivo quantification of chemical species etc. In this article, we introduce Single-particle LSPR Imaging (SLI), a wide-field spectral imaging method for high throughput LSPR biosensing. The SLI utilizes a transmission grating to generate the diffraction spectra from multiple mNPs, which are captured using a Charge Coupled Device (CCD). With the SLI, we are able to simultaneously image and track the spectral changes of up to 50 mNPs in a single (∼1 s) exposure and yet still retain a reasonable spectral resolution for biosensing. Using the SLI, we could observe spectral shift under different local refractive index environments and demonstrate biosensing using biotin-streptavidin as a model system. To the best of our knowledge, this is the first time a transmission grating based spectral imaging approach has been used for mNPs LSPR sensing. The higher throughput LSPR sensing, offered by SLI, opens up a new possibility of performing label-free, single-molecule experiments in a high-throughput manner.

Features of Thiolated Ligands Promoting Resistance to Ligand Exchange in Self-Assembled Monolayers on Gold Nanoparticles

An important feature necessary for biological stability of gold nanoparticles is resistance to ligand exchange. Here, we design and synthesize self-assembled monolayers of mixtures of small ligands on gold nanoparticles promoting high resistance to ligand exchange. We use as ligands short thiolated peptidols, e.g. H-CVVVT-ol, and ethylene glycol terminated alkane thiols (HS-C11-EG4). We present a straightforward method to evaluate the relative stability of each ligand shell against ligand exchange with small thiolated molecules. The results show that a ligand with a ‘thin’ stem, such as HS-C11-EG4, is an important feature to build a highly packed self-assembled monolayer and provide high resistance to ligand exchange. The greatest resistance to ligand exchange was found for the mixed ligand shells of the pentapeptidols H-CAVLT-ol or H-CAVYT-ol and the ligand HS-C11-EG4 at 30:70 (mole/mole). Mixtures of ligands of very different diameters, such as the peptidol H-CFFFY-ol and the ligand HS-C11-EG4, provide only a slightly lower stability against ligand exchange. These ligand shells are thus likely to be suitable for long-term use in biological environments. The method developed here provides a rapid screening tool to identify nanoparticles likely to be suitable for use in biological and biomedical applications.

Nanoscale phase domain structure and associated device performance of organic solar cells based on a diketopyrrolopyrrole polymer

We investigate the blend morphology and performance of bulk heterojunction organic photovoltaic devices comprising the donor polymer, pDPP-TNT (poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1, 4-dione-alt-naphthalene}) and the fullerene acceptor, [70]PCBM ([6,6]-phenyl C71-butyric acid methyl ester). The blend morphology is heavily dependent upon the solvent system used in the fabrication of thin films. Thin films spin-coated from chloroform possess a cobblestone-like morphology, consisting of thick, round-shaped [70]PCBM-rich mounds separated by thin polymer-rich valleys. The size of the [70]PCBM domains is found to depend on the overall film thickness. Thin films spin-coated from a chloroform:dichlorobenzene mixed solvent system are smooth and consist of a network of pDPP-TNT nanofibers embedded in a [70]PCBM-rich matrix. Rinsing the films in hexane selectively removes [70]PCBM and allows for analysis of domain size and purity. It also provides a means for investigating exciton dissociation efficiency through relative photoluminescence yield measurements. Devices fabricated from chloroform solutions show much poorer performance than the devices fabricated from the mixed solvent system; this disparity in performance is seen to be more pronounced with increasing film thickness. The primary cause for the improved performance of devices fabricated from mixed solvents is attributed to the greater donor-acceptor interfacial area and resulting greater capacity for charge carrier generation.

End-on Covalent Antibody Immobilization on Dual Polarization Interferometry Sensor Chip for Enhanced Immuno-sensing

End-on immobilization of antibody is an important technology to greatly improve the sensitivity of immuno-sensing. The end-on, or constant fragment (Fc) site-specifically oriented antibodies expose more active antigen binding sites (Fab) and tend to capture more analytes from the solution. In this study, dual polarization interferometry (DPI), which is the only available equipment that can concurrently obtain the mass, thickness, density, and refractive index in real time, was applied to investigate two end-on antibody immobilization methods, as exemplified by prostate-specific antigen (PSA) antibody. In the first method, antibody was immobilized via the saccharide chain linked to Fc portion of the antibody, by chelation to the surface-bound boronic acid. In the second method, antibody was partially reduced by tris(2-carboxyethyl) phosphine (TCEP) under mild conditions, followed by covalent conjugation to the surface via thiol-maleimide reaction. Time-resolved measurement from DPI verifies the end-on conformation of the antibody on the sensor surface. The second method shows better detection performance, with enhanced sensitivity and reproducibility than the first method, due to the optimal alignment of the antibody. Finally, these two methods were compared with the protein G-based antibody orientation control and random antibody immobilization in terms of the mass, thickness, density, refractive index, reproducibility, and stability. The detailed antibody immobilization parameters obtained in this paper are of great importance in the developing of solid–liquid phase immunosensors with enhanced detection sensitivity.

Delayed onset of photochromism in molybdenum oxide films caused by photoinduced defect formation

Abstract We report the photochromic properties of amorphous MoO3 films deposited by dc sputtering with different O2 flow rates. The kinetics of film coloration under UV light irradiation is determined using optical transmission spectroscopy. Changes in the absorbance and refractive index were derived from the analysis of transmittance spectra. The absorbance spectra exhibited a growing broad peak centered around 830 nm, which was induced by the UV irradiation. In the early stages of irradiation, the absorbance of the films did not change but their refractive indices did change. This induction time was correlated with the O2 partial pressure during the film deposition, which was controlled by the O2 flow rate. The origins of this observation are discussed.

Dynamics of Volume Expansion of De-Mixing Liquids after Pulsed IR Heating

Triethylamine (TEA)–water mixtures have a critical-temperature (Tc). Below Tc the mixture exists as one phase and above Tc it exists in two phases. The de-mixed volume is different to the mixed volume. A nanosecond pulsed-laser heated a TEA–water mixture so that it de-mixed. The resulting dynamics of volume expansion were monitored using interferometry. For T-jumps within the one phase region the dynamics of volume change were limited by the speed of sound. However, T-jumps between the one and two phase regions also manifested a slower volume change associated with the de-mixing process. After 150 ns, the volume of the de-mixed TEA–water was consistent with the equilibrium volume change. This suggests that, within 150 ns, the system had split into phase-domains having equilibrium compositions of TEA and water. Subsequently the phase domains would simply merge and grow resulting in no further volume change to reduce surface tension between the phases.

Excited-state dynamics in diketopyrrolopyrrole-based copolymer for organic photovoltaics investigated by transient optical spectroscopy

We investigate the photoexcited state dynamics in a donor-acceptor copolymer, poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]- pyrrole-1,4-dione-alt-naphthalene} (pDPP-TNT), by picosecond fluorescence and femtosecond transient absorption spectroscopies. Timeresolved fluorescence lifetime measurements of pDPP-TNT thin films reveal that the lifetime of the singlet excited state is 185 ± 5 ps and that singlet-singlet annihilation occurs at excitation photon densities above 6 × 1017 photons/cm3. From the results of singlet-singlet annihilation analysis, we estimate that the single-singlet annihilation rate constant is (6.0 ± 0.2) × 109cm3 s-1 and the singlet diffusion length is -7 nm. From the comparison of femtosecond transient absorption measurements and picosecond fluorescence measurements, it is found that the time profile of the photobleaching signal in the charge-transfer (CT) absorption band coincides with that of the fluorescence intensity and there is no indication of long-lived species, which clearly suggests that charged species, such as polaron pairs and triplet excitons, are not effectively photogenerated in the neat pDPP-TNT polymer.

Raman mapping glucose metabolism during adipogenesis from human mesenchymal stem cells

Raman mapping was used to determine the distribution of fats inside of adipocytes and human mesenchymal stem cells during adipogenesis. This proved to be a successful way of mapping the lipid distribution within the cells because of the strong C-H stretching bands of the fats inside the lipid droplets. Furthermore using deuterated glucose in the cell culture medium it was possible to distinguish any fats in droplets or in the cytoplasm that were formed before and after adipogenesis was initiated, because those formed after displayed both C-H and C-D stretching bands. The distributions of the initial metabolites of glucose and the resulting fats in the lipid drops could also be mapped in this way.

Cooperative photoinduced two-dimensional condensation in Langmuir films observed using nanosecond pump-probe Brewster angle microscopy

Two-dimensional condensation was initiated in a self-assembled mixed monolayer of spiropyran and octadecanol by a nanosecond laser pulse. The dynamics of the process were monitored using nanosecond pump-probe Brewster angle microscopy. Domain growth followed a power law with a growth exponent of 0.47 at a velocity approaching 20 ms−1. This represents a limit for the rate of longitudinal signaling of pressure waves through a self-assembled amphiphilic layer at an interface and adds to our understanding of signal transmission rates in biomimetic membranes where morphological change in one region can be signaled to a more remote region.