Electron paramagnetic resonance as a tool to determine the sodium charge storage mechanism of hard carbon.

Hard carbon is a promising negative electrode material for rechargeable sodium-ion batteries due to the ready availability of their precursors and high reversible charge storage. The reaction mechanisms that drive the sodiation properties in hard carbons and subsequent electrochemical performance are strictly linked to the characteristic slope and plateau regions observed in the voltage profile of these materials. This work shows that electron paramagnetic resonance (EPR) spectroscopy is a powerful and fast diagnostic tool to predict the extent of the charge stored in the slope and plateau regions during galvanostatic tests in hard carbon materials. EPR lineshape simulation and temperature-dependent measurements help to separate the nature of the spins in mechanochemically modified hard carbon materials synthesised at different temperatures. This proves relationships between structure modification and electrochemical signatures in the galvanostatic curves to obtain information on their sodium storage mechanism. Furthermore, through ex situ EPR studies we study the evolution of these EPR signals at different states of charge to further elucidate the storage mechanisms in these carbons. Finally, we discuss the interrelationship between EPR spectroscopy data of the hard carbon samples studied and their corresponding charging storage mechanism.

Eco-friendly voltammetric platform for trace metal determination using a conductive polymer sensor modified with bismuth nanoparticles generated by spark discharge.

The fabrication of a low-cost eco-friendly sensor platform for the voltammetric determination of trace metals by electrochemical stripping analysis is reported. Plastic conductive electrodes were manufactured via injection moulding from polysterene reinforced with carbon fibres. The platform comprises a carbon counter electrode, a working electrode modified with bismuth nanoparticles generated by spark discharge and a reference electrode coated with AgCl. The sensor fabrication and modification procedures are simple, cost-effective and fast while the materials used are environment-friendly. The utility of the voltammetric platform is demonstrated for stripping analysis of Cd(II) and Pb(II); the limits of detection are 0.7 µg L-1 and 0.6 µg L-1, respectively (with a deposition time of 240 s) which are comparable to conventional Bi-modified sensors and are sufficient to determine the target metals in water and food samples. The scope of the analytical platform for multi-element assays and for the determination of other trace metals is discussed with representative examples. Therefore, this sustainable and economical platform holds great potential for electrochemical sensing of trace metals.

Alvarez varifocal X-ray lens.

Visible light optical elements such as lenses and mirrors have counterparts for X-rays. In the visible regime, a variable focusing power can be achieved by an Alvarez lens which consists of a pair of inline planar refractors with a cubic thickness profile. When the two refractors are laterally displaced in opposite directions, the parabolic component of the wavefront is changed resulting in a longitudinal displacement of the focus. This paper reports an implementation of this concept for X-rays using two planar microfabricated refractive elements. The Alvarez X-ray lens can vary the focal distance of an elliptical X-ray mirror or a planar compound X-ray lens over several millimetres. The study presents the first demonstration of an Alvarez X-ray lens which adaptively corrects defocus and astigmatism aberrations of X-ray optics. In addition, the Alvarez X-ray lens eliminates coma aberration in an elliptical mirror, to the lowest order, when combining the lens with an adjustment of the pitch angle of the mirror.

Rapid imaging and product screening with low-cost line-field Fourier domain optical coherence tomography.

Fourier domain optical coherence tomography (FD-OCT) is a well-established imaging technique that provides high-resolution internal structure images of an object at a fast speed. Modern FD-OCT systems typically operate at speeds of 40,000-100,000 A-scans/s, but are priced at least tens of thousands of pounds. In this study, we demonstrate a line-field FD-OCT (LF-FD-OCT) system that achieves an OCT imaging speed of 100,000 A-scan/s at a hardware cost of thousands of pounds. We demonstrate the potential of LF-FD-OCT for biomedical and industrial imaging applications such as corneas, 3D printed electronics, and printed circuit boards.

Gold nanoparticle-modified sustainable plastic sensor chip for voltammetric monitoring of Hg(II).

Mercury is a toxic environmental contaminant that can cause serious health problems. This work describes a new type of eco-friendly three-electrode plastic sensor chip for the determination of trace Hg(II) by means of anodic stripping voltammetry (ASV). The sensor chip is entirely fabricated by injection moulding, which is a sustainable manufacturing method, and consists of three conductive carbon-based electrodes embedded in a plastic holder while the reference electrode is coated with Ag using e-beam evaporation. The sample is spiked with Au(III) which deposits on the working electrode in the form of gold nanoparicles during the analysis; the target Hg(II) co-deposits on the gold nanoparticles forming a Au(Hg) amalgam in situ. The accumulated Hg is stripped off the electrode and quantified by an anodic square wave potential scan. The relevant conditions and the potential interferences are investigated. The limit of detection for Hg(II) is 0.4 µg L-1 and the repeatability at the 20 µg L-1 Hg(III) level (n = 10) is 5.3%. The sensor is applied to water, honey, fish oil and mussel samples with recoveries between 98 and 107%.

Electrochemically Enhanced Delivery of Pemetrexed from Electroactive Hydrogels.

Electroactive hydrogels based on derivatives of polyethyleneglycol (PEG), chitosan and polypyrrole were prepared via a combination of photopolymerization and oxidative chemical polymerization, and optionally doped with anions (e.g., lignin, drugs, etc.). The products were analyzed with a variety of techniques, including: FT-IR, UV-Vis, 1H NMR (solution state), 13C NMR (solid state), XRD, TGA, SEM, swelling ratios and rheology. The conductive gels swell ca. 8 times less than the non-conductive gels due to the presence of the interpenetrating network (IPN) of polypyrrole and lignin. A rheological study showed that the non-conductive gels are soft (G' 0.35 kPa, G″ 0.02 kPa) with properties analogous to brain tissue, whereas the conductive gels are significantly stronger (G' 30 kPa, G″ 19 kPa) analogous to breast tissue due to the presence of the IPN of polypyrrole and lignin. The potential of these biomaterials to be used for biomedical applications was validated in vitro by cell culture studies (assessing adhesion and proliferation of fibroblasts) and drug delivery studies (electrochemically loading the FDA-approved chemotherapeutic pemetrexed and measuring passive and stimulated release); indeed, the application of electrical stimulus enhanced the release of PEM from gels by ca. 10-15% relative to the passive release control experiment for each application of electrical stimulation over a short period analogous to the duration of stimulation applied for electrochemotherapy. It is foreseeable that such materials could be integrated in electrochemotherapeutic medical devices, e.g., electrode arrays or plates currently used in the clinic.

A Non-Destructive, Tuneable Method to Isolate Live Cells for High-Speed AFM Analysis.

Suitable immobilisation of microorganisms and single cells is key for high-resolution topographical imaging and study of mechanical properties with atomic force microscopy (AFM) under physiologically relevant conditions. Sample preparation techniques must be able to withstand the forces exerted by the Z range-limited cantilever tip, and not negatively affect the sample surface for data acquisition. Here, we describe an inherently flexible methodology, utilising the high-resolution three-dimensional based printing technique of multiphoton polymerisation to rapidly generate bespoke arrays for cellular AFM analysis. As an example, we present data collected from live Emiliania huxleyi cells, unicellular microalgae, imaged by contact mode High-Speed Atomic Force Microscopy (HS-AFM), including one cell that was imaged continuously for over 90 min.

Correction of the X-ray wavefront from compound refractive lenses using 3D printed refractive structures.

A refractive phase corrector optics is proposed for the compensation of fabrication error of X-ray optical elements. Here, at-wavelength wavefront measurements of the focused X-ray beam by knife-edge imaging technique, the design of a three-dimensional corrector plate, its fabrication by 3D printing, and use of a corrector to compensate for X-ray lens figure errors are presented. A rotationally invariant corrector was manufactured in the polymer IP-STM using additive manufacturing based on the two-photon polymerization technique. The fabricated corrector was characterized at the B16 Test beamline, Diamond Light Source, UK, showing a reduction in r.m.s. wavefront error of a Be compound refractive Lens (CRL) by a factor of six. The r.m.s. wavefront error is a figure of merit for the wavefront quality but, for X-ray lenses, with significant X-ray absorption, a form of the r.m.s. error with weighting proportional to the transmitted X-ray intensity has been proposed. The knife-edge imaging wavefront-sensing technique was adapted to measure rotationally variant wavefront errors from two different sets of Be CRL consisting of 98 and 24 lenses. The optical aberrations were then quantified using a Zernike polynomial expansion of the 2D wavefront error. The compensation by a rotationally invariant corrector plate was partial as the Be CRL wavefront error distribution was found to vary with polar angle indicating the presence of non-spherical aberration terms. A wavefront correction plate with rotationally anisotropic thickness is proposed to compensate for anisotropy in order to achieve good focusing by CRLs at beamlines operating at diffraction-limited storage rings.

Bioactive silver phosphate/polyindole nanocomposites.

Materials capable of releasing reactive oxygen species (ROS) can display antibacterial and anticancer activity, and may also have anti-oxidant capacity if they suppress intracellular ROS (e.g. nitric oxide, NO) resulting in anti-inflammatory activity. Herein we report silver phosphate (Ag3PO4)/polyindole (Pln) nanocomposites which display antibacterial, anticancer and anti-inflammatory activity, and have therefore potential for a variety of biomedical applications.

Biocompatibility Investigation of Hybrid Organometallic Polymers for Sub-Micron 3D Printing via Laser Two-Photon Polymerisation.

Hybrid organometallic polymers are a class of functional materials which can be used to produce structures with sub-micron features via laser two-photon polymerisation. Previous studies demonstrated the relative biocompatibility of Al and Zr containing hybrid organometallic polymers in vitro. However, a deeper understanding of their effects on intracellular processes is needed if a tissue engineering strategy based on these materials is to be envisioned. Herein, primary rat myogenic cells were cultured on spin-coated Al and Zr containing polymer surfaces to investigate how each material affects the viability, adhesion strength, adhesion-associated protein expression, rate of cellular metabolism and collagen secretion. We found that the investigated surfaces supported cellular growth to full confluency. A subsequent MTT assay showed that glass and Zr surfaces led to higher rates of metabolism than did the Al surfaces. A viability assay revealed that all surfaces supported comparable levels of cell viability. Cellular adhesion strength assessment showed an insignificantly stronger relative adhesion after 4 h of culture than after 24 h. The largest amount of collagen was secreted by cells grown on the Al-containing surface. In conclusion, the materials were found to be biocompatible in vitro and have potential for bioengineering applications.

Disposable Injection Molded Conductive Electrodes Modified with Antimony Film for the Electrochemical Determination of Trace Pb(II) and Cd(II).

This work describes a novel electrochemical sensor fabricated by an injection molding process. This device features a conductive polymer electrode encased in a plastic holder and electroplated in situ with a thin antimony film. The antimony film sensor was applied to the determination of Pb(II) and Cd(II) by anodic stripping voltammetry (ASV). The deposition of Sb on the sensor was studied by cyclic voltammetry (CV) and microscopy. The experimental variables (concentration of the antimony plating solution, deposition potential and time, stripping waveform) were investigated, and the potential interferences were studied and addressed. The limits of detection were 0.95 µg L-1 for Pb(II) and 1.3 for Cd(II) (at 240 s of preconcentration) and the within-sensor percentage relative standard deviations were 4.2% and 4.9%, respectively, at the 25 µg L-1 level (n = 8). Finally, the sensor was applied to the determination of Pb(II) and Cd(II) in a phosphorite sample and a lake water sample.

Electrochemically Enhanced Drug Delivery Using Polypyrrole Films.

The delivery of drugs in a controllable fashion is a topic of intense research activity in both academia and industry because of its impact in healthcare. Implantable electronic interfaces for the body have great potential for positive economic, health, and societal impacts; however, the implantation of such interfaces results in inflammatory responses due to a mechanical mismatch between the inorganic substrate and soft tissue, and also results in the potential for microbial infection during complex surgical procedures. Here, we report the use of conducting polypyrrole (PPY)-based coatings loaded with clinically relevant drugs (either an anti-inflammatory, dexamethasone phosphate (DMP), or an antibiotic, meropenem (MER)). The films were characterized and were shown to enhance the delivery of the drugs upon the application of an electrochemical stimulus in vitro, by circa (ca.) 10⁻30% relative to the passive release from non-stimulated samples. Interestingly, the loading and release of the drugs was correlated with the physical descriptors of the drugs. In the long term, such materials have the potential for application to the surfaces of medical devices to diminish adverse reactions to their implantation in vivo.

Determination of Pb(II) by sequential injection/stripping analysis at all-plastic electrochemical fluidic cells with integrated composite electrodes.

This work reports the development of a sequential injection/stripping analysis method for the determination of trace Pb(II) at injection-moulded electrochemical fluidic cells. Conducting carbon fibre-loaded polystyrene electrodes were integrated within the plastic cells. The flow-through cells were incorporated into a home-made sequential injection analysis (SIA) manifold. Different experimental parameters for the detection of Pb(II) were investigated including the type and concentration of the supporting electrolyte, the conditions of the stripping step, the volume of the sample, the flow rate and the accumulation potential. The LOD for Pb(II) was 0.5µgL(-1), the within-cell % relative standard deviation (n=8) was 3.1% and the between-cell % relative standard deviation (n=5) was 8.9% for 25µgL(-1) Pb(II). The cells were applied to the determination of Pb(II) in tapwater and a phosphate fertilizer sample.

Microfluidic channel-assisted screening of hematopoietic malignancies.

A simple microfluidic fluorescence in situ hybridization (FISH) device allowing accurate analysis of interphase nuclei in 1 hr in narrow channels is presented. Photolithography and fluorosilicic acid etching were used to fabricate microfluidic channels (referred to as FISHing lines) that allowed analysis of 10 samples on a glass microscope slide 0.2 µl of sample volume was used to fill a micro-channel, which resembled a 250-fold reduction compared to conventional FISH. FISH signals were comparable to conventional FISH, with 50-fold less probe consumption and 10-fold less time. Cells were immobilized in single file in channels just exceeding the diameter of the cells, and were used for minimal residual disease (MRD) analysis. To test the micro-channels for application in FISH, MRD was simulated by mixing K562 cells (an established chronic myeloid leukemia cell line) carrying the BCR/ABL fusion gene across 1:1 to 1:1,000 Jurkat cells (an established acute lymphoblastic leukemia cell line). The limit of detection was seen to be 1:100 cells and 1:1,000 cells for FISHing lines and conventional FISH, respectively; however, the conventional method seemed to over-score the presence of K562 cells. This may in part be attributed to FISHing lines practically eliminating the chance of duplicate screening of cells and hastened the time of screening, enhancing scoring of all cells within the channels. This was compared to 1 in 500 cells on the slide being analyzed with the conventional FISH.

Miniaturised free flow isotachophoresis of bacteria using an injection moulded separation device.

A new design of miniaturised free flow electrophoresis device has been produced. The design contains a separation chamber that is 45 mm long by 31.7 mm wide with a depth of 50 µm and has nine inlet and nine outlet holes to allow for fraction collection. The devices were formed of polystyrene with carbon fibre loaded polystyrene drive electrodes and produced using injection moulding. This means that the devices are low cost and can potentially be mass produced. The devices were used for free flow isotachophoresis (FFITP), a technique that can be used for focussing and concentrating analytes contained within complex sample matrices. The operation of the devices was demonstrated by performing separations of dyes and bacterial samples. Analysis of the output from FFITP separations of samples containing the bacterium Erwinia herbicola, a biological pathogen, by cell culturing and counting showed that fractionation of the output was achieved.

A microfluidic device for self-synchronised production of droplets.

The primary requirement for a mixing operation in droplet-based microfluidic devices is an accurate pairing of droplets of reaction fluids over an extended period of time. In this paper, a novel device for self-synchronous production of droplets has been demonstrated. The device uses a change in impedance across a pair of electrodes introduced due to the passage of a pre-formed droplet to generate a second droplet at a second pair of electrodes. The device was characterised using image analysis. Droplets with a volume of ~23.5 ± 3.1 nl (i.e.~93% of the volume of pre-formed droplets) were produced on applying a voltage of 500 V. The synchronisation efficiency of the device was 83%. As the device enables self-synchronised production of droplets, it has a potential to increase the reliability and robustness of mixing operations in droplet-based microfluidic devices.

Capillary zone electrophoresis for the analysis of glycoforms of cellobiohydrolase.

Cellobiohydrolase (CBH) is an important enzyme for the conversion of lignocellulosic biomass to ethanol. This work separated the glycoforms of CBH possessing different numbers of neutral mannoses using capillary zone electrophoresis (CZE) in a 50 mM, pH 7.5 phosphate buffer. The method analysed CBH in an intact form using a polyacrylamide coated fused silica capillary without requiring additives or labelling of the enzyme. The migration time of the major peak was found to be 21.6±0.1 min (n=3) and the approach is suitable for testing of batch-to-batch consistency of CBH. Ease-of-use, automation and speed are the other benefits due to which the use of CZE for analysing glycoforms of CBH was concluded to be ideal.

Thiocyanate and nitrite analysis using miniaturised isotachophoresis on a planar polymer chip.

A new method has been developed to improve the determination of thiocyanate using isotachophoresis. This method uses complexation with copper(II) as a mechanism for improving the separation of thiocyanate from chlorate and perchlorate. By using a pH of 3.25 the method can also be used to analyse nitrite. Separations were carried out using a miniaturised poly(methyl methacrylate) (PMMA) separation device. Linearity was observed from 1.25 to 75 mg dm(-3) with a correlation coefficient of 0.998 for both thiocyanate and nitrite. Limits of detection for these two species were calculated to be 0.8 mg dm(-3) and 0.9 mg dm(-3) respectively. The method was successfully applied to the analysis of these anions in a range of samples including explosive residues.

A specific, robust, and automated method for routine at-line monitoring of the concentration of cellulases in genetically modified sugarcane plants.

Bagasse is one of the waste crop materials highlighted as commercially viable for cellulosic bio-ethanol production via enzymatic conversion to release fermentable sugars. Genetically modified sugarcane expressing cellobiohydrolases (CBH), endoglucanase (EG), and ß-glucosidases (BG) provide a more cost-effective route to cellulose breakdown compared to culturing these enzymes in microbial tanks. Hence, process monitoring of the concentration profile of these key cellulases in incoming batches of sugarcane is required for fiscal measures and bio-ethanol process control. The existing methods due to their non-specificity, requirement of trained analysts, low sample throughput, and low amenability to automation are unsuitable for this purpose. Therefore, this paper explores a membrane-based sample preparation method coupled to capillary zone electrophoresis (CZE) to quantify these enzymes. The maximum enzyme extraction efficiency was obtained by using a polyethersulfone membrane with molecular cut-off of 10 kDa. The use of 15 mM, pH 7.75, phosphate buffer resulted in CZE separation and quantification of CBH, EG, and BG within 10 min. Migration time reproducibility was between 0.56% and 0.7% and hence, suitable for use with automatic peak detection software. Therefore, the developed CZE method is suitable for at-line analysis of BG, CBH, and EG in every batch of harvested sugarcane.

Determination of the potassium content of explosive residues using miniaturised isotachophoresis.

A new method has been developed to allow the determination of potassium in post-explosion residues to be made using miniaturised isotachophoresis. The method is based on the use of a caesium leading ion with 4.5 mM 18-crown-6 ether added to retard the potassium to allow reliable determinations to be made. With the conditions selected no interference was noted from other small inorganic cations, such as ammonium, barium, calcium, magnesium, sodium or strontium. The method was successfully applied to the analysis of seven samples containing explosive residues obtained from the unconfined burning of several flash powders. The procedure was found to offer good linearity for potassium determinations over the concentration range of 1.25-150 µg/mL with a coefficient of determination of 0.999 achieved.