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. Graphical abstract

This work reports the fabrication of portable system for the determination of trace As(III) in water samples by mean of anodic stripping voltammetry (ASV). The portable detection system consists of a three-electrode mini cell featuring injection-moulded plastic conductive electrodes. As(III) accumulates on the disposable working electrode by electrolysis forming in situ an alloy with co-deposited gold. Then, the accumulated arsenic is detected by applying an anodic potential scan on the working electrode. The chemical and instru-mental conditions were studied and the analytical parameters for the determination of As(III) were estab-lished. The limit of detection was 0.2 mu g L-1 and the repeatability at the 5.0 mu g L-1 As(III) level (n = 10) was 4.7 %. The portable set-up was applied to different groundwater samples with recoveries between 95 and 105 %.

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 & mu;g L-1 and the repeatability at the 20 & mu;g L-1 Hg(III) level (n = 10) is 5.3%. The sensor is applied to water, honey, fish oil and mussel samples with re-coveries between 98 and 107%.

This work describes a sequential injection analysis (SIA) method for on-line strippping voltammetric determination of Pb(II), Cd(II) and Zn(II) using an injection-moulded electrochemical fluidic chip consisting of 3 conductive carbon fiber-loaded polymer electrodes embedded in a plastic fluidic holder. The sample containing the target metals and a solution containing Bi(III) were aspirated in the holding coil of the SIA manifold. Then, the flow was reversed and the two solutions were directed to the fluidic cell through a mixing coil which induced mixing of the two zones. Upon reaching the cell, simultaneous reduction of the target metals and Bi(III) occurred resulting in the formation of a metal-Bi alloy on the working electrode. Finally, the accumulated metals were stripped off the bismuth-film electrode via a positive potential scan and the oxidation current was recorded. The experimental variables (concentration of the bismuth plating solution, deposition potential, sample volume, stripping mode) were investigated and the potential interferences were assessed. The limits of quantification were 2.8 mu g L-1 for Pb(II), 3.6 mu g L-1 for Cd(II) and 4.2 mu g L-1 for Zn(II) and the the within-chip and between-chip % relative standard deviations were <= 6.3 % and <= 14 %, respectively. Finally, the sensor was applied to the determination of trace metals in a fish food sample.

Microalga biomass is considered as a potential feedstock for renewable energy owing to its high lipid content. Conventional microalgae cell culturing methods mostly require lengthy procedures and involve laborious and time-consuming steps. On the other hand, microalgae culturing in microfluidics offers several advantages over conventional methods, such as high sensitivity, enhanced mass and heat transfer, reduced runtime and cost, lower consumption of reagent, and better interaction of species. In this study, initially, a novel hybrid microfluidic differential carbonator (µ-DC) platform was constructed in-house. Then, the performance of this system was tested by microalgae culturing. In this regard, Picochlorum sp. was selected as a model microalgae cell due to its fast growth and high lipid content. The operating conditions for the microalgae growth were 2–6% (vol) inlet CO2 concentration, 49 µmole m2/s light intensity, and 1:0.025 inlet ratio of algae to media. Both spatial and temporal changes of the microalgae growth were investigated. A maximum microalgae growth after 45 h was found to be $$3.37\times {10}^{10}$$ cells/mL in a 50 µm depth cell culture (µ-CC), which is higher cell density than literature values. Such inflate of cell density can be attributed to the fact in improving the mass transfer and providing better contact of microalgae with the ingredients of the photosynthesis process. This remarkable improvement in the growth of cells is of significant importance for many applications, especially for biodiesel production.

This work reports the fabrication of a new environmentally friendly three-electrode electrochemical sensor suitable for on-site voltammetric determination of two toxic emerging ‘technology-critical elements’ (TCEs), namely indium and thallium. The sensor is fully fabricated by injection-moulding and features three conductive polymer electrodes encased in a plastic holder; the reference electrode is further coated with AgCl or AgBr. The sensor is applied to the determination of trace In(III) and Tl(I) by anodic stripping voltammetry using a portable electrochemical set-up featuring a miniature smartphone-based potentiostat and a vibrating device for agitation. For the analysis, the sample containing the target metal ions is spiked with Bi(III) and a bismuth film is electroplated in situ forming an alloy with the accumulated target metals on the working electrode of the sensor; the metals are stripped off by applying a square-wave anodic voltametric scan. Potential interferences in the determination of In(III) and Tl(I) were alleviated by judicious selection of the solution chemistry. Limits of quantification for the target ions were in the low μg L−1 range and the sensors were applied to the analysis of lake water samples spiked with In(III) and Tl(I) with recoveries in the range of 95–103%.

A simple device for the conduct of stepped pressure filtration measurements is described together with methods for making the empirical measurements and interpreting the data obtained. The data interpretation method applies a multi-step systematic approach, with each step supported by statistical justification, to characterise: filter cake particle stress, filtration diffusivity and cake hydraulic resistivity from a single stepped pressure experiment. The methods enable different flocculant materials to be more rapidly and more appropriately screened than conventional jar tests and large scale filtration trials. The methods are applied to the characterisation of a paint residue treated with aluminium sulphate and “PolyClay”.The work shows that the addition of “PolyClay” as a filter aide reduces the hydraulic resistivity at lower solids concentrations but increases it at higher concentrations whilst simultaneously increasing the particle stress. Together these have a combined deleterious effect on the time and energy required to dewater the residues to high solids concentration by filtration. The results also show that a significant change in suspension behaviour occurs between the “PolyClay” doses of 140 mg l-1 and 660 mg l-1 and that further changes up to “PolyClay” doses of 1600 mg l-1 are more modest. The results indicate the existence an opportunity to reduce “PolyClay” dose into a range between 10% and 50% of current practice. In addition the results provide evidence that alternative, centrifuge based, technology is worthy of investigation.

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.

Liquid droplets may be manipulated within microfluidic channel structures, or on planar surfaces to provide experimental platforms where each droplet is a discrete experimental entity. Sometimes described as digital methodology, this provides a unique approach within the fields of chemistry and biochemistry. Subsequent splitting, combining and sorting processes with the droplets offer a limitless opportunity for complex experimental design that includes high sample numbers with high-throughput capability. Distinct advantages include nanolitre, or lower sample volumes, rapid mixing and short diffusion distances. When placed within an automated microfluidic environment, droplets may be driven sequentially or in parallel through a pre-set pattern of unit operations. Many applications have been reported that include the broad fields of synthesis and sample assay. Synthetic applications have been reported for organic synthesis, biochemical synthesis and materials synthesis. The majority of assay-based applications have been reported for bio-assays and biological assays with single cells. The distinct advantages of low sample volumes and high-throughput have been the primary drivers for the development of droplet and digital-based methods.

A reagentless biosensor has been successfully developed to measure glutamate in food and clinical samples. The enzyme, glutamate dehydrogenase (GLDH) and the cofactor, nicotinamide adenine dinucleotide (NAD(+)) are fully integrated onto the surface of a Meldola's Blue screen-printed carbon electrode (MB-SPCE). The biological components are immobilized by utilizing unpurified multi-walled carbon nanotubes (MWCNT's) mixed with the biopolymer chitosan (CHIT), which are drop-coated onto the surface of the MB-SPCE in a layer-by-layer fashion. Meldola's Blue mediator is also incorporated into the biosensor cocktail in order to increase and facilitate electron shuttling between the reaction layers and the surface of the electrode. The loadings of each component are optimized by using amperometry in stirred solution at a low fixed potential of +0.1 V. The optimum temperature and pH are also determined using this technique. Quantification of glutamate in real samples is performed using the method of standard addition. The method of standard addition involves the addition of a sample containing an unknown concentration of glutamate, followed by additions of known concentrations of glutamate to a buffered solution in the cell. The currents generated by each addition are then plotted and the resulting line is extrapolated in order to determine the concentration of glutamate in the sample (Pemberton et al., Biosens Bioelectron 24: 1246-1252, 2009). This layer-by-layer approach holds promise as a generic platform for the fabrication of reagentless biosensors.

The development of biosensors for the determination of glutamate has been of great research interest for the past 25 years due to its importance in biomedical and food studies. This review focusses on the various strategies used to fabricate glutamate biosensors as well as their performance characteristics. A brief comparison of the enzyme immobilisation method employed and the performance characteristics of a range of glutamate biosensors are described in tabular form and then described in detail throughout the review: some selected examples have been included to demonstrate the various applications of these biosensors to real samples.

A reagentless glutamate biosensor was applied to the determination of glutamate released from liver hepatocellular carcinoma cells (HepG2) in response to toxic challenge from various concentrations of paracetamol. A screen printed carbon electrode (SPCE) containing the electrocatalyst Meldola's Blue (MB-SPCE) served as the electron mediator for the oxidation of NADH.A mixture of the enzyme glutamate dehydrogenase (GLDH), cofactor nicotinamide adenine dinucleotide (NAD(+)) and the biopolymer chitosan (CHIT) were drop-coated onto the surface of the transducer (MB-SPCE) in a simple one step fabrication process.The reagentless biosensor was used with amperometry in stirred solution at an applied potential of +0.1 V (vs. Ag/AgCl). All experiments were carried out at the following conditions: pH 7, temperature 37 degrees C, atmosphere 5% CO2.The linear range of the device was found to be 25-125 mu M in phosphate buffer (75 mu M, containing 0.05 M NaCl) and 25-150 mu M in cell culture medium. The limits of detection (LOD) were found to be 1.2 mu M and 4.2 mu M based on three times signal to noise, using PBS and culture medium respectively. The sensitivity was calculated to be 106 nA mu M-1 cm(-2) and 210 nA mu M-1 cm(-2) in PBS and cell medium respectively. The response time was similar to 60 s in an agitated solution.HepG2 cells were exposed to various concentrations of paracetamol (1 mM, 5 mM and 10 mM) in order to investigate the drug-induced release of glutamate into the culture medium in real time. Two toxicity studies were investigated using different methods of exposure and analysis.The first method consisted of a single measurement of the glutamate concentration, using the method of standard addition, after 24 h incubation. The concentrations of glutamate were found to be 52 mu M, 93 mu M and 177 mu M, released on exposure to 1 mM, 5 mM and 10 mM paracetamol respectively.The second method involved the continuous monitoring of glutamate released from HepG2 cells upon exposure to paracetamol over 8 h. The concentrations of glutamate released in the presence of 1 mM, 5 mM and 10 mM paracetamol, increased in proportion to the drug concentration, ie: 16 mu M, 28 mu M and 62 mu M respectively. This result demonstrates the feasibility of using this approach to monitor early metabolic changes after exposure to a model toxic compound. (C) 2016 Elsevier B.V. All rights reserved.

This study presents the degradation of methyl orange in a synthetic solution using an electro-oxidation technique. A novel polymer disk electrode was fabricated in this work using injection molding. Such an electrode is low cost, mass produced, and efficient to achieve a complete decolorization of methyl orange in the synthetic solution. The performance of the electrode was studied comprehensively. The degradation of methyl orange was accomplished in only 800s. at optimum operating conditions of 0.1M KCl electrolyte solution and constant applied current of 5mA. The results revealed that the degradation of dye follows an indirect electro oxidation mechanism. It was also found that stirring is a crucial requirement to improve the mass transfer and to enhance the decolorization rate. The effect of changing the applied current, supporting electrolyte, electrolyte concentration, and initial dye concentration were also investigated.

This study investigates the effectiveness of a novel micro electrochemical flow-cell containing carbon fiber electrodes for the degradation of Azo dye solutions. The flow-cell was fabricated by an injection moulding technique, integrating three electrodes system design using an overmoulding procedure. All electrodes were fabricated from carbon fiber polymer, however, the reference electrode was then coated with Ag/AgCl paste. The effect of the process variables such as flow-rate, NaCl concentration, applied bias current, and solution pH on the degradation process were comprehensively studied. At optimum conditions, complete degradation of the dye was achieved on the bare carbon fiber electrode, without the need for surface modification, in 150min upon the application of 15mA bias current. The degradation process was suggested to follow the indirect oxidation mechanism where the presence of chlorine ions was very essential. Moreover, the micro-flow-cell had proven its stability over the entire operation time, which indicates its practicality for such on-line applications.

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 0.5 μg L−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 25 μg L−1 Pb(II). The cells were applied to the determination of Pb(II) in tapwater and a phosphate fertilizer sample.

Droplet microfluidic technology has the potential to significantly reduce reagent use, and therefore, lower costs of assays employed in drug discovery campaigns. In addition to the reduction in costs, this technology can also reduce evaporation and contamination which are often problems seen in miniaturized microtitre plate formats. Despite these advantages, we currently advise caution in the use of these microfluidic approaches as there remains a lack of understanding of the artefacts of the systems such as reagent partitioning from droplet to carrier oil and interaction of the biological reagents with the water-oil interface. Both types of artefact can lead to inaccurate and misleading data. In this paper, we present a study of the partitioning of a number of drug-like molecules in a range of oils and evidence of protein binding at the water-oil interface which results in reduced activity of a cytochrome P450 enzyme. Data presented show that the drug-like molecules partitioned the least into fluorocarbon oils and the interaction of the 1A2 cytochrome at the water-oil interface resulted in a lower or complete absence of enzyme activity. This loss of activity of cytochrome 1A2 could be restored by the use of secondary blocking proteins although changes in the pharmacology of known 1A2 inhibitors were observed. The artefacts described here due to reagents partitioning into the carrier oil or protein binding at the water-oil interface significantly impact the potential use of these microfluidic systems as a means to carry out miniaturized biological assays, and further work is needed to understand the impact and reduction of these phenomena.

A screen printed carbon electrode (SPCE) containing the electrocatalyst Meldola's Blue (MB) has been investigated as the base transducer for a glutamate biosensor. The sandwich biosensor was fabricated by firstly depositing a chitosan (CHIT) layer onto the surface of the transducer (MB-SPCE), followed by glutamate dehydrogenase (GLDH): this device is designated GLDH-CHIT-MB-SPCE. NAD(+) was added to buffer solutions prior to the measurement of glutamate. This biosensor was used in conjunction with amperometry in stirred solution at an applied potential of +0.1 V (vs. Ag/AgCl). Optimum conditions for the analysis of glutamate were found to be as follows: temperature, 35 degrees C; buffer, pH 7; ionic strength, 75 mM; NAD(+), 4 mM; CHIT 0.05% in 0.05 M HCl; GLDH, 30 U. The linear range of the biosensor was found to be 12.5 mu M to 150 mu M, the calculated limit of detection (based on three times signal to noise) was 1.5 mu M and the sensitivity was 0.44 nA/mu M. The proposed biosensor was used to measure glutamate in serum before and after fortification with glutamate. The endogenous concentration of glutamate was found to be 1.68 mM and the coefficient of variation (CV) was 4.1%. The serum was then fortified with 2 mM of glutamate, and the resulting mean recovery was 96% with a CV of 3.3% (n=6). An unfiltered beef OXO cube was analysed for monosodium glutamate (MSG) content. The endogenous content of MSG was 125.43 mg/g with a CV of 8.98%. The OXO cube solution was fortified with 0.935 g (100 mM) of glutamate, the resulting mean recovery was 91% with a CV of 6.39%.

IR spectroscopy is an excellent method for biological analyses. It enables the nonperturbative, label-free extraction of biochemical information and images toward diagnosis and the assessment of cell functionality. Although not strictly microscopy in the conventional sense, it allows the construction of images of tissue or cell architecture by the passing of spectral data through a variety of computational algorithms. Because such images are constructed from fingerprint spectra, the notion is that they can be an objective reflection of the underlying health status of the analyzed sample. One of the major difficulties in the field has been determining a consensus on spectral pre-processing and data analysis. This manuscript brings together as coauthors some of the leaders in this field to allow the standardization of methods and procedures for adapting a multistage approach to a methodology that can be applied to a variety of cell biological questions or used within a clinical setting for disease screening or diagnosis. We describe a protocol for collecting IR spectra and images from biological samples (e.g., fixed cytology and tissue sections, live cells or biofluids) that assesses the instrumental options available, appropriate sample preparation, different sampling modes as well as important advances in spectral data acquisition. After acquisition, data processing consists of a sequence of steps including quality control, spectral pre- processing, feature extraction and classification of the supervised or unsupervised type. A typical experiment can be completed and analyzed within hours. Example results are presented on the use of IR spectra combined with multivariate data processing.

Particle concentration and filtration is a key stage in a wide range of processing industries and also one that can be present challenges for high throughput, continuous operation. Here we demonstrate some features which increase the efficiency of ultrasound enhanced sedimentation and could enable the technology the potential to be scaled up. In this work, 20 mm piezoelectric plates were used to drive 100 mm high chambers formed from single structural elements. The coherent structural resonances were able to drive particles (yeast cells) in the water to nodes throughout the chamber. Ultrasound enhanced sedimentation was used to demonstrate the efficiency of the system (>99% particle clearance). Sub-wavelength pin protrusions were used for the contacts between the resonant chamber and other elements. The pins provided support and transferred power, replacing glue which is inefficient for power transfer. Filtration energies of ∼4 J/ml of suspension were measured. A calculation of thermal convection indicates that the circulation could disrupt cell alignment in ducts >35 mm high when a 1K temperature gradient is present; we predict higher efficiencies when this maximum height is observed. For the acoustic design, although modelling was minimal before construction, the very simple construction allowed us to form 3D models of the nodal patterns in the fluid and the duct structure. The models were compared with visual observations of particle movement, Chladni figures and scanning laser vibrometer mapping. This demonstrates that nodal planes in the fluid can be controlled by the position of clamping points and that the contacts could be positioned to increase the efficiency and reliability of particle manipulations in standing waves.

We characterise novel propagation modes that occur when semi-infinite air fingers and finite air bubbles displace viscous fluid from microchannels. The presence of an axially-uniform rectangular occlusion within a rectangular cross-section leads to a mul- tiplicity of modes, in contrast to the single symmetric mode present in unoccluded channels. For air fingers, the asymmetric 1, oscillatory 2 and localised modes 3 first identified in millimetric channels persist at the micron-scale, confirming that significant gravitational effects are not necessary to support these states. Sufficiently large finite bubbles exhibit analogous modes with quanti- tatively similar flow measures, indicating that the physical mechanisms supporting the propagation modes of finite bubbles are the same as those identified for the air fingers 4. In contrast to the air fingers, in which oscillations are always initiated near the finger tip and propagate backwards, oscillations in finite bubbles can arise from either end of the bubble.