Highly Active Ice-Nucleating Particles at the Summer North Pole.

The amount of ice versus supercooled water in clouds is important for their radiative properties and role in climate feedbacks. Hence, knowledge of the concentration of ice-nucleating particles (INPs) is needed. Generally, the concentrations of INPs are found to be very low in remote marine locations allowing cloud water to persist in a supercooled state.

Homogeneous Freezing of Water Using Microfluidics.

The homogeneous freezing of water is important in the formation of ice in clouds, but there remains a great deal of variability in the representation of the homogeneous freezing of water in the literature. The development of new instrumentation, such as droplet microfluidic platforms, may help to constrain our understanding of the kinetics of homogeneous freezing via the analysis of monodisperse, size-selected water droplets in temporally and spatially controlled environments. Here, we evaluate droplet freezing data obtained using the Lab-on-a-Chip Nucleation by Immersed Particle Instrument (LOC-NIPI), in which droplets are generated and frozen in continuous flow.

On-chip density-based sorting of supercooled droplets and frozen droplets in continuous flow.

The freezing of supercooled water to ice and the materials which catalyse this process are of fundamental interest to a wide range of fields. At present, our ability to control, predict or monitor ice formation processes is poor. The isolation and characterisation of frozen droplets from supercooled liquid droplets would provide a means of improving our understanding and control of these processes.

On-chip analysis of atmospheric ice-nucleating particles in continuous flow.

Ice-nucleating particles (INPs) are of atmospheric importance because they catalyse the freezing of supercooled cloud droplets, strongly affecting the lifetime and radiative properties of clouds. There is a need to improve our knowledge of the global distribution of INPs, their seasonal cycles and long-term trends, but our capability to make these measurements is limited. Atmospheric INP concentrations are often determined using assays involving arrays of droplets on a cold stage, but such assays are frequently limited by the number of droplets that can be analysed per experiment, often involve manual processing (e.

On-chip electrochemical detection of glucose towards the miniaturised quality control of carbohydrate-based radiotracers.

The miniaturisation of positron emission tomography (PET) radiotracer production is facilitating a move towards a dose-on-demand strategy that would enable a stratified approach to patient diagnostics, but while the on-chip synthesis steps have been demonstrated, the subsequent quality control (QC) testing steps have received much less attention. As part of the development of an integrated QC platform for PET tracers, we have developed two microfluidic electrochemical detectors for the pulsed amperometric detection (PAD) of carbohydrate-based radiotracers, with a particular view to the QC testing of the most important tracer, [F]2-fluoro-2-deoxy-d-glucose ([F]FDG). The first device employed a commercial screen-printed electrode (SPE) to enable a single-use format, while the second device incorporated wire electrodes for use as a more permanent fixture in a QC instrument.

High-speed imaging of ice nucleation in water proves the existence of active sites.

Understanding how surfaces direct nucleation is a complex problem that limits our ability to predict and control crystal formation. We here address this challenge using high-speed imaging to identify and quantify the sites at which ice nucleates in water droplets on the two natural cleavage faces of macroscopic feldspar substrates. Our data show that ice nucleation only occurs at a few locations, all of which are associated with micron-size surface pits.

Plastic Scintillator-Based Microfluidic Devices for Miniaturized Detection of Positron Emission Tomography Radiopharmaceuticals.

A miniaturized radio-HPLC detector has been developed comprising a microfluidic device fabricated from plastic scintillator in combination with a silicon photomultiplier light sensor, and tested with samples containing a positron-emitting radionuclide, [ F]fluoride. This cost-effective, small footprint analytical tool is ideal for incorporation into integrated quality control systems for the testing of positron emission tomography (PET) radiopharmaceuticals to good manufacturing practice (GMP) standards.

The study of atmospheric ice-nucleating particles via microfluidically generated droplets.

Ice-nucleating particles (INPs) play a significant role in the climate and hydrological cycle by triggering ice formation in supercooled clouds, thereby causing precipitation and affecting cloud lifetimes and their radiative properties. However, despite their importance, INP often comprise only 1 in 10-10 ambient particles, making it difficult to ascertain and predict their type, source, and concentration. The typical techniques for quantifying INP concentrations tend to be highly labour-intensive, suffer from poor time resolution, or are limited in sensitivity to low concentrations.

Correction: On-chip polyelectrolyte coating onto magnetic droplets - towards continuous flow assembly of drug delivery capsules.

Correction for 'On-chip polyelectrolyte coating onto magnetic droplets - towards continuous flow assembly of drug delivery capsules' by Ali Q. Alorabi et al., Lab Chip, 2017, DOI: 10.

On-chip polyelectrolyte coating onto magnetic droplets - towards continuous flow assembly of drug delivery capsules.

Polyelectrolyte (PE) microcapsules for drug delivery are typically fabricated via layer-by-layer (LbL) deposition of PE layers of alternating charge on sacrificial template microparticles, which usually requires multiple incubation and washing steps that render the process repetitive and time-consuming. Here, ferrofluid droplets were explored for this purpose as an elegant alternative of templates that can be easily manipulated via an external magnetic field, and require only a simple microfluidic chip design and setup. Glass microfluidic devices featuring T-junctions or flow focusing junctions for the generation of oil-based ferrofluid droplets in an aqueous continuous phase were investigated.

Van de Graaff generator for capillary electrophoresis.

A new approach for high voltage capillary electrophoresis (CE) is proposed, which replaces the standard high voltage power supply with a Van de Graaff generator, a low current power source. Because the Van de Graaff generator is a current-limited source (10μA), potentials exceeding 100kV can be generated for CE when the electrical resistance of the capillary is maximized. This was achieved by decreasing the capillary diameter and reducing the buffer ionic strength.

A Microfluidic Device for Rapid Screening of E. coli O157:H7 Based on IFAST and ATP Bioluminescence Assay for Water Analysis.

We present a simple microfluidic system for rapid screening of Escherichia coli (E. coli) O157:H7 employing the specificity of immunomagnetic separation (IMS) via immiscible filtration assisted by surface tension (IFAST), and the sensitivity of the subsequent adenosine triphosphate (ATP) assay by the bioluminescence luciferin/luciferase reaction. The developed device was capable of detecting E.

On-Chip Magnetic Particle-Based Immunoassays Using Multilaminar Flow for Clinical Diagnostics.

Magnetic particles have become popular in recent years for immunoassays due to their high surface-to-volume ratio and the ease of their manipulation. However, such assays also require multiple reaction and washing steps that are both time-consuming and manually laborious. Here, we describe a setup and methodology for performing rapid immunoassays on magnetic particles in continuous flow via their deflection through multiple laminar flow streams of reagents and washing solutions.

Magnetic Particle Plug-Based Assays for Biomarker Analysis.

Conventional immunoassays offer selective and quantitative detection of a number of biomarkers, but are laborious and time-consuming. Magnetic particle-based assays allow easy and rapid selection of analytes, but still suffer from the requirement of tedious multiple reaction and washing steps. Here, we demonstrate the trapping of functionalised magnetic particles within a microchannel for performing rapid immunoassays by flushing consecutive reagent and washing solutions over the trapped particle plug.

Development of radiodetection systems towards miniaturised quality control of PET and SPECT radiopharmaceuticals.

The ability to detect radiation in microfluidic devices is important for the on-chip analysis of radiopharmaceuticals, but previously reported systems have largely suffered from various limitations including cost, complexity of fabrication, and insufficient sensitivity and/or speed. Here, we present the use of sensitive, low cost, small-sized, commercially available silicon photomultipliers (SiPMs) for the detection of radioactivity inside microfluidic channels fabricated from a range of conventional microfluidic chip substrates. We demonstrate the effects of chip material and thickness on the detection of the positron-emitting isotope, [(18)F]fluoride, and find that, while the SiPMs are light sensors, they are able to detect radiation even through opaque chip materials via direct positron and gamma (γ) ray interaction.

Positron detection in silica monoliths for miniaturised quality control of PET radiotracers.

We demonstrate the use of the miniaturised Medipix positron sensor for detection of the clinical PET radiotracer, [(68)Ga]gallium-citrate, on a silica-based monolith, towards microfluidic quality control. The system achieved a far superior signal-to-noise ratio compared to conventional sodium iodide-based radio-HPLC detection and allowed real-time visualisation of positrons in the monolith.

Lab-on-a-chip workshop activities for secondary school students.

The ability to engage and inspire younger generations in novel areas of science is important for bringing new researchers into a burgeoning field, such as lab-on-a-chip. We recently held a lab-on-a-chip workshop for secondary school students, for which we developed a number of hands-on activities that explained various aspects of microfluidic technology, including fabrication (milling and moulding of microfluidic devices, and wax printing of microfluidic paper-based analytical devices, so-called μPADs), flow regimes (gradient formation via diffusive mixing), and applications (tissue analysis and μPADs). Questionnaires completed by the students indicated that they found the workshop both interesting and informative, with all activities proving successful, while providing feedback that could be incorporated into later iterations of the event.

On-chip determination of C-reactive protein using magnetic particles in continuous flow.

We demonstrate the application of a multilaminar flow platform, in which functionalized magnetic particles are deflected through alternating laminar flow streams of reagents and washing solutions via an external magnet, for the rapid detection of the inflammatory biomarker, C-reactive protein (CRP). The two-step sandwich immunoassay was accomplished in less than 60 s, a vast improvement on the 80-300 min time frame required for enzyme-linked immunosorbent assays (ELISA) and the 50 min necessary for off-chip magnetic particle-based assays. The combination of continuous flow and a stationary magnet enables a degree of autonomy in the system, while a detection limit of 0.

Phaseguide assisted liquid lamination for magnetic particle-based assays.

We have developed a magnetic particle-based assay platform in which functionalised magnetic particles are transferred sequentially through laminated volumes of reagents and washing buffers. Lamination of aqueous liquids is achieved via the use of phaseguide technology; microstructures that control the advancing air-liquid interface of solutions as they enter a microfluidic chamber. This allows manual filling of the device, eliminating the need for external pumping systems, and preparation of the system requires only a few minutes.

On-chip processing of particles and cells via multilaminar flow streams.

The processing of particles, cells, and droplets for reactions, analyses, labeling, and coating is an important aspect of many microfluidic workflows. However, performing multi-step processes is typically a laborious and time-consuming endeavor. By exploiting the laminar nature of flow within microchannels, such procedures can benefit in terms of both speed and simplicity.

Radiochemistry on chip: towards dose-on-demand synthesis of PET radiopharmaceuticals.

We have developed an integrated microfluidic platform for producing 2-[(18)F]-fluoro-2-deoxy-D-glucose ((18)F-FDG) in continuous flow from a single bolus of radioactive isotope solution, with constant product yields achieved throughout the operation that were comparable to those reported for commercially available vessel-based synthesisers (40-80%). The system would allow researchers to obtain radiopharmaceuticals in a dose-on-demand setting within a few minutes. The flexible architecture of the platform, based on a modular design, can potentially be applied to the synthesis of other radiotracers that require a two-step synthetic approach, and may be adaptable to more complex synthetic routes by implementing additional modules.

Purification of 2-[18F]fluoro-2-deoxy-d-glucose by on-chip solid-phase extraction.

Microfluidic devices have shown great potential for the production of positron emission tomography (PET) radiotracers, but most devices have focused only on the synthesis step of the procedure, typically neglecting the other important steps such as [(18)F]fluoride pre-concentration and radiotracer purification that could equally benefit from miniaturisation. Here, we demonstrate the development of microfluidic modules for the purification of PET radiotracers, particularly 2-[(18)F]fluoro-2-deoxy-d-glucose ([(18)F]FDG), via the use of on-chip solid-phase extraction (SPE). In these initial tests, the SPE modules were able to yield [(18)F]FDG with up to 90% radiochemical purity, and methods are proposed for further increasing this value.

Microfluidic platforms for performing surface-based clinical assays.

The need for fast, specific and portable diagnostic systems for clinical assays has, in recent years, led to an explosion of research into microfluidic chip-based immunoassays towards rapid point-of-care analysis. Such devices exploit small dimensions, superior fluidic control and low reagent volumes to allow a number of clinically important procedures to be achieved with improvements on conventional methods, many of which rely on the surface-based binding of antigens to antibodies. Here, we discuss recent developments and innovations in the area of on-chip surface-based immunoassays and provide an outlook on the potential of such platforms for future diagnostics.

Flow focussing of particles and cells based on their intrinsic properties using a simple diamagnetic repulsion setup.

The continuous flow focussing and manipulation of particles and cells are important factors in microfluidic applications for performing accurate and reproducible procedures downstream. Many particle focussing methods require complex setups or channel designs that can limit the process and its applications. Here, we present diamagnetic repulsion as a simple means of focussing objects in continuous flow, based only on their intrinsic properties without the requirement of any label.