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, [18F]2-fluoro-2-deoxy-d-glucose ([18F]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. A flow-injection analysis (FIA)-style setup was used to inject boluses of d-glucose into the chips in a proxy for intended chromatographic separations prior to PAD. In proof-of-concept testing of the devices, the chips featuring the SPE and the wire electrodes yielded limits of detection of 0.1 ppm and 9 ppm, respectively, each below the required limits for [18F]FDG, and thus making both methodologies viable for the QC testing of PET radiotracers in a dose-on-demand format.

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, [18 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.

Modular microfluidics enables kinetic insight from time-resolved cryo-EM.

Mechanistic understanding of biochemical reactions requires structural and kinetic characterization of the underlying chemical processes. However, no single experimental technique can provide this information in a broadly applicable manner and thus structural studies of static macromolecules are often complemented by biophysical analysis. Moreover, the common strategy of utilizing mutants or crosslinking probes to stabilize intermediates is prone to trapping off-pathway artefacts and precludes determining the order of molecular events. Here we report a time-resolved sample preparation method for cryo-electron microscopy (trEM) using a modular microfluidic device, featuring a 3D-mixing unit and variable delay lines that enables automated, fast, and blot-free sample vitrification. This approach not only preserves high-resolution structural detail but also substantially improves sample integrity and protein distribution across the vitreous ice. We validate the method by visualising reaction intermediates of early RecA filament growth across three orders of magnitude on sub-second timescales. The trEM method reported here is versatile, reproducible, and readily adaptable to a broad spectrum of fundamental questions in biology.

Multiplex sorting of foodborne pathogens by on-chip free-flow magnetophoresis.

This study reports multiplex sorting of Salmonella typhimurium and Escherichia coli 0157, from broth cultures and from pathogen-spiked skinned chicken breast enrichment broths by employing microfluidic free-flow magnetophoresis. Magnetic beads of different sizes and magnetite content, namely Dynabeads anti-salmonella and Hyglos-Streptavidin beads together with the corresponding pathogen-specific biotinylated recombinant phages, were utilised as affinity solid phases for the capture and concentration of viable S. typhimurium and E. coli 0157. Following optimisation, the protocol was used to demonstrate continuous magnetophoretic sorting of the two pathogen-bound magnetic bead populations from mixed cultures and from pathogen-spiked chicken pre-enrichment broths under the influence of a Halbach magnet array. For example, in the latter case, a pure population of S. typhimurium-bound Dynabeads (72% recovery) was sorted from a 100 µL mixture containing E. coli 0157-bound Hyglos beads (67% recovery) within 1.2 min in the presence of 0.1% Tween 20. This proof-of-principle study demonstrates how more than one pathogen type can be simultaneously isolated/enriched from a single food pre-enrichment broth (e.g. Universal food enrichment broth).

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. Finally, we employed the SiPM platform for analysis of the PET (positron emission tomography) radiotracers 2-[(18)F]fluoro-2-deoxy-d-glucose ([(18)F]FDG) and [(68)Ga]gallium-citrate, and highlight the ability to detect the γ ray emitting SPECT (single photon emission computed tomography) radiotracer, [(99m)Tc]pertechnetate.

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.