On-demand generation and mixing of liquid-in-gas slugs with digitally-programmable composition and size

Accelerating radiochemistry development: Automated robotic platform for performing up to 64 droplet radiochemical reactions in a morning

The growing discovery and development of novel radiopharmaceuticals and radiolabeling methods requires an increasing capacity for radiochemistry experiments. However, such studies typically rely on radiosynthesizers designed for clinical batch production rather than research, greatly limiting throughput. Two general solutions are being pursued to address this: developing new synthesis optimization algorithms to minimize how many experiments are needed, and developing apparatus with enhanced experiment throughput. We describe here a novel high-throughput system based on performing arrays of droplet-based reactions at 10 μL volume scale in parallel. The automatic robotic platform can perform a set of 64 experiments in ~3 h (from isotope loading to crude product, plus sampling onto TLC plates), plus ~1 h for off-line radio-TLC analysis and radioactivity measurements, rather than the weeks or months that would be needed using a conventional system. We show the high repeatability and low crosstalk of the platform and demonstrate optimization studies for two 18F-labeled tracers. This novel automated platform greatly increases the practicality of performing arrays of droplet reactions by eliminating human error, vastly reducing tedium and fatigue, minimizing radiation exposure, and freeing up radiochemist time for other intellectually valuable pursuits.

Microliter-scale reaction arrays for economical high-throughput experimentation in radiochemistry

The increasing number of positron-emission tomography (PET) tracers being developed to aid drug development and create new diagnostics has led to an increased need for radiosynthesis development and optimization. Current radiosynthesis instruments are designed to produce large-scale clinical batches and are often limited to performing a single synthesis before they must be decontaminated by waiting for radionuclide decay, followed by thorough cleaning or disposal of synthesizer components. Though with some radiosynthesizers it is possible to perform a few sequential radiosyntheses in a day, none allow for parallel radiosyntheses. Throughput of one or a few experiments per day is not well suited for rapid optimization experiments. To combat these limitations, we leverage the advantages of droplet-radiochemistry to create a new platform for high-throughput experimentation in radiochemistry. This system contains an array of 4 heaters, each used to heat a set of 16 reactions on a small chip, enabling 64 parallel reactions for the rapid optimization of conditions in any stage of a multi-step radiosynthesis process. As examples, we study the syntheses of several ¹⁸F-labeled radiopharmaceuticals ([¹⁸F]Flumazenil, [¹⁸F]PBR06, [¹⁸F]Fallypride, and [¹⁸F]FEPPA), performing > 800 experiments to explore the influence of parameters including base type, base amount, precursor amount, solvent, reaction temperature, and reaction time. The experiments were carried out within only 15 experiment days, and the small volume (~ 10 μL compared to the ~ 1 mL scale of conventional instruments) consumed ~ 100 × less precursor per datapoint. This new method paves the way for more comprehensive optimization studies in radiochemistry and substantially shortening PET tracer development timelines.

Cerenkov Luminescence Imaging in the Development and Production of Radiopharmaceuticals

Over the past several years there has been an explosion of interest in exploiting Cerenkov radiation to enable in vivo and intraoperative optical imaging of subjects injected with trace amounts of radiopharmaceuticals. At the same time, Cerenkov luminescence imaging (CLI) also has been serving as a critical tool in radiochemistry, especially for the development of novel microfluidic devices for producing radiopharmaceuticals. By enabling microfluidic processes to be monitored non-destructively in situ, CLI has made it possible to literally watch the activity distribution as the synthesis occurs, and to quantitatively measure activity propagation and losses at each step of synthesis, paving the way for significant strides forward in performance and robustness of those devices. In some cases, CLI has enabled detection and resolution of unexpected problems not observable via standard optical methods. CLI is also being used in analytical radiochemistry to increase the reliability of radio-thin layer chromatography (radio-TLC) assays. Rapid and high-resolution Cerenkov imaging of radio-TLC plates enables detection of issues in the spotting or separation process, improves chromatographic resolution (and/or allows reduced separation distance and time), and enables increased throughput by allowing multiple samples to be spotted side-by-side on a single TLC plate for parallel separation and readout. In combination with new multi-reaction microfluidic chips, this is creating a new possibility for high-throughput optimization in radiochemistry. In this mini review, we provide an overview of the role that CLI has played to date in the radiochemistry side of radiopharmaceuticals.

Novel volumetric method for highly repeatable injection in microchip electrophoresis

A novel injector for microchip electrophoresis (MCE) has been designed and evaluated that achieves very high repeatability of injection volume suitable for quantitative analysis. It eliminates the injection biases in electrokinetic injection and the dependence on pressure and sample properties in hydrodynamic injection. The microfluidic injector, made of poly(dimethylsiloxane) (PDMS), operates similarly to an HPLC injection valve. It contains a channel segment (chamber) with a well-defined volume that serves as an "injection loop". Using on-chip microvalves, the chamber can be connected to the sample source during the "loading" step, and to the CE separation channel during the "injection" step. Once the valves are opened in the second state, electrophoretic potential is applied to separate the sample. For evaluation and demonstration purposes, the microinjector was connected to a 75 μm ID capillary and UV absorbance detector. For single compounds, a relative standard deviation (RSD) of peak area as low as 1.04% (n = 11) was obtained, and for compound mixtures, RSD as low as 0.40% (n = 4) was observed. Using the same microchip, the performance of this new injection technique was compared to hydrodynamic injection and found to have improved repeatability and less dependence on sample viscosity. Furthermore, a non-radioactive version of the positron-emission tomography (PET) imaging probe, FLT, was successfully separated from its known 3 structurally-similar byproducts with baseline resolution, demonstrating the potential for rapid, quantitative analysis of impurities to ensure the safety of batches of short-lived radiotracers. Both the separation efficiency and injection repeatability were found to be substantially higher when using the novel volumetric injection approach compared to electrokinetic injection (performed in the same chip). This novel microinjector provides a straightforward way to improve the performance of hydrodynamic injection and enables extremely repeatable sample volume injection in MCE. It could be used in any MCE application where volume repeatability is needed, including the quantitation of impurities in pharmaceutical or radiopharmaceutical samples.