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Representative Results






Optimization of Radiochemical Reactions using Droplet Arrays

Published: February 12th, 2021



1Physics and Biology in Medicine Interdepartmental Graduate Program, University of California Los Angeles (UCLA), 2Crump Institute of Molecular Imaging, UCLA, 3Department of Molecular & Medical Pharmacology, David Geffen School of Medicine, 4Department of Bioengineering, UCLA

This method describes the use of a novel high-throughput methodology, based on droplet chemical reactions, for the rapid and economical optimization of radiopharmaceuticals using nanomole amounts of reagents.

Current automated radiosynthesizers are designed to produce large clinical batches of radiopharmaceuticals. They are not well suited for reaction optimization or novel radiopharmaceutical development since each data point involves significant reagent consumption, and contamination of the apparatus requires time for radioactive decay before the next use. To address these limitations, a platform for performing arrays of miniature droplet-based reactions in parallel, each confined within a surface-tension trap on a patterned polytetrafluoroethylene-coated silicon "chip", was developed. These chips enable rapid and convenient studies of reaction parameters including reagent concentrations, reaction solvent, reaction temperature and time. This platform permits the completion of hundreds of reactions in a few days with minimal reagent consumption, instead of taking months using a conventional radiosynthesizer.

Positron-emission tomography (PET) radiopharmaceuticals are widely used as research tools to monitor specific in vivo biochemical processes and study diseases, and for the development of new drugs and therapies. Moreover, PET is a critical tool for diagnosing or staging disease and monitoring a patient's response to therapy1,2,3. Due to the short half-life of PET radioisotopes (e.g., 110 min for fluorine-18-labeled radiopharmaceuticals) and radiation hazard, these compounds are prepared using specialized automated systems operating behind radiation shielding and must be p....

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CAUTION: This protocol involves the handling of radioactive materials. Experiments should not be undertaken without the necessary training and personal protective equipment and approval from the radiation safety office at your organization. Experiments should be performed behind radiation shielding, preferably in a ventilated hot cell

1. Fabrication of multi-reaction chips

NOTE: Batches of multi-reaction microdroplet chips are fabricated from 4" silicon wafers usi.......

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A representative experiment was performed to illustrate this method. Using 16 reactions, optimization studies of the radiopharmaceutical [18F]fallypride were performed by varying precursor concentration (77, 39, 19, 9.6, 4.8, 2.4, 1.2, and 0.6 mM) in thexyl alcohol:MeCN (1:1, v/v) as the reaction solvent. Reactions were performed at 110 °C for 7 min. Collection efficiency, sample composition (i.e., proportions of [18F]fallypride product, unreacted [18.......

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Due to limitations of conventional radiochemistry systems that allow only one or a small number of reactions per day and consume a significant quantity of reagents per data point, only a tiny portion of the overall reaction parameter space can be explored in practice, and many times results are reported with no repeats (n=1). Compared to conventional systems, this multi-reaction droplet radiosynthesis platform makes it practical to accomplish more comprehensive and rigorous studies of radiosynthesis conditions while cons.......

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We thank the UCLA Biomedical Cyclotron Facility and Dr. Roger Slavik and Dr. Giuseppe Carlucci for generously providing [18F]fluoride for these studies and the UCLA NanoLab for support with equipment for chip fabrication.


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Name Company Catalog Number Comments
2,3-dimethyl-2-butanol (thexyl alcohol) Sigma-Aldrich 594-60-5 98%
Acetone KMG Chemicals Cleanroom LP grade
Ammonium formate (NH4HCO2) Sigma-Aldrich 540-69-2 97%
Anhydrous acetonitrile (MeCN) Sigma-Aldrich 75-05-8 99.80%
Ceramic heater Watlow Utramic CER-1-01-0093 25 mm x 25 mm
Cerenkov imaging chamber Custom built Other instruments can be used for TLC plate readout including: small animal in vivo optical imaging system, 2D radio-TLC scanner, 1D radio-TLC scanner
DI water Sigma-Aldrich 7732-18-5
Disposable transfer pipets, 3 mL Falcon 13-680-50
Dose calibrator Capintec, Inc. CRC-25 PET
Fallypride ABX Advanced Biochemical Compounds 1560.0010.000 Fallypride reference standard, >95%
[18F]fluoride in [18O]H2O UCLA Ahmanson Biomedical Cyclotron Facility Due to short half-life this must be obtained from local radiochemistry lab or commercial radiopharmacy
Glass cover plates (76.2 mm x 50.8 mm x 1 mm thick) C&A Scientific 6101
Headway spin coater Headway Research, Inc. PWM50-PS-R790 Sipinner system PWM50-control box, PS-motor, R790-bowl
High temperature oven Carbolite HTCR 6 28
Hot plate Thermo Scientific Super-Nuova HP133425
Isopropanol (IPA) KMG Chemicals Cleanroom LP grade
Mask aligner Karl Suss MA/BA6
Methanol (MeOH) Sigma-Aldrich 67-56-1 ≥99.9%
Microcentrifuge tube Eppendorf 0030 123.301 500 µL, colorless, polypropylene
Micropipette (0.5-10 µL) Labnet BioPette P3940-10
Micropipette (100-1000 µL) Labnet BioPette P3940-1000
Micropipette (10-100 µL) Labnet BioPette P3940-100
Micropipette tips (0.1-10 µL) USA Scientific Inc Tips 11113810
Micropipette tips (2-200 µL) BrandTech 13-889-143
Micropipette tips (50-1000 µL) BrandTech 13-889-145
Photoresist developer solution MicroChem MEGAPOSIT MF-26A
Positive photoresist MicroChem MEGAPOSIT 220-7.0
Reactive-ion etcher (RIE) Oxford Instruments Plasma Lab 80 Plus
Silicon wafer cutter Euro Tool CSCB-431.00
Silicon wafer; 4" diameter Silicon Valley Microelectronics Inc.  0017227-048 P type, boron doped, thickness 525 ± 25 µm
Teflon AF 2400 Chemours  D14896765 1% solids
Tetrabutylammonium bicarbonate (TBAHCO3) ABX Advanced Biochemical Compounds 808 Aqueous solution stabilized with ethanol, 0.075 M
Themal conducting paste OMEGA OT-201-2
TLC plates Merck KGaA 1.05554.0001 Silica gel 60 F254, 50 mm x 60 mm, aluminum back
Tosyl-fallypride ABX Advanced Biochemical Compounds 1550.004.000 Fallypride precursor, >90%
Trimethylamine (TEA) Sigma-Aldrich 75-50-3 ≥ 99%
Tweezers Cole-Parmer UX-07387-08 Stainless steel, fine tip

  1. Matthews, P. M., Rabiner, E. A., Passchier, J., Gunn, R. N. Positron emission tomography molecular imaging for drug development. British Journal of Clinical Pharmacology. 73 (2), 175-186 (2012).
  2. Piel, M., Vernaleken, I., Rösch, F. Positron emission tomography in CNS drug discovery and drug monitoring. Journal of Medicinal Chemistry. 57 (22), 9232-9258 (2014).
  3. Cherry, S. R., Sorenson, J. A., Phelps, M. E. . Physics in Nuclear Medicine. , (2012).
  4. Knapp, K. -. A., Nickels, M. L., Manning, H. C. The current role of microfluidics in radiofluorination chemistry. Molecular Imaging and Biology. 22 (3), 463-475 (2020).
  5. Rensch, C., et al. Microfluidics: A groundbreaking technology for PET tracer production. Molecules. 18 (7), 7930-7956 (2013).
  6. Pascali, G., Watts, P., Salvadori, P. A. Microfluidics in radiopharmaceutical chemistry. Nuclear Medicine and Biology. 40 (6), 776-787 (2013).
  7. Keng, P. Y., van Dam, R. M. Digital microfluidics: A new paradigm for radiochemistry. Molecular Imaging. 14, 579-594 (2015).
  8. Wang, J., Chao, P. H., Janet, S., van Dam, R. M. Performing multi-step chemical reactions in microliter-sized droplets by leveraging a simple passive transport mechanism. Lab on a Chip. 17 (24), 4342-4355 (2017).
  9. Wang, J., Chao, P. H., van Dam, R. M. Ultra-compact, automated microdroplet radiosynthesizer. Lab on a Chip. (19), 2415-2424 (2019).
  10. Rios, A., Wang, J., Chao, P. H., van Dam, R. M. A novel multi-reaction microdroplet platform for rapid radiochemistry optimization. RSC Advances. 9 (35), 20370-20374 (2019).
  11. Sergeev, M., et al. Performing radiosynthesis in microvolumes to maximize molar activity of tracers for positron emission tomography. Communications Chemistry. 1 (1), 10 (2018).
  12. Pascali, G., et al. Optimization of nucleophilic 18F radiofluorinations using a microfluidic reaction approach. Nature Protocols. 9 (9), 2017-2029 (2014).
  13. Lisova, K., et al. Microscale radiosynthesis, preclinical imaging and dosimetry study of [18F]AMBF3-TATE: A potential PET tracer for clinical imaging of somatostatin receptors. Nuclear Medicine and Biology. 61, 36-44 (2018).
  14. Wang, J., et al. High-throughput radio-TLC analysis. Nuclear Medicine and Biology. 82-83, 41-48 (2020).
  15. Dooraghi, A. A., et al. Optimization of microfluidic PET tracer synthesis with Cerenkov imaging. Analyst. 138 (19), 5654-5664 (2013).
  16. Collins, J., et al. Production of diverse PET probes with limited resources: 24 18F-labeled compounds prepared with a single radiosynthesizer. Proceedings of the National Academy of Sciences. 114 (43), 11309-11314 (2017).
  17. Lazari, M., et al. Fully automated production of diverse 18F-labeled PET tracers on the ELIXYS multireactor radiosynthesizer without hardware modification. Journal of Nuclear Medicine Technology. 42 (3), 203-210 (2014).
  18. Lisova, K., et al. Rapid, efficient, and economical synthesis of PET tracers in a droplet microreactor: application to O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET). EJNMMI Radiopharmacy and Chemistry. 5 (1), 1 (2019).
  19. Wang, J., Holloway, T., Lisova, K., van Dam, R. M. Green and efficient synthesis of the radiopharmaceutical [18F]FDOPA using a microdroplet reactor. Reaction Chemistry & Engineering. 5 (2), 320-329 (2020).
  20. Lisova, K., Wang, J., Rios, A., van Dam, R. M. Adaptation and optimization of [F-18] Florbetaben ([F-18] FBB) radiosynthesis to a microdroplet reactor. Journal of Labelled Compounds and Radiopharmaceuticals. 62, 353-354 (2019).
  21. Wang, J., Chao, P. H., Slavik, R., van Dam, R. M. Multi-GBq production of the radiotracer [18F]fallypride in a droplet microreactor. RSC Advances. 10 (13), 7828-7838 (2020).

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