The translation of batch chemistries onto continuous flow platforms requires addressing the issues of consistent fluidic behaviour, channel fouling and high-throughput processing. Droplet microfluidic technologies reduce channel fouling and provide an improved level of control over heat and mass transfer to control reaction kinetics. However, in conventional geometries, the droplet size is sensitive to changes in flow rates. Here we report a three-dimensional droplet generating device that exhibits flow invariant behaviour and is robust to fluctuations in flow rate. In addition, the droplet generator is capable of producing droplet volumes spanning four orders of magnitude. We apply this device in a parallel network to synthesize platinum nanoparticles using an ionic liquid solvent, demonstrate reproducible synthesis after recycling the ionic liquid, and double the reaction yield compared with an analogous batch synthesis.

Droplet-based microfluidic platforms have the potential to provide superior control over mixing as compared to traditional batch reactions. Ionic liquids have advantageous properties for metal nanoparticle synthesis as a result of their low interfacial tension and complexing ability; however, droplet formation of ionic liquids within microfluidic channels in a two-phase system has not yet been attained because of their complex interfacial properties and high viscosities. Here, breakup of an imidazolium-based ionic liquid into droplets in a simple two-phase system has for the first time been achieved and characterized by using a microchannel modified with a thin film fluoropolymer. This microfluidic/ionic liquid droplet system was used to produce small, spherical gold (4.28 ± 0.84 nm) and silver (3.73 ± 0.77 nm) nanoparticles.

We have employed a simple modular approach to install small chalcogenol ligands on the surface of CdSe nanocrystals. This versatile modification strategy provides access to thiol, selenol, and tellurol ligand sets via the in situ reduction of R2E2 (R=tBu, Bn, Ph; E=S, Se, Te) by diphenylphosphine (Ph2PH). The ligand exchange chemistry was analyzed by solution NMR spectroscopy, which reveals that reduction of the R2E2 precursors by Ph2PH directly yields active chalcogenol ligands that subsequently bind to the surface of the CdSe nanocrystals. Thermogravimetric analysis, FT-IR spectroscopy, and energy dispersive X-ray spectroscopy provide further evidence for chalcogenol addition to the CdSe surface with a concomitant reduction in overall organic content from the displacement of native ligands. Time-resolved and low temperature photoluminescence measurements showed that all of the phenylchalcogenol ligands rapidly quench the photoluminescence by hole localization onto the ligand. Selenol and tellurol ligands exhibit a larger driving force for hole transfer than thiol ligands and therefore quench the photoluminescence more efficiently. The hole transfer process could lead to engineering long-lived, partially separated excited states.

We have studied the dynamics of Lissamine Rhodamine B dye sensitization-induced oxidation of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) giant unilamellar vesicles (GUVs), where the progression of the underlying chemical processes was followed via vesicle membrane area changes. The surface-area-to-volume ratio of our spherical GUVs increased after as little as ten seconds of irradiation. The membrane area expansion was coupled with high amplitude fluctuations not typical of GUVs in isoosmotic conditions. To accurately measure the area of deformed and fluctuating membranes, we utilized a dual-beam optical trap (DBOT) to stretch GUV membranes into a geometrically regular shape. Further oxidation led to vesicle contraction, and the GUVs became tense, with micron-scale pores forming in the bilayer. We analyzed the GUV morphological behaviors as two consecutive rate-limiting steps. We also considered the effects of altering DOPC and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(lissamine rhodamine B sulfonyl) (RhDPPE) concentrations. The resulting kinetic model allows us to measure how lipid molecular area changes during oxidation, as well as to determine the rate constants controlling how quickly oxidation products are formed. Controlled membrane oxidation leading to permeabilization is also a potential tool for drug delivery based on engineered photosensitizer-containing lipid vesicles.

Droplet microfluidics has become a powerful tool in precision medicine, green biotechnology, and cell therapy for single-cell analysis and selection by virtue of its ability to effectively confine cells. However, there remains a fundamental trade-off between droplet volume and sorting throughput, limiting the advantages of droplet microfluidics to small droplets (<10 pl) that are incompatible with long-term maintenance and growth of most cells. We present a sequentially addressable dielectrophoretic array (SADA) sorter to overcome this problem. The SADA sorter uses an on-chip array of electrodes activated and deactivated in a sequence synchronized to the speed and position of a passing target droplet to deliver an accumulated dielectrophoretic force and gently pull it in the direction of sorting in a high-speed flow. We use it to demonstrate large-droplet sorting with ~20-fold higher throughputs than conventional techniques and apply it to long-term single-cell analysis of Saccharomyces cerevisiae based on their growth rate.