Microfluidic Shrinking Droplet Concentrator for Analyte Detection and Phase Separation of Protein Solutions.

We develop a droplet microfluidic platform to increase the concentration of analytes in solution via reduction of the sample volume under well-defined conditions. This approach improves the detection and quantification of analytes without requiring any a priori information on their structure nor physical chemical properties. Samples are compartmentalized and processed in water-in-oil droplets that are individually stored in cylindrical microwells located on top of a microfluidic channel. The individual droplets shrink over time due to water extraction in the surrounding oil, leading to an increase in the analyte concentration up to 100,000-fold within the droplet. We demonstrate the power of this approach for detection applications by quantifying a broad range of single analytes such as small molecules, proteins, nanoparticles, exosomes, and amyloid fibrils. With this setup, we can measure pM concentrations, corresponding to zeptomole (10-21 mol) amounts encapsulated in individual droplets. We further show that the droplet concentrator device, or DroMiCo, can quantify unlabeled proteins in nM concentrations and analyze multicomponent mixtures when coupled with a prefractionation step. We illustrate this concept by detecting femtomoles (10-15 mol) of soluble protein oligomers prefractionated by size exclusion chromatography. Finally, we apply the DroMiCo to the analysis of phase diagrams of macromolecules, including synthetic polymers and proteins. Specifically, we analyze the liquid-liquid phase separation of an in vitro model of cellular membraneless compartments, composed of a phase separating protein in the presence of defined concentrations of molecular modulators such as RNA and ATP.

Enhancing Light Absorption and Charge Transfer Efficiency in Carbon Dots through Graphitization and Core Nitrogen Doping.

Single-source precursor syntheses have been devised for the preparation of structurally similar graphitic carbon dots (CDs), with (g-N-CD) and without (g-CD) core nitrogen doping for artificial photosynthesis. An order of magnitude improvement has been realized in the rate of solar (AM1.5G) H2 evolution using g-N-CD (7950 µmolH2 (gCD )-1 h-1 ) compared to undoped CDs. All graphitized CDs show significantly enhanced light absorption compared to amorphous CDs (a-CD) yet undoped g-CD display limited photosensitizer ability due to low extraction of photogenerated charges. Transient absorption spectroscopy showed that nitrogen doping in g-N-CD increases the efficiency of hole scavenging by the electron donor and thereby significantly extends the lifetime of the photogenerated electrons. Thus, nitrogen doping allows the high absorption coefficient of graphitic CDs to be translated into high charge extraction for efficient photocatalysis.

Solar H2 evolution in water with modified diketopyrrolopyrrole dyes immobilised on molecular Co and Ni catalyst-TiO2 hybrids.

A series of diketopyrrolopyrrole (DPP) dyes with a terminal phosphonic acid group for attachment to metal oxide surfaces were synthesised and the effect of side chain modification on their properties investigated. The organic photosensitisers feature strong visible light absorption (λ = 400 to 575 nm) and electrochemical and fluorescence studies revealed that the excited state of all dyes provides sufficient driving force for electron injection into the TiO2 conduction band. The performance of the DPP chromophores attached to TiO2 nanoparticles for photocatalytic H2 evolution with co-immobilised molecular Co and Ni catalysts was subsequently studied, resulting in solar fuel generation with a dye-sensitised semiconductor nanoparticle system suspended in water without precious metal components. The performance of the DPP dyes in photocatalysis did not only depend on electronic parameters, but also on properties of the side chain such as polarity, steric hinderance and hydrophobicity as well as the specific experimental conditions and the nature of the sacrificial electron donor. In an aqueous pH 4.5 ascorbic acid solution with a phosphonated DuBois-type Ni catalyst, a DPP-based turnover number (TONDPP) of up to 205 was obtained during UV-free simulated solar light irradiation (100 mW cm-2, AM 1.5G, λ > 420 nm) after 1 day. DPP-sensitised TiO2 nanoparticles were also successfully used in combination with a hydrogenase or platinum instead of the synthetic H2 evolution catalysts and the platinum-based system achieved a TONDPP of up to 2660, which significantly outperforms an analogous system using a phosphonated Ru tris(bipyridine) dye (TONRu = 431). Finally, transient absorption spectroscopy was performed to study interfacial recombination and dye regeneration kinetics revealing that the different performances of the DPP dyes are most likely dictated by the different regeneration efficiencies of the oxidised chromophores.