Interfacial Partitioning Enhances Microextraction by Multicomponent Nanodroplets

Sensitive and reliable in-droplet chemical analysis benefits from enhanced partition of an analyte into the droplets. In this work, we will show that colorimetric chemical reactions in surface nanodroplets can shift the partition of acid analytes from a highly diluted solution to the droplets. As a result, acids appear to be more acidic in the droplets. In our experiments, seven types of organic acids with partition coefficients (LgP) ranging from −0.7 to 1.87 dissolved in an oil solution are extracted into aqueous nanodroplets on a substrate. The timescale of coupled extraction and colorimetric reaction in the droplets was revealed by the decoloration time of the droplets. Our results show that the distribution coefficient of the acid can be shifted by 3–11 times of that in bulk. Such significantly shifted partition is attributed to enhanced transfer of the acid across the droplet surface from a highly diluted solution. The interfacial activity of the analyte may be advantageous as it may also improve extraction and partition. Such enhanced extraction by chemical reaction in droplets may be leveraged for ultrasensitive chemical detection using reactive droplets

Effects of chemical and geometric microstructures on the crystallization of surface droplets during solvent exchange

In this work, we investigate the crystallization of droplets formed on micropatterned surfaces. By solvent exchange in a microchamber, a ternary solution consisting of a model compound β-alanine, water, and isopropanol was displaced by a flow of isopropanol. In the process, oiling-out droplets formed and crystallized. Our results showed that the shape and size of the crystals on surfaces with chemical micropatterns could be simply mediated by the flow conditions of solvent exchange. More uniform crystals formed on hydrophilic microdomains compared to hydrophobic microdomains or homogeneous surfaces. Varying flow rates or channel heights led to the formation of thin films with microholes, connected networks of crystals, or small diamond-shaped crystals. Physical microstructures (represented by microlenses) on the surface allowed the easy detachment of crystals from the surface. Beyond oiling-out crystallization, we demonstrated that the crystal formation of another solute dissolved in the droplets could be triggered by solvent exchange. The length of crystal fibers after the solvent-exchange process was shorter at a faster flow rate. This study may provide further understanding to effectively obtain the crystallization of surface droplets through the solvent-exchange approach

Additional file 1 of Adsorption of Hg2+/Cr6+ by metal-binding proteins heterologously expressed in Escherichia coli

Additional file 1: Table S1. The sources of genes used in this study. Table S2. Cell dry weight (g) of the engineered strains at different Hg2+/Cr6+ concentrations. Figure S1. Recombinant plasmid PCR verification gel. Figure S2. Growth curves of engineered strains

Oiling-out crystallization of Beta-Alanine on solid surfaces controlled by solvent exchange

© 2020 Wiley-VCH GmbH In this work, the solvent-exchange crystallization processes of beta-alanine in mixture of isopropanol and water on solid surfaces are reported. As the antisolvent isopropanol displaces the alanine solution pre-filled in a microchamber, liquid–liquid phase separation occurs at the mixing front. The alanine-rich subphase forms surface microdroplets that subsequently crystallize with during the solvent exchange. It is found that the flow rates and solid surfaces have significant influence on the droplet size, growth rate, and crystal size and morphology. At fast flow rates, the droplets solidify rapidly, forming spherical-cap structures resembling the shape of droplets, in contrast to crystal microdomains or thin films formed at slow flow rates. On a highly hydrophilic surface, the crystals form thin film without droplets formation. It is further demonstrated that by the solvent exchange, the crystals, generated by using a stock solution with a very low concentration of the precursor, can be used as seeds to facilitate crystallization in bulk solution. The results suggest that the solvent exchange has the potential to be an effective approach for controlling oiling-out crystallization, and to be wider applied in, such as, separation and purification of many food, medical, and therapeutic ingredients

Effects of chemical and geometric microstructures on the crystallization of surface droplets during solvent exchange

In this work, we investigate the crystallization of droplets formed on micropatterned surfaces. By solvent exchange in a microchamber, a ternary solution consisting of a model compound β-alanine, water, and isopropanol was displaced by a flow of isopropanol. In the process, oiling-out droplets formed and crystallized. Our results showed that the shape and size of the crystals on surfaces with chemical micropatterns could be simply mediated by the flow conditions of solvent exchange. More uniform crystals formed on hydrophilic microdomains compared to hydrophobic microdomains or homogeneous surfaces. Varying flow rates or channel heights led to the formation of thin films with microholes, connected networks of crystals, or small diamond-shaped crystals. Physical microstructures (represented by microlenses) on the surface allowed the easy detachment of crystals from the surface. Beyond oiling-out crystallization, we demonstrated that the crystal formation of another solute dissolved in the droplets could be triggered by solvent exchange. The length of crystal fibers after the solvent-exchange process was shorter at a faster flow rate. This study may provide further understanding to effectively obtain the crystallization of surface droplets through the solvent-exchange approach

Ultrasensitive Picomolar Detection of Aqueous Acids in Microscale Fluorescent Droplets

We report on a fluorescent-droplet-based acid-sensing scheme that allows limits of detection below 100 pM for weak acids. The concept is based on a strong partitioning of acid from an aqueous phase into octanol droplets. Using salicylic acid as a demonstration, we show that at a high concentration, the acid partitions into the organic phase by a factor of 260, which is approximately consistent with literature values. However, at lower concentrations, we obtain a partition coefficient as high as 106, which is partly responsible for the excellent sensing performance. The enhanced equilibrium partitioning is likely due to the interaction of the dissociated acid phase with the sensor dye employed for this work. The effect of droplet size was determined, after which we derived a simple model to predict the time dependence of the color change as a function of droplet size. This work shows that color-change fluorescent-droplet-based detection is a promising avenue that can lead to exceptional sensing performance from an aqueous analyte

NIR-II Luminescent and Multi-Responsive Rare Earth Nanocrystals for Improved Chemodynamic Therapy

Chemodynamic therapy (CDT) based on the Fe2+-mediated Fenton reaction can amplify intracellular oxidative stress by producing toxic •OH. However, the high-dose need for Fe2+ delivery in tumors and its significant cytotoxicity to normal tissues set a challenge. Therefore, a controllable delivery to activate the Fenton reaction and enhance Fe2+ tumor accumulation has become an approach to solve this conflict. Herein, we report a rare-earth-nanocrystal (RENC)-based Fe2+ delivery system using light-control techniques and DNA nanotechnology to realize programmable Fe2+ delivery. Ferrocenes, the source of Fe2+, are modified on the surface of RENCs through pH-responsive DNAs, which are further shielded by a PEG layer to elongate blood circulation and “turn off” the cytotoxicity of ferrocene. The up-/down-conversion dual-mode emissions of RENCs endow the delivery system with both capabilities of diagnosis and delivery control. The down-conversion NIR-II fluorescence can locate tumors. Consequently, up-conversion UV light spatiotemporally activates the catalytic activity of Fe2+ by shedding off the protective PEG layer. The exposed ferrocene-DNAs not only can “turn on” Fenton catalytic activity but also respond to tumor acidity, driving cross-linking and enhanced Fe2+ enrichment in tumors by 4.5-fold. Accordingly, this novel design concept will be inspiring for developing CDT nanomedicines in the future

Self-Immolative Photosensitizers for Self-Reported Cancer Phototheranostics

Photosensitizers to precise target and change fluorescence upon light illumination could accurately self-report where and when the photosensitizers work, enabling us to visualize the therapeutic process and precisely regulate treatment outcomes, which is the unremitting pursuit of precision and personalized medicine. Here, we report self-immolative photosensitizers by adopting a strategy of light-manipulated oxidative cleavage of CC bonds that can generate a burst of reactive oxygen species, to cleave to release self-reported red-emitting products and trigger nonapoptotic cell oncosis. Strong electron-withdrawing groups are found to effectively suppress the CC bond cleavage and phototoxicity via studying the structure–activity relationship, allowing us to elaborate NG1–NG5 that could temporarily inactivate the photosensitizer and quench the fluorescence by different glutathione (GSH)-responsive groups. Thereinto, NG2 with 2-cyano-4-nitrobenzene-1-sulfonyl group displays excellent GSH responsiveness than the other four. Surprisingly, NG2 shows better reactivity with GSH in weakly acidic condition, which inspires the application in weakly acidic tumor microenvironment where GSH elevates. To this end, we further synthesize NG-cRGD by anchoring integrin αvβ3 binding cyclic pentapeptide (cRGD) for tumor targeting. In A549 xenografted tumor mice, NG-cRGD successfully deprotects to restore near-infrared fluorescence because of elevated GSH in tumor site, which is subsequently cleaved upon light irradiation releasing red-emitting products to report photosensitizer working, while effectively ablating tumors via triggered oncosis. The advanced self-immolative organic photosensitizer may accelerate the development of self-reported phototheranostics in future precision oncology

Backbone Tuning Enhances the Solution Aggregation to Refine Fibrillization Network Morphology for Efficient All-Chlorinated Polymer Donor

An ideal nanoscale interpenetrating network morphology that is formed spontaneously upon a prepared active layer film is the key to efficient exciton dissociation and charge transport. Here, a new strategy is described for optimization of morphology by enhancing polymer solution aggregation ability to effectively improve device performance. Polymers PBDQx-Cl, PBDQx-TCl, and PBDQx-2TCl were designed and synthesized systematically by tuning the polymer backbones. Structural manipulation has been found to have a profound effect on the regulation of electronic structure and solution aggregation behavior. Compared with PBDQx-Cl and PBDQx-TCl, PBDQx-2TCl exhibits enhanced solution aggregation ability and contributes to a fibrous phase separation in primitive pure film morphology. After blending with BTP-eC9, evolution of a nanoscale fibrillization interpenetrating network morphology is gradually demonstrated, in which the phase separation and microstructure form are collectively refined, which can provide more interface regions and charge transport channels. The resulting PBDQx-2TCl:BTP-eC9 micromorphologically meets the requirements for efficient exciton splitting, charge transfer, and decreased recombination loss. Thus, among the three polymers, the device based on PBDQx-2TCl:BTP-eC9 shows the highest PCE of 16.17% with superior JSC of 26.49 mA cm–2 and FF of 74.28%. These results demonstrate that the well-refined fibrillar network morphology can be achieved by adjusting the aggregation ability of a polymer solution. This in turn promotes a deeper understanding of the relationships between micromorphology and solution aggregation behavior

Divergent Radical Cyclization and Hydroaminoalkylation of <i>N</i>‑Arylacrylamides Using Photoredox Catalysis

The ability to selectively synthesize multiple products from the same sets of substrates is a highly appealing and challenging concept in synthetic chemistry. In this manuscript, we describe the visible-light photoredox intermolecular catalysis of N-arylacrylamides that are α-C–H functionalized with aryl tertiary amines. The photocatalyst acts as a chemical switch to trigger two different reaction pathways and to obtain two different products from the same starting material. Simple adjustments to the reaction conditions enable the divergent synthesis of the oxidative cyclizations or the addition products in good to high yields with excellent atom economy