In this work, we developed a chip-based continuously flowing system for online liquid–liquid extraction by using monodisperse droplets, and the droplets containing target compounds after extraction were collected on the microchip. Monodisperse droplets of extracting reagent were on-chip generated and dispersed in continuously flowing sample solution, and then liquid–liquid extraction happened when organic droplets moved forward with sample solution flow. After liquid–liquid extraction, guiding tracks were designed in our system to capture the organic droplets, which allowed the aqueous solution flowing over at the same time. Structures of the microchip were optimized to achieve generation and collection of monodisperse droplets more efficiently. To verify the feasibility of droplet based liquid–liquid extraction on the established platform, we used aqueous solution containing 10 μM fluorescein sodium as sample solution and butanol as the extracting reagent to perform the whole procedures. Fluorescein sodium was successfully extracted by the butanol droplets, and the butanol droplets were successfully collected. The results demonstrated that the developed microfluidic device was a useful tool for monodisperse droplet based liquid–liquid extraction. As all the procedures including droplet generation, extraction and collection were performed on one chip, the established platform had the potential of time-resolved monitoring.
Electrochemical stimulus is a clean and simple choice of stimulating source in the field of stimuli-responsive materials. Herein, we report an electrochemically-responsive hybrid assembly of magnetic nanoparticles (Fe3O4@SiO2-PGMA-CD) and polyethylene glycol-Fc (PEG-Fc) based on the host-guest interaction between β-cyclodextrin and ferrocene groups. Through electrochemical control, the hydrophilic polymer chains can be reversibly linked to or dropped off from the surface of the magnetic nanoparticles. Thus, the hydrophobic property of the surface together with the protein adsorption ability of the magnetic nanoparticles can be conveniently adjusted by voltages applied. A reversible protein adsorption/release transition from this novel hybrid material has been realized, demonstrated by the bovine serum albumin adsorption experiment. Therefore, an elegant material is introduced to achieve electrochemically-controlled reversible magnetic separation of proteins.
CO2-responsive polymer poly(N,N-diethylaminoethylmethacrylate)-modified magnetic nanoparticles (Fe3O4@dye/SiO2-PDEAEMA) were synthesized by atom transfer radical polymerization from the surfaces of silica coated, dye-labelled iron oxide nanoparticles (Fe3O4@dye/SiO2). TEM, FT-IR, and TGA confirmed and quantified the grafted polymer brushes. The prepared magnetic nanoparticles (MNPs) were fluorescence labelled, as shown by the fluorescence spectra and fluorescence microscopy images. This indicated that the nanoparticles could be utilized as imaging probes to monitor the movement of biological cells or other systems. The PDEAEMA polymer brushes on the surface of MNPs endowed them with a protein adsorption ability. The polymer was also CO2-responsive, so it was a CO2-triggered reversible protein adsorption/release material, which was demonstrated by the bovine serum albumin (BSA) adsorption experiments. The results indicated that the reversible adsorption/release of protein by bubbling CO2 and N2 alternately was easy to achieve.
An integrated microfluidic device was developed for high-throughput drug screening with an online electrospray ionization quadrupole time-of-flight mass spectrometer (ESI-Q-TOF MS). The multiple gradient generator followed by an array of microscale cell culture chambers and on-chip solid-phase extraction (SPE) columns for sample pretreatment prior to mass analysis was integrated in the device which was fabricated in one single step. By using the combination system, the process for characterization of drug absorption and evaluation of cytotoxicity could be simultaneously realized. To validate the feasibility, the absorption of methotrexate and its effects on HepG2 and Caco-2 cells were investigated. With the increasing concentration of drugs, the percentage of apoptotic cells appeared in a dose-dependent fashion. By comparison with the results obtained from ESI-Q-TOF MS analysis and cytotoxicity assay, we found that higher intracellular drug concentration resulted in increased cell cytotoxicity. The technique presented herein provides an easy protocol to screen drugs rapidly with low drug consumption, high throughput, and high sensitivity.
In this work, the establishment of a microdialysis-paper spray ionization-mass spectrometry (MS) system was described. A homemade microdialysis module was employed for sampling, and microdroplets were generated at the outlet of the capillary conducting the dialysate. Online MS analysis of each microdroplet was immediately accomplished, interfacing by paper spray ionization. Analytical performance of the method was investigated and improved through the introduction of thinner capillary tubes and the optimization of spray solvent and paper substrate. For microdroplets with concentrated salt at 50 nL, the limit of detection at 0.8 ppm (or 40 pg absolute) and a highest resolution at about 1.5 s were achieved. The integrated system was applied into the online monitoring of glucose concentration in cell culture mediums. A satisfactory linearity of the calibration curve between the relative MS intensity and the glucose concentration was observed. Furthermore, as a model, hormone regulation of the glucose concentration was investigated. This work demonstrated the potential application of the label-free, online “MS sensor” into studies on cellular metabolism.
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