Effect of [EMIM][BF4] ionic liquid on the properties of ultrafiltration membranes
Authors: Lessan, Fatemeh; Foudazi, Reza
We employ a miscible mixture of an imidazolium based ionic liquid (IL) and dimethylformamide (DMF) as a good solvent of polyethersulfone (PES) for fabrication of membranes by nonsolvent induced phase separation (NIPS) method. The addition of IL to the cast solution changes solvent quality, which leads to variation of rheological behavior of polymer solution as well as developed membranes performance. We characterize the prepared membranes in terms of water flux, bovine serum albumin (BSA) rejection, pore size, porosity, and water contact angle. Results show that IL influences the kinetics and thermodynamic of phase separation of PES solution. Viscosity values as well as thermodynamic instability of PES solution increase with IL concentration, which lead to higher porosity and pore size of final membranes. Consequently, 17 wt% IL in formulation leads to an increase of mean pore size from 2.0 to 12.7 nm which improves water flux of final membranes from 0.5 to 77 kg/m(2)h. The results of fouling measurements show that by increasing IL content, the reversible fouling increases. Additionally, the irreversible fouling ratio reduces from 0.42 to 0.28 for 0 and 17 wt% IL containing formulations, respectively. The newly developed membranes provide 97% rejection of BSA solution and can be used as ultrafiltration membranes for the separation and concentration of macromolecules and proteins.
Novel electrochemical biosensing platform for microRNA detection based on G-quadruplex formation in nanochannels
SENSORS AND ACTUATORS B-CHEMICAL
Authors: Zhao, Fei; Zhang, Hongfang; Zheng, Jianbin
Ultrasensitive detection of microRNA is crucial important in the diagnosis of related diseases. By immobilizing the capture probes in nanochannels, we developed a label-free electrochemical biosensing platform based on guanine-quadruplex (G-quadruplex) formation in nanochannels. The designed capture probe contains both the microRNA-21 (MiR-21) recognition sequence and guanine-rich sequence. The presence of the target MiR-21 would trigger the enzymatic cleaving of the RNA/DNA heteroduplexes which led some of the guanine-rich sequences escape from the nanochannels and thus reduced the formation of the G-quadruplex/hemin complex. Therefore, the quantity of methylene blue fluxed through the nanochannels changed because of the variation of the steric hindrance. A optimized carbon nanofibers modified electrode was applied to monitor the quantity difference of methylene blue. In this way, the biosensing platform realized the label-free electrochemical detection of MiR-21 with a ultralow detection limit of 0.5 aM. Meanwhile, this biosensing platform was assessed for MiR-21 detection in serum samples. The biosensing platform can be readily extended to the assay of other scarcetumor-related genes.