Electrospun dextran fibrous membranes

Ultra-fine fiber mats of dextran (powder; M _w = 64,000–76,000 Da) were fabricated by electrospinning, using water as the solvent. The effects of solution concentration (i.e., 0.7–1.3 g mL⁻¹) and applied electric field (9–21 kV/15 cm) on morphological appearance and size of the obtained fibers were investigated. Under a fixed electric field of 15 kV/15 cm and a fixed solution flow rate of 0.25 mL h⁻¹, beaded fibers were observed up to a critical concentration of about 0.9 g mL⁻¹, beyond which only smooth fibers were obtained. The average diameter of these fibers increased monotonically with increasing the solution concentration (i.e., from ∼290 to ∼1950 nm). For the dextran solutions investigated, increasing the electric field generally caused the diameters of the obtained fibers to increase, with the average diameter of the obtained fibers ranging between 520 and 1760 nm. To improve the usefulness of the electrospun dextran fiber mats in an aqueous medium, cross-linking with glutaraldehyde was necessary. The effects of curing temperature (i.e., 70–90 °C), curing time (i.e., 3–48 h), and added MgCl₂ catalyst (i.e., 0.01–0.03 g) on physical integrity of the cross-linked dextran membranes in water were investigated. Both the swelling and the weight loss in water of the cross-linked membranes were generally found to decrease with increasing curing temperature, curing time, and MgCl₂ loading and the cross-linking did not affect the morphology of the obtained membranes.     

Graphene-loaded nanofiber-modified electrodes for the ultrasensitive determination of dopamine

A novel and highly sensitive electrochemical system based on electrospun graphene/polyaniline/polystyrene (G/PANI/PS) nanofiber-modified screen-printed carbon electrodes has been developed for dopamine (DA) determination. A dramatic increase (9 times) in the current signal for the redox reaction of a standard, ferri/ferrocyanide [Fe(CN)₆]^3−/4− couple was found when compared to an unmodified electrode. This modified electrode also exhibited favorable electron transfer kinetics and excellent electrocatalytic activity toward the oxidation of DA. When used together with square wave voltammetry (SWV), DA can be selectively determined in the presence of the common interferents (i.e. ascorbic acid and uric acid). Under optimal conditions, a very low limit of detection (0.05 nM) and limit of quantification (0.30 nM) were achieved for DA. In addition, a wide dynamic range of 0.1 nM to 100 μM was found for this electrode system. Finally, the system can be successfully applied to determine DA in complex biological environment (e.g. human serum, urine) with excellent reproducibility.