Nanostructured electrospun membranes for efficient fluorescence-based optical sensors

The research described herein is the first demonstration of the feasibility of electrospun polymer membranes for fluorescence quenching-based optical sensors. For the proof-of-concept, two types of sensing fluorophores, pyrene-based dyes and a polythiophene derivative, were used as model indicators for the preparation and characterization of the sensors. The combination of electrospinning and a number of techniques such as post-electrospinning coupling reaction, surface migration of hyperbranched polymer, and layer-by-layer assembly for further improvement of the sensor performance has also been investigated.; In the first study, it was demonstrated that electrospun nanofibrous membranes can be used as highly responsive fluorescence quenching-based sensors. The sensors were fabricated by electrospinning fluorophore-tagged polymers, poly (acrylic acid)-pyrene methanol (PAA-PM) and poly (methylmethacrylate)-pyrene methanol (PMMA-PM). The fluorescence of these sensors could be efficiently quenched by metal ions (Fe3+ and Hg2+) and 2,4-dinitrotoluene (DNT). The sensitivities of these sensors, quantified by the Stern Volmer constant (Ksv), possessed detection limits up to tens of parts per billion. These values were roughly two to three orders of magnitude greater, despite not being optimized, than those obtained previously from thin film based sensors of the same materials.{09}The significant sensitivity enhancement of these sensors was attributed to the higher surface-area of the electrospun membranes.; Further efforts were focused on the incorporation of fluorophores on the electrospun fiber surface. In the first approach, the fluorescent probe, pyrenebutyric acid (PBA), was covalently attached onto the surface of poly (2-hydroxyethyl methacrylate) (PHEMA) electrospun nanofibrous membranes. This localization of the fluorescent tag to the surface of an already high surface area nanofibrous membrane provided the possibility of further improvement of sensitivity and reversibility compared to similar systems in which the fluorophores were dispersed throughout the electrospun nanofibers. This approach also allowed for more direct control over the type and concentration of fluorophore used.; In another approach, a pyrenebutyric acid-tagged hyperbranched polyester (HBP-PBA) was blended into a matrix polymer for the electrospinning of the sensing films. It was demonstrated that significant migration of HBP-PBA to the fiber surface occurred in electrospun fibers. The quenching behavior of these electrospun polymer nanofibrous membranes with different concentration of HBP-PBA fluorophore by Hg2+ and cytochrome c has been investigated. This study demonstrated a pathway for surface functionalization of electrospun fibers for sensing membrane designs.; A novel approach to enhance the sensitivity of the electrospun membranes was demonstrated by combining electrospinning with layer-by-layer assembly. The fluorescent tag, hydrolyzed poly [2-(3-thienyl) ethanol butoxy carbonyl-methyl urethane] (H-PURET), was electrostatically assembled onto the surface of a cellulose acetate (CA) electrospun nanofibrous membrane. This localization of the fluorescent tag to the surface of the high surface area nanofibrous membrane resulted in significantly improved sensitivities in comparison to small fluorophore systems. The fluorescence of these membranes can be quenched by extremely low concentrations of electron acceptors (cytochrome c and methyl viologen). The detection limits were up to tens of parts per billion. These results suggest a promising approach to the fabrication of chemical sensors and biosensors.; This research has laid the groundwork for several new and promising approaches to the design and fabrication of a new class of high sensitive nanofibrous based sensors. New directions of this work include further optimization of the performance of the sensors including selectivity and reproducibility, as well as sensitivity.