Highly sensitive optical sensors using electrospun polymeric nanofibrous membranes

In recent years, polymer films have found an increasing role in sensors due to their unique characteristics. It is widely accepted that the sensitivity of a film is proportional to the surface area per unit mass. Thin films with very large surface areas can be easily fabricated by electrospinning, wherein a polymer solution is exposed to a high static voltage, creating sub-micron or nanometer scale fibers collected as a non-woven membrane. Electrospun nanofibrous membranes have surface areas approximately one to two orders of the magnitude higher than those found in continuous thin films. It is expected that their sensitivities are potentially as large. In this paper, the first use of an electrospun membrane as a highly responsive fluorescence quenching-based optical sensor is reported. A new fluorescent polyrner, polyacrylic acid - poly (pyrene methanol) (PAA-PM), was synthesized via covalent attachment of the fluorescent indicator, pyrene methanol (PM), onto polyacrylic acid (PAA). Optical chemical sensors were then fabricated by electrospinning PAA-PM and thermal crosslinkable polyurethane latex mixture solutions. The synthesis, characterization, electrospinning fabrication, and comparison of the sensitivities to analytes such as ferric ions, mercury, and 2,4-dinitrotoluene between the electrospun membranes and electrostatically layer-by-layer (ELBL) assembled films are presented.