Polymer coatings with rare-earth activated phosphors for optical fiber fluorosensors

Tryptophan fluorescence offers a means for tracking cellular proliferation in events such as wounds closure, neoplasm and others chronic conditions. The peak fluorescence emission is located around 345 nm (UV range) and is typically analyzed through spectroscopic measurements. In general, optical fibers show poor transmission in this wavelength range, and this hinders the use of this waveguides for tryptophan fluorescence monitoring or other molecule with UV fluorescence. However, down conversion phosphors attached to conventional fiber tips may provide a mechanism for improved fluorescence detection in this spectral range. In this work, we explore the use of UV-sensitive phosphors hosted by a polymer matrix that can be incorporated on the tip of conventional optical fibers for UV-fluorescence monitoring. In particular, we evaluate the performance of Eu-activated phosphors absorbing at 345 nm and emitting multiple fluorescence peaks in the 450-650 nm range. The phosphors are incorporated in polydimethylsiloxane (PDMS) by a simple mixing procedure, yielding a UV-sensitive polymer composite. Membranes of this composited were fabricated using different concentrations of the phosphors (i.e. 0.1, 0.5, 2.5, 12.5 and 62.5% wt./wt.), and their optical and thermal properties were evaluated. The polymer composites show good thermal stability and can be incorporated on conventional optical fibers. The resulting fiber optic fluorosensors may serve as a tool for fluorescence monitoring of tryptophan or other UV emitters.