Upconverter-powered oxygen sensing in electrospun polymeric bilayers

Abstract

Optical oxygen sensors based on luminescent quenching are attractive as they are easily miniaturized, offer excellent sensitivity, and in the appropriate vehicle exhibit no cytotoxicity. However, these sensors must be energized by violet or blue wavelengths to report variations in oxygen content. These wavelengths experience high levels of absorption and scattering in biological tissue. Upconverting particles (UCPs) sidestep this limitation due to their ability to sequentially absorb two or more longer wavelength photons to emit a single, shorter wavelength photon. In this work, UCPs were utilized to emit blue light upon near infrared (NIR) absorption. A key advantage is that NIR light efficiently penetrates tissue barriers associated with potential biomedical applications. A layer of polycaprolactone (PCL) fibers containing Ru(dpp)3Cl2 was electrospun directly on top of a layer of fibers containing UCPs. We chose a bilayer configuration as it allowed direct examination of the ‘handshake’ interaction and investigation of significant design issues. Configurational aspects of the bilayer format were studied. Additionally, gaseous oxygen sensing following NIR excitation was confirmed. These upconverter-powered sensors were found to have a rapid response ( <0.25 s).

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