The fluorescent decay kinetics of an exogenous fluorescent dye injected or immobilized in a polymer implant can be sensitive to the biochemical environment of the tissue and can provide quantitative in vivo biochemical information of the tissue site. In this research project, we develop the rationale for NIR fluorescence spectroscopy of biologically relevant dyes for the sensing of analyte concentration, such as Ca<sup>2+</sup>, pH, glucose, etc. <i>In vivo</i> analytical sensing using fluorescence spectroscopy is complicated not only by the scattering of tissue, but also by the fact that most sensing fluorophores exhibit more than one (multi-exponential) decay lifetime. The objective of this paper is to demonstrate the concept of fluorescence lifetime spectroscopy in scattering media using a pH sensing dye, Carboxy Seminaphthofluorescein-1 (C-SNAFL-1). Work to extrapolate our results to an analyte-sensing dye construct embedded in a polymer are also presented.
Supported by the National Institutes of Health (R01 CA67176).
A bulk design of optical interleaver with 50 GHz free spectral range (FSR) is experimentally demonstrated. The optical interleaver consists of three cascaded stages of modified Mach-Zehnder interferometers (MZIs), which are fabricated with beam splitters, end-mirror and delay-blocks. Beam splitters are used to split a propagating beam into two beams or coherently recombine two split beams, and delay-blocks located in one arm of each MZI are used to control the phase difference. The interleaver processes square-like spectral response with nearly zero ripple, wide flat-top, and rather low crosstalk, sharp steepness, and ease in fabrication as well. The bandwidth of passband at -0.5 dB and stopband at -15 dB are over 30 GHz and about 25 GHz, respectively. The insertion loss is smaller than 1.5 dB and the polarization dependent loss (PDL) is about 0.15 dB. The crosstalk is lower than -25 dB. The return loss is larger than 45 dB.