In a nitrobenzo-2-oxa-1,3-diazole (NBD) –based, 9-anthrol-responsive site selectively templated and tagged xerogel (SSTTX) sensor platform, there are two reporter molecule site types (responsive and non-responsive) that are responsible for the observed fluorescence signals. These NBD sites function independently. Site 1 alone binds the target analyte and yields an analyte-dependent signal. This signal arises from analyte binding decreasing the photo-induced electron transfer (PET) efficiency between a strategically placed amine residue and the excited NBD reporter molecule within the template site. Site 2 does not respond to analyte, it is not fully formed, and it manifests itself as a background signal. In an <i>n</i>-octyl residue-free SSTTX, the local microviscosity sensed by the site 1 NBD reporter molecules in the absence and presence of target analyte is ∼260 cP and ∼540 cP, respectively. These local microviscosity values are substantially greater in comparison to free NBD dissolved in THF (η = 0.46 cP at 298 K, ϕ ∼25 ps). As the SSTTX <i>n</i>-octyl content is increased, the local microviscosity sensed by the site 1 NBD reporter molecules in the absence and presence of target analyte is ∼360 cP and ∼760 cP, respectively. This behavior is consistent with the <i>n</i>-octyl chains crowding the cybotactic region surrounding the site 1 NBD reporter molecules. This <i>n</i>-octyl-induced site 1 "crowding" is also associated with improved analyte binding to site 1 and better overall SSTTX analytical performance.
Vol. 5, Iss. 14 Virtual Journal for Biomedical Optics
Frank V. Bright and Ellen L. Holthoff, "Dynamics Within Site Selectively Templated and Tagged Xerogel Sensor Platforms," Appl. Spectrosc. 64, 1073-1077 (2010)