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Dynamics Within Site Selectively Templated and Tagged Xerogel Sensor Platforms
Volume 64, Number 10 (Oct. 2010) Page 1073-1077
Bright, Frank V.; Holthoff, Ellen L.
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 n-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 n-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 n-octyl chains crowding the cybotactic region surrounding the site 1 NBD reporter molecules. This n-octyl-induced site 1 "crowding" is also associated with improved analyte binding to site 1 and better overall SSTTX analytical performance.