Creating diversified response profiles from a single quenchometric sensor element by using phase-resolved luminescence.

We report a new strategy for generating a continuum of response profiles from a single luminescence-based sensor element by using phase-resolved detection. This strategy yields reliable responses that depend in a predictable manner on changes in the luminescent reporter lifetime in the presence of the target analyte, the excitation modulation frequency, and the detector (lock-in amplifier) phase angle. In the traditional steady-state mode, the sensor that we evaluate exhibits a linear, positive going response to changes in the target analyte concentration. Under phase-resolved conditions the analyte-dependent response profiles: (i) can become highly non-linear; (ii) yield negative going responses; (iii) can be biphasic; and (iv) can exhibit super sensitivity (e.g., sensitivities up to 300 fold greater in comparison to steady-state conditions).

O(2)-responsive chemical sensors based on hybrid xerogels that contain fluorinated precursors.

We report the development and analytical figures of merit associated with several new O(2)-responsive sensor materials. These new sensing materials are formed by sequestering the luminophore tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ([Ru(dpp)(3)](2+)) within hybrid xerogels that are composed of two of the following methoxysilanes: tetramethoxysilane, n-propyl-trimethoxysilane, 3,3,3-trifluoropropyl-trimethoxysilane, phenethyl-trimethoxysilane, and pentafluorophenylpropyl-trimethoxysilane. Steady-state and time-resolved luminescence measurements are used to investigate these hybrid xerogel-based sensor materials and elucidate the underlying reasons for the observed performance. The results show that many of the [Ru(dpp)(3)](2+)-doped composites form visually uniform, crack-free xerogel films that can be used to construct O(2) sensors that have linear calibration curves and excellent long-term stability. To the best of our knowledge, the [Ru(dpp)(3)](2+)-doped fluorinated hybrid xerogels also exhibit the highest O(2) sensitivity of any reported [Ru(dpp)(3)](2+)-based sensor platform.

Tailored xerogel-based sensor arrays and artificial neural networks yield improved O2 detection accuracy and precision.

The objective of this research is to develop arrays of tuned chemical sensors wherein each sensor element responds to a particular target analyte in a unique manner. By creating sol-gel-derived xerogels that are co-doped with two luminophores at a range of molar ratios, we can form suites of sensor elements that can exhibit a continuum of response profiles. We trained an artificial neural network (ANN) to "learn" to identify the optical outputs from these xerogel-based sensor arrays. By using the ANN in concert with our tailored sensor arrays we obtained a 5-10 fold improvement in accuracy and precision for quantifying O2 in unknown samples. We also explored the response characteristics of these types of sensor elements after they had been contacted with rat plasma/blood. Contact with plasma/blood caused approximately 15% of the luminophore molecules within the xerogels to become non-responsive to O2. This behavior is consistent with rat albumin blocking certain pore sub-populations within the mesoporous xerogel matrix thereby limiting O2 access to the luminophores.

Templated xerogels as platforms for biomolecule-less biomolecule sensors.

We report on a new sensor strategy that we have termed protein imprinted xerogels with integrated emission sites (PIXIES). The PIXIES platform is completely self-contained, and it achieves analyte recognition without a biorecognition element (e.g., antibody). The PIXIES relies upon sol-gel-derived xerogels, molecular imprinting, and the selective installation of a luminescent reporter molecule directly within the molecularly imprint site. In operation the templated xerogel selectively recognizes the target analyte, the analyte binds to the template site, and binding causes a change in the physicochemical properties within the template site that are sensed and reported by the luminescent probe molecule. We report the PIXIES analytical figures of merit for and compare these results to a standard ELISA. For human interleukin-1 the PIXIES-based sensor elements exhibited the following analytical figures of merit: (i) approximately 2 pg/mL detection limits; (ii) <2 min response times; (iii) >85 selectivity; (iv) <6% R.S.D. long term drift over 16 weeks of ambient storage; (v) >95% reversibility after more than 25 cycles; and (vi) >85% recoveries on spiked samples.

High-performance quenchometric oxygen sensors based on fluorinated xerogels doped with [Ru(dpp)3]2+.

By using hybrid xerogels that are composed of alkyl and perfluoroalkyl ORMOSILs (organically modified silicates) doped with the luminophore tris(4,7'-diphenyl-1,10'-phenanthroline) ruthenium(II), we have produced highly sensitive O2 sensors (i.e., I(N2)/I(O2) = 35 +/- 4) with linear calibration curves that exhibit less than 2% drift over 6 months.

Radioluminescent light source for the development of optical sensor arrays.

A radioluminescent (RL) light source is evaluated for the development of photonically based chemical-responsive sensor arrays (CRSAs). The RL light source is comprised of a strontium-90 (90Sr) radionuclide and a plastic scintillator. The beta particles emitted from the 90Sr generate blue light (lambda(max) = 435 nm) from the plastic scintillator, and the blue light excites the analyte-responsive luminophores within the CRSA. To assess the RL light source utility, we have determined the analytical figures of merit from two tris(4,7'-diphenyl-1,10'-phenathroline)ruthenium(II)-doped xerogel-based sensor platforms: (i) a planar 5 x 5 multielement array and (ii) a discrete sensor element formed on the proximal face of poly(styrene) pillars that have a frustrated cone (frustum) geometry. We compare the performance from each platform when it is excited by a He-Cd laser (442 nm), a blue light-emitting diode (460-470 nm), and the RL light source. The RL light source yields results that are statistically equivalent to results from either electrically powered light source. The RL light source consumes no electrical power, is compact and simple, and has an extremely stable time-averaged signal. The primary trade-offs for these advantages are the RL light source's lower radiant power and the corresponding longer data acquisition times.