Spectroscopic system for direct lanthanide photoluminescence spectroscopy with nanomolar detection limits.

A new spectroscopic system for direct photoluminescence of lanthanide ions (Ln(III)) through electronic transitions within the 4f(n) manifold is described. The system is based on an injection seeded frequency tripled (lambda = 355 nm) Nd:YAG pump laser coupled with a master oscillator power oscillator (MOPO). The MOPO delivers an average pulse energy of approximately 60 mJ/pulse, is continuously tunable from 425 to 690 nm (Signal) and 735 to 1800 nm (Idler) with a linewidth of <0.2 cm(-1), and has a pulse duration of 10-12 ns. Aqueous solutions containing two polyaminocarboxylate complexes, ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA), and Ln(3+) aqua ion for several lanthanides including Eu(III), Tb(III), Dy(III), and Sm(III)) are used as steady-state and time-resolved photoluminescence standards. The versatility of the instrument is demonstrated by excitation scans over a broad visible range for aqueous solutions of complexes of Eu(III), Dy(III), Sm(III), and Tb(III). The Eu(III) excitation band ((7)F(o)-->(5)D(o)) is recorded over a range of complex concentrations that are 1000-fold less than reported previously, including Eu(EDTA) (1.00 nM), Eu(DTPA) (1.00 nM), and Eu(III) aqua ion (50.0 nM). Emission spectra are recorded in the visible range for Ln(III) complexes at pH 6.5 and 1.00 mM. Excited-state lifetimes for the standards were constant as a function of concentration from 10.0 nM to 1.00 mM for Eu(EDTA) and Eu(DTPA) and from 100 nM to 1.00 mM for Eu(III) aqua ion. Photoluminescence lifetimes in H(2)O and D(2)O are recorded and used to calculate the number of bound water molecules for all complexes.

Probe-dependent microenvironments within biodegradable films formed from poly(l-lactic acid) and pluronic 104.

We report on the local microenvironment surrounding three small fluorescent probe molecules (pyrene, [6-propionyl-2-(N,N-dimethylamino) naphthalene] (PRODAN), and [4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran] (DCM)) when they are sequestered at low concentration within thin biodegradable films formed from poly( L-lactic acid) (PLLA) and Pluronic P104 blends. Despite each probe molecule being neutral, they sense and report from much different microenvironments in comparison to each other. Specifically, the non-polar pyrene probe senses a slightly more polar microenvironment as the PLLA content in the polymer blend increases. In contrast, the polar PRODAN and DCM probes sense less polar microenvironments as the PLLA content within the polymer blend increases. Time-resolved fluorescence intensity decay experiments on pure PLLA films reveal that each probe molecule encounters significant heterogeneity. Pyrene emits simultaneously from three discrete microenvironments. This is consistent with pyrene molecules reporting from crystalline, amorphous-crystalline intermediate, and amorphous regions. PRODAN and DCM appear to emit from a continuum of microenvironments. These results have ramifications on the performance of biodegradable drug delivery platforms loaded with small drug molecules.

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.

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.