Analytische Chemie
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- 2017 (33) (entfernen)
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- Fluorescence (22)
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Eingeladener Vortrag
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Upconversion nanoparticles (UCNPs) are attractive candidates for energy transfer-based analytical applications. In contrast to classical donor−acceptor pairs, these particles contain many emitting lanthanide ions together with numerous acceptor dye molecules at different distances to each other, strongly depending on the particle diameter.
UCNPs with precisely controlled sizes between 10 and 43 nm were prepared and functionalized with rose bengal and sulforhodamine B by a ligand-exchange procedure. Timeresolved studies of the upconversion luminescence of the UCNP donor revealed a considerable shortening of the donor lifetime as a clear hint for Förster resonance energy transfer (FRET). FRET was most pronounced for 21 nm-sized UCNPs, yielding a FRET efficiency of 60%. At larger surface-to-volume ratios, the FRET efficiency decreased by an increasing competition of nonradiative surface deactivation. Such dye-UCNP architectures can also provide an elegant way to shift the UCNP emission color, since the fluorescence intensity of the organic dyes excited by FRET was comparable to that of the upconversion emission of smaller particles.
In a proof-of-concept study, we assessed different analytical and spectroscopic parameters for stability screening of differently sized β-NaYF4:20 mol % Yb3+, 2 mol % Tm3+ upconversion nanoparticles (UCNPs) exemplarily in the bioanalytically relevant buffer phosphate buffered saline (PBS; pH 7.4) at 37 and 50 °C. This included the potentiometric determination of the amount of released fluoride ions, surface analysis with X-ray photoelectron spectroscopy (XPS), and steady-state and time-resolved fluorescence measurements.
Based on these results, the luminescence lifetime of the 800 nm upconversion emission was identified as an Optimum parameter for stability screening of UCNPs and changes in particle surface chemistry.
Lanthanide-doped up-converting nanoparticles (UCNPs) are promising reporters for medical diagnostics and bioimaging, which are excited in the near infrared (NIR) by multiphoton absorption processes, and show multiple narrow emission bands in the visible (vis) and NIR, long luminescence lifetimes in the μs range, and excellent photostability. Current limitations present their relative low absorption cross sections and low fluorescence efficiencies, with the latter being affected by particle size, surface chemistry, and microenvironment, particularly water.
Here, we present results from systematic studies of the excitation power density dependent upconversion luminescence spectra, intensities/intensity ratios of the individual emission bands, slope factors, and quantum yields of UCNPs of varying size, dopant concentration, and surface chemistry in different microenvironments as well as the up- and downconversion luminescence decay kinetics of the different emission bands. Moreover, first studies of the energy transfer from UCNPs to surface-bound organic dyes acting as fluorescence acceptors are shown. Based upon these measurements, fluorescence deactivation channels are identified and spectroscopic parameters for the screening of material performance are derived.