Abstract
A photomodulatable amphiphilic polymer has been synthesized with a backbone of poly[isobutylene-alt-maleic anhydride] and pendant dodecyl alkyl chains, Lucifer Yellow (LY) fluorescent probes, and diheteroarylethenes photochromic (PC) groups. The latter serve as reversible UV-activated FRET acceptors for the LY donors. We characterized the spectral and switching properties of the polymer in an organic solvent (CHCl(3)). In an aqueous medium the polymer forms polymersomes, constituting fluorescence probes ~75 nm in diameter. Self-assembly of the polymer on the surface of a quantum dot (QD) serving as a template creates a dual-color photoswitchable nanoparticle (psNP) with improved properties due to the increase in polymer density and efficiency of PC photoconversion. The psNP exhibits a second QD red emission band that functions as an internal standard requiring only a single excitation wavelength, and is much reduced in size (<20 nm diameter) compared to the polymersomes. The QD template also greatly increases the depth of modulation by photochromic FRET of the LY emission monitored by both steady-state and time-resolved (lifetime) fluorescence (from 20%→70%, and from 12%→55%, respectively).
Highlights
Nanoparticles (NPs) employed as imaging probes are indispensable tools for the observation of biological systems.[1,2] NPs can be organic [polymersomes, dendrimers, polymeric nanocapsules]3 or primarily inorganic, as in the case of metallic [Au, Ag, Pt],4 magnetic [Fe3O4],4 silica based [SiO2],4 and semiconductor nanocrystals.[5]
Numerous modulatable probes have been developed for enhancing selective detection by suppression of background contributions and degradation by photobleaching.[12−15] By satisfying certain spectroscopic and structural criteria, Förster resonance energy transfer (FRET) can be employed as an efficient means for generating modulation of fluorescence.[16−18] Of particular interest are probes whose emission can be controlled by an external light source.[19−21] Photochromic (PC) molecules, e.g., diheteroarylethenes, function well as versatile acceptors, creating FRET pairs that can be switched between transfer/ nontransfer states by light.[22,23]
Reversible FRET based on photochromic acceptors, which we have denoted as photochromic FRET,[22] has been exploited in a variety of systems, including those based on nanoparticles.[24,25]
Summary
Nanoparticles (NPs) employed as imaging probes are indispensable tools for the observation of biological systems.[1,2] NPs can be organic [polymersomes, dendrimers, polymeric nanocapsules]3 or primarily inorganic, as in the case of metallic [Au, Ag, Pt],4 magnetic [Fe3O4],4 silica based [SiO2],4 and semiconductor nanocrystals (quantum dots, QDs).[5]. An interesting property of fluorescent probes is their potential for systematic modulation of one or more specific parameters, for example emission intensity.[10,11] Numerous modulatable probes have been developed for enhancing selective detection by suppression of background contributions and degradation by photobleaching.[12−15] By satisfying certain spectroscopic and structural criteria, Förster resonance energy transfer (FRET) can be employed as an efficient means for generating modulation of fluorescence.[16−18] Of particular interest are probes whose emission can be controlled by an external light source.[19−21] Photochromic (PC) molecules, e.g., diheteroarylethenes, function well as versatile acceptors, creating FRET pairs that can be switched between transfer/ nontransfer states by light.[22,23] Reversible FRET based on photochromic acceptors, which we have denoted as photochromic FRET (pcFRET),[22] has been exploited in a variety of systems, including those based on nanoparticles.[24,25]
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