Abstract
Photoswitchable molecules and nanoparticles constitute superior biosensors for a wide range of industrial, research and biomedical applications. Rendered reversible by spontaneous or deterministic means, such probes facilitate many of the techniques in fluorescence microscopy that surpass the optical resolution dictated by diffraction. Here we have devised a family of photoswitchable quantum dots (psQDs) in which the semiconductor core functions as a fluorescence donor in Förster resonance energy transfer (FRET), and multiple photochromic diheteroarylethene groups function as acceptors upon activation by ultraviolet light. The QDs were coated with a polymer bearing photochromic groups attached via linkers of different length. Despite the resulting nominal differences in donor-acceptor separation and anticipated FRET efficiencies, the maximum quenching of all psQD preparations was 38±2%. This result was attributable to the large ultraviolet absorption cross-section of the QDs, leading to preferential cycloreversion of photochromic groups situated closer to the nanoparticle surface and/or with a more favourable orientation.
Highlights
Photoswitchable molecules and nanoparticles constitute superior biosensors for a wide range of industrial, research and biomedical applications
The photoswitchable quantum dots (psQDs) consisted of a quantum dots (QDs) Forster resonance energy transfer (FRET) donor and a cap of multiple photochromic (PC) diheteroarylethene FRET acceptors attached to an amphiphilic comb-like polymer via linkers of variable length (Fig. 1a)
Previous publications from our laboratory have shown that such a system constitutes a photoswitchable nanoparticle, denoted as psQD, that can be utilized in aqueous environments[16,17]
Summary
Photoswitchable molecules and nanoparticles constitute superior biosensors for a wide range of industrial, research and biomedical applications. Despite the resulting nominal differences in donor–acceptor separation and anticipated FRET efficiencies, the maximum quenching of all psQD preparations was 38±2% This result was attributable to the large ultraviolet absorption cross-section of the QDs, leading to preferential cycloreversion of photochromic groups situated closer to the nanoparticle surface and/or with a more favourable orientation. Using selected irradiation wavelengths a photochrome is reversibly converted between a non-acceptor isomer (with a small FRET overlap integral) and an acceptor isomer (with a large FRET overlap integral)[1] In the latter case, the fluorescence of the donor is quenched by FRET and the conventional FRET formalism can be applied to the donor (D) and acceptor (A) pair. In spite of pronounced differences in individual FRET efficiencies, the end-point ultraviolet-photomodulation of psQD fluorescence was an invariant 38±2% We attribute this result to FRETinduced cycloreversion, functioning so as to compensate distance–orientation variations by adjustment of the steady-state distribution of acceptor groups
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