Reversible Modulation of Quantum Dot Photoluminescence Using a Protein- Bound Photochromic Fluorescence Resonance Energy Transfer Acceptor

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Abstract
Multiple copies (∼20) of Escherichia coli maltose binding protein (MBP) were coordinated to luminescent semiconductor quantum dots (QDs) via a C-terminal oligohistidine segment. The MBP was labeled with a sulfo-N-hydroxysuccinimide-activated photochromic BIPS molecule (1‘,3-dihydro-1‘-(2-carboxyethyl)-3,3-dimethyl-6-nitrospiro[2H-1-benzopyran-2,2‘-(2H)-indoline]) at two different dye-to-MBP ratios; D/P = 1 and 5. The ability of MBP−BIPS to modulate QD photoluminescence was tested by switching BIPS from the colorless spiropyran (SP) to the colored merocyanine (MC) using white light (>500 nm) or UV light (∼365 nm), respectively. QDs surrounded by MBP−BIPS with D/P = 1 were quenched on average ∼25% with consecutive repeated switches, while QDs surrounded by MBP−BIPS with D/P = 5 were quenched ∼60%. This result suggests a possible use of BIPS-labeled proteins in QD-based nanostructures as part of a threshold switch or other biosensing device.