Fluorescence loss of commercial aqueous quantum dots during preparation for bioimaging
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Research Letter
Fluorescence loss of commercial aqueous quantum dots during preparation for bioimaging Kil Ho Lee*, and Thomas Porter*, William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, 151 W. Woodruff Ave. Columbus, OH 43210, USA Jessica O. Winter, William G. Lowrie Department of Chemical and Biomolecular Engineering, The Ohio State University, 151 W. Woodruff Ave. Columbus, OH 43210, USA; Department of Biomedical Engineering, The Ohio State University, 151 W. Woodruff Ave. Columbus, OH 43210, USA Address all correspondence to Jessica O. Winter at [email protected] (Received 31 December 2018; accepted 26 March 2019)
Abstract Quantum dots (QDs) are increasingly employed in biologic imaging applications; however, anecdotal reports suggest difficulties in QD bioconjugation. Further, the stability of commercial QDs during bioconjugation has not been systematically evaluated. Thus, we examined fluorescence losses resulting from aggregation and declining photoluminescence quantum yield (QY) for commercial CdSe/ZnS QD products from four different vendors. QDs were most stable in the aqueous media in which they were supplied. The largest QY declines were observed during centrifugal filtration, whereas the largest declines in colloidal stability occurred in 2-(N-morpholino)ethanesulfonic acid (MES) buffer. These results enable optimization of bioconjugation protocols.
Introduction The introduction of quantum dots (QDs) for biologic imaging in 1998[1,2] was thought to herald a coming revolution in the field. QDs, crystalline semiconductor nanoparticles, exhibit many properties conducive to imaging because of their small size. Broad excitation spectra enable imaging of multiple colors with a wide variety of excitation sources. High absorption cross sections enable improved photon generation compared to molecular fluorescent dyes.[3] Narrow emission spectra and size-tunable fluorescence are ideal for multiplexed applications that require several distinct colors to be distinguished in the visible spectrum. Building on these initial reports, QD labels were demonstrated for in vitro[4] and in vivo[5] labeling applications across many organismal models. However, researchers were poised for a revolution that never came. Although QD products have been introduced by a variety of vendors, there are no clinically approved QDs, and fluorescent dyes remain the mainstay of biologic imaging. One obvious limitation to the clinical adoption of QDs is their toxicity.[6] The most popular QDs for imaging applications are composed of CdSe cores with ZnS passivating shells (CdSe/ZnS). Cadmium is a heavy metal that yields chronic toxicity and carcinogenesis in humans, disrupting DNA repair, hindering mitochondrial respiration, and interfering with systems that employ cations of similar charge (e.g., Zn2+, Mn2+) as co-factors.[7] Despite the fact that studies in primate models
* These authors have contributed equally to this work.
yielded no observable effects over 90 days, most of the administered dose
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