Lighting up phytoplankton cells with quantum dots

Abstract

Quantum dots (Qdots) are semiconducting nanocrystals composed of periodic elements with different intrinsic band‐gap energies that yield unique fluorescent signatures. Unlike conventional organic fluorophores, Qdots are photo‐chemically stable and have a wide absorption spectrum, but a narrow, tunable emission spectrum. Multiple colors can be imaged from a single excitation wavelength allowing for labeling of many different target sites (e.g., membrane proteins) simultaneously.We conjugated Qdots to primary antibodies specific for the soluble enzyme nitrate reductase (NR) and a light‐harvesting structural protein localized in the chloroplast, the fucoxanthin chlorophyll a/c protein (FCP), in the marine diatom Skeletonema costatum. By fluorescence microscopy, we successfully detected NR and FCP in single cells of S. costatum with a clarity and definition that was not obtainable with conventional organic fluorophores. Biotinylated cells labeled with Qdot‐strepavidin conjugate and Qdot‐FCP immuno‐labeled cells were detected by flow cytometry. Qdot bioconjugates provide an alternative photostable probe for surface or intracellular protein immuno‐localization in the study of marine bacteria and phytoplankton metabolism and physiology.