Facile preparation of oligo(ethylene glycol)-capped fluorescent carbon dots from glutamic acid for plant cell imaging

Fluorescent carbon dots are potential candidates for replacing traditional dyes for cell imaging, but their bulky sizes may hinder their passage through cell membranes, which may result in extra work to inject them into the cells. Here, a simple one-step method is proposed to synthesize brightly fluorescent carbon dots that can be endocytosed by intact plant cells and can thus directly dye the nucleus. The morphology, composition and effects of acidity and excitation wavelength on the photoluminescence of the obtained glutamic acid-based carbon dots were systematically investigated. The particles have a size of 4-8 nm and possess large amounts of oligo(ethylene glycol) groups with a quantum yield of 30.7%. The material exhibited high biocompatibility and low cytotoxicity. Confocal microscopy confirmed that the carbon dots prepared with the proposed method could dye HeLa cells within I min and intact onion epidermal cells in 10 min through endocytosis. (C) 2014 Elsevier B.V. All rights reserved.