Quantum dots: bright and versatile in vitro and in vivo fluorescence imaging biosensors

Abstract

Semiconductor quantum dots (QDs) have become important fluorescent probes for in vitro and in vivo bioimaging research. Their nanoparticle surfaces for versatile bioconjugation, their adaptable photophysical properties for multiplexed detection, and their superior stability for longer investigation times are the main advantages of QDs compared to other fluorescence imaging agents. Here, we review the recent literature dealing with the design and application of QD-bioconjugates for advanced in vitro and in vivo imaging. After a short summary of QD preparation and their most important properties, different QD-based imaging applications will be discussed from the technological and the biological point of view, ranging from super-resolution microscopy and single-particle tracking over in vitro cell and tissue imaging to in vivo investigations. A substantial part of the review will focus on multifunctional applications, in which the QD fluorescence is combined with drug or gene delivery towards theranostic approaches or with complementary technologies for multimodal imaging. We also briefly discuss QD toxicity issues and give a short outlook on future directions of QD-based bioimaging.

Cytosolic Delivery of Nanolabels Prevents Their Asymmetric Inheritance and Enables Extended Quantitative in Vivo Cell Imaging

“…1a. Cells are first incubated with plasmonic NPs, such as gold NPs (AuNPs), for [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] min. During that time the AuNP can adsorb to the cells and are internalized just below the plasma membrane by endocytic uptake (see TEM images in Figure S1).…”

“…The second strategy is to label the cells with exogenous contrast agents, being either organic probes or inorganic nanoparticles (NPs) 14,15 . Examples are fluorescently labelled dextrans 16,17 and quantum dots (QD) for optical fluorescence imaging [18][19][20] , or superparamagnetic iron oxide NPs and Gadolinium complexes for magnetic resonance imaging (MRI) 4,21,22 . Traditionally, these contrast agents are simply incubated with the cells, in some cases in combination with transfecting agents, so that they are internalized primarily by endocytic uptake.…”

Skin-derived mesenchymal stem cells as quantum dot vehicles to tumors

“…22 Together with the quantum confinement effect, which implements the size-dependent PL emission of QDs, such spectral characteristics enable the use of several QDs with different wavelengths in a single experiment and the construction of nanocrystals that fluoresce in a tissue optical window. 23,24 QDs are also characterized by their brightness and high photostability. 22 These optical properties permit QDs to be used in long-term tissue imaging and in vivo cell tracking.…”

Molecular Imaging with 68Ga Radio-Nanomaterials: Shedding Light on Nanoparticles

“…QDs possess unique size-dependent photo luminescent properties due to the quantum confinement effect [124][125][126]. They produce bright emissions spanning the visible and infrared spectrum when excited by high-energy photons.…”