Quantum dot surface engineering: Toward inert fluorophores with compact size and bright, stable emission

Abstract

The surfaces of colloidal nanocrystals are complex interfaces between solid crystals, coordinating ligands, and liquid solutions. For fluorescent quantum dots, the properties of the surface vastly influence the efficiency of light emission, stability, and physical interactions, and thus determine their sensitivity and specificity when they are used to detect and image biological molecules. But after more than 30 years of study, the surfaces of quantum dots remain poorly understood and continue to be an important subject of both experimental and theoretical research. In this article, we review the physics and chemistry of quantum dot surfaces and describe approaches to engineer optimal fluorescent probes for applications in biomolecular imaging and sensing. We describe the structure and electronic properties of crystalline facets, the chemistry of ligand coordination, and the impact of ligands on optical properties. We further describe recent advances in compact coatings that have significantly improved their properties by providing small hydrodynamic size, high stability and fluorescence efficiency, and minimal nonspecific interactions with cells and biological molecules. While major progress has been made in both basic and applied research, many questions remain in the chemistry and physics of quantum dot surfaces that have hindered key breakthroughs to fully optimize their properties.

DNA‐Mediated Self‐Assembly of Plasmonic Antennas with a Single Quantum Dot in the Hot Spot

“…Interestingly, antennas assembled with ultrasmooth spherical NPs display fewer on‐states than the ones assembled with conventional AuNPs. The photoemission of QDs have been observed to depend greatly on thesurrounding environment, such as the thickness of the passivating shell and capping ligands, leading to effects including significant long off‐states and erratic behavior to reduced blinking . The QDs used in this study have a quantum yield (QY) of ≈5% (Note S4, Supporting Information).…”

Single quantum dot tracking reveals the impact of nanoparticle surface on intracellular state

“…QDs also provide the ability to widely tune colloidal physicochemical properties due to the diverse range of surface coatings that have been developed 41 , 42 . We used thin coatings to yield similar h.d.…”

A strain-induced exciton transition energy shift in CdSe nanoplatelets: the impact of an organic ligand shell

“…Generally NCs' organic capping layers are considered as an analogue of self-assembled monolayers (SAMs), what allows extrapolation of the extensive information about the organicinorganic interfaces on the interaction of ligands with NCs surfaces. 2,29 However, unlike SAM substrates such NCs as quantum dots (QDs) or nanorods possess highly curved surface faceted with different lattice planes and enriched with vertex and edge sites. Such difference affects ligand packing density, introduces disorder in the ligand layer and sometimes makes the data difficult to interpret unambiguously.…”