Bioconjugation of quantum dots: Review & impact on future application

Abstract

Nowadays luminescent semiconductor quantum dots (QDs) are widely applied in different areas due to their unique optical properties. QDs can be used as photoluminescent labels with excellent possibilities for high-throughput detection and diagnostics. For most of such applications QDs must be coupled to biomolecules, which often represents a fundamental challenge. Although QDs have a lot of advantages over organic dyes, most of the techniques that have been developed for QD functionalization and bioconjugation, are more complicated than the corresponding techniques for organic fluorescent dyes. Here, the importance of choosing a suitable bioconjugation strategy in different applications, such as imaging and assays is described. The main goal of this review is to give a structured and detailed overview and comparison of the most widely used conjugation strategies in function of the active groups (carboxyl, amine, thiol, epoxy, hydroxyl and aldehyde groups) present on QD surface.

(Bio)conjugation Strategies Applied to Fluorescent Semiconductor Quantum Dots

“…Since these breakthroughs, conjugation of fluorescent nanocrystals has grown exponentially, and many other conjugation strategies have been developed. 2,16,41,42 In general, during a bioconjugation process, it is necessary to take into account the following observations: (i) the bioconjugation procedure cannot affect the biomolecule intrinsic activity; (ii) the procedure cannot quench the nanoprobe optical properties; (iii) the quantity of the biomolecules on the QDs' surface should be controlled; (iv) the obtained bioconjugate should be stable under physiological conditions; (v) the bioconjugate cannot establish unspecific bindings with biological systems and therefore, when needed, blocking the unreacted coupling agents should be applied.…”

“…Covalent binding require that a covalent bond is formed between the QDs' coating agent and the biomolecule, and many coupling agents can be used to accomplish this. 42,43 Here, we describe the majority of the non-covalent and covalent strategies currently applied to associate QDs with molecules, surfaces or other particles. We present the chemical principles behind each conjugation method and some well succeeded examples from the literature.…”

Detection of Rare Objects by Flow Cytometry: Imaging, Cell Sorting, and Deep Learning Approaches

“…As the size of fluorescent labels is comparable with the size of amino acid residues, the target protein structure generally remained the same, preserving the specificity and avidity of the antibody. Unlike the small-molecule dyes, QDs have a much larger size and a considerable surface area that can be modified by the biomolecules at many different sites as well as with irregular orientation of the antibodies on the QD surface, which affects biological activity [89]. This makes challenging the conjugation of QDs with antibodies regarding effective cell labeling and sorting.…”

Screening and characterisation of CdTe/CdS quantum dot-binding peptides for material surface functionalisation

“…12,13 Non-covalent bonds, such as electrostatic force, also can cause non-specic and unstable conjugates. 14,15 Peptides are increasingly being used as recognition probes for both organic and inorganic molecules owing to several reasons, including their small molecular size and good stability. 16,17 Because peptides can be chemically synthesised in large batch scales, many functional peptides have been discovered from rational and systematic studies for a wide range of applications (e.g., targeting, sensing, imaging).…”