Fluorescent semiconductor nanoplatelets (NPLs) are a new generation of fluorescent labels. NPLs are colloidal two-dimensional materials that exhibit several unique optical properties including high brilliance, high fluorescent photostability, high extinction coefficients, broad excitation and narrow emission spectra. However, NPLs are synthetized in organic solvents and coated with hydrophobic ligands that render them insoluble in water. A current challenge is to stabilize NPLs in aqueous media compatible with biological environments. Here we propose, for the first time, a ligand exchange method to disperse different colors of NPLs in water while maintaining good optical properties. NPLs were transferred in aqueous media by ligand exchange with a small monodentate hydrophilic ligand, namely 3-mercaptopropionic acid. Monothiol anchoring to semiconductors are prone to photo-oxidation and can desorb in dilute solutions. In order to circumvent these issues, we developed a multidentate polymeric ligand that binds to the surface of NPLs. NPLs showed then exceptional long term colloidal stability regardless of several medium conditions, such as a broad pH range from 5.3 to 9.5, high ionic strength buffer (200 mM NaCl), and storage at nanomolar concentration (10 nM). After ligand exchange, at least 70% of NPLs quantum yield is conserved (from an initial 90% in organic media) and their fluorescence emission bandwidth remained narrow (around 25 nm full width at half maximum).<br/>To demonstrate NPLs potential for biodetection, we functionalized them with different biological molecules through self-assembly strategies based on histidine-tagged biomolecules or by covalent bonds. We conjugated genetically engineered proteins that incorporated 15-unit long histidine tags, specifically protein A, mCherry and GFP, on the surface of NPLs with a bioconjugation yield efficiency of 95%. Afterwards, we immobilized anti-human CD3 antibody (Ab) on the surface of NPLs by using protein A as intermediate layer that specifically binds Ab We also immobilized streptavidin (SAV) on the surface of NPLs by sulfhydryl-maleimide chemistry. NPLs-SAV conjugates were used to stain human lymphocytes through biotinylated Ab. We compared the staining index of these NPLs-SAV alongside popular fluorochromes like Phycoerythrin (PE) and Brilliant Violet 650™ (BV650™) using flow cytometry. We obtained a staining index of 39, 32 and 23 for NPLs, BV650™ and PE, respectively.

Semiconductor nanoplatelets: A new class of ultrabright and biocompatible probes for biological applications

256th National Meeting (2018)

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