Sarkar, Suresh

Applications of colloidal nanocrystals in polar solvents often require nanocrystals synthesized in non-polar solvents. However, solvent transfer processes are problematic and deteriorate nanocrystal quality. Here we report syntheses of nanocrystals with nearly universal solvent dispersibility using ligands and solvents with alkoxy repeating units. Core syntheses, shell deposition and cation exchange proceed similarly to traditional methods while products are more stable in aqueous solution than those generated by solvent transfer. (CdSe)CdZnS nanocrystals retain photoluminescence in cells for single-particle tracking experiments and outperform other nanocrystal classes in diffusion metrics reflecting stability and resistance to non-specific binding. Distinct reaction classes yield nanocrystals with either methoxy or hydroxy ligand terminations, both of which can be purified by aqueous methods that are chemically greener than traditional methods. These reactions can further generate nanocrystals with diverse oxide, sulfide and selenide compositions, shapes and spectral bands with wide dispersibility that may make applications in polar solvents more widely accessible. (Figure presented.) © The Author(s), under exclusive licence to Springer Nature Limited 2025.

Antibodies and their conjugates of fluorescent labels are widely applied in life sciences research and clinical pathology. Among diverse label types, compact quantum dots (QDs) provide advantages of multispectral multiplexing, bright signals in the deep red and infrared, and low steric hindrance. However, QD-antibody conjugates have random orientation of the antigen-binding domain which may interfere with labeling and are large (20-30 nm) and heterogeneous, which limits penetration into biospecimens. Here, we develop conjugates of compact QDs and Fab′ antibody fragments as primary immunolabels. Fab′ fragments are conjugated site-specifically through sulfhydryl groups distal to antigen-binding domains, and the multivalent conjugates have small and homogeneous sizes (∼12 nm) near those of full-sized antibodies. Their performance as immunolabels for intracellular antigens is evaluated quantitatively by metrics of microtubule labeling density and connectivity in fixed cells and for cytological identification in fixed brain specimens, comparing results with probes based on spectrally-matched dyes. QD-Fab′ conjugates outperformed QD conjugates of full-sized antibodies and could be imaged with bright signals with 1-photon and 2-photon excitation. The results demonstrate a requirement for smaller bioaffinity agents and site-specific orientation for the success of nanomaterial-based labels to enhance penetration in biospecimens and minimize nonspecific staining.