A quantum dot-based ratiometric pH sensor that responds to the pH range 6–8 was developed using FITC (fluorescein isothiocyanate) conjugated CdSe/CdZnS nanocrystals.

We report a one-step synthetic strategy for the preparation of recombinant protein (EGFP-Protein G)-coated PbS quantum dots for dual (visible and second-NIR) fluorescence imaging of breast tumors.

Fluorescent proteins have been widely used in biology because of their compatibility and varied applications in living specimens. Fluorescent proteins are often undesirably sensitive to intracellular conditions such as pH and ion concentration, generating considerable issues at times. However, harnessing these intrinsic sensitivities can help develop functional probes. In this study, we found that the fluorescence of yellow fluorescent protein (YFP) depends on the protein concentration in the solution and that this dependence can be enhanced by adding a glycine residue in to the YFP; we applied this finding to construct an intracellular protein-crowding sensor. A Förster resonance energy transfer (FRET) pair, involving a cyan fluorescent protein (CFP) insensitive to protein concentration and a glycine-inserted YFP, works as a genetically encoded probe to evaluate intracellular crowding. By measuring the fluorescence of the present FRET probe, we were able to detect dynamic changes in protein crowding in living cells.

Antibodies are therapeutic proteins that are becoming indispensable for the treatment of serious diseases. Their efficacies depend on their folded structures, the loss of which, through unfolding or aggregation, should be closely monitored during their manufacture, storage, and dosing for safe usage. In downstream processes, exposure of the crude antibody solution to acid, followed by neutralization, is an established standard protocol for antibody purification and inactivation of viruses in antibody preparations. Nevertheless, this treatment also triggers an unwanted side reaction, i.e., antibody aggregation. The aggregates continuously evolve at neutral pH. It remains unclear whether the aggregates progressively incorporate the native, folded, monomers into themselves, enabling aggregate growth as seen in amyloid fibrils. In the present study, the diffusion of fluorescently labeled monoclonal humanized immunoglobulin G1 monomers in aggregates produced by pH-shift stress was tracked by fluorescence correlation spectroscopy. This method was used in addition to monitoring aggregate formation by dynamic light scattering. The diffusing velocities of the monomers indicated that the folded monomers were not involved in aggregate formation, in contrast with unfolded monomers. On the basis of the results, we propose a bifurcated pathway for the refolding and aggregation of antibodies triggered by a pH shift from acidic to neutral. In the scheme, the refolded monomers survive until their unfolding. The insights in this study will contribute to the manufacture of aggregation-resistant therapeutic antibodies.