Visualizing the intracellular aggregation behavior of gold nanoclusters via structured illumination microscopy and scanning transmission electron microscopy

Given the growing concerns about nanotoxicity, numerous studies have focused on providing mechanistic insights into nanotoxicity by imaging the intracellular fate of nanoparticles. A suitable imaging strategy is necessary to uncover the intracellular behavior of nanoparticles. Although each conventional technique has its own limitations, scanning transmission electron microscopy (STEM) and three-dimensional structured illumination microscopy (3D-SIM) combine the advantages of chemical element mapping, ultrastructural analysis, and cell dynamic tracking. Gold nanoclusters (AuNCs), synthesized using 6-aza-2 thiothymine (ATT) and L-arginine (Arg) as reducing and protecting ligands, referred to as Arg@ATT-AuNCs, have been widely used in biological sensing and imaging, medicine, and catalyst yield. Based on their intrinsic fluorescence and high electron density, Arg@ATT-AuNCs were selected as a model. STEM imaging showed that both the single-particle and aggregated states of Arg@ATT-AuNCs were compartmentally distributed within a single cell. Real-time 3D-SIM imaging showed that the fluorescent Arg@ATT-AuNCs gradually aggregated after being located in the lysosomes of living cells, causing lysosomal damage. The aggregate formation of Arg@ATT-AuNCs was triggered by the low-pH medium, particularly in the lysosomal acidic environment. The proposed dual imaging strategy was verified using other types of AuNCs, which is valuable for studying nano-cell interactions and any associated cytotoxicity, and has the potential to be a useful approach for exploring the interaction of cells with various nanoparticles.

In cellulo synthesis of dendrimeric sensors for fluorescence-on imaging of bacterial phagocytosis

Methods for optical tracking of pathogen-host interactions are of biomedical significance. We herein have reported a high molecular weight pH sensor (Den-pH) that is assembled in bacteria and then stably trapped in bacteria irrespective of bacterial membrane potentials. Endowed with acidity-triggered red fluorescence, Den-pH allows signal-on tracking of S. aureus in phagocytosis by macrophages. Intra-bacterial formation of multifunctional optical probes, which offers the advantage of overcoming the liability of conventional potential-sensitive dyes to dissipate from stressed bacteria, offers a new tool to study stressed pathogens.

Lysosome-targeting pH indicator based on peri-fused naphthalene monoimide with superior stability for long term live cell imaging

Lysosomal pH is altered in many pathophysiological conditions. We describe synthesis and spectral properties of a new lysosomal fluorescent marker dye suitable for microscopic evaluation of lysosomal distribution and pH changes.

A novel photochemical sensor based on quinoline-functionalized phenazine derivatives for multiple substrate detection

A novel photochemical sensor based on quinoline-functionalized phenazine derivatives for highly sensitive detection of multiple substrates (l-Arg, CO₂, and pH) was designed and synthesized.

Organelle-Directed Metabolic Glycan Labeling and Optical Tracking of Dysfunctional Lysosomes Thereof

Metabolic glycan labeling (MGL) has been employed for diverse purposes, such as cell surface glycan imaging and tumor surface engineering. We herein reported organelle-specific MGL (OMGL) for selective tagging of the inner limiting membrane of lysosomes over the cell surface. This is operated via acidity-promoted accumulation of optical probes in lysosomes and bioorthogonal ligation of the trapped probes with 9-azidosialic acid (AzSia) metabolically installed on lysosomal membrane proteins. Overcoming the limitation of classical organelle probes to dissipate from stressed organelles, OMGL enables optical tracking of pH-elevated lysosomes in exocytosis and membrane-permeabilized lysosomes in different cell death pathways. Thus, OMGL offers a new tool to study lysosome biology.