Nanoscopy for nanoscience: how super-resolution microscopy extends imaging for nanotechnology

Protein-based fluorescent nanoparticles for super-resolution STED imaging of live cells

Protein-based fluorescent nanoparticles with excellent biocompatibility, good colloidal stability and photostability have been synthesized as attractive markers for STED nanoscopy in biological imaging.

Development of nanoparticles for super-resolution imaging (sriNPs) can greatly enrich the toolbox of robust optical probes for biological studies. Moreover, sriNPs enable us to monitor the behavior of engineered nanomaterials in complex biological environments with high spatial resolution, which is important for advancing our understanding of nano–bio interactions. Up to now, reports on sriNPs have been scarce. In this work, we report a facile strategy to prepare protein-based fluorescent NPs that can be utilized as probes in super-resolution microscopy. The method is simple and straightforward, and easily extendible to other types of fluorophores. By using Atto647N–transferrin NPs as an example, we have achieved a roughly four-fold resolution improvement by using STED nanoscopy. These protein-based sriNPs possess excellent biocompatibility, good colloidal stability and photostability, making them attractive candidates for biological studies. Moreover, STED nanoscopy enables the precise imaging of NP structures in living cells, and revealed the co-existence of multiple NPs within one endosomal vesicle.

Beyond quantification: in situ analysis of transcriptome and pre-mRNA alternative splicing at the nanoscale

In situ analysis offers a venue for dissecting the complex transcriptome in its natural context to tap into cellular processes that could explain the phenotypic physiology and pathology yet to be understood. Over the past decades, enormous progress has been made to improve the resolution, sensitivity, and specificity of single-cell technologies. The continued efforts in RNA research not only facilitates mechanistic studies of molecular biology but also provides state-of-the-art strategies for diagnostic purposes. The implementation of novel bio-imaging platforms has yielded valuable information for inspecting gene expression, mapping regulatory networks, and classifying cell types. In this article, we discuss the merits and technical challenges in single-molecule in situ RNA profiling. Advanced in situ hybridization methodologies developed for a variety of detection modalities are reviewed. Considering the fact that in mammalian cells the number of protein products immensely exceeds that of the actual coding genes due to pre-mRNA alternative splicing, tools capable of elucidating this process in intact cells are highlighted. To conclude, we point out future directions for in situ transcriptome analysis and expect a plethora of opportunities and discoveries in this field. WIREs Nanomed Nanobiotechnol 2017, 9:e1443. doi: 10.1002/wnan.1443 For further resources related to this article, please visit the WIREs website.

Super-resolution imaging-based single particle tracking reveals dynamics of nanoparticle internalization by live cells

By combining super-resolution photoactivation localization microscopy with single particle tracking, we have visualized the endocytic process in the live-cell environment with nanoparticles (NPs) of different size and surface functionalization. This allowed us to analyze the dynamics of NPs interacting with cells with high spatial and temporal resolution. We identified two distinctly different types of pathways by which NPs are internalized via clathrin-coated pits (CCPs). Predominantly, NPs first bind to the membrane and, subsequently, CCPs form at this site. However, there are also instances where a NP diffuses on the membrane and utilizes a preformed CCP. Moreover, we have applied this new method to further explore the effects of size and surface functionalization on the NP dynamics on the plasma membrane and the ensuing endocytosis.