Live Cell Imaging

Live cell imaging is an important analytical tool to provide clues into the fundamental nature of cellular and tissue structure and function. It plays an important role in cell biology, neurobiology, pharmacology, and developmental biology. Traditionally, genetic modification of cells with encoded fluorescent proteins is widely used for live cell imaging. However, it has limited applicability due to the permanent modifications made on cells. With the development of the new labeling agents and modification strategy, many endeavors have been made to develop surface engineering techniques that can circumvent the limitations of genetic modification. Cell surface engineering provides a novel, effective and simple platform to promote the development of live cell imaging strategy.

Cell Surface Engineering Technology

Cell surface engineering offers more transient and reversible modifications to endow new characteristics and functions to cells. This technology has drawn continuous interest in biomedical science, especially in cell-based therapy. Compared with genetic modification at the gene and protein level, surface engineering modifies the cell using the characteristics of lipids, proteins, and glycans present in the cell membrane, which protecting cells from the sheer stress and immune response, avoiding the possibility of endogenous gene disruption and the limitation of permanent genetic modification. Therefore, direct modification of the cell surface to introduce small molecule probes (such as fluorescent and biophysical probes) is highly desirable to advance live cell imaging. There are a series of non-genetic cell surface modification strategies have been developed, including chemical conjugations, polymeric encapsulation, hydrophobic insertion, enzymatic and metabolic addition.

Applications of Cell Surface Engineering in Live Cell Imaging

In the last decade, many researches have reported that cells can be labeled with a series of molecules or nanoparticles to increase imaging sensitivity.

• Case 1

Fluorescent conjugated polymer nanoparticles (CPNs) show outstanding optical properties and biocompatibility, as a result, they are favorable candidates for bioimaging application. However, few CPNs could achieve stable cell membrane labeling due to cell endocytosis. To address this challenge, Li, et al developed conjugated polymer nanoparticles (PFPNP-PLE) by encapsulating poly(fluorene-co-phenylene) (PFP) and PLGA-PEG-N₃ in the matrix. PFPNP-PLE was functionalized with the small-molecule drug plerixafor (PLE) on the surface. PFPNP-PLE exhibits excellent photophysical properties, low cytotoxicity, and specific cytomembrane location, which makes it a potential cell membrane labeling reagent with blue fluorescence emission, an important component for multilabel/multicolor bioimaging.

Fig.1 Cellular location of PFPNP-PLE in different cells. (Li, 2014)

• Case 2

Jia, et al. developed a two-step synergistic cell surface modification and labeling strategy to realize long-time plasma membrane imaging. They firstly incubated cells with glycol chitosan-10% PEG2000 cholesterol-10% biotin (a multisite plasma membrane anchoring reagent) to modify the plasma membranes with biotin groups. Secondly, they introduced fluorescein isothiocyanate (FITC)-conjugated avidin to achieve the fluorescence-labeled plasma membranes based on the supramolecular recognition between biotin and avidin. This strategy not only achieved stable plasma membrane imaging for up to 8 h without substantial internalization of the dyes, but also avoided the quick fluorescence loss caused by the detachment of dyes from plasma membranes.

Fig.2 Long-time plasma membrane imaging based on a two-step synergistic cell surface modification strategy. (Jia, 2016)

• Case 3

Jia, et al. reported a new strategy to re-engineer cell surfaces with structured and functionalized poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) copolymers through electrostatic adsorption. This PLL-g-PEG copolymer bearing terminally functionalized PEG grafts can be used as ‘cell surface active’ polymeric carriers for biotin, hydrazide, and azide moieties, offering a promising tool for bio/chemically remodeling cells and tissues with broad potential in bioimaging.

Fig.3 Applications of PLL-g-PEG. (Wilson, 2009)

Surface engineering techniques can circumvent the limitations of genetic modification and have been a promising methodology applied in bioimaging. As a leading service provider of cell surface engineering, Creative Biolabs has developed various cell surface engineering strategies to introduce a broad scope of conjugates for our global customers. If you are interested in our services, please feel free to contact us.

References

1. Li, M.; et al. Conjugated polymer nanoparticles for cell membrane imaging. Chemistry-An Asian Journal. 2014, 9(11): 3121-3124.
2. Jia, H. R.; et al. Long-time plasma membrane imaging based on a two-step synergistic cell surface modification strategy. Bioconjugate chemistry. 2016, 27(3): 782-789.
3. Wilson, J. T.; et al. Noncovalent cell surface engineering with cationic graft copolymers. Journal of the American Chemical Society. 2009, 131(51): 18228-18229.