Gauging surface charge distribution of live cell membrane by ionic current change using scanning ion conductance microscopy.

The distribution of surface charge and potential of cell membrane plays an indispensable role in cellular activities. However, probing surface charge of live cells under physiological conditions, until recently, remains an arduous challenge owing to the lack of effective methods. Scanning ion conductance microscopy (SICM) is an emerging imaging technique for imaging a live cell membrane in its native state. Here, we introduce a simple SICM based imaging technique to effectively map the surface charge contrast distribution of soft substrates including cell membranes by utilizing the higher surface charge sensitivity of the ionic current when the nanopipette tip is close to the substrate with a relatively high current change. This technique was assessed on charged model substrates made of polydimethylsiloxane, and the surface charge sensitivity of ionic current change was supported by finite element method simulations. With this method, we can distinguish the surface charge difference between the cell membrane and the supporting collagen matrix. We also observed the surface charge change induced by the small membrane damage after 1% dimethyl sulfoxide (DMSO) treatment. This new SICM technique provides opportunities to study interfacial and cell membrane processes with high spatial resolution.

Extracellular Surface Potential Mapping by Scanning Ion Conductance Microscopy Revealed Transient Transmembrane Pore Formation Induced by Conjugated Polymer Nanoparticles.

In-depth understanding of the biophysicochemical interactions at the nano-bio interface is important for basic cell biology and applications in nanomedicine and nanobiosensors. Here, the extracellular surface potential and topography changes of live cell membranes interacting with polymeric nanomaterials using a scanning ion conductance microscopy-based potential imaging technique are investigated. Two structurally similar amphiphilic conjugated polymer nanoparticles (CPNs) containing different functional groups (i.e., primary amine versus guanidine) are used to study incubation time and functional group-dependent extracellular surface potential and topographic changes. Transmembrane pores, which induce significant changes in potential, only appear transiently in the live cell membranes during the initial interactions. The cells are able to self-repair the damaged membrane and become resilient to prolonged CPN exposure. This study provides an important observation on how the cells interact with and respond to extracellular polymeric nanomaterials at the early stage. This study also demonstrates that extracellular surface potential imaging can provide a new insight to help understand the complicated interactions at the nano-bio interface and the following cellular responses.

Phenyleneethynylene trimer-based rigid-flexible [2+2] macrocycles for nucleic acid labelling in live cells.

Fluorescent macromolecules were developed for intracellular labeling in live cells. Coupling rigid rod phenyleneethynylene trimers with flexible amphiphilic diamines via the imine-bond formation chemistry yielded rigid-flexible [2+2] macromolecules showing nucleic acid selectivity and nontoxicity in live cells.

A guanylurea-functionalized conjugated polymer enables RNA interference in ex vivo human airway epithelium.

We demonstrate a successful target gene knockdown in ex vivo normal human bronchial epithelium (NHBE) cells covered with mucus layers using the guanylurea functionalization technique modulating the chemical environment at the positive charge of a gene carrier.