BackgroundEffects of man-made electromagnetic fields (EMF) on living organisms potentially include transient and permanent changes in cell behaviour, physiology and morphology. At present, these EMF-induced effects are poorly defined, yet their understanding may provide important insights into consequences of uncontrolled (e.g., environmental) as well as intentional (e.g., therapeutic or diagnostic) exposure of biota to EMFs. In this work, for the first time, we study mechanisms by which a high frequency (18 GHz) EMF radiation affects the physiology of membrane transport in pheochromocytoma PC 12, a convenient model system for neurotoxicological and membrane transport studies.Methods and resultsSuspensions of the PC 12 cells were subjected to three consecutive cycles of 30s EMF treatment with a specific absorption rate (SAR) of 1.17 kW kg−1, with cells cooled between exposures to reduce bulk dielectric heating. The EMF exposure resulted in a transient increase in membrane permeability for 9 min in up to 90 % of the treated cells, as demonstrated by rapid internalisation of silica nanospheres (diameter d ≈ 23.5 nm) and their clusters (d ≈ 63 nm). In contrast, the PC 12 cells that received an equivalent bulk heat treatment behaved similar to the untreated controls, showing lack to minimal nanosphere uptake of approximately 1–2 %. Morphology and growth of the EMF treated cells were not altered, indicating that the PC 12 cells were able to remain viable after the EMF exposure. The metabolic activity of EMF treated PC 12 cells was similar to that of the heat treated and control samples, with no difference in the total protein concentration and lactate dehydrogenase (LDH) release between these groups.ConclusionThese results provide new insights into the mechanisms of EMF-induced biological activity in mammalian cells, suggesting a possible use of EMFs to facilitate efficient transport of biomolecules, dyes and tracers, and genetic material across cell membrane in drug delivery and gene therapy, where permanent permeabilisation or cell death is undesirable.

High frequency (HF) electromagnetic fields (EMFs) have been widely used in many wireless communication devices, yet within the terahertz (THz) range, their effects on biological systems are poorly understood. In this study, electromagnetic radiation in the range of 0.3–19.5 × 1012 Hz, generated using a synchrotron light source, was used to investigate the response of PC 12 neuron-like pheochromocytoma cells to THz irradiation. The PC 12 cells remained viable and physiologically healthy, as confirmed by a panel of biological assays; however, exposure to THz radiation for 10 min at 25.2 ± 0.4 °C was sufficient to induce a temporary increase in their cell membrane permeability. High-resolution transmission electron microscopy (TEM) confirmed cell membrane permeabilization via visualisation of the translocation of silica nanospheres (d = 23.5 ± 0.2 nm) and their clusters (d = 63 nm) into the PC 12 cells. Analysis of scanning electron microscopy (SEM) micrographs revealed the formation of atypically large (up to 1 µm) blebs on the surface of PC 12 cells when exposed to THz radiation. Long-term analysis showed no substantial differences in metabolic activity between the PC 12 cells exposed to THz radiation and untreated cells; however, a higher population of the THz-treated PC 12 cells responded to the nerve growth factor (NGF) by extending longer neurites (up to 0–20 µm) compared to the untreated PC12 cells (up to 20 µm). These findings present implications for the development of nanoparticle-mediated drug delivery and gene therapy strategies since THz irradiation can promote nanoparticle uptake by cells without causing apoptosis, necrosis or physiological damage, as well as provide a deeper fundamental insight into the biological effects of environmental exposure of cells to electromagnetic radiation of super high frequencies.

Ultrasmall metal nanoclusters (NCs) are employed in an array of diagnostic and therapeutic applications due to their tunable photoluminescence, high biocompatibility, polyvalent effect, ease of modification, and photothermal stability. However, gold nanoclusters’ (AuNCs’) intrinsically antimicrobial properties remain poorly explored and are not well understood. Here, we share an insight into the antimicrobial action of atomically precise AuNCs based on their ability to passively translocate across the bacterial membrane. Functionalized by a hydrophilic modified-bidentate sulfobetaine zwitterionic molecule (AuNC-ZwBuEt) or a more hydrophobic monodentate-thiolate, mercaptohexanoic acid (AuNC-MHA) molecule, 2 nm AuNCs were lethal to both Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus bacteria. The bactericidal efficiency was found to be bacterial strain-, time-, and concentration-dependent. The direct visualizations of the translocation of AuNCs and AuNC–cell and subcellular interactions were investigated using cryo-soft X-ray nano-tomography, transmission electron microscopy (TEM), and scanning TEM energy-dispersive spectroscopy analyses. AuNC-MHA were identified in the bacterial cytoplasm within 30 min, without evidence of the loss of membrane integrity. It is proposed that the bactericidal effect of AuNCs is attributed to their size, which allows for efficient energy-independent translocation across the cell membrane. The internalization of both AuNCs caused massive internal damage to the cells, including collapsed subcellular structures and altered cell morphology, leading to the eventual loss of cellular integrity.

Self-organized bacteria have been the subject of interest for a number of applications, including the construction of microbial fuel cells. In this paper, we describe the formation of a self-organized, three-dimensional network that is constructed using Gluconobacter oxydans B-1280 cells in a hydrogel consisting of poly(vinyl alcohol) (PVA) with N-vinyl pyrrolidone (VP) as a cross-linker, in which the bacterial cells are organized in a particular side-by-side alignment. We demonstrated that nonmotile G. oxydans cells are able to reorganize themselves, transforming and utilizing PVA–VP polymeric networks through the molecular interactions of bacterial extracellular polysaccharide (EPS) components such as acetan, cellulose, dextran, and levan. Molecular dynamics simulations of the G. oxydans EPS components interacting with the hydrogel polymeric network showed that the solvent-exposed loops of PVA–VP extended and engaged in bacterial self-encapsulation.

Membrane model systems capable of mimicking live cell membranes were used for the first time in studying the effects arising from electromagnetic fields (EMFs) of 18 GHz where membrane permeability was observed following exposure.

Exposure to high-frequency (HF) electromagnetic fields (EMFs) at 18 GHz was previously found to induce reversible cell permeabilization in eukaryotic cells; however, the fate of internalized foreign objects inside the cell remains unclear. Here, silica core–shell gold nanospheres (Au NS) of 20 ± 5 nm diameter were used to study the localization of Au NS in pheochromocytoma (PC 12) cells after exposure to HF EMFs at 18 GHz. Internalization of Au NS was confirmed using fluorescence microscopy and transmission electron microscopy. Analysis based on corresponding scanning transmission electron microscopy energy-dispersive spectroscopy revealed the presence of the Au NS free within the PC 12 cell membrane, cytoplasm, enclosed within intracellular vesicles and sequestered in vacuoles. The results obtained in this work highlight that exposure to HF EMFs could be used as an efficient technique with potential for effective delivery of drugs, genetic material, and nanomaterials into cells for the purpose of cellular manipulation or therapy.

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Ultrasmall gold nanoclusters (AuNC) show great promise for application in theranostics due to their unique optical and physicochemical properties; however, the associated nanotoxicology concerns need to be carefully considered because of their high diffusion across the cellular barrier. Herein, new insights into the role of surface modification of 2 nm AuNC on their toxicity with impact on the metabolism of COS‐7 fibroblast‐like cells are revealed. AuNCs are chemically modified with either a monodentate‐thiolated molecule (AuNC‐MHA) or a modified‐bidentate sulfobetaine zwitterionic molecule (AuNC‐ZwBuEt). Uptake and localization inside fibroblasts and the resultant influence on cell ultrastructure are carefully evaluated using scanning transmission electron microscopy (STEM) and cryo‐soft‐X‐ray tomography (cryo‐SXT). At concentrations of ≥25 μg Au mL−1, AuNC‐ZwBuEt are cytotoxic toward COS‐7 cells and are observed to cross the nuclear membrane. Cryo‐SXT analysis shows that fibroblasts develop an acute stress response in the form of swollen mitochondria, nuclear membrane blebbing, and large cytoplasmic vacuoles as early as 1 h postexposure. By contrast, AuNC‐MHA are not cytotoxic toward COS‐7 cells. Endosomal escape and translocation of the AuNC‐ZwBuEt into the nucleus and other organelles may be the cause for the observed cytotoxicity and highlight the need for further study of metal nanocluster‐cell interactions.