Effects of Surface Charges on the Bactericide Activity of CdTe/ZnS Quantum Dots: A Cell Membrane Disruption Perspective

Human serum albumin directed formation of cadmium telluride quantum dots: Applications in biosensing, anti-bacterial activities and cell cytotoxicity measurements

Although cadmium-based quantum dots (QDs) are highly promising candidates for numerous biological applications, their intrinsic toxicity limits their pertinency in living systems. Surface functionalization of QDs with appropriate molecules could reduce the toxicity level. Herein, we have synthesized the smaller sized (1-5 nm) aqueous-compatible biogenic CdTe QDs using human serum albumin (HSA) as a surface passivating agent via a greener approach. HSA-functionalized CdTe QDs have been explored in multiple in vitro sensing and biological applications, namely, (1) sensing, (2) anti-bacterial and (3) anti-cancer properties. Using CdTe-HSA QDs as a fluorescence probe, a simple fluorometric method has been developed for highly sensitive and selective detection of blood marker bilirubin and hazardous Hg2+ ion with a limit of detection (LOD) of 3.38 and 0.53 ng/mL, respectively. CdTe-HSA QDs also acts as a sensor for standard antibiotics, tetracycline and rifampicin with LOD values of 41.34 and 114.99 ng/mL, respectively. Nano-sized biogenic CdTe-HSA QDs have shown promising anti-bacterial activities against both gram-negative, E. coli and gram-positive, E. faecalis strains confirming more effectiveness against E. faecalis strains. The treatment of human cervical cancer cell lines (HeLa cells) with the synthesized QDs reflected the proficient cytotoxic properties of QDs.

Physico-Chemical Properties of CdTe/Glutathione Quantum Dots Obtained by Microwave Irradiation for Use in Monoclonal Antibody and Biomarker Testing

In this report, we present the results on the physicochemical characterization of cadmium telluride quantum dots (QDs) stabilized with glutathione and prepared by optimizing the synthesis conditions. An excellent control of emissions and the composition of the nanocrystal surface for its potential application in monoclonal antibody and biomarker testing was achieved. Two samples (QDYellow, QDOrange, corresponding to their emission colors) were analyzed by dynamic light scattering (DLS), and their hydrodynamic sizes were 6.7 nm and 19.4 nm, respectively. Optical characterization by UV-vis absorbance spectroscopy showed excitonic peaks at 517 nm and 554 nm. Photoluminescence spectroscopy indicated that the samples have a maximum intensity emission at 570 and 606 nm, respectively, within the visible range from yellow to orange. Infrared spectroscopy showed vibrational modes corresponding to the functional groups OH-C-H, C-N, C=C, C-O, C-OH, and COOH, which allows for the formation of functionalized QDs for the manufacture of biomarkers. In addition, the hydrodynamic radius, zeta potential, and approximate molecular weight were determined by dynamic light scattering (DLS), electrophoretic light scattering (ELS), and static light scattering (SLS) techniques. Size dispersion and the structure of nanoparticles was obtained by Transmission Electron Microscopy (TEM) and by X-ray diffraction. In the same way, we calculated the concentration of Cd2+ ions expressed in mg/L by using the Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-OES). In addition to the characterization of the nanoparticles, the labeling of murine myeloid cells was carried out with both samples of quantum dots, where it was demonstrated that quantum dots can diffuse into these cells and connect mostly with the cell nucleus.

Mitochondrial-targeting and NIR-responsive Mn3O4@PDA@Pd-SS31 nanozymes reduce oxidative stress and reverse mitochondrial dysfunction to alleviate osteoarthritis

Mitochondrial reactive oxygen species (mROS) play a crucial role in the process of osteoarthritis (OA), which may be a promising target for therapy of OA. In this study, novel mitochondrial-targeting and SOD-mimic Mn3O4@PDA@Pd-SS31 nanozymes with near-infrared (NIR) responsiveness and synergistic cascade to scavenge mROS were designed for the therapy of OA. Results showed that the nanozymes accelerated the release of Pd and Mn3O4 under NIR irradiation, exhibiting enhanced activities of SOD and CAT mimic enzymes with reversed mitochondrial dysfunction and promoted mitophagy to effectively scavenge mROS from chondrocytes, modulate the microenvironment of oxidative stress, and eventually inhibit the inflammatory response. Nanozymes were excreted in vivo through intestinal metabolic pathway and had good biocompatibility, effectively reducing the inflammatory response and relieving articular cartilage degeneration in OA joints, with a reduction of 93.7 % and 93.8 % in OARSCI scores for 4 and 8 weeks respectively. Thus, this study demonstrated that the mitochondria targeting and NIR responsive Mn3O4@PDA@Pd-SS31 nanozymes could efficiently scavenge mROS, repair damaged mitochondrial function and promote cartilage regeneration, which are promising for the treatment of OA in clinical applications.

Effect of Cobalt Ferrite Nanoparticles in a Hydrophilic Shell on the Conductance of Bilayer Lipid Membrane

We measured the conductance of bilayer lipid membranes of diphytanoylphosphatidylcholine induced by interaction with cubic magnetic nanoparticles (MNPs) of cobalt ferrite 12 and 27 nm in size and coated with a hydrophilic shell. The MNP coating is human serum albumin (HSA) or polyethylene glycol (PEG). The interaction of nanoparticles added to the bulk solution with the lipid bilayer causes the formation of metastable conductive pores, which, in turn, increases the integral conductance of the membranes. The increase in conductance with increasing MNP concentration was practically independent of the particle size. The dependence of the bilayer conductance on the concentration of PEG-coated MNPs was much weaker than that on the concentration with a shell of HSA. Analyzing the current traces, we believe that the conductive pores formed as a result of the interaction of nanoparticles with the membrane can change their size, remaining metastable. The form of multilevel current traces allows us to assume that there are several metastable pore states close in energy. The average radius of the putative cylindrical pores is in the range of 0.4-1.3 nm.

The role of size, charge, and cholesterol of cell membrane models in interactions with graphene oxide

The growing in manufacturing and applications of graphene oxide (GO), a two-dimensional nanomaterial, highlights the need for a better understanding of its environmental impact and toxicity. This work investigates the interaction of GO with cell membrane models as an indication for GO's potential harmfulness. A wide range of biologically-relevant membrane parameters (size, charge and, cholesterol content) and simple optical techniques were used to evaluate the outcome of interactions of vesicular cell membrane models with GO. Loss of membrane integrity was found to be positively correlated with electrostatic attraction and negatively correlated with cholesterol content. The size of vesicle-GO aggregates increased as a function of initial vesicle size, while cholesterol content was found to have a negligible effect on aggregation. Interestingly, charged vesicles reduced vesicle-GO aggregate size either by electrostatic repulsion of negatively charge vesicles or by GO folding following attachment of positively charge vesicles. Overall, by examining how key biologically-relevant parameters of membrane models affect interactions with GO, we have augmented the understanding of the potential threats of GO towards biological cell and to the environment.

Photocatalytic nanoparticles - From membrane interactions to antimicrobial and antiviral effects

As a result of increasing resistance among pathogens against antibiotics and anti-viral therapeutics, nanomaterials are attracting current interest as antimicrobial agents. Such materials offer triggered functionalities to combat challenging infections, based on either direct membrane action, effects of released ions, thermal shock induced by either light or magnetic fields, or oxidative photocatalysis. In the present overview, we focus on photocatalytic antimicrobial effects, in which light exposure triggers generation of reactive oxygen species. These, in turn, cause oxidative damage to key components in bacteria and viruses, including lipid membranes, lipopolysaccharides, proteins, and DNA/RNA. While an increasing body of studies demonstrate that potent antimicrobial effects can be achieved by photocatalytic nanomaterials, understanding of the mechanistic foundation underlying such effects is still in its infancy. Addressing this, we here provide an overview of the current understanding of the interaction of photocatalytic nanomaterials with pathogen membranes and membrane components, and how this translates into antibacterial and antiviral effects.

Plant-derived nanotherapeutic systems to counter the overgrowing threat of resistant microbes and biofilms

Since antiquity, the survival of human civilization has always been threatened by the microbial infections. An alarming surge in the resistant microbial strains against the conventional drugs is quite evident in the preceding years. Furthermore, failure of currently available regimens of antibiotics has been highlighted by the emerging threat of biofilms in the community and hospital settings. Biofilms are complex dynamic composites rich in extracellular polysaccharides and DNA, supporting plethora of symbiotic microbial life forms, that can grow on both living and non-living surfaces. These enforced structures are impervious to the drugs and lead to spread of recurrent and non-treatable infections. There is a strong realization among the scientists and healthcare providers to work out alternative strategies to combat the issue of drug resistance and biofilms. Plants are a traditional but rich source of effective antimicrobials with wider spectrum due to presence of multiple constituents in perfect synergy. Other than the biocompatibility and the safety profile, these phytochemicals have been repeatedly proven to overcome the non-responsiveness of resistant microbes and films via multiple pathways such as blocking the efflux pumps, better penetration across the cell membranes or biofilms, and anti-adhesive properties. However, the unfavorable physicochemical attributes and stability issues of these phytochemicals have hampered their commercialization. These issues of the phytochemicals can be solved by designing suitably constructed nanoscaled structures. Nanosized systems can not only improve the physicochemical features of the encapsulated payloads but can also enhance their pharmacokinetic and therapeutic profile. This review encompasses why and how various types of phytochemicals and their nanosized preparations counter the microbial resistance and the biofouling. We believe that phytochemical in tandem with nanotechnological innovations can be employed to defeat the microbial resistance and biofilms. This review will help in better understanding of the challenges associated with developing such platforms and their future prospects.

Direct conjugation of fluorescent quantum dots with E. coli via surface-displayed histidine-containing peptides

Biocompatible approaches to labeling bacteria with fluorescent nanoparticles are essential in order to create living bacterial bioconjugates for imaging, biosensors, medicine, and other applications. Herein we report the direct conjugation of carboxyl quantum dots (QDs) with E. coli outer membrane via surface-displayed binding peptides. The histidine-containing peptide H6G9 was displayed at the N-terminus of membrane-embedded enhanced circularly permuted outer membrane protein X (eCPX) scaffold, which was expressed upon chemical induction. The presence of the binding peptide creates an environment distinct from the negatively charged E. coli surface and provides strong binding affinity to carboxyl quantum dots (QDs). Transmission electron microscopy (TEM) analysis of E. coli-QD bioconjugates revealed high loading densities of these QDs immobilized on the cell surface, even when adding a very low concentration (10 μg/mL) of QDs in order to reduce the cell exposure. These hybrid cells strongly fluoresce with each of the distinct colors of loaded QDs with different emission wavelengths, which can be easily visualized by fluorescence microscopy or differentiated using flow cytometry. Importantly, the E. coli-QD bioconjugates were highly viable and maintained the ability to grow and divide. This study demonstrates a simple, direct, and highly efficient method for labelling bacteria with QDs, without significantly compromising the vitality of the cells.

Compressibility of Multicomponent, Charged Model Biomembranes Tunes Permeation of Cationic Nanoparticles

Cells respond to external stress by altering their membrane lipid composition to maintain fluidity, integrity and net charge. However, in interactions with charged nanoparticles (NPs), altering membrane charge could adversely affect its ability to transport ions across the cell membrane. Hence, it is important to understand possible pathways by which cells could alter zwitterionic lipid composition to respond to NPs without compromising membrane integrity and charge. Here, we report in situ synchrotron X-ray reflectivity (XR) measurements to monitor the interaction of cationic NPs in the form of quantum dots, with phase-separated supported lipid bilayers of different compositions containing an anionic lipid and zwitterionic lipids having variable degrees of stiffness. We observe that the extent of NP penetration into the respective membranes, as estimated from XR data analysis, is inversely related to membrane compression moduli, which was tuned by altering the stiffness of the zwitterionic lipid component. For a particular membrane composition with a discernible height difference between ordered and disordered phases, we were able to observe subtle correlations between the extent of charge on the NPs and the specificity to bind to the charged and ordered phase, contrary to that observed earlier for phase-separated model biomembranes containing no charged lipids. Our results provide microscopic insight into the role of membrane rigidity and electrostatics in determining membrane permeation. This can lead to great potential benefits in rational designing of NPs for bioimaging and drug delivery applications as well as in assessing and alleviating cytotoxicity of NPs.

Revisiting the cytotoxicity of quantum dots: an in-depth overview

Recently, medical research has been shifting its focus to nanomedicine and nanotherapeutics in the pursuit of drug development research. Quantum dots (QDs) are a critical class of nanomaterials due to their unique properties, which include optical, electronic, and engineered biocompatibility in physiological environments. These properties have made QDs an attractive biomedical resource such that they have found application as both in vitro labeling and in vivo theranostic (therapy-diagnostic) agents. Considerable research has been conducted exploring the suitability of QDs in theranostic applications, but the cytotoxicity of QDs remains an obstacle. Several types of QDs have been investigated over the past decades, which may be suitable for use in biomedical applications if the barrier of cytotoxicity can be resolved. This review attempts to report and analyze the cytotoxicity of the major QDs along with relevant related aspects.

Evaluation of the biocompatibility of the GSH-coated Ag2S quantum dots in vitro: a perfect example for the non-toxic optical probes

Near-infrared quantum dots (NIR QDs) are promising candidate for the fluorescent probes due to their better penetration depth, long-lived luminescence with size-tunable photoluminescence wavelengths. Glutathione-coated silver sulfide quantum dots (GSH-Ag₂S QDs) were synthesized using AgNO₃ and Na₂S in the aqueous media and they can give reaction with glutathione reductase (GR) and glutathione-s transferase (GST) enzymes as acting substrate analogue in vitro. Investigation of the toxicity of the nanomaterials are necessary to use them in the medical field and biomedical applications. Thus, in this study we investigated biocompatibility of the GSH-Ag₂S QDs in vitro using 293 T and CFPAC-1 cell lines. Cell viability by MTT assay, light microscopy, fluorescence microscopy, oxidative stress enzyme activities and ICP-MS analysis were performed to evaluate the cytotoxicity and internalization of the GSH-Ag₂S QDs. GSH-Ag₂S QDs showed great biocompatibility with both cell lines and did not cause imbalance in the oxidative stress metabolism. The ultralow solubility product constant of Ag₂S QDs (K_sp = 6.3 × 10^-50) prevents release of Ag ions into the biological systems that is in agreement with data obtained by ICP-MS. In conclusion, this data prove potential of GSH-Ag₂S QDs as a biocompatible optical probe to be used for the detection and/or targeting of GSH impaired diseases including cancer.

Leakage and Rupture of Lipid Membranes by Charged Polymers and Nanoparticles

Understanding and controlling the interactions between lipid membranes and nanomaterials are important for drug delivery, toxicity studies, and sensing. In the literature, the perception is that cationic nanomaterials can damage lipid membranes, although some reports suggest the opposite. In this work, instead of using different materials for testing the effect of charge, we used the same material and adjusted the pH. A total of three types of liposomes including zwitterionic phosphocholine (PC) and negatively charged phosphoserine (PS) with saturated and unsaturated tails were tested with three types of metal oxide nanoparticles and two types of cationic polymers. A calcein leakage assay was used to probe membrane leakage. We found that cationic polymers had very little advantage for leaking PC liposomes. On the other hand, the PS liposomes were leaked by TiO₂ nanoparticles regardless of their charge tuned by pH. ZnO with a high pK_a value was studied in detail, and it only leaked the 1,2-dioleoyl-sn-glycero-3-phosphocholine liposomes at low pH when ZnO was positively charged, but leakage was inhibited by adding NaCl to weaken electrostatic attraction and by capping ZnO. In addition, dissolution of adsorbed ZnO also caused leakage, suggesting that adsorption and desorption induced reversible lipid phase transitions. Overall, the interaction strength was a key factor for leakage. Leakage does not necessarily mean membrane damage, and cryogenic transmission electron microscopy was used to study membrane integrity. Previously observed cationic polymer/nanoparticle-induced damages in supported membranes could be due to electrostatic attraction between the polymers and the underlying negatively charged supporting surface.

Antimicrobial Activity and Mechanism of Functionalized Quantum Dots

An essential characteristic of quantum dots (QDs) is their antimicrobial activity. Compared with conventional antibiotics, QDs not only possess photoluminescence properties for imaging and photodynamic therapy but also have high structural stability. To enhance their antimicrobial efficiency, QDs usually are functionalized by polymers, including poly(ethylene glycol), polyethyleneimine, and poly-l-lysine. Also, QDs conjugated with polymers, such as poly(vinylpyrrolidone) and polyvinylidene fluoride, are prepared as antimicrobial membranes. The main antimicrobial mechanisms of QDs are associated with inducing free radicals, disrupting cell walls/membranes, and arresting gene expression. The different mechanisms from traditional antibiotics allow QDs to play antimicrobial roles in multi-drug-resistant bacteria and fungi. Since the toxicity of the QDs on animal cells is relatively low, they have broad application in antimicrobial research as an effective alternative of traditional antibiotics.

Understanding Nanoparticle Toxicity Mechanisms To Inform Redesign Strategies To Reduce Environmental Impact

There has been a surge of consumer products that incorporate nanoparticles, which are used to improve or impart new functionalities to the products based on their unique physicochemical properties. With such an increase in products containing nanomaterials, there is a need to understand their potential impacts on the environment. This is often done using various biological models that are abundant in the different environmental compartments where the nanomaterials may end up after use. Beyond studying whether nanomaterials simply kill an organism, the molecular mechanisms by which nanoparticles exhibit toxicity have been extensively studied. Some of the main mechanisms include (1) direct nanoparticle association with an organism's cell surface, where the membrane can be damaged or initiate internal signaling pathways that damage the cell, (2) dissolution of the material, releasing toxic ions that impact the organism, generally through impairing important enzyme functions or through direct interaction with a cell's DNA, and (3) the generation of reactive oxygen species and subsequent oxidative stress on an organism, which can also damage important enzymes or an organism's genetic material. This Account reviews these toxicity mechanisms, presenting examples for each with different types of nanomaterials. Understanding the mechanism of nanoparticle toxicity will inform efforts to redesign nanoparticles with reduced environmental impact. The redesign strategies will need to be chosen based on the major mode of toxicity, but also considering what changes can be made to the nanomaterial without impacting its ability to perform in its intended application. To reduce interactions with the cell surface, nanomaterials can be designed to have a negative surface charge, use ligands such as polyethylene glycol that reduce protein binding, or have a morphology that discourages binding with a cell surface. To reduce the nanoparticle dissolution to toxic ions, the toxic species can be replaced with less toxic elements that have similar properties, the nanoparticle can be capped with a shell material, the morphology of the nanoparticle can be chosen to minimize surface area and thus minimize dissolution, or a chelating agent can be co-introduced or functionalized onto the nanomaterial's surface. To reduce the production of reactive oxygen species, the band gap of the material can be tuned either by using different elements or by doping, a shell layer can be added to inhibit direct contact with the core, or antioxidant molecules can be tethered to the nanoparticle surface. When redesigning nanoparticles, it will be important to test that the redesign strategy actually reduces toxicity to organisms from relevant environmental compartments. It is also necessary to confirm that the nanomaterial still demonstrates the critical physicochemical properties that inspired its inclusion in a product or device.

Lipid bilayer disruption induced by amphiphilic Janus nanoparticles: the non-monotonic effect of charged lipids

In this study, we report the complex effects of charged lipids on the interaction between amphiphilic Janus nanoparticles and lipid bilayers. Janus nanoparticles are cationic on one hemisphere and hydrophobic on the other. We show that the nanoparticles, beyond threshold concentrations, induce holes in both cationic and anionic lipid bilayers mainly driven by hydrophobic interactions. However, the formation of these defects is non-monotonically dependent on ionic lipid composition. The electrostatic attraction between the particles and anionic lipid bilayers enhances particle adsorption and lowers the particle concentration threshold for defect initiation, but leads to more localized membrane disruption. Electrostatic repulsion leads to reduced particle adsorption on cationic bilayers and extensive defect formation that peaks at intermediate contents of cationic lipids. This study elucidates the significant role lipid composition plays in influencing how amphiphilic Janus nanoparticles interact with and perturb lipid membranes.

Adverse Interactions of Luminescent Semiconductor Quantum Dots with Liposomes and Shewanella oneidensis

Cadmium-containing luminescent quantum dots (QD) are increasingly used in display, bioimaging, and energy technologies; however, significant concerns have been raised about their potentially adverse impact on human health and the environment. This study makes use of a broad toolkit of analytical methods to investigate and increase our understanding of the interactions of luminescent cadmium-containing (CdSe) and cadmium-free (ZnSe) QD, with and without a passivating higher bandgap energy ZnS shell, with phospholipid vesicles (liposomes), which model bacterial membranes, and with Shewanella oneidensis MR-1, an environmentally relevant bacteria. A unique feature of this study is that all QD types have the same surface chemistry, being capped with uncharged poly(ethylene glycol) ligands. This enables focusing the study on the impact of the QD core on liposomes and bacterial cells. The study reveals that QD association with liposome and bacterial cell membranes is imperative for their adverse impact on liposomes and bacterial cells. The QD' concentration-dependent association with liposomes and bacterial cells destabilizes the membranes mechanically, which leads to membrane disruption and lysis in liposomes and to bacterial cell death. The study also shows that cadmium-containing QD exhibit a higher level of membrane disruption in bacterial cells than cadmium-free QD. ZnSe QD have low membrane impact, and coating them with a ZnS shell decreases their membrane disruption activity. In contrast, CdSe QD exhibit a high level of membrane impact, and coating them with a ZnS shell does not decrease, but in fact further increases, their membrane disruption activity. This behavior might be attributed to higher affinity and association of CdSe/ZnS QD with liposomes and bacterial cells and to a contribution of dissolved zinc ions from the ZnS shell to increased membrane disruption activity.

Antifungal effects of BiOBr nanosheets carrying surfactant cetyltrimethylammonium bromide

BiOBr nanosheets are important photocatalytic nanomaterials. However, their biological effects remain to be explored. In this study, we investigated the antifungal effect of BiOBr nanosheets on Candida albicans. Strikingly, the nanosheets strongly inhibited the growth of C. albicans [IC₅₀=(96±4.7) mg/L], hyphal development and biofilm formation. Compareed to the antifungal effect of the cationic surfactant cetyltrimethylammonium bromide, the inhibitory effect of the nanosheets on fungal pathogen was attributed to cetyltrimethylammonium bromide adsorbed by the nanosheets. Thermal gravity analysis and cetyltrimethylammonium bromide release experiment indicated that only 0.42% cetyltrimethylammonium bromide on BiOBr nanosheets was released. Taken together, this study uncovers the contribution of surfactant released from the nanosheets to their antifungal activity.

A Review on Quantum Dots: Synthesis to In- silico Analysis as Next Generation Antibacterial Agents

Succumbing to Multi-Drug Resistant (MDR) bacteria is a great distress to the recent health care system. Out of the several attempts that have been made to kill MDR pathogens, a few gained short-lived success. The failures, of the discovered or innovated antimicrobials, were mostly due to their high level of toxicity to hosts and the phenomenal rate of developing resistance by the pathogens against the new arsenal. Recently, a few quantum dots were tested against the pathogenic bacteria and therefore, justified for potential stockpiling of next-generation antibacterial agents. The key players for antimicrobial properties of quantum dots are considered to be Reactive Oxygen Species (ROS). The mechanism of reaction between bacteria and quantum dots needs to be better understood. They are generally targeted towards the cell wall and membrane components as lipoteichoic acid and phosphatidyl glycerol of bacteria have been documented here. In this paper, we have attempted to simulate ZnS quantum dots and have analysed their mechanism of reaction as well as binding potential to the above bacterial membrane components using CDOCKER. Results have shown a high level of antibacterial activity towards several pathogenic bacteria which specify their potentiality for future generation antibacterial drug development.

Nanoscale Heterogeneities Drive Enhanced Binding and Anomalous Diffusion of Nanoparticles in Model Biomembranes

Interaction of functional nanoparticles with cells and model biomembranes has been widely studied to evaluate the effectiveness of the particles as potential drug delivery vehicles and bioimaging labels as well as in understanding nanoparticle cytotoxicity effects. Charged nanoparticles, in particular, with tunable surface charge have been found to be effective in targeting cellular membranes as well as the subcellular matrix. However, a microscopic understanding of the underlying physical principles that govern nanoparticle binding, uptake, or diffusion on cells is lacking. Here, we report the first experimental studies of nanoparticle diffusion on model biomembranes and correlate this to the existence of nanoscale dynamics and structural heterogeneities using super-resolution stimulated emission depletion (STED) microscopy. Using confocal and STED microscopy coupled with fluorescence correlation spectroscopy (FCS), we provide novel insight on why these nanoparticles show enhanced binding on two-component lipid bilayers as compared to single-component membranes and how binding and diffusion is correlated to subdiffraction nanoscale dynamics and structure. The enhanced binding is also dictated, in part, by the presence of structural and dynamic heterogeneity, as revealed by STED-FCS studies, which could potentially be used to understand enhanced nanoparticle binding in raft-like domains in cell membranes. In addition, we also observe a clear correlation between the enhanced nanoparticle diffusion on membranes and the extent of membrane penetration by the nanoparticles. Our results not only have a significant impact on our understanding of nanoparticle binding and uptake as well as diffusion in cell and biomembranes, but have very strong implications for uptake mechanisms and diffusion of other biomolecules, like proteins on cell membranes and their connections to functional membrane nanoscale platform.

Membrane interactions and antimicrobial effects of inorganic nanoparticles

Interactions between nanoparticles and biological membranes are attracting increasing attention in current nanomedicine, and play a key role both for nanotoxicology and for utilizing nanomaterials in diagnostics, drug delivery, functional biomaterials, as well as combinations of these, e.g., in theranostics. In addition, there is considerable current interest in the use of nanomaterials as antimicrobial agents, motivated by increasing resistance development against conventional antibiotics. Here, various nanomaterials offer opportunities for triggered functionalites to combat challenging infections. Although the performance in these diverse applications is governed by a complex interplay between the nanomaterial, the properties of included drugs (if any), and the biological system, nanoparticle-membrane interactions constitute a key initial step and play a key role for the subsequent biological response. In the present overview, the current understanding of inorganic nanomaterials as antimicrobial agents is outlined, with special focus on the interplay between antimicrobial effects and membrane interactions, and how membrane interactions and antimicrobial effects of such materials depend on nanoparticle properties, membrane composition, and external (e.g., light and magnetic) fields.