Nanodiamond decorated liposomes as highly biocompatible delivery vehicles and a comparison with carbon nanotubes and graphene oxide

Graphene-Based Nanomaterials and Their Interactions with Lipid Membranes

Graphene-based nanomaterials (GNMs) have captured increasing attention in the recent advancement of materials science and nanotechnology owing to their excellent physicochemical properties. Despite having unquestionable advances, the application of GNMs in biological and medical sciences is still limited due to the lack of knowledge and precise control over their interaction with the biological milieu. The cellular membrane is the first barrier with which GNMs interact before entering a cell. Therefore, understanding how they interact with cell membranes is important from the perspective of safe use in biological and biomedical fields. In this review, we systematically summarize the recent efforts in predicting the interactions between GNMs and model cellular membranes. This review provides insights into how GNMs interact with lipid membranes and self-assemble in and around them. Both the computational simulations and experimental observations are summarized. The interactions are classified depending on the physicochemical properties (structure, chemistry, and orientation) of GNMs and various model membranes. The thermodynamic parameters, structural details, and supramolecular forces are listed to understand the interactions which would help circumvent potential risks and provide guidance for safe use in the future. At the end of this review, future prospective and emerging challenges in this research field are discussed.

Stimuli-Responsive Boron-Based Materials in Drug Delivery

Drug delivery systems, which use components at the nanoscale level as diagnostic tools or to release therapeutic drugs to particular target areas in a regulated manner, are a fast-evolving field of science. The active pharmaceutical substance can be released via the drug delivery system to produce the desired therapeutic effect. The poor bioavailability and irregular plasma drug levels of conventional drug delivery systems (tablets, capsules, syrups, etc.) prevent them from achieving sustained delivery. The entire therapy process may be ineffective without a reliable delivery system. To achieve optimal safety and effectiveness, the drug must also be administered at a precision-controlled rate and the targeted spot. The issues with traditional drug delivery are overcome by the development of stimuli-responsive controlled drug release. Over the past decades, regulated drug delivery has evolved considerably, progressing from large- and nanoscale to smart-controlled drug delivery for several diseases. The current review provides an updated overview of recent developments in the field of stimuli-responsive boron-based materials in drug delivery for various diseases. Boron-containing compounds such as boron nitride, boronic acid, and boron dipyrromethene have been developed as a moving field of research in drug delivery. Due to their ability to achieve precise control over drug release through the response to particular stimuli (pH, light, glutathione, glucose or temperature), stimuli-responsive nanoscale drug delivery systems are attracting a lot of attention. The potential of developing their capabilities to a wide range of nanoscale systems, such as nanoparticles, nanosheets/nanospheres, nanotubes, nanocarriers, microneedles, nanocapsules, hydrogel, nanoassembly, etc., is also addressed and examined. This review also provides overall design principles to include stimuli-responsive boron nanomaterial-based drug delivery systems, which might inspire new concepts and applications.

Understanding interactions between biomolecules and two-dimensional nanomaterials using in silico microscopes

Two-dimensional (2D) nanomaterials such as graphene are increasingly used in research and industry for various biomedical applications. Extensive experimental and theoretical studies have revealed that 2D nanomaterials are promising drug delivery vehicles, yet certain materials exhibit toxicity under biological conditions. So far, it is known that 2D nanomaterials possess strong adsorption propensities for biomolecules. To mitigate potential toxicity and retain favorable physical and chemical properties of 2D nanomaterials, it is necessary to explore the underlying mechanisms of interactions between biomolecules and nanomaterials for the subsequent design of biocompatible 2D nanomaterials for nanomedicine. The purpose of this review is to integrate experimental findings with theoretical observations and facilitate the study of 2D nanomaterial interaction with biomolecules at the molecular level. We discuss the current understanding and progress of 2D nanomaterial interaction with proteins, lipid membranes, and DNA based on molecular dynamics (MD) simulation. In this review, we focus on the 2D graphene nanosheet and briefly discuss other 2D nanomaterials. With the ever-growing computing power, we can image nanoscale processes using MD simulation that are otherwise not observable in experiment. We expect that molecular characterization of the complex behavior between 2D nanomaterials and biomolecules will help fulfill the goal of designing effective 2D nanomaterials as drug delivery platforms.

Nanodiamond Integration into Niosomes as an Emerging and Efficient Gene Therapy Nanoplatform for Central Nervous System Diseases

Nanodiamonds (NDs) are promising materials for gene delivery because of their unique physicochemical and biological features, along with their possibility of combination with other nonviral systems. Our aim was to evaluate the biophysical performance of NDs as helper components of niosomes, named nanodiasomes, to address a potential nonviral gene delivery nanoplatform for therapeutic applications in central nervous system (CNS) diseases. Nanodiasomes, niosomes, and their corresponding complexes, obtained after genetic material addition at different ratios (w/w), were evaluated in terms of physicochemical properties, cellular uptake, intracellular disposition, biocompatibility, and transfection efficiency in HEK-293 cells. Nanodiasomes, niosomes, and complexes fulfilled the physicochemical features for gene therapy applications. Biologically, the incorporation of NDs into niosomes enhanced 75% transfection efficiency (p < 0.001) and biocompatibility (p < 0.05) to values over 90%, accompanied by a higher cellular uptake (p < 0.05). Intracellular trafficking analysis showed higher endocytosis via clathrins (p < 0.05) in nanodiaplexes compared with nioplexes, followed by higher lysosomal colocalization (p < 0.05), that coexisted with endosomal escape properties, whereas endocytosis mediated by caveolae was the most efficient pathway in the case of nanodiaplexes. Moreover, studies in CNS primary cells revealed that nanodiaplexes successfully transfected neuronal and retinal cells. This proof-of-concept study points out that ND integration into niosomes represents an encouraging nonviral nanoplatform strategy for the treatment of CNS diseases by gene therapy.

Targeted drug delivery in cervical cancer: Current perspectives

Cervical cancer is preventable yet one of the most prevalent cancers among women around the globe. Though regular screening has resulted in the decline in incidence, the disease claims a high number of lives every year, especially in the developing countries. Owing to rather aggressive and non-specific nature of the conventional chemotherapeutics, there is a growing need for newer treatment modalities. The advent of nanotechnology has assisted in this through the use of nanocarriers for targeted drug delivery. A number of nanocarriers are continuously being developed and studied for their application in drug delivery. The present review summarises the different drug delivery approaches and nanocarriers that can be useful, their advantages and limitation.

Nanotechnology Strategies for Plant Genetic Engineering

Plant genetic engineering is essential for improving crop yield, quality, and resistance to abiotic/biotic stresses for sustainable agriculture. Agrobacterium-, biolistic bombardment-, electroporation-, and poly(ethylene glycol) (PEG)-mediated genetic-transformation systems are extensively used in plant genetic engineering. However, these systems have limitations, including species dependency, destruction of plant tissues, low transformation efficiency, and high cost. Recently, nanotechnology-based gene-delivery methods have been developed for plant genetic transformation. This nanostrategy shows excellent transformation efficiency, good biocompatibility, adequate protection of exogenous nucleic acids, and the potential for plant regeneration. However, the nanomaterial-mediated gene-delivery system in plants is still in its infancy, and there are many challenges for its broad applications. Herein, the conventional genetic transformation techniques used in plants are briefly discussed. After that, the progress in the development of nanomaterial-based gene-delivery systems is considered. CRISPR-Cas-mediated genome editing and its combined applications with plant nanotechnology are also discussed. The conceptual innovations, methods, and practical applications of nanomaterial-mediated genetic transformation summarized herein will be beneficial for promoting plant genetic engineering in modern agriculture.

PM2.5 and the typical components cause organelle damage, apoptosis and necrosis: Role of reactive oxygen species

In this research, the organelle damage, apoptosis and necrosis induced by PM_2.5, BC and Kaolin were studied using human bronchial epithelial (16HBE) cells. PM_2.5, BC and Kaolin all induce cell death, LDH release and excess intracellular ROS generation. For the organelle injuries, Kaolin and high-dose PM_2.5 (240 μg/mL) cause lysosomal acidification, but BC causes lysosomal alkalization (lysosomal membrane permeabilization, LMP). BC and Kaolin cause the loss of mitochondrial membrane potential (MMP), while PM_2.5 does not. For the cell death mode, PM_2.5 causes both apoptosis and necrosis. However only necrosis has been detected in the BC and Kaolin treated groups, indicating the more severe cellular insult. Excess ROS generation is involved in the organelle damage and cell death. ROS contributes to the BC-induced LMP and necrosis, but does not significantly affect the Kaolin-induced MMP loss and necrosis. Therefore, the BC component in PM_2.5 may cause cytotoxicity via ROS-dependent pathways, the Kaolin component may damage cells via ROS-independent mechanisms such as strong interaction. The PM_2.5-induced apoptosis and necrosis can be partially mitigated after the removal of ROS, indicating the existence of both the ROS-dependent and ROS-independent mechanisms due to the complicated PM_2.5 components. BC represents the anthropogenic source component in PM_2.5, while Kaolin represents the natural source component. Our results provide knowledge on the toxic mechanisms of typical PM_2.5 components at the cellular and subcellular levels.

Charge-Enhanced Separation of Organic Pollutants in Water by Anionic Covalent Organic Frameworks

The effective removal of organic pollutants in wastewater is a key environmental challenge. In this work, an anionic covalent organic framework (named TpPa-SO₃Na) was synthesized through a green two-in-one synthesis strategy with autocatalytic imine formation. The slowly generated acetic acid as a catalyst is favorable to sustain the reversibility of the covalent organic framework (COF) formation reaction and improve the crystallinity of TpPa-SO₃Na. TpPa-SO₃Na consists of a homogeneous distribution of sulfonate groups to produce negatively charged regular channels. The strong electrostatic and hydrogen-bonding interactions between the sulfonate groups anchored in the nanochannels and the amine groups in organic pollutants improve the adsorption selectivity and capacity. These structures allow a high degree of control over adsorption processes to boost the adsorption kinetics and improve selective separation. TpPa-SO₃Na exhibits ultrafast adsorption (<1 min) of cationic antibiotics and dyes (average over 95%). Furthermore, TpPa-SO₃Na exhibits high selectivity for the uptake of dye molecules on the basis of the differences in charge and molecular size. This work explored functional designs and green manufacturing of anionic COFs for removal of hydrophilic organic pollutants.

Molecular Design of Layer-by-Layer Functionalized Liposomes for Oral Drug Delivery

Liposomes are small spherical vesicles composed mainly of phospholipids and cholesterol. Over the years, a number of liposomal formulations have shown clinical promise, but the use of liposomes in oral drug delivery is limited. This is partly due to the vulnerability of conventional liposomes to the detrimental effect of gastrointestinal destabilizing factors and also to the poor efficiency in intestinal absorption of liposomes. Some of these issues can be ameliorated using the layer-by-layer (LbL) assembly technology, which has been widely applied to modify the surface of various nanoparticulate systems. Discussions about LbL functionalization of liposomes as oral drug carriers, however, are scant in the literature. To fill this gap, this review presents an overview of the roles of LbL functionalization in the development of liposomes, followed by a discussion about major principles of molecular design and engineering of LbL-functionalized liposomes for oral drug delivery. Regarding the versatility offered by LbL assembly, it is anticipated that LbL-functionalized liposomes may emerge as one of the important carriers for oral drug administration in the future.

The effect of ethanol evaporation on the properties of inkjet produced liposomes

Background

Inkjet method has been used to produce nano-sized liposomes with a uniform size distribution. However, following the production of liposomes by inkjet method, the solvent residue in the product could have a significant effect on the properties of the final liposomes.

Objective

This research paper aimed to find a suitable method to remove ethanol content and to study its effect on the properties of the final liposomal suspension.

Method

Egg phosphatidylcholine and lidocaine were dissolved in ethanol; and inkjet method at 80 kHz was applied to produce uniform droplets, which were deposited in an aqueous solution to form liposomes. Dry nitrogen gas flow, air-drying, and rotary evaporator were tested to remove the ethanol content. Liposome properties such as size, polydispersity index (PDI), and charge were screened before and after ethanol evaporation.

Results

Only rotary evaporator (at constant speed and room temperature for 2 h) removed all of the ethanol content, with a final drug entrapment efficiency (EE) of 29.44 ± 6.77%. This was higher than a conventional method. Furthermore, removing ethanol led to liposome size reduction from approximately 200 nm to less than 100 nm in most samples. Additionally, this increased the liposomal net charge, which contributed to maintain the uniform and narrow size distribution of liposomes.

Conclusion

Nano-sized liposomes were produced with a narrow PDI and higher EE compared to a conventional method by using an inkjet method. Moreover, rotary evaporator for 2 h reduced effectively the ethanol content, while maintaining the narrow size distribution.

Nanoparticles and organized lipid assemblies: from interaction to design of hybrid soft devices

This contribution reviews the state of art on hybrid soft matter assemblies composed of inorganic nanoparticles (NP) and lamellar or non-lamellar lipid bilayers. After a short outline of the relevant energetic contributions, we address the interaction of NPs with synthetic lamellar bilayers, meant as cell membrane mimics. We then review the design of hybrid nanostructured materials composed of lipid bilayers and some classes of inorganic NPs, with particular emphasis on the effects on the amphiphilic phase diagram and on the additional properties contributed by the NPs. Then, we present the latest developments on the use of lipid bilayers as coating agents for inorganic NPs. Finally, we remark on the main achievements of the last years and our vision for the development of the field.

Lipid Nanoparticles-Encapsulated YF4: A Potential Therapeutic Oral Peptide Delivery System for Hypertension Treatment

Drugs are administered orally in the clinical treatment of hypertension. Antihypertensive peptides have excellent angiotensin converting enzyme inhibitors activity in vitro. However, the poor oral bioavailability and therapeutic effect of antihypertensive peptides were mainly caused by rapid degradation in gastrointestinal and the short circulation time in blood, which remain to be further optimized. Therefore, the novel oral peptide delivery system is urged to improve the oral absorption and efficacy of peptide drugs. In this work, Tyr-Gly-Leu-Phe (YF4)-loaded lipid nanoparticles (YF4-LNPs) combined the advantages of polymer nanoparticles and liposomes were developed, which could greatly enhance the oral bioavailability and ameliorate the sustained release of peptide drug. YF4 loaded nanoparticles (YF4-NPs) were firstly prepared by a double-emulsion internal phase/organic phase/external phase (W1/O/W2) solvent evaporation method. YF4-NPs were further coated by membrane hydration-ultrasonic dispersion method to obtain the YF4-LNPs. The optimal YF4-LNPs showed a small particle size of 227.3 ± 3.8 nm, zeta potential of -7.27 ± 0.85 mV and high entrapment efficiency of 90.28 ± 1.23%. Transmission electronic microscopy analysis showed that the core-shell lipid nanoparticles were spherical shapes with an apparent lipid bilayer on the surface. Differential scanning calorimetry further proved that YF4 was successfully entrapped into YF4-LNPs. The optimal preparation of YF4-LNPs exhibited sustained release of YF4 in vitro and a 5 days long-term antihypertensive effect in vivo. In summary, the lipid nanoparticles for oral antihypertensive peptide delivery were successfully constructed, which might have a promising future for hypertension treatment.

Stabilization of Liposomes by Perfluorinated Compounds

Perfluorinated compounds (PFCs) are emerging persistent environmental contaminants that may be toxic to animals and humans. To gain fundamental insights into the mechanism of their toxicity, the interactions of phosphocholine (PC) liposomes as model membranes were studied with three types of PFCs, including perfluorooctanoic acid, perfluorooctane sulfonate, and perfluorohexanesulfonic acid potassium salt, together with three common surfactants: sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and sodium 1-heptanesulfonate (SHS). The interactions were systematically characterized by zeta potential measurement, dynamic light scattering, negative-stain transmission electron microscopy, and fluorescence spectroscopy. Unmodified liposomes, calcein-loaded liposomes, and Laurdan dye-embedded liposomes were all tested. By gradually increasing the temperature, the three PFCs and SHS decreased the leakage of calcein-loaded 1,2-dipalmitoyl-sn-glycero-3-phosphocholine liposomes, whereas SDS and CTAB increased the leakage. The PFCs that affected the lipid membranes stronger than SHS were attributable to their perfluoroalkyl carbon chains. Packing of the lipids was further studied using Laurdan dye as a probe. Calcein leakage tests also indicated that PFCs inhibited lipid membrane leakage induced by inorganic nanoparticles such as silica and gold nanoparticles. This study confirmed the similar effect of the PFCs as cholesterol in affecting membrane properties and would be helpful for understanding the interaction mechanism of PFCs and cell membranes.

Sub-Angstrom Gold Nanoparticle/Liposome Interfaces Controlled by Halides

A hallmark of nanoscience is size-dependent and distance-dependent physical properties. Although most previous studies focused on optical properties, which are often tuned at nanometer scale, we herein report on the interaction between halide-capped gold nanoparticles (AuNPs) and phosphocholine (PC) liposomes at the sub-Angstrom level. Halide-capped AuNPs are adsorbed by PC liposomes attributable to van der Waals force. Iodide-capped AuNPs interact much more weakly with the liposomes compared with bromide- and chloride-capped AuNPs, as indicated by a liposome leakage assay and differential scanning calorimetry. This is explained by the slightly larger size of iodide separating the AuNP core more from the liposome surface. Cryo-transmission electron microscopy indicates that the liposomes remain intact when mixed with these halide-capped AuNPs of 13 or 70 nm in diameter. Other even larger ligands, including small thiol compounds, DNA oligonucleotides, proteins, and polymers, fully blocked the interaction, whereas AuNPs dispersed in noninteracting ions, including fluoride, phosphate, perchlorate, nitrate, sulfate, and bicarbonate, are still adsorbed strongly by 1,2-dioleoyl- sn-glycero-3-phosphocholine liposomes. Taken together, halides can be used to control interparticle distances at an extremely small scale with remarkable effects on materials properties, allowing surface probing, biosensor development, and fundamental surface science studies.

Layer-by-layer assembly of graphene oxide on thermosensitive liposomes for photo-chemotherapy

Stimuli responsive polyelectrolyte nanoparticles have been developed for chemo-photothermal destruction of breast cancer cells. This novel system, called layer by layer Lipo-graph (LBL Lipo-graph), is composed of alternate layers of graphene oxide (GO) and graphene oxide conjugated poly (l-lysine) (GO-PLL) deposited on cationic liposomes encapsulating doxorubicin. Various concentrations of GO and GO-PLL were examined and the optimal LBL Lipo-graph was found to have a particle size of 267.9 ± 13 nm, zeta potential of +43.9 ± 6.9 mV and encapsulation efficiency of 86.4 ± 4.7%. The morphology of LBL Lipo-graph was examined by cryogenic-transmission electron microscopy (Cryo-TEM), atomic force microcopy (AFM) and scanning electron microscopy (SEM). The buildup of LBL Lipo-graph was confirmed via ultraviolet-visible (UV-Vis) spectrophotometry, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis. Infra-red (IR) response suggests that four layers are sufficient to induce a gel-to-liquid phase transition in response to near infra-red (NIR) laser irradiation. Light-matter interaction of LBL Lipo-graph was studied by calculating the absorption cross section in the frequency domain by utilizing Fourier analysis. Drug release assay indicates that the LBL Lipo-graph releases much faster in an acidic environment than a liposome control. A cytotoxicity assay was conducted to prove the efficacy of LBL Lipo-graph to destroy MD-MB-231 cells in response to NIR laser emission. Also, image stream flow cytometry and two photon microcopy provide supportive data for the potential application of LBL Lipo-graph for photothermal therapy. Study results suggest the novel dual-sensitive nanoparticles allow intracellular doxorubin delivery and respond to either acidic environments or NIR excitation.

STATEMENT OF SIGNIFICANCE

Stimuli sensitive hybrid nanoparticles have been synthesized using a layer-by-layer technique and demonstrated for dual chemo-photothermal destruction of breast cancer cells. The hybrid nanoparticles are composed of alternating layers of graphene oxide and graphene oxide conjugated poly-l-lysine coating the surface of a thermosensitive cationic liposome containing doxorubicin as a core. Data suggests that the hybrid nanoparticles may offer many advantages for chemo-photothermal therapy. Advantages include a decrease of the initial burst release which may result in the reduction in systemic toxicity, increase in pH responsivity around the tumor environment and improved NIR light absorption.

Hybrid nanomaterials of WS2 or MoS2 nanosheets with liposomes: biointerfaces and multiplexed drug delivery

Lipid containing hybrid materials are of significant interest for biointerface research and drug delivery applications, and a large number of previous studies have focused on graphene oxide (GO). In this work, novel hybrid materials made of transition metal dichalcogenides (TMDCs) and phosphocholine (DOPC) liposomes were prepared and compared with GO. All these inorganic materials are 2D nanosheets. DOPC liposomes are adsorbed by tungsten disulfide (WS₂) as intact liposomes as indicated by cryo-TEM and liposome leakage assays. WS₂ likely uses van der Waals forces for liposome adsorption as determined from urea, salt, and surfactant washing experiments. In addition, WS₂ adsorbed doxorubicin (DOX) and DOPC liposomes synergistically. The adsorption capacity of DOPC on bare WS₂ was 22.5% of the weight of WS₂. After adsorbing DOX on WS₂, the liposome adsorption capacity increased to ∼110%. Hydrogen bonding also contributed to liposome adsorption on DOX-loaded WS₂. Confocal fluorescence microscopy confirmed the uptake of the DOPC/WS₂ hybrid material by HeLa cells, and the co-delivery of DOX and calcein was achieved by loading calcein inside the liposomes. This study provides fundamental insights into the interaction between PC liposomes and WS₂. Furthermore, preliminary biomedical applications of this hybrid material were explored.

Biomedical applications of nanodiamond (Review)

The interest in nanodiamond applications in biology and medicine is on the rise over recent years. This is due to the unique combination of properties that nanodiamond provides. Small size (∼5 nm), low cost, scalable production, negligible toxicity, chemical inertness of diamond core and rich chemistry of nanodiamond surface, as well as bright and robust fluorescence resistant to photobleaching are the distinct parameters that render nanodiamond superior to any other nanomaterial when it comes to biomedical applications. The most exciting recent results have been related to the use of nanodiamonds for drug delivery and diagnostics-two components of a quickly growing area of biomedical research dubbed theranostics. However, nanodiamond offers much more in addition: it can be used to produce biodegradable bone surgery devices, tissue engineering scaffolds, kill drug resistant microbes, help us to fight viruses, and deliver genetic material into cell nucleus. All these exciting opportunities require an in-depth understanding of nanodiamond. This review covers the recent progress as well as general trends in biomedical applications of nanodiamond, and underlines the importance of purification, characterization, and rational modification of this nanomaterial when designing nanodiamond based theranostic platforms.

Nanodiamonds Mediate Oral Delivery of Proteins for Stem Cell Activation and Intestinal Remodeling in Drosophila

Introduction of exogenous biomacromolecules into living systems is of great interest in genome editing, cancer immunotherapy, and stem cell reprogramming. Whereas current strategies generally depend on nucleic acids transfection, direct delivery of functional proteins that provides enhanced specificity, increased safety, and fast and temporal regulation is highly desirable. Nevertheless, intracellular delivery of intact and bioactive proteins, especially in vivo, remains poorly explored. In this study, we developed a nanodiamonds (NDs)-based protein delivery system in cultured cells and in Drosophila that showed high adsorption, high efficiency, and effective cytosolic release of fully functional proteins. Through live-cell imaging, we observed a novel phenomenon wherein a substantial amount of internalized NDs-protein complex rejected fusion with the early endosome, thereby evading protein degradation in the lysosome. More significantly, we demonstrated that dietary NDs-RNase induced apoptosis in enterocytes, stimulating regenerative divisions in intestinal stem cells and increasing the number of stem cells and precursor cells in Drosophila intestine. As stem cells are poorly accessible by exogenous agents in vivo, NDs-mediated oral delivery of proteins provides a new approach to modulate the stem cell microenvironment for intestinal remodeling, which has important implications for colorectal cancer therapy and regenerative medicine.

Adsorption of Nanoceria by Phosphocholine Liposomes

Nanoceria (CeO₂ nanoparticle) possesses a number of enzyme-like activities. In particular, it scavenges reactive oxygen species based on in vitro and in vivo antioxidation studies. An important aspect of fundamental physical understanding is its interaction with lipid membranes that are the main components of the cell membrane. In this work, adsorption of nanoceria onto phosphocholine (PC) liposomes was performed. PC lipids are the main constituents of the cell outer membrane. Using a fluorescence quenching assay, a nanoceria adsorption isotherm was determined at various pH values and ionic strengths. A non-Langmuir isotherm occurred at pH 4 because of lateral electrostatic repulsion among the adsorbed cationic nanoceria. The phosphate group in the PC lipid is mainly responsible for the interaction, and the adsorbed nanoceria can be displaced by free inorganic phosphate. The tendency of the system to form large aggregates is a function of pH and the concentration of nanoceria, attributable to nanoceria being positively charged at pH 4 and neutral at physiological pH. Calcein leakage tests indicate that nanoceria induces liposome leakage because of transient lipid phase transition, and cryo-transmission electron microscopy indicates that the overall shape of the liposome is retained although deformation is still observed. This study provides fundamental biointerfacial information at a molecular level regarding the interaction of nanoceria and model cell membranes.

Interfacing Zwitterionic Liposomes with Inorganic Nanomaterials: Surface Forces, Membrane Integrity, and Applications

Zwitterionic phosphocholine (PC) lipids are the main constituent of the mammalian cell membrane. PC bilayers are known for their antifouling properties, yet they are adsorbed by all tested inorganic nanoparticles. This feature article is focused on the developments in my laboratory in the past few years on this topic. The main experimental techniques include fluorescence-based liposome leakage assays, adsorption and desorption, and cryo-TEM. Different materials interact with PC liposomes differently. PC liposomes adsorb on SiO2, followed by membrane fusion with the surface forming supported lipid bilayers. TiO2 and other metal oxides adsorb only intact PC liposomes via lipid phosphate bonding; the steric effect from the choline group hinders subsequent liposome fusion onto the particles. Citrate-capped AuNPs are adsorbed very strongly via van der Waals forces, inducing local gelation. The result is transient liposome leakage upon AuNP adsorption or desorption and AuNP aggregation on the liposome surface. All carbon-based nanomaterials (graphene oxides, carbon nanotubes, and nanodiamond) are adsorbed mainly via hydrogen bonding. The oxidation level of graphene oxide strongly influences the outcome of the final hybrid material. In the context of inorganic nanoparticle adsorption, insights are given regarding the lack of protein adsorption by PC bilayers. These inorganic/lipid hybrid materials can be used for controlled release, drug delivery, and fundamental studies. A few examples of application are covered toward the end, and future perspectives are given.

Liposome/Graphene Oxide Interaction Studied by Isothermal Titration Calorimetry

The interaction between graphene oxide (GO) and lipid bilayers is important for fundamental surface science and many applications. In this work, isothermal titration calorimetry (ITC), cryo-TEM, and fluorescence spectroscopy were used to study the adsorption of three types of liposomes. Heat release was observed when GO was mixed with zwitterionic DOPC liposomes, while heat absorption occurred with cationic DOTAP liposomes. For comparison, anionic DOPG liposomes released heat when mixed with DOTAP. DOPC was adsorbed as intact liposomes, but DOTAP ruptured and induced stacking and folding of GO sheets. This study suggests the release of more water molecules from the GO surface when mixed with DOTAP liposomes. This can be rationalized by the full rupture of the DOTAP liposomes interacting with the whole GO surface, including hydrophobic regions, while DOPC liposomes only interact with a small area on GO near the edge, which is likely to be more hydrophilic. This interesting biointerfacial observation has enhanced our fundamental understanding of lipid/GO interactions.

Dispersion of atmospheric fine particulate matters in simulated lung fluid and their effects on model cell membranes

Atmospheric fine particulate matter (PM2.5) was collected to investigate its dispersion in simulated lung fluid (SLF) and its interaction with model cell membranes. Organic acids, NH4(+), SO4(2-) and NO3(-) were detected in PM2.5 soluble fraction, and heavy metals were detected from the total mass. The insoluble fraction contained kaolinite, CaCO3, aliphatic carbons, aromatic rings, carboxyl and hydroxyl groups reflected by the infrared spectra. Proteins dispersed PM2.5 in SLF, resulted in smaller hydrodynamic diameter (dH) and slower sedimentation rate. Conversely, phospholipids increased dH value and accelerated sedimentation rate. Giant unilamellar vesicles (GUVs) and supported lipid bilayers (SLBs) were used as model cell membranes. PM2.5 adhered on and disrupted the membrane containing positively-charged lipids but not the membrane containing neutrally- and negatively-charged lipids, which was monitored by microscopy and a quartz crystal microbalance with dissipation (QCM-D). The cationic sites on membrane were necessary for PM2.5 adhesion, but membrane should be disrupted by the combined action of electrostatic forces and hydrogen bonds between PM2.5 oxygen containing groups and the lipid phosphate groups. Our results specified the roles of proteins and phospholipids in PM2.5 dispersion and transport, highly suggested that the health hazard of PM2.5 was related to the biomolecules in the lung fluid and the particle surface groups.

Driving Adsorbed Gold Nanoparticle Assembly by Merging Lipid Gel/Fluid Interfaces

Surface forces between inorganic nanoparticles and lipid bilayer is of great relevance to biophysics, medicine, and nanobiotechnology. Adsorbed nanoparticles may influence the fluidity of the underlying lipids, which may in turn influence nanoparticle assembly. Herein three types of lipids (DOPC, Tc = -20 °C; DMPC, Tc = 23 °C; and DPPC, Tc = 41 °C) are used, all with the same phosphocholine (PC) headgroup. Gold nanoparticle (AuNP) color change is monitored as a function of lipid phase transition temperature (Tc), surface ligands on AuNPs, and temperature. Liposomes with higher fluidity induce much faster aggregation of AuNPs. Aside from the kinetic aspect of faster diffusion on fluid bilayers, this faster color change is attributed to the local lipid gelation and merging of gelled regions to eliminate the interface between different lipid phases.

Interactions of Graphene Oxide with Model Cell Membranes: Probing Nanoparticle Attachment and Lipid Bilayer Disruption

With the rapid growth in the application of graphene oxide (GO) in diverse fields, the toxicity of GO toward bacterial and mammalian cells has recently attracted extensive research attention. While several mechanisms have been proposed for the cytotoxicity of GO, the attachment of GO to cell membranes is expected to be the key initial process that precedes these mechanisms. In this study, we investigate the propensity for GO to attach to and disrupt model cell membranes using supported lipid bilayers (SLBs) and supported vesicular layers (SVLs) that are composed of zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). The deposition kinetics of GO on SLBs were determined using quartz crystal microbalance with dissipation monitoring and were observed to increase with increasing electrolyte (NaCl and CaCl2) concentrations, indicating that GO attachment to SLBs was controlled by electrostatic interactions. The GO deposition kinetics measured at elevated electrolyte concentrations were lower than mass-transfer-limited kinetics, likely due to the presence of hydration forces between GO and SLBs. Upon the attachment of GO to supported vesicles that were encapsulated with a fluorescent dye, dye leakage was detected, thus indicating that the lipid vesicles were disrupted. When the exposure of the SVL to the GO suspension was terminated, the leakage of dye decreased significantly, demonstrating that the pores on the lipid bilayers have a self-healing ability.

Self-healable and reversible liposome leakage by citrate-capped gold nanoparticles: probing the initial adsorption/desorption induced lipid phase transition

We herein report that the adsorption/desorption of citrate-capped gold nanoparticles (AuNPs) transiently causes leakage in fluid phase DOPC liposomes, while the liposomes do not leak with AuNPs capped with mercaptopropionic acid (MPA). Leakage also fails to occur for gel phase DPPC liposomes. Citrate-capped (but not MPA-capped) AuNPs raise the phase transition temperature of DPPC. We conclude that citrate-capped AuNPs interact with the PC liposomes very strongly, inducing a local fluid-to-gel lipid phase transition for DOPC. Leakage takes place during this transition, and the membrane integrity is resumed after the transition. Citrate-capped AuNPs allow stronger van der Waals forces than MPA-capped AuNPs with PC liposomes, since the latter are separated from the liposome surface by the ∼0.3 nm MPA layer.

Inhibiting the VIM-2 Metallo-β-Lactamase by Graphene Oxide and Carbon Nanotubes

Metallo-β-lactamases (MBLs) degrade a broad spectrum of antibiotics including the latest carbapenems. So far, limited success has been achieved in developing its inhibitors using small organic molecules. VIM-2 is one of the most studied and important MBLs. In this work, we screened 10 nanomaterials, covering a diverse range of surface properties including charge, hydrophobicity, and specific chemical bonding. Among these, graphene oxide and carbon nanotubes are the most potent inhibitors, while most other materials do not show much inhibition effect. The inhibition is noncompetitive and is attributed to the hydrophobic interaction with the enzyme. Adsorption of VIM-2 was further probed using protein displacement assays where it cannot displace or be displaced by bovine serum albumin (BSA). This information is useful for rational design inhibitors for MBLs and more specific inhibition might be achieved by further surface modifications on these nanocarbons.

Monitoring the multitask mechanism of DNase I activity using graphene nanoassemblies

Here we have demonstrated that graphene serves as a remarkable platform for monitoring the multitask activity of an enzyme with fluorescence spectroscopy. Our studies showed that four different simultaneous enzymatic tasks of DNase I can be observed and measured in a high throughput fashion using graphene oxide and oligonucleotide nanoassemblies. We have used phosphorothioate modified oligonucleotides to pinpoint the individual and highly specific functions of DNase I with single stranded DNA, RNA, and DNA/DNA and DNA/RNA duplexes. DNase I resulted in fluorescence recovery in the nanoassemblies and enhanced the intensity tremendously in the presence of sequence specific DNA or RNA molecules with different degrees of amplification. Our study enabled us to discover the sources of this remarkable signal enhancement, which has been used for biomedical applications of graphene for sensitive detection of specific oncogenes. The significant difference in the signal amplification observed for the detection of DNA and RNA molecules is a result of the positive and/or reductive signal generating events with the enzyme. In the presence of DNA there are four possible ways that the fluorescence reading is influenced, with two of them resulting in a gain in signal while the other two result in a loss. Since the observed signal is a summation of all the events together, the absence of the two fluorescence reduction events with RNA gives a greater degree of fluorescence signal enhancement when compared to target DNA molecules. Overall, our study demonstrates that graphene has powerful features for determining the enzymatic functions of a protein and reveals some of the unknowns observed in the graphene and oligonucleotide assemblies with DNase I.

Real-time detection of lipid bilayer assembly and detergent-initiated solubilization using optical cavities

The cellular membrane governs numerous fundamental biological processes. Therefore, developing a comprehensive understanding of its structure and function is critical. However, its inherent biological complexity gives rise to numerous inter-dependent physical phenomena. In an attempt to develop a model, two different experimental approaches are being pursued in parallel: performing single cell experiments (top down) and using biomimetic structures (bottom up), such as lipid bilayers. One challenge in many of these experiments is the reliance on fluorescent probes for detection which can create confounds in this already complex system. In the present work, a label-free detection method based on an optical resonant cavity is used to detect one of the fundamental physical phenomena in the system: assembly and solubilization of the lipid bilayer. The evanescent field of the cavity strongly interacts with the lipid bilayer, enabling the detection of the bilayer behavior in real-time. Two independent detection mechanisms confirm the formation and detergent-assisted solubilization of the lipid bilayers: (1) a refractive index change and (2) a material loss change. Both mechanisms can be monitored in parallel, on the same device, thus allowing for cross-confirmation of the results. To verify the proposed method, we have detected the formation of self-assembled phosphatidylcholine lipid bilayers from small unilamellar vesicles on the device surface in real-time. Subsequently, we exposed the bilayers to two different detergents (non-ionic Triton X-100 and anionic sodium dodecyl sulfate) to initiate solubilization, and this process was also detected in real-time. After the bilayer solubilization, the device returned to its initial state, exhibiting minimal hysteresis. The experimental wash-off was also collected and analyzed using dynamic light scattering.

Green and facile synthesis of highly biocompatible carbon nanospheres and their pH-responsive delivery of doxorubicin to cancer cells

Carbon nanospheres with size below 71 nm are synthesized from bacterial cellulose nanofibers using a one-pot hydrothermal synthesis method.

Morphology change and detachment of lipid bilayers from the mica substrate driven by graphene oxide sheets

Understanding the interaction between graphene oxide (GO) and a lipid membrane is significant for exploring the biocompatibility and cytotoxicity of GO, which is the basis for utilizing GO in the fields of biosensors, bioimaging, drug delivery, antibacterials, and so on. In this article, we monitored the dynamic process of the morphology change and detachment of lipid bilayers on mica substrates prompted by GO sheets by in situ atomic force microscope (AFM) imaging. It was found that the bare lipid bilayer dramatically expanded in height and would be unstable and detachable from the mica substrates as induced by GO. The detached lipid molecules were found to bind to the GO surface. The results also imply that GO is likely to influence the height and stability of the supported lipid bilayers (SLBs) by adsorbing metal ions such as calcium ions that were used to stabilize the bilayer structures on the mica substrate. These findings illustrate a complicated effect of GO on the SLBs and should be helpful in future applications of GO in biotechnology.

The use of lipid-coated nanodiamond to improve bioavailability and efficacy of sorafenib in resisting metastasis of gastric cancer

The metastasis is one of the greatest challenges for successful cancer therapy. Herein, we report a lipid-coated nanodiamond (ND) system loading water-insoluble sorafenib (SND) to improve the bioavailability and efficacy on suppression of cancer metastasis. SND was homogenous nanoassemblies with the mean diameter of 127.6 ± 12.9 nm. Compared with the drug suspension, the sorafenib concentration in gastrointestinal (GI) tract and major organs was significantly increased by SND. Moreover, the oral bioavailability of sorafenib was greatly improved 7.64-fold by SND. However, the ND in SND could not be absorbed into the mucus of GI tract or distributed into major organs after oral administration. Furthermore, the sorafenib concentration in tumor tissue was markedly improved 14.95 folds by SND, and SND demonstrated an efficient and impressive tumor growth inhibition effect in tumor xenograft models. In particular, the metastasis of gastric cancer to distant organs of liver and kidney was remarkably suppressed by SND, which was verified by the detection of macroscopic metastatic nodules, histological examination and immunofluorescence measurements. Thereby, the lipid-coated ND could be a promising drug delivery platform for improving the oral bioavailability of lipophilic drugs and treatment of cancer metastasis.