Mohammad Al Kobaisi

Graphene Induces Formation of Pores That Kill Spherical and Rod-Shaped Bacteria

Pristine graphene, its derivatives, and composites have been widely reported to possess antibacterial properties. Most of the studies simulating the interaction between bacterial cell membranes and the surface of graphene have proposed that the graphene-induced bacterial cell death is caused either by (1) the insertion of blade-like graphene-based nanosheets or (2) the destructive extraction of lipid molecules by the presence of the lipophilic graphene. These simulation studies have, however, only take into account graphene-cell membrane interactions where the graphene is in a dispersed form. In this paper, we report the antimicrobial behavior of graphene sheet surfaces in an attempt to further advance the current knowledge pertaining to graphene cytotoxicity using both experimental and computer simulation approaches. Graphene nanofilms were fabricated to exhibit different edge lengths and different angles of orientation in the graphene sheets. These substrates were placed in contact with Pseudomonas aeruginosa and Staphylococcus aureus bacteria, where it was seen that these substrates exhibited variable bactericidal efficiency toward these two pathogenic bacteria. It was demonstrated that the density of the edges of the graphene was one of the principal parameters that contributed to the antibacterial behavior of the graphene nanosheet films. The study provides both experimental and theoretical evidence that the antibacterial behavior of graphene nanosheets arises from the formation of pores in the bacterial cell wall, causing a subsequent osmotic imbalance and cell death.

Chitosan Microparticles and Nanoparticles as Biocompatible Delivery Vehicles for Peptide and Protein-Based Immunocontraceptive Vaccines

It has become increasingly recognized that polymer particle size can have a profound effect on the interactions of particle-based vaccines with antigen presenting cells (APCs) thereby influencing and modulating ensuing immune responses. With the aim of developing chitosan particle-based immunocontraceptive vaccines, we have compared the use of chitosan-based nanoparticles and chitosan-based microparticles as vaccine delivery vehicles for vaccine candidates based on luteinizing hormone-releasing hormone (LHRH). Particles, functionalized with chloroacetyl groups, which allows the covalent attachment of thiol-containing antigens, were able to adsorb ~60-70% of their weight of peptide-based antigen and 10-20% of their weight of protein-based antigen. Quantitation by amino acid analysis of antigen associated with particles demonstrated a correlation between associated antigen and the degree of chloracetylation of particles. Visualization of fluorescently labeled antigen-loaded particles by confocal microscopy indicated that the majority of antigen was localized at the particle surface with a smaller amount located in the interior. We also found that uptake of both fluoresceinated nanoparticles and microparticles by dendritic cells occurred in a manner dependent on particle concentration. Nanoparticles trafficked from the injection site to draining lymph nodes faster than microparticles; high numbers of nanoparticle-bearing cells appeared in draining lymph nodes on day 3 and microparticles on day 4. This difference in trafficking rate did not, however, appear to have any significant impact on the ensuing immune response because inoculation with both peptide-conjugated and protein-conjugated particles induced high levels of LHRH-specific antibodies. In the case of protein-conjugated particles, the levels of antibodies elicited were similar to those elicited following inoculation with antigen emulsified with complete Freunds adjuvant. The approach to vaccine design that we have described here could represent another useful method for inducing immune responses against microbial, viral and tumorigenic protein antigens.

Antibacterial titanium nano-patterned arrays inspired by dragonfly wings

Titanium and its alloys remain the most popular choice as a medical implant material because of its desirable properties. The successful osseointegration of titanium implants is, however, adversely affected by the presence of bacterial biofilms that can form on the surface, and hence methods for preventing the formation of surface biofilms have been the subject of intensive research over the past few years. In this study, we report the response of bacteria and primary human fibroblasts to the antibacterial nanoarrays fabricated on titanium surfaces using a simple hydrothermal etching process. These fabricated titanium surfaces were shown to possess selective bactericidal activity, eliminating almost 50% of Pseudomonas aeruginosa cells and about 20% of the Staphylococcus aureus cells coming into contact with the surface. These nano-patterned surfaces were also shown to enhance the aligned attachment behavior and proliferation of primary human fibroblasts over 10 days of growth. These antibacterial surfaces, which are capable of exhibiting differential responses to bacterial and eukaryotic cells, represent surfaces that have excellent prospects for biomedical applications.

Flower-like supramolecular self-assembly of phosphonic acid appended naphthalene diimide and melamine.

Diverse supramolecular assemblies ranging from nanometres to micrometers of small aromatic π-conjugated functional molecules have attracted enormous research interest in light of their applications in optoelectronics, chemosensors, nanotechnology, biotechnology and biomedicines. Here we study the mechanism of the formation of a flower-shaped supramolecular structure of phosphonic acid appended naphthalene diimide with melamine. The flower-shaped assembly formation was visualised by scanning electron microscope (SEM) and transmission electron microscopy (TEM) imaging, furthermore, XRD and DLS used to determined mode of aggregation. Characteristically, phosphonic acid-substituted at imide position of NDIs possess two important properties resulting in the formation of controlled flower-like nanostructures: (i) the aromatic core of the NDI which is designed to optimize the dispersive interactions (π-π stacking and van der Waals interactions) between the cores within a construct and (ii) phosphonic acid of NDI interact with malamine through molecular recognition i.e. strong hydrogen-bonding (H-bonding). We believe such arrangements prevent crystallization and favour the directional growth of flower-like nanostructure in 3D fashion. These works demonstrate that complex self-assembly can indeed be attained through hierarchical non-covalent interactions of two components. Furthermore, flower-like structures built from molecular recognition by these molecules indicate their potential in other fields if combined with other chemical entities.

Precise aggregation-induced emission enhancement via H+ sensing and its use in ratiometric detection of intracellular pH values

A pyridyl functionalised tetraphenylethylene (Py-TPE) for ratiometric fluorescent detection of intracellular pH values is reported. The Py-TPE fluorescent probe can be used for H+ sensing in organic solvents (CHCl3, DMF and MeOH) and the change in optical density through absorption, emission and naked eye detection was modulated. On addition of TFA, an aggregation-induced enhancement of emission with an increase in quantum yield of 0.11 to 0.63, due to an intramolecular charge transfer (ICT) process was observed. This process is reversed by addition of TEA resulting in a cycle that can be repeated several times.

Flower-like superstructures of AIE-active tetraphenylethylene through solvophobic controlled self-assembly

The development of well-organized structures with high luminescent properties in the solid and aggregated states is of both scientific and technological interest due to their applications in nanotechnology. In this paper we described the synthesis of amphiphilic and dumbbell shaped AIE-active tetraphenylethylene (TPE) derivatives and studied their self-assembly with solvophobic control. Interestingly, both TPE derivatives form a 3D flower-shape supramolecular structure from THF/water solutions at varying water fractions. SEM microscopy was used to visualise step-wise growth of flower-shape assembly. TPE derivatives also show good mechanochromic properties which can be observed in the process of grinding, fuming and heating. These TPE derivative self-assemblies are formed due to two main important properties: (i) the TPE-core along with alkyl chains, optimizing the dispersive interactions within a construct, and (ii) amide-linkage through molecular recognition. We believe such arrangements prevent crystallization and favour the directional growth of flower-shape nanostructures in a 3D fashion.

Photomodulation of fluoride ion binding through anion-π interactions using a photoswitchable azobenzene system.

The discovery of photoswitchable azobenzene-systems that undergo trans-to-cis photoisomerisation was a milestone in supramolecular chemistry. Such photoswitches have possible applications in data storage, stimuli responsive delivery systems, and molecular machines due to fast and selective switching. However, the light induced cis isomer of azobenzene is rather unstable and reverts thermally and photochemically to the thermodynamically stable trans configuration. We report, for the first time, controlled photoswitching of an azo-naphthalenediimide (azo-NDI) which can be achieved upon binding of fluoride ions through anion-π interaction. This NDI-F–NDI “sandwich” stabilises the cis configuration through the generation of an NDI•− radical anion, and a dianionic, NDI2− species that becomes unusually stable in the cis form. The sandwiched cis form reverts to the trans form only upon decomplexation of F−. A model pollutant was successfully degraded using the photogenerated NDI-F–NDI sandwich. This opens a wide range of applications in molecular and supramolecular nanotechnology.

Nanotopography as a trigger for the microscale, autogenous and passive lysis of erythrocytes

Microscale devices are increasingly being developed for diagnostic analysis although conventional lysis as an initial step presents limitations due to its scale or complexity. Here, we detail the physical response of erythrocytes to the surface nanoarchitecture of black Si (bSi) and foreshadow their potential in microanalysis. The physical interaction brought about by the spatial convergence of the two topologies: (a) the nanopillar array present on the bSi and (b) the erythrocyte cytoskeleton present on the red blood cells (RBCs), provides spontaneous stress-induced cell deformation, rupture and passive lysis within an elapsed time of ∼3 min from immobilisation to rupture and without external chemical or mechanical intervention. The mechano-responsive bSi surface provides highly active yet autogenous RBC lysis and a prospect as a front-end platform technology in evolving micro-fluidic platforms for cellular analyses.

Adsorption of Human Plasma Albumin and Fibronectin onto Nanostructured Black Silicon Surfaces

The protein adsorption of two human plasma proteins-albumin (Alb) and fibronectin (Fn)-onto synthetic nanostructured bactericidal material-black silicon (bSi) surfaces (that contain an array of nanopillars) and silicon wafer (nonstructured) surfaces-was investigated. The adsorption behavior of Alb and Fn onto two types of substrata was studied using a combination of complementary analytical techniques. A two-step Alb adsorption mechanism onto the bSi surface has been proposed. At low bulk concentrations (below 40 μg/mL), the Alb preferentially adsorbed at the base of the nanopillars. At higher bulk concentrations, the Alb adsorbed on the top of the nanopillars. In the case of Fn, the protein preferentially adsorbed on the top of the nanopillars, irrespective of its bulk concentration.

Unusual Nature of Fingerprints and the Implications for Easy-to-Clean Coatings

Irrespective of the technology, we now rely on touch to interact with devices such as smart phones, tablet computers, and control panels. As a result, touch screen technologies are frequently in contact with body grease. Hence, surface deposition arises from localized inhomogeneous finger-derived contaminants adhering to a surface, impairing the visual/optical experience of the user. In this study, we examined the contamination itself in order to understand its static and dynamic behavior with respect to deposition and cleaning. A process for standardized deposition of fingerprints was developed. Artificial sebum was used in this process to enable reproducibility for quantitative analysis. Fingerprint contamination was shown to be hygroscopic and to possess temperature- and shear-dependent properties. These results have implications for the design of easily cleanable surfaces.