Responsive nanostructured materials for bioanalyte detection and triggered antimicrobial therapy

Inorganic nanomaterials are attractive candidates for biomedicine as they can offer increased stability including light, temperature and chemical stability while also offering the benefits of high-throughput synthetic techniques such as flame spray pyrolysis. In this thesis work will be described describing novel inorganic nanoparticle systems for biomedical applications presented in four papers of which three are published in peer-reviewed scientific journals. The first project in Paper I presents a surface treatment to address what is thought to be the major cause of implant associated infections which is biofilm formation. A near infrared (near-IR) activated plasmonic nanoparticle system with photothermal properties is developed which utilises the inter-particle coupling of spherical silver nanoparticles. This inter-particle coupling produces a strong plasmonic extinction with a wavelength dependence on the spacing between neighbouring spherical silver nanoparticles. Therefore by using a SiO2 dielectric spacer to control the average spacing between spherical silver nanoparticles in the synthesised nanoaggregates the optical and photothermal behaviour of the nanoaggregates can be tuned into the near-IR. The effectiveness of these nanoaggregates for the photothermal eradication of biofilms formed on catheter mimicking surfaces was evaluated. Nanoaggregates were directly deposited onto silicone substrates and entirely encased in a second layer of silicone. Biofilms of Escherichia coli and Staphylococcus aureus were grown on the silicone surface and near-IR light was used to activate the photothermal response of the nanoaggregates with complete eradication of biofilms achieved in a temperature dependent manner. Applications of nanomaterials to biofilms was further continued in Paper II, a characteristic of biofilms is their dense nature as they are embedded in a glue-like self produced extracellular matrix which also attaches them to the substrate on which they grow. This can promote the formation of heterogeneous microenvironments, with concentration gradients of parameters such as oxygen, nutrients and pH readily occurring between the substrate-attached interface and the liquid in which they are grown. An understanding of the pH of these interfacial microenvironments and a high-throughput compatible measurement system is desirable to help guide the development of targeted anti-biofilm systems. In Paper II a novel all-inorganic system based on calcium phosphate nanoparticles doped with europium is presented which display pH dependent luminescence as a deposited film. Growth of bacterial biofilms of different species on these nanoparticle coatings allows the measurement of the acidic microenvironments which they produce in an ordinary well-plate luminescence spectrometer. Bacterial bioanalyte detection can be challenging due to the complex growth media which bacteria can require and the dynamic changes to the optical properties of the medium as the bacteria grow. Moreover, the developed detection mechanism must be resistant to bacterial degradation, therefore the development of robust sensors for such applications is essential. In Paper III the development of a dual-emission ratiometric luminescence sensor for the detection of hydrogen peroxide from bacterial cultures is described. The sensing system consists of a reference emission from Y2O3:Tb3+ which are decorated with CeO2:Eu3+ nanoparticles which provide the hydrogen peroxide sensitive emission. This system was applied for the determination of hydrogen peroxide production levels by the known hydrogen peroxide producing bacterium and major human pathogen Streptococcus pneumoniae. Finally the manuscript Paper IVapplies inorganic nanomaterials for the detection of ammonia (here used to refer to total NH3 and NH+ 4 levels) which is an important diagnostic bioanalyte. Ammonia production by urease producing gut bacteria is a major contributor to blood ammonia levels and must be effectively detoxified by the liver for excretion by the kidneys. Over production of ammonia or failure of the liver or kidney can lead to high levels of ammonia which are neurotoxic. However, the symptoms of this hyperammonemia are diffuse ranging from mild confusion to coma and death. Therefore a readily available system for the measurement of ammonia levels is highly desirable. In Paper IVa plasmonic silver nanoparticle based system is described for the detection of ammonia. The system relies on the reactivity of the ClO– with both ammonia and silver nanoparticles, if no ammonia is present upon addition of ClO– to the silver nanoparticles a strong decrease in their plasmonic colour is observed. However, in the presence of ammonia the ClO– is removed and therefore no colour change is observed. This system was able to detect ammonia levels at the 50 μM limit defined as hyperammonemia

Stability of Hydrogen Hydrates from Second-Order Møller–Plesset Perturbation Theory

The formation of gas hydrates and clathrates critically depends on the interaction between the host water network and the guest gas species. Density functional calculations can struggle to quantitatively capture these dispersion-type interactions. Here, we report wave function-based calculations on hydrogen hydrates that combine periodic Hartree–Fock with a localized treatment of electronic correlation. We show that local second-order Møller–Plesset perturbation theory (LMP2) reproduces the stability of the different filled-ice-like hydrates in excellent agreement with experimental data. In contrast to various dispersion-corrected density functional theory implementations, LMP2 correctly identifies the pressures needed to stabilize the C₀, C₁, and C₂ hydrates and does not find a spurious region of stability for an ice-I_h-based dihydrate. Our results suggest that LMP2 or similar approaches can provide quantitative insights into the mechanisms of formation and eventual decomposition of molecular host–guest compounds

Antiviral Activity of Silver, Copper Oxide and Zinc Oxide Nanoparticle Coatings against SARS-CoV-2

SARS-CoV-2 is responsible for several million deaths to date globally, and both fomite transmission from surfaces as well as airborne transmission from aerosols may be largely responsible for the spread of the virus. Here, nanoparticle coatings of three antimicrobial materials (Ag, CuO and ZnO) are deposited on both solid flat surfaces as well as porous filter media, and their activity against SARS-CoV-2 viability is compared with a viral plaque assay. These nanocoatings are manufactured by aerosol nanoparticle self-assembly during their flame synthesis. Nanosilver particles as a coating exhibit the strongest antiviral activity of the three studied nanomaterials, while copper oxide exhibits moderate activity, and zinc oxide does not appear to significantly reduce the virus infectivity. Thus, nanosilver and copper oxide show potential as antiviral coatings on solid surfaces and on filter media to minimize transmission and super-spreading events while also providing critical information for the current and any future pandemic mitigation efforts

Silica-coated phosphorescent nanoprobes for selective cell targeting and dynamic bioimaging of pathogen–host cell interactions

Fluorescence in vitro bioimaging suffers from photobleaching of organic dyes, thus, functional probes with superior photostability are urgently needed. Here, we address this challenge by developing novel silica-coated nanophosphors that may serve as superior luminescent nanoprobes compatible with conventional fluorescence microscopes. We specifically explore their suitability for dynamic in vitro bioimaging of interactions between bacterial pathogens and host cells, and further demonstrate the facile surface functionalization of the amorphous silica layer with antibodies for selective cell targeting.ISSN:1359-7345ISSN:1364-548

The Influence of Drug-Polymer Solubility on Laser-Induced In Situ Drug Amorphization Using Photothermal Plasmonic Nanoparticles

In this study, laser-induced in situ amorphization (i.e., amorphization inside the final dosage form) of the model drug celecoxib (CCX) with six different polymers was investigated. The drug-polymer combinations were studied with regard to the influence of (i) the physicochemical properties of the polymer, e.g., the glass transition temperature (T-g) and (ii) the drug-polymer solubility on the rate and degree of in situ drug amorphization. Compacts were prepared containing 30 wt% CCX, 69.25 wt% polymer, 0.5 wt% lubricant, and 0.25 wt% plasmonic nanoparticles (PNs) and exposed to near-infrared laser radiation. Upon exposure to laser radiation, the PNs generated heat, which allowed drug dissolution into the polymer at temperatures above its T-g, yielding an amorphous solid dispersion. It was found that in situ drug amorphization was possible for drug-polymer combinations, where the temperature reached during exposure to laser radiation was above the onset temperature for a dissolution process of the drug into the polymer, i.e., T-DStart. The findings of this study showed that the concept of laser-induced in situ drug amorphization is applicable to a range of polymers if the drug is soluble in the polymer and temperatures during the process are above T-DStart

The Effect of the Molecular Weight of Polyvinylpyrrolidone and the Model Drug on Laser-Induced In Situ Amorphization

Laser radiation has been shown to be a promising approach for in situ amorphization, i.e., drug amorphization inside the final dosage form. Upon exposure to laser radiation, elevated temperatures in the compacts are obtained. At temperatures above the glass transition temperature (T-g) of the polymer, the drug dissolves into the mobile polymer. Hence, the dissolution kinetics are dependent on the viscosity of the polymer, indirectly determined by the molecular weight (M-w) of the polymer, the solubility of the drug in the polymer, the particle size of the drug and the molecular size of the drug. Using compacts containing 30 wt% of the drug celecoxib (CCX), 69.25 wt% of three different M-w of polyvinylpyrrolidone (PVP: PVP12, PVP17 or PVP25), 0.25 wt% plasmonic nanoaggregates (PNs) and 0.5 wt% lubricant, the effect of the polymer M-w on the dissolution kinetics upon exposure to laser radiation was investigated. Furthermore, the effect of the model drug on the dissolution kinetics was investigated using compacts containing 30 wt% of three different drugs (CCX, indomethacin (IND) and naproxen (NAP)), 69.25 wt% PVP12, 0.25 wt% PN and 0.5 wt% lubricant. In perfect correlation to the Noyes-Whitney equation, this study showed that the use of PVP with the lowest viscosity, i.e., the lowest M-w (here PVP12), led to the fastest rate of amorphization compared to PVP17 and PVP25. Furthermore, NAP showed the fastest rate of amorphization, followed by IND and CCX in PVP12 due to its high solubility and small molecular size

Mannose receptor‐derived peptides neutralize pore‐forming toxins and reduce inflammation and development of pneumococcal disease

Abstract Cholesterol‐dependent cytolysins (CDCs) are essential virulence factors for many human pathogens like Streptococcus pneumoniae (pneumolysin, PLY), Streptococcus pyogenes (streptolysin O, SLO), and Listeria monocytogenes (Listeriolysin, LLO) and induce cytolysis and inflammation. Recently, we identified that pneumococcal PLY interacts with the mannose receptor (MRC‐1) on specific immune cells thereby evoking an anti‐inflammatory response at sublytic doses. Here, we identified the interaction sites between MRC‐1 and CDCs using computational docking. We designed peptides from the CTLD4 domain of MRC‐1 that binds to PLY, SLO, and LLO, respectively. In vitro, the peptides blocked CDC‐induced cytolysis and inflammatory cytokine production by human macrophages. Also, they reduced PLY‐induced damage of the epithelial barrier integrity as well as blocked bacterial invasion into the epithelium in a 3D lung tissue model. Pre‐treatment of human DCs with peptides blocked bacterial uptake via MRC‐1 and reduced intracellular bacterial survival by targeting bacteria to autophagosomes. In order to use the peptides for treatment in vivo, we developed calcium phosphate nanoparticles (CaP NPs) as peptide nanocarriers for intranasal delivery of peptides and enhanced bioactivity. Co‐administration of peptide‐loaded CaP NPs during infection improved survival and bacterial clearance in both zebrafish and mice models of pneumococcal infection. We suggest that MRC‐1 peptides can be employed as adjunctive therapeutics with antibiotics to treat bacterial infections by countering the action of CDCs