Abstract We use functionalized iron oxide magnetic multi-core particles of 100nm in size (hydrodynamic particle diameter) and AC susceptometry (ACS) methods to measure the binding reactions between the magnetic nanoparticles (MNPs) and bio-analyte products produced from DNA segments using the rolling circle amplification (RCA) method. We use sensitive induction detection techniques in order to measure the ACS response. The DNA is amplified via RCA to generate RCA coils with a specific size that is dependent on the amplification time. After about 75min of amplification we obtain an average RCA coil diameter of about 1µm. We determine a theoretical limit of detection (LOD) in the range of 11 attomole (corresponding to an analyte concentration of 55 fM for a sample volume of 200µL) from the ACS dynamic response after the MNPs have bound to the RCA coils and the measured ACS readout noise. We also discuss further possible improvements of the LOD.
We use functionalized iron oxide magnetic multi-core particles of 100 nm in size (hydrodynamic particle diameter) and AC susceptometry (ACS) methods to measure the binding reactions between the magnetic nanoparticles (MNPs) and bio-analyte products produced from DNA segments using the rolling circle amplification (RCA) method. We use sensitive induction detection techniques in order to measure the ACS response. The DNA is amplified via RCA to generate RCA coils with a specific size that is dependent on the amplification time. After about 75 min of amplification we obtain an average RCA coil diameter of about 1 µm. We determine a theoretical limit of detection (LOD) in the range of 11 attomole (corresponding to an analyte concentration of 55 fM for a sample volume of 200 µL) from the ACS dynamic response after the MNPs have bound to the RCA coils and the measured ACS readout noise. We also discuss further possible improvements of the LOD.
Recently, the activity on functionalized nano-objects has strongly increased. Yet, there are, to our knowledge no techniques available that visualize the attachment of molecules to nano-entities such as nanoparticles and graphene. In this work, we show a methodology to analyse the attachment of molecules to nanoparticles and graphene. The difficulty of such transmission electron microscopy (TEM) characterization consists in the high beam sensitivity of these nanoobjects. We employed a high resolution- as well as diffraction contrast-imaging methods to characterize graphene. First, we have developed a method to measure the thickness of free-standing graphene-like layers. The refinement of these imaging techniques enabled the imaging of functionalized C60 (fullerene) on top of a few-layer graphene flake by TEM. We also developed a methodology to visualize the attachment of functionalized gold and magnetic nanoparticles (different sizes) to nonstained and unlabeled single strand DNA-coils. This technique can be used to understand the interaction of a large variety of functionalized nanoparticles with their solution environment and/or macromolecular structures for their large applications.
The present work provides the first real-space analysis of nanobead-DNA coil interactions. Immobilization of oligonucleotide-functionalized magnetic nanobeads in rolling circle amplified DNA-coils was studied by complex magnetization measurements and transmission electron microscopy (TEM), and a statistical analysis of the number of beads hybridized to the DNA-coils was performed. The average number of beads per DNAcoil using the results from both methods was found to be around 6 and slightly above 2 for samples with 40 and 130 nm beads, respectively. The TEM analysis supported an earlier hypothesis that 40 nm beads are preferably immobilized in the interior of DNA-coils whereas 130 nm beads, to a larger extent, are immobilized closer to the exterior of the coils. The methodology demonstrated in the present work should open up new possibilities for characterization of interactions of a large variety of functionalized nanoparticles with macromolecules, useful for gaining more fundamental understanding of such interactions as well as for optimizing a number of biosensor applications.
Effective and compound-sparing methods to evaluate promising drug delivery systems are a prerequisite for successful selection of formulations in early development stages. The aim of the study was to develop a small-scale in situ method to determine drug release and supersaturation in highly concentrated suspensions of enabling formulations. Mesoporous magnesium carbonate (MMC), which delivers the drug in an amorphous form, was selected as a drug carrier. Five model compounds were loaded into the MMC at a 1:10 ratio using a solvent evaporation technique. The μDiss Profiler was used to study the drug release from MMC in fasted-state simulated intestinal fluid. To avoid extensive light scattering previously seen in particle-rich suspensions in the μDiss Profiler, an in-house-designed protective nylon filter was placed on the in situ UV probes. Three types of release experiments were conducted for each compound: micronized crystalline drug with MMC present, drug-loaded MMC, and drug-loaded MMC with 0.01% w/w hydroxypropyl methyl cellulose. The nylon filters effectively diminished interference with the UV absorption; however, the release profiles obtained were heavily compound dependent. For one of the compounds, changes in the UV spectra were detected during the release from the MMC, and these were consistent with degradation of the compound. To conclude, the addition of protective nylon filters to the probes of the μDiss Profiler is a useful contribution to the method, making evaluations of particle-rich suspensions feasible. The method is a valuable addition to the current ones, allowing for fast and effective evaluation of advanced drug delivery systems.
Conducting polymers are being considered promising candidates for sustainable organic batteries mainly due to their fast electron transport properties and high recyclability. In this work, key properties of polythiophene and polypyridine have been assessed through a combined theoretical and experimental study focusing on such applications. A theoretical protocol has been developed to calculate redox potentials in solution within the framework of the density functional theory and using continuous solvation models. Here, the evolution of the electrochemical properties of solvated oligomers as a function of the length of the chain is analyzed and then the polymer properties are estimated via linear regressions using ordinary least square. The predicted values were verified against our electrochemical experiments. This protocol can now be employed to screen a large database of compounds in order to identify organic electrodes with superior properties.
Organic compounds evolve as a promising alternative to the currently used inorganic materials in rechargeable batteries due to their low-cost, environmentally friendliness and flexibility. One of the strategies to reach acceptable energy densities and to deal with the high solubility of known organic compounds is to combine small redox active molecules, acting as capacity carrying centres, with conducting polymers. Following this strategy, it is important to achieve redox matching between the chosen molecule and the polymer backbone. Here, a synergetic approach combining theory and experiment has been employed to investigate this strategy. The framework of density functional theory connected with the reaction field method has been applied to predict the formal potential of 137 molecules and identify promising candidates for the referent application. The effects of including different ring types, e.g. fused rings or bonded rings, heteroatoms, [small pi] bonds, as well as carboxyl groups on the formal potential, has been rationalized. Finally, we have identified a number of molecules with acceptable theoretical capacities that show redox matching with thiophene-based conducting polymers which, hence, are suggested as pendent groups for the development of conducting redox polymer based electrode materials.
Development of advanced dressings with antimicrobial properties for the treatment of infected wounds is an important approach in the fight against evolution of antibiotic resistant bacterial strains. Herein, the effects of ion-crosslinked nanocellulose hydrogels on bacteria commonly found in infected wounds were investigated in vitro. By using divalent calcium or copper ions as crosslinking agents, different antibacterial properties against the bacterial strains Staphylococcus epidermidis and Pseudomonas aeruginosa were obtained. Calcium crosslinked hydrogels were found to retard S. epidermidis growth (up to 266% increase in lag time, 36% increase in doubling time) and inhibited P. aeruginosa biofilm formation, while copper crosslinked hydrogels prevented S. epidermidis growth and were bacteriostatic towards P. aeruginosa (49% increase in lag time, 78% increase in doubling time). The wound dressing candidates furthermore displayed barrier properties towards both S. epidermidis and P. aeruginosa, hence making them interesting for further development of advanced wound dressings with tunable antibacterial properties.
Calcium ion-crosslinked nanofibrillated cellulose (NFC) hydrogels were investigated as potential materials for wound healing dressings. The physicochemical properties of the hydrogels were examined by rheology and water retention tests. Skin cells and monocytes were selected for application-oriented bio-compatibility studies. The NFC hydrogels presented entangled fibrous networks and solid-like behavior. Water retention tests showed the material's potential to maintain a suitable moist environment for different type of wounds. The hydrogels did not affect dermal fibroblasts monolayer cultures upon directcontact, as cell monolayers remained intact after application, incubation and removal of the materials. Inflammatory response studies with blood-derived mononuclear cells revealed the inert nature of the hydrogels in terms of cytokine secretion and reactive oxygen species production. Results highlight the great potential of ion-crosslinked NFC hydrogels for the development of advanced wound dressings, where further functionalization of the material could lead to improved properties towards the healing of specific wound types.
A Ca2+-crosslinked wood-based nanofibrillated cellulose (NFC) hydrogel was investigated to build knowledge toward the use of nanocellulose for topical drug delivery applications in a chronic wound healing context. Proteins of varying size and isoelectric point were loaded into the hydrogel in a simple soaking procedure. The release of the proteins from the hydrogel was monitored and kinetics determining parameters of the release processes were assessed. The integrity of the hydrogel and proteins were also studied. The results showed that electrostatic interactions between the proteins and the negatively-charged NFC hydrogel structure played a central role in the loading process. The release of the proteins were governed by Fickian diffusion. An increased protein size, as well as a positive protein charge facilitated a slower and more sustained release process from the hydrogel matrix. At the same time, the positively-charged protein was shown to increase the post-loading hydrogel strength. Released proteins maintained structural stability and activity, thus indicating that the Ca2+-crosslinked NFC hydrogel could function as a carrier of therapeutic proteins without compromising protein function. It is foreseen that, by utilizing tunable charge properties of the NFC hydrogel, release profiles can be tailored to meet very specific treatment needs.
Magnetic biosensors are promising candidates for low-cost point-of-care biodiagnostic devices. For optimal efficiency it is crucial to minimize the time and complexity of the assay protocol including target recognition, amplification, labeling and read-out. In this work, possibilities for protocol simplifications for a DNA biodetection principle relying on hybridization of magnetic nanobeads to rolling circle amplification (RCA) products are investigated. The target DNA is recognized through a padlock ligation assay resulting in DNA circles serving as templates for the RCA process. It is found that beads can be present during amplification without noticeably interfering with the enzyme used for RCA (phi29 polymerase). As a result, the bead-coil hybridization can be performed immediately after amplification in a one-step manner at elevated temperature within a few minutes prior to read-out in an AC susceptometer setup, i.e. a combined protocol approach. Moreover, by recording the phase angle xi = arctan(chi ''/chi'), where chi and chi '' are the in-phase and out-of-phase components of the AC susceptibility, respectively, at one single frequency the total assay time for the optimized combined protocol would be no more than 1.5 hours, often a relevant time frame for diagnosis of cancer and infectious disease. Also, applying the phase angle method normalization of AC susceptibility data is not needed. These findings are useful for the development of point-of-care biodiagnostic devices relying on bead-coil binding and magnetic AC susceptometry.
Nanoelectrodes were fabricated combining photolithography, electron beam lithography and focused ion beam milling allowing for large scale integration and nanoengineering of the electrode properties. The structure determination by transmission and scanning electron microscopy showed a highly reproducible gap width. The atomic scale electrode structure was characterized using scanning and transmission electron microscopy. The nanogap resistances were found to be the highest hitherto reported for nanogaps, namely in the 300–1300 TΩ range. Gold nanoparticles were trapped by ac dielectrophoresis, and the electrodes were shown to be stable enough to endure empty gap voltages as high as 5 V as well as currents high enough to induce fusing of trapped nanoparticles.
We developed a novel biodetection method for influenza virus based on AC magnetic susceptibility measurement techniques (the DynoMag induction technique) together with functionalized multi-core magnetic nanoparticles. The sample consisting of an incubated mixture of magnetic nanoparticles and rolling circle amplified DNA coils is injected into a tube by a peristaltic pump. The sample is moved as a plug to the two well-balanced detection coils and the dynamic magnetic moment in each position is read over a range of excitation frequencies. The time for making a complete frequency sweep over the relaxation peak is about 5 minutes (10 Hz⁻10 kHz with 20 data points). The obtained standard deviation of the magnetic signal at the relaxation frequency (around 100 Hz) is equal to about 10-5 (volume susceptibility SI units), which is in the same range obtained with the DynoMag system. The limit of detection with this method is found to be in the range of 1 pM.
We present here a detailed study of the controlled release of amino acid derived amphiphilic molecules from the internal pore structure of mesoporous nanoparticle drug delivery systems with different structural properties; namely cubic and hexagonal structures of various degrees of complexity. The internal pore surface of the nanomaterials presented has been functionalised with amine moieties through a one pot method. Release profiles obtained by Alternating Ionic Current measurements are interpreted in terms of specific structural and textural parameters of the porous nanoparticles such as pore geometry and connectivity. Results indicate that diffusion coefficients are lower by as much as four orders of magnitude in 2-dimensional structures in comparison to 3-dimensional mesoporous solids. A fast release in turn is observed from mesocaged materials AMS-9 and AMS-8 where the presence of structural defects is thought to lead to a slightly lower diffusion coefficient in the latter. Amount of pore wall functionalisation and number of binding sites on the model drug are found to have little effect on the drug release rate.
The aim of this study is to show the potential of using electrodynamic methods as characterization tools in the controlled drug release process, on complex drug release systems. The two formulations under study were a Carbopol gel containing diphenhydramine and an identical gel also containing the surfactant sodium dodecyl sulfate which forms catanionic vesicles with the diphenhydramine. The average diffusion coefficients were calculated from both the dielectric spectroscopy and the transient current measurements. Comparing the herein-obtained diffusion coefficients with those obtained in another study using a traditional USP technique for the same system, the values are virtually the same. The two electrodynamic methods proved to be potentially valuable tools for obtaining information about the concentration and the motion of the drug molecules inside the gel. The transient current measurements are particularly interesting in this case, as the method gives information not only on an average level, but also of the different charged moieties separately. Interestingly, it seems that the methods also are applicable for obtaining information about the mesh size in the gel.
The possibility to fast-load biomimetic hydroxyapatite coatings on surgical implant with the antibiotics Amoxicillin, Gentamicin sulfate, Tobramycin and Cephalothin has been investigated in order to develop a multifunctional implant device offering sustained local anti-bacterial treatment and giving the surgeon the possibility to choose which antibiotics to incorporate in the implant at the site of surgery. Physical vapor deposition was used to coat titanium surfaces with an adhesion enhancing gradient layer of titanium oxide having an amorphous oxygen poor composition at the interface and a crystalline bioactive anatase TiO2 composition at the surface. Hydroxyapatite (HA) was biomimetically grown on the bioactive TiO2 to serve as a combined bone in-growth promoter and drug delivery vehicle. The coating was characterized using scanning and transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The antibiotics were loaded into the HA coatings via soaking and the subsequent release and antibacterial effect were analyzed using UV spectroscopy and examination of inhibition zones in a Staphylococcus aureus containing agar. It was found that a short drug loading time of 15 min ensured antibacterial effects after 24 h for all antibiotics under study. It was further found that the release processes of Cephalothin and Amoxicillin consisted of an initial rapid drug release that varied unpredictably in amount followed by a reproducible and sustained release process with a release rate independent of the drug loading times under study. Thus, implants that have been fast-loaded with drugs could be stored for ~10 min in a simulated body fluid after loading to ensure reproducibility in the subsequent release process. Calculated release rates and measurements of drug amounts remaining in the samples after 22 h of release indicated that a therapeutically relevant dose could be achieved close to the implant surface for about 2 days. Concluding, the present study provides an outline for the development of a fast-loading slow-release surgical implant kit where the implant and the drug are separated when delivered to the surgeon, thus constituting a flexible solution for the surgeon by offering the choice of quick addition of antibiotics to the implant coating based on the patient need.
Temperature-dependent drug release from disintegrating tablets made of NaCl-containing agglomerated micronized cellulose (AMC) granules has been studied to characterize the release process. Release measurements on tablets compacted at three different compaction pressures; 50, 100, and 200 MPa, were performed at seven different temperatures; 6, 23, 33, 43, 50, 55, and 63°C using the recently developed alternating ionic current method. Tablets compacted at different compaction pressures showed similar release rates. The release process was found to be diffusion-controlled, and the activation energy of the diffusion coefficient was comparable to that obtained for diffusion in pure water. The results show that the AMC granules in contact with water swell to a size and shape that is only slightly affected by their compaction history and the ion diffusion operates mainly within liquid-filled pores within the AMC granules. By using the temperature dependence of the release process, it was possible to reach this conclusion without any assumptions concerning the number and radii of the granules into which the tablets disintegrated. Further, the magnitude of the effective diffusion coefficient was found to be ∼7.5 · 10−10 cm2/s, which is ∼four orders of magnitude lower than for unhindered diffusion of Na+ and Cl− in water but similar to the diffusion coefficient for protons and OH− ions in microcrystalline cellulose.
We investigate the ion transportpercolationproperties of a binary system of an ion conductor (NaCl) and an insulator (ethyl cellulose) for which the ac component of the conductivity is non-negligible over the entire measured frequency range. We find that the dc conductivity, extracted from a well-defined range of frequencies, can be described by a low percolation threshold, ϕc=0.06 three-dimensional conducting network. The low ϕc was explained by the water-layer-assisted ion conduction in micrometer-sized ethyl cellulose channels between NaCl grains. The present findings provide valuable knowledge for the analysis and design of a broad class of ion conducting functional materials.
The combined radial and axial ionic drug release from – as well as the percolating ionic conductivity in – cylindrical tablets was investigated by the alternating ionic current (AIC) method and dielectric spectroscopy (DS), respectively. The binary tablets consisted of mixtures of insulating ethyl cellulose and the poor ionic conductor model drug NaCl at nine different concentrations. We found that the dc conductivity, extracted from DS in a well-defined range of frequencies by a power-law method, could be described by a NaCl volume fraction percolation threshold of 0.06 in a 3D conducting network. The low threshold was explained by water-layer-assisted ion conduction in μm-sized ethyl cellulose channels between NaCl grains as probed by Hg porosimetry and SEM. The drug release process, as probed by AIC, could be described by a matrix porosity percolation threshold of 0.22, equivalent to a NaCl volume fraction of 0.13. The higher percolation threshold found in the drug release experiments as compared to the DS recordings could be explained by the different probing mechanisms of the analysis methods. The present study should provide valuable knowledge for the analysis of a broad class of ion conducting systems for which the frequency response of the dc ion conductivity is superimposed on other dielectric processes in the dielectric spectrum. It also brings forward knowledge important for the development of controlled drug-delivery vehicles as the presented findings show that the drug release from matrix tablets with unsealed tablet walls substantially differs from earlier investigated release processes for which the drug has only been allowed to escape through one of the flat tablet surfaces.
Release of NaCl in both the axial and radial directions from cylindrical ethyl cellulose tablets were investigated by the alternating ionic current method. The pore structure of the investigated binary mixtures was examined by mercury porosimetry and scanning electron microscopy, and the nm range fractal surface dimension of tablet pore walls was extracted from krypton gas adsorption isotherms. The drug release was shown to consist of two overlapping processes of which the first was ascribed to dissolution of NaCl close to the tablet boundary followed by subsequent diffusion through a thin ethyl cellulose layer and a second from which a porosity percolation threshold of 0.22 could be extracted. As well, a cross-over to effective-medium behaviour at a porosity of 0.44 was observed. The presented findings showed that drug release from matrix tablets with unsealed tablet walls substantially differs from earlier investigated release processes for which the drug has only been allowed to escape through one of the flat tablet surfaces. Thus, the present study brings forward knowledge important for the tailoring of controlled drug delivery vehicles with optimum release patterns.
One method to increase the clinical success rate of metal implants is to increase their bone bonding properties, i.e. to develop a bone bioactive surface leading to reduced risks of interfacial problems. Much research has been devoted to modifying the surface of metals to make them become bioactive. Many of the proposed methods include depositing a coating on the implant. However, there is a risk of coating failure due to low substrate adhesion. This paper describes a method to obtain bioactivity combined with a high coating adhesion via a gradient structure of the coating. Gradient coatings were deposited on Ti (grade 5) using reactive magnetron sputtering with increasing oxygen content. To increase the grain size in the coating, all coatings were post annealed at 385 degrees C. The obtained coating exhibited a gradual transition over 70 nm from crystalline titanium oxide (anatase) at the surface to metallic Ti in the substrate, as shown using cross-section transmission electron microscopy and X-ray photoelectron spectroscopy depth pro. ling. Using scratch testing, it could be shown that the adhesion to the substrate was well above 1 GPa. The bioactivity of the coating was verified in vitro by the spontaneous formation of hydroxylapatite upon storage in phosphate buffer solution at 37 degrees C for one week. The described process can be applied to implants irrespective of bulk metal in the base and should introduce the possibility to create safer permanent implants like reconstructive devices, dental, or spinal implants.