Biomedical subjects

Andrew G Mayes

Publications and source records attributed to Andrew G Mayes.

6 recordsLinked to original sources

PubMed2006

A micro-reactor for preparing uniform molecularly imprinted polymer beads.

In this study, uniform spherical molecularly imprinted polymer beads were prepared via controlled suspension polymerization in a spiral-shaped microchannel using mineral oil and perfluorocarbon liquid as continuous phases. Monodisperse droplets containing the monomers, template, initiator, and porogenic solvent were introduced into the microchannel, and particles of uniform size were produced by subsequent UV polymerization, quickly and without wasting polymer materials. The droplet/particle size was varied by changing the flow conditions in the microfluidic device. The diameter of the resulting products typically had a coefficient of variation (CV) below 2%. The specific binding sites that were created during the imprinting process were analysed via radioligand binding analysis. The molecularly imprinted microspheres produced in the liquid perfluorocarbon continuous phase had a higher binding capacity compared with the particles produced in the mineral oil continuous phase, though it should be noted that the aim of this study was not to optimize or maximize imprinting performance, but rather to demonstrate broad applicability and compatibility with known MIP production methods. The successful imprinting against a model compound using two very different continuous phases (one requiring a surfactant to stabilize the droplets the other not) demonstrates the generality of this current simple approach.

Equipment Design↗

PubMed2005

Direct rapid synthesis of MIP beads in SPE cartridges.

Selecting optimal compositions for non-covalent molecularly imprinted polymers (MIPs) and screening for appropriate rebinding conditions necessitates synthesising a large number of polymers. This is extremely labour-intensive and usually results in very limited "optimisation" in studies of MIPs. Here, a new method is proposed for rapid synthesis of MIPs in a beaded form that can be used directly in many different performance evaluation studies. The method is based on synthesis of spherical particles by suspension polymerisation in liquid fluorocarbon [Mayes, A., Mosbach, K., 1996. Molecularly imprinted polymer beads: suspension polymerisation using a liquid perfluorocarbon as the dispersing phase. Anal. Chem. 68, 3769-3774]. The polymers were directly polymerised under UV light in solid phase extraction (SPE) cartridges, then washed and extracted in the same cartridges where they had been synthesised, resulting in a rapid and automatable process that requires no transfer or manipulation of the polymer particles. The particles were similar in terms of size, morphology and functional performance to particles obtained by suspension polymerisation in fluorocarbon solvent using a conventional reactor. In this initial study, 36 polymers were synthesised to study the effect of a variation in the type and amount of four different functional monomers, methacrylic acid (MAA), acrylic acid (AA), hydroxyethyl methacrylate (HEMA) and 2-vinylpyridine (2-VPy), for the imprinting of propranolol and morphine. The performance of polymers synthesised using MAA was as expected, but those synthesised with AA as functional monomer showed more surprising rebinding properties as a function of monomer to cross-linker ratios, demonstrating the potential value of pragmatic synthesis and screening approaches to polymer optimisation.

Biocompatible Materials↗

PubMed2005

Tethered DNA hairpins facilitate electrochemical detection of DNA ligation.

A novel electrochemical assay for DNA ligase activity is described. The assay exploits the properties of DNA hairpins tethered at one terminus to a gold electrode and labelled at the other with a ferrocene group for rapid characterisation of DNA status by cyclic voltammetry. Successful ligation of 'nicked' DNA hairpins is indicated by retention of the ferrocene couple when exposure to DNA ligase is followed by conditions that denature the hairpin. The results demonstrate the simplicity of integrating electrochemical detection with hairpin based biosensors and illustrate a new approach to the assay of DNA ligases, of which the NAD(+)-dependent enzymes represent a potential broad spectrum antibacterial drug target.

Biosensing Techniques↗

PubMed2004

A direct comparison of the performance of ground, beaded and silica-grafted MIPs in HPLC and turbulent flow chromatography applications.

Spherical molecularly imprinted polymers (MIPs) specific to the beta-blocker propranolol have been synthesised using two different approaches and compared to traditional ground monolithic MIPs in HPLC and TFC applications. TFC is a LC technique used for rapid extraction of compounds directly from complex matrices. It can be easily coupled to HPLC and MS for automation of an extraction/analysis procedure. Spherical MIP beads were produced using a suspension polymerisation technique and silica/MIP composite beads by grafting MIP to spherical silica particles using a surface-bound initiator species. Synthesis of both beaded and silica-grafted MIPs was more practical than using the traditional grinding method and yields of spherical particles of the required size between 80 and 100% were routinely achieved. Under HPLC conditions, beaded and ground MIP materials showed a degree of chiral separation for all of the nine beta-blockers tested. The beaded MIP, however, showed much better flow properties and peak shape than the ground material. Silica-grafted MIP showed some separation in five of the drugs and a large improvement in peak shape and analysis times compared with both ground and beaded MIPs. The materials prepared were also used in extraction columns for Turbulent Flow Chromatography (TFC). Although no imprinting effect was observed under typical TFC conditions, beaded polymer materials showed promise for use as TFC extraction columns due to the good flow properties and clean extracts obtained.

Adrenergic beta-Antagonists↗

PubMed2004

Noncovalent imprinting in the shell of core-shell nanoparticles.

Propranolol was imprinted using noncovalent interactions in the shell of core-shell nanoparticles prepared by aqueous emulsion polymerization in the presence and absence of toluene. The imprinted particles were characterized, and their capacity to rebind propranolol from both organic and aqueous media was analyzed. Results showed that the amount of template incorporated into the polymer and the presence of toluene as a "porogenic" agent influenced the ability of the nanoparticles obtained to rebind propranolol. The presence of toluene during imprinting increased rebinding by about 2-fold in buffer and by 3-fold in toluene, compared with similar materials made in the absence of toluene during imprinting. It also influenced the final surface area of the particles. Binding site affinity, assessed by radioligand displacement, was measured as IC50 values of about 1-10 microM. This compares with about 3 microM for bulk polymer made with a similar composition. Finally, to demonstrate the advantages of structured particles for analytical applications a new property, fluorescence, was incorporated into the core of the particles without interfering with the imprinted shell and its ability to rebind propranolol.

Journal Article↗

PubMed2002

Metal ion-sensitive holographic sensors.

Holographic sensors for Na+ and K+ have been fabricated from crown ethers incorporated into polymeric hydrogels. The methacrylate esters of a homologous series of hydroxyether crown ethers were synthesized and copolymerized with hydroxyethyl methacrylate and the cross-linker ethylene dimethacrylate (3 mol %) to form stable hydrogel films (approximately 10 m thick) containing covalently bound (0-97 mol %) 12-crown-4, 15-crown-5, and 18-crown-6 pendant functionalities. The films were transformed into silver-based volume holograms using a diffusion method coupled with a holographic recording using a frequency-doubled Nd:YAG laser. The resulting holographic reflection spectrum was used to characterize the shrinkage and swelling behavior of the holograms as a function of polymer composition and the nature and concentration of alkali, alkaline earth, and NH4+ ions in the test media. Optimized film compositions containing 50 mol % crown ether showed substantial responses (< or = 200 nm) within 30 s at ion concentrations of < or = 30 mM, which could be rationalized on the basis of the known complexation behavior of the crown ethers. An 18-crown-6 holographic film was shown to be able to quantitate K+ concentrations over the physiologically relevant range. It was virtually unaffected by variations in the Na+ background concentration within the normal physiological variation (approximately 0.13-0.15 M) and shows promise for developing simple, low-cost K+ sensors for medical applications.

Ethers, Cyclic↗