1,875 research outputs found
A development of a molecularly imprinted polymer: Specific for ochratoxin A: Theoretical and sensor applications
No full textIn this work the development of two molecularly imprinted polymers, specific
for ochratoxin A, is presented. Ochratoxin A is produced by several
Aspergillus and Penicillium species and is common in cereals and other
starch rich foods and has also been found in coffee, dried fruits, wine, beer
and meats. It demonstrates potent teratogenic, immunosuppressive,
mutagenic and carcinogenic properties. The toxin is also linked to Balkan
Endemic Nephropathy, a chronic kidney disease found in South-Eastern
Europe. Due to this the European Union has set limits on foodstuffs ranging
between 2-10 ng g-1. Therefore the requirement of a simple and inexpensive
biosensor to monitor this legislation is a necessity. Currently detection is
performed by chromatographic methods such as HPLC, and by ELISA
formats.
In this work two polymeric materials, rationally designed by computational
modelling and synthesised using molecular imprinting, are studied. The
modelling is complimented with a Nuclear Magnetic Resonance (NMR) study.
The first polymer (Polymer A) consisted of 1 mol of acrylamide and 1 mol of
methacrylic acid to 1 mol of template. This material demonstrated an unusual
binding mechanism, working solely in aqueous solvents. A theoretical
mechanism for this binding is presented and discussed.
The second polymer, again rationally designed, but under different conditions,
consisted of 1 mol of N,N- diethylamino ethyl methacrylate (DEAEM) to 1 mol
of template. This polymer demonstrated high affinity for the template in
acetonitrile.
Polymer A is used in combination with an ion-exchange SPE protocol
(developed for this purpose) for the extraction of OTA from maize.
Both polymer compositions are used in development of a MIP membrane
optical sensor, with partial success seen in the detection of OTA in grape juice
and white wine
Improvements in electrochemical glucose biosensors
No full textDiabetes is one of the leading causes of death and disability in the world. Even
though insulin was discovered in 1920, an intense research on diabetes has been
conducted during the last five decades and this is because of the market size. The
huge demand is creating the need for the development of new approaches. This
project involved the research aimed at better understanding and improvements in
performance of glucose biosensors.
In general, high surface area electrodes are desired as the high surface area
provides more active sites for electrochemical reactions, and hence higher kinetic
rate capability. Therefore, the determination of the active electrochemical surface
area of the electrode is very important. A study has been conducted to determine the
real electrochemical surface area of the Pelikan screen printed electrodes (SPEs)
and a method has been optimised and established by Pelikan for the evaluation of
their SPEs. Another very important issue that most of the current blood glucose
monitoring tests are facing is the haematocrit effect, since the haematocrit
differences observed in the blood samples can significantly affect glucose
measurements. Therefore a study has been conducted in order to observe the
absorption of the blood samples into the working electrode paste according to the
haematocrit level.
The second part of the study included the characterisation of the novel conjugated
polymer made of N-(N, N’ diethyldicarbamoyl ethyl amido ethyl) aniline (NDDEAEA),
the optimization of the conditions for the electrochemical polymerization, their
application in grafting and finally the development of NDDEAEA based glucose
biosensor. The new conducting polymer, acted as a matrix for the biosensor
fabrication in this study, possesses macroiniferter properties and is capable of
initiation free radical initiated addition polymerisation after formation of the
polyaniline (PANI) material while preserving or even enhancing some of the PANI’s
electrochemical properties. This material can potentially be used in the construction
of novel Pelikan electrodes with enhanced integration functionalities, e.g. grafting
non adhesive polymer coatings to assure that the poor performance in sensors as a
result of impact of blood components can be mitigated.
The final study included the development and optimisation of the reaction conditions
for grafting a hyperbranched polymer onto the surface of the multi walled carbon
nanotubes (MWCNT), using the A3 and B2 approach (described below). The aim of
this work was achieving further increase in the sensitivity of Pelikan sensors
Development of sensors for the detection of clinically relevant substances using molecular imprinting
No full textThis thesis investigates the development of sensing devices based on molecularly
imprinted polymers for the detection of clinically relevant analytes. Three analytes
were considered, metronidazole, creatinine and propofol.
A molecularly imprinted polymer (MIP) was computationally designed for
metronidazole and tested using SPE techniques. This polymer was then grafted onto a
transducer surface using an immobilised initiator. Amperometric and impedance
detection of metronidazole were investigated.
The capacitive detection of creatinine was reproduced from the literature (Panasyuk-
Delaney et al., 2002) as this approach could be applied to other MIPs to form a
universal platform for sensor development. However, the sensors produced using this
methodology were difficult to reproduce and attempts to improve them were
unsuccessful. A model for capacitive electrodes was developed to explain the obtained
results.
To address the key challenges found in the aforementioned work, a dual polymerisable
monomer was used as a conductive anchor for the amperometric and impedance
detection of propofol. The developed amperometric sensors demonstrated very high
sensitivity (limit of detection was below 5 µM), although the electrodes lacked in
selectivity.
In conclusion, this thesis illustrates some of the key areas which need to be considered
in the development of MIP-based devices and investigates some innovative solutions to
these problems
Biomimetic sensors for HbA1c
No full textDiabetes mellitus is a growing health problem worldwide. Suitable long-term control
and management of this disease are enabled by determination of glycated haemoglobin
(HbA1c) in blood. The results are given as %HbA1c of total haemoglobin. Presently
available tests vary in cost and convenience and there is an identified need to introduce
improved equipment for self-monitoring. This dissertation focuses on fast and
straightforward detection of glycated haemoglobin (HbA1c) using cyclic voltammetry
and chronoamperometry. Haemoglobin was determined by monitoring its reaction with
potassium ferricyanide on screen printed electrodes at an oxidative potential +500 mV.
A working electrode was modified with carbon nanotubes to enhance electron transfer.
A calibration curve was linear in a range from 0.83 to 83 mg/mL. Another innovative
approach to detecting haemoglobin using its enzymatic activity was also developed.
Detection of haemoglobin was performed with hydroquinone and hydrogen peroxide on
screen printed electrodes at a potential -400 mV in a Flow Injection Analysis system
(FIA). Cont/d
Design of molecularly imprinted polymers for sensors and solid phase extraction
No full textThis thesis presents broadly the applications of molecularly imprinted polymers in
sensors and solid phase extraction. Sensors for creatine and creatinine have been
reported using a novel method of rational design of molecularly imprinted polymers
(MIPs), and solid phase extraction of aflatoxin-B 1 has also been described in the
thesis.
A method for the selective detection of creataine and creatinine is reported in this
thesis, which is based on the reaction between polymerised hemithioacetal, formed by
allyl mercaptan, o-phthalic aldehyde, and primary amine leading to the formation of
fluorescent isoindole complex. This method was demonstrated for the detection of
creatine using creatine-imprinted MIPs. Since MIPs created using traditional methods
were unable to differentiate between creatine and creatinine, a new approach to the
rational design of a MIP selective for creatinine was developed using computer
simulation. A virtual library of functional monomers was assigned and screened
against the target molecule, creatinine, using molecular modeling software. The
monomers giving the highest binding score were further tested using simulated
annealing in order to mimic the complexation of the functional monomers with
template in the monomer mixture. The result of this simulation gave an optimised
MIP composition. The computationally designed polymer demonstrated superior
selectivity in comparison to the polymer prepared using traditional approach, a
detection limit of 25 μM and good stability. The 'Bite-and- Switch' approach
combined with molecular imprinting can be used for the design of assays and sensors,
selective for amino containing substances.
MEP for the selective binding properties for aflatoxin-B 1 was prepared using the
computational approach. The results obtained demonstrate that the MISPE offers a
simple, convenient and a rapid methodology for solid phase extraction of aflatoxin-B 1
even at very low concentrations of 2 ppb. The commercially available C-18 cartridges
were able to recover only about 52% of aflatoxin-B 1 at concentrations of 2 ppb when
compared with almost complete recovery by the MIP. We have proved here that,
MIPs as a solid phase extraction materials offer important and practical advantages
with respect to other solid phase extraction methodologies
Molecularly Imprinted Polymers for Cell Recognition
No full textSince their conception 50 years ago, molecularly imprinted polymers (MIPs) have seen extensive development both in terms of synthetic routes and applications. Cells are perhaps the most challenging target for molecular imprinting. Although early work was based almost entirely around microprinting methods, recent developments have shifted towards epitope imprinting to generate MIP nanoparticles (NPs). Simultaneously, the development of techniques such as solid phase MIP synthesis has solved many historic issues of MIP production. This review briefly describes various approaches used in cell imprinting with a focus on applications of the created materials in imaging, drug delivery, diagnostics, and tissue engineering
Automatic solid-phase synthesis of molecularly imprinted nanoparticles (MIP NPs)
No full textMolecularly Imprinted Polymers (MIPs) are potential generic alternatives to antibodies in diagnostics and separations. To compete with biomolecules in these technological niches, MIPs need to share the characteristics of antibodies (solubility, size, specificity and affinity) whilst maintaining the advantages of MIPs (low cost, short development time and high stability). For this reason the interest in preparing MIPs as nanoparticles (MIP NPs) has increased exponentially in the last decade. Cont/d
Attenuation of quorum sensing using computationally designed polymers
No full textIt is generally accepted that the majority of Gram-negative and Gram-positive bacteria
communicate via production and sensing of small signal molecules, autoinducers. The ability
of bacteria to sense their population density is termed quorum sensing (QS). Quorum sensing
controls certain phenotypic traits, particularly virulence factors and biofilm formation. In this
project a new solution for the attenuation of quorum sensing which involves selective
sequestering of the signal molecules using rationally designed synthetic polymers was
explored. Cont/d
Interactions between heavy metals and photosynthetic materials studied by optical techniques
No full textIn this work studies on rapid inhibitory interactions between heavy metals and
photosynthetic materials at different organization levels were carried out by
optical assay techniques, investigating the possibility of applications in the
heavy metal detection field. Spinach chloroplasts, thylakoids and Photosystem II
proteins were employed as biotools in combination with colorimetric assays based
on dichlorophenol indophenole (DCIP) photoreduction and on fluorescence emission
techniques. It was found that copper and mercury demonstrated a strong and rapid
photosynthetic activity inhibition, that varied from proteins to membranes,
while other metals like nickel, cobalt and manganese produced only slight
inhibition effects on all tested photosynthetic materials. By emission
measurements, only copper was found to rapidly influence the photosynthetic
material signals. These findings give interesting information about the rapid
effects of heavy metals on isolated photosynthetic samples, and are in addition
to the literature data concerning the effects of growth in heavy metal enriched
media
Surface imprinted beads for the recognition of human serum albumin
No full textThe synthesis of poly-aminophenylboronic acid (ABPA) imprinted beads for the
recognition of the protein human serum albumin (HSA) is reported. In order to
create homogeneous recognition sites, covalent immobilisation of the template
HSA was exploited. The resulting imprinted beads were selective for HSA. The
indirect imprinting factor (IF) calculated from supernatant was 1.6 and the
direct IF, evaluated from the protein recovered from the beads, was 1.9. The
binding capacity was 1.4 mg/g, which is comparable to commercially available
affinity materials. The specificity of the HSA recognition was evaluated with
competitive experiments, indicating a molar ratio 4.5/1 of competitor was
necessary to displace half of the bound HSA. The recognition and binding of the
imprinted beads was also tested with a complex sample, human serum and targeted
removal of HSA without a loss of the other protein components was demonstrated.
The easy preparation protocol of derivatised beads and a good protein
recognition properties make the approach an attractive solution to analytical
and bio-analytical problems in the field of biotechnology
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