There is a need for accurate and instant measurement of pH values in a wide range of applications. The research on
miniaturized polymer based pH sensors has recently emerged due to the progress made in polymer materials science.
Novel method of manufacturing micro sensors arrays for biomedical applications using BioForce NanoeNabler<sup>TM</sup> is
reported. This nanopatterning system uses a liquid dispensing process via specially designed surface patterning tool
(SPT), which is microfabricated cantilever with an integrated passive microfluidic system. During the deposition
process, which typically takes less than 100 msec, SPT end touches the surface and a volume of fluid is instantly
transferred. The NanoeNabler<sup>TM</sup> can deliver attoliter to picoliter volumes of liquid with a high degree of spatial accuracy,
which resulted in sensor heads measuring 1-2.5 μm to 30 μm. These sensors were developed for biomedical applications,
in particular pH monitoring. It is envisaged that findings of this work would form the basis for miniaturised point-of-care
diagnostic system. The operation of the sensing elements is based on the properties of polymers, which exhibit a change
in their electrical characteristics (such as resistance or capacitance) on exposure to solutions with different concentrations
of pH value.
Biosensor designs are emerging at a significant rate and play an increasingly important role in foodborne pathogen
detection. Conducting polymers are excellent tools for the fabrication of biosensors and polypyrrole has been used in the
detection of biomolecules due to its unique properties. The prime intention of this paper was to pioneer the design and
fabrication of a single-strand (ss) DNA biosensor for the detection of the <i>Bacillus cereus</i> (<i>B.cereus</i>) group species.
Growth of <i>B. cereus</i>, results in production of several highly active toxins. Therefore, consumption of food containing
>10<sup>6</sup> bacteria/gm may results in emetic and diarrhoeal syndromes. The most common source of this bacterium is found
in liquid food products, milk powder, mixed food products and is of particular concern in the baby formula industry.
The electrochemical deposition technique, such as cyclic voltammetry, was used to develop and test a model DNA-based
biosensor on a gold electrode electropolymerized with polypyrrole. The electrically conducting polymer, polypyrrole is
used as a platform for immobilizing DNA (1μg) on the gold electrode surface, since it can be more easily deposited from
neutral pH aqueous solutions of pyrrolemonomers. The average current peak during the electrodeposition event is
288μA. There is a clear change in the current after hybridization of the complementary oligonucleotide (6.35μA) and for
the noncomplementary oligonucleotide (5.77μA). The drop in current after each event was clearly noticeable and it
proved to be effective.
Due to the demand for accurate, reliable and highly sensitive pH sensors, research is being pursued to find novel
materials to achieve this goal. Semiconducting metal oxides, such as TiO, SnO and SnO<sub>2</sub> and insulating oxides such as
Nb<sub>2</sub>O<sub>5</sub> and Bi<sub>2</sub>O<sub>3</sub>, and their mixtures in different proportions are being investigated for this purpose. The films of these
materials mixtures are used in conjunction with an interdigitated electrode pattern to produce a conductimetric/capacitive
pH sensor. The advantages of this approach include straightforward manufacturing, versatility and cost-effectiveness. It
was noted that upon contact with a solution, the electrical parameters of the films, such as resistance etc., change. The
correlation of these changes with pH values is the basis for the proposed system development. The ultimate goal is to
find materials composition, which would have the highest sensitivity towards the pH level of the solutions. It was found
that the materials that produced the highest sensitivity either had a long response time or were unstable over a wide pH
range. Those exhibiting lower sensitivities were found to be more stable over a wide pH range. All oxide films tested
demonstrated a change in electrical parameters upon contact with buffers of known pH value.
This work explores the radiation and ozone sensing properties of mixed oxides in the form of thin films. External effects,
such as radiation and ozone, cause defects in the materials it interacts with and, consequently, it causes changes in their
properties. These changes manifest themselves as the alterations in both the electrical and the optical parameters, which
are being measured and employed for dosimetry sensor development.
An Edwards E306A thermal coating system was used for In<sub>2</sub>O<sub>3</sub>:ZnO:SnO<sub>2</sub> (90% : 5% : 5%) films deposition. For the
electrical properties measurements, Cu electrodes were manufactured on the glass substrate via thermal evaporation of
Cu; then AZ5214 photoresist was spin-coated over it and exposed to UV light via the acetate, containing the desired
electrodes patterns. After the exposure, the substrate was placed in Electrolube PDN250ML developer solution and then
rinsed in water and placed in the etching solution of SEMO 3207 fine etch crystals to reveal the electrode pattern.
The optical properties of In<sub>2</sub>O<sub>3</sub>:ZnO:SnO<sub>2</sub> thin films were explored using CARY 1E UV-Visible Spectrophotometer. The
values of the optical band gap E<sub>opt</sub> are estimated in the view of the Mott and Davis' theory. It was noted that E<sub>opt</sub>
decreases with the increase in radiation dose, i.e. the overall disorder of the system is increased. Doping of In<sub>2</sub>O<sub>3</sub> with
5% ZnO and 5% SnO<sub>2</sub> dramatically changes the overall structure of the film and thus affected its sensing to gamma
radiation and ozone. Mixing metal oxides in certain proportions provides a tool for controlling the sensors response.
This paper explores the use of mixed oxide materials such as In<sub>2</sub>O<sub>3</sub> and SiO with various compositions in the form of thermally deposited thin films for gamma radiation dosimetry application. 137Cs radiation source with an activity of 370 kBq was used for exposing the samples to γ-radiation. The absorption spectra for as-deposited and γ-irradiated films were recorded using CARY 1E UV-Visible Spectrophotometer. The values of the optical band gap E<sub>opt</sub> were obtained in the view of the Mott and Davis’ theory. It was found that the optical properties of thin films were highly affected by composition and manufacturing conditions. For comparison, E<sub>opt</sub> of as-deposited thin film with composition 75 wt.% of In2O3 and 25 wt.% of SiO was found to be 0.9 eV, whereas films with 50 wt.% of In2O3 and 50 wt.% of SiO have E<sub>opt</sub>=1.15 eV, in all cases assuming indirect allowed transition. It was noted that E<sub>opt</sub> decreased with the increase in radiation dose, i.e. the overall disorder of the system has increased. Thin films of In<sub>2</sub>O<sub>3</sub> and SiO mixtures might be regarded as a cost-effective alternative to the existing commercially available radiation detectors.