This research discusses the development of biosensors with vertically aligned nanowires,
and the evaluation of their physical properties, electrochemical performance and biocompatibility.
The developments include neurotransmitter (dopamine) sensors, glucose sensors for continuous
monitoring, potassium ion sensors and integration of those sensors. A hemi-cylindrical nanocavity
structure has been developed for dopamine sensing using redox cycling with radial diffusion
within the cavities. By immobilization of enzymes in a conducting polymer matrix on vertically
aligned nanowires, glucose sensing electrodes have been obtained with high sensitivity and
selectivity. In addition, potassium sensing, potentially useful for monitoring changes of
extracellular potassium concentration during myocardial ischemia, has been demonstrated using
ion selective membranes (ISM) on nanowires. Sensor developments and measurement results are
included in the presentation along with descriptions of top-down and bottom-up
nano-/micro-fabrication technologies such as lithography and thin film deposition.
We discuss the development of a novel amperometric sensor
to detect glucose concentrations in solution. Inorganic, vertically aligned
nanowire arrays were employed as the sensing electrode in place of
planar electrodes to utilize the unique properties of nanostructures, resulting
in enhanced sensing signal from a smaller area. Heterostructured
gold/platinum nanowires were used so that the dual functions of the
nanoelectrodes for covalent immobilization of glucose oxidase and enhanced
oxidation of hydrogen peroxide can be achieved using modified
microfabrication methods. Two different enzyme immobilization
methods—using self-assembled monolayers of alkanethiols and a porous
conducting polypyrrole matrix—were investigated as methods
for functionalizing the electrodes. Glucose sensing results were
compared for planar and nanowire electrodes and the heterostructured
nanowire electrodes. The results indicate that the unique structure of
the sensing electrode delivers superior sensing performance from a
smaller geometric area of electrodes, thus enabling further miniaturization
of the sensor.
This research discusses the development of a novel amperometric sensor to detect glucose concentrations in solution
without the need for an artificial mediator. Since the intended goal of this research is to develop a glucose sensor to
subcutaneously monitor glucose levels in the body, it is important that the sensor does not require a mediator, since such
chemicals would prove harmful to the body. Nanowire arrays were used as the sensing electrode in place of planar
electrodes to utilize the unique properties of nanostructures. Heterostructured Au/Pt nanowires were used so that the
dual roles of covalent immobilization of glucose oxidase and oxidation of hydrogen peroxide could be carried out by the
sensing electrode. Glucose oxidase was immobilized on these nanowires using self- assembled monolayers of
alkanethiols and using a conducting polypyrrole matrix. Results indicate that the unique structure of the sensing
electrode delivers superior performance with regards to sensitivity and response time in the absence of an artificial
mediator. The development of such a sensor would assist the treatment of patients in an effective and timely manner.
Ongoing efforts will help understand the process fabrication and analysis in detail.
This presentation demonstrates the fabrication of bio-inspired electric cilia structures using
bottom-up hetero-nanowires and ionic electro active polymer on flexible polyimide substrates. In
order to obtain sensing function of fluid velocity in meso-scale vessels and minimally disturb original
flow condition, parallel arrays of "electronic cilium" with the size of few micrometers in length and
few hundreds nanometers in diameter are vertically fabricated on a thin flexible film. For active layers,
ionic electro active polymer has been applied on hetero-structured nanowires, which provide low
Young's modulus and sensitive to bending moment by lateral force in fluid. This research works
include the characterization of electro active polymer fabrication processes on nanowires and their
mechanical properties by atomic force microscopy and electrochemical analysis tools. In addition, a
three-dimensional microfluidic channel fabrication method using micro-stereo-lithography (MSL) is
introduced in this presentation, which is an efficient method to simulate fluid conditions in blood vessels.
The fabrication of hetero-structured vertically aligned nanowire arrays and enzyme immobilization on their surface is presented for a glucose sensor with high sensitivity. Hetero-structured nanowires of gold and platinum are fabricated by hybrid polycarbonate membrane assembly and electrochemical deposition processes and glucose oxidase are attached on their surface by covalent immobilization. Platinum and gold hetero-structured nanoelectrodes with enzyme are evaluated to detect hydrogen peroxide produced in the enzyme reaction without the need for the artificial redox mediator, which is not viable on a homogenous gold electrode. Chronoamperometric current behavior is demonstrated with various concentrations from 0.5 mM to 28 mM. In this research, the combination of enzyme immobilization and sensing surfaces on nanowire arrays has shown superior performance with regards to the sensitivity and response time.
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