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.
According to a report by the American Heart Association, there are approximately 3-4
million Americans that may experience silent Myocardial Ischemia (MI). Silent MI is a serious
heart condition that can progress to a severe heart attack without any warning and the consequences
of such an event can turn fatal quickly. Therefore, there is a strong need for a sensor that can
continuously monitor the onset of the condition to prevent high risk individuals from deadly heart
attacks. An increase in extracellular potassium levels is the first sign of MI and timely sensing with
an implantable potassium sensing biosensor could play a critical role in detecting and expediting
care. There are challenges in the development of an implantable potassium sensing electrode one of
which includes signal drift. The incorporation of novel nanostructures and smarter materials hold
the potential to combat these problems. This paper presents a unique design for an all-solid-state
potassium sensing device which offers miniaturization along with enhanced signal transduction.
These characteristics are important when it comes to implantable devices and signal drift. Sensor
design details along with fabrication processes and sensing results are discussed.
Myocardial Ischemia is a condition which affects millions of people in the U.S. It is known
that a rise in levels of extracellular potassium indicates the onset of this condition. This presentation
demonstrates the fabrication of a unique potassium sensing device which combines a conducting
polymer, polypyrrole, with micro/nano fabrication and nanowire technology. We discuss the
fabrication of gold/polypyrrole electrodes on a flexible polyimide substrate. Conducting polymers
offer numerous advantages when it comes to ion sensing including increased stability in response
while micro/nanofabrication aids in the overall miniaturization. The small size and flexibility makes
this device suitable for future biomedical applications involving implantation. In this presentation,
various electrode structures including nanowire electrodes ware investigated. Testing is conducted
with an electrochemical analyzer where changes in open circuit potentials reflect changes in
potassium ion concentration.
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.
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