Exploratory research works have demonstrated the capability of conducting nanowire arrays in enhancing the
sensitivity and selectivity of bio-electrodes in sensing applications. With the help of different surface manipulation
techniques, a wide range of biomolecules have been successfully immobilized on these nanowires. Flexible organic
electronics, thin film transistor (TFT) fabricated on flexible substrate, was a breakthrough that enabled development
of logic circuits on flexible substrate. In many health monitoring scenarios, a series of biomarkers, physical
properties and vital signals need to be observed. Since the nano-bio-electrodes are capable of measuring all or most
of them, it has been aptly suggested that a series of electrode (array) on single substrate shall be an excellent point of
care tool. This requires an efficient control system for signal acquisition and telemetry. An array of flexible TFTs
has been designed that acts as active matrix for controlled switching of or scanning by the sensor array. This array is
a scale up of the flexible organic TFT that has been fabricated and rigorously tested in previous studies. The
integration of nanowire electrodes to the organic electronics was approached by growing nanowires on the same
substrate as TFTs and fl ip chip packaging, where the nanowires and TFTs are made on separate substrates. As a
proof of concept, its application has been explored in various multi-focal biomedical sensing applications, such as
neural probes for monitoring neurite growth, dopamine, and neuron activity; myocardial ischemia for spatial
monitoring of myocardium.
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.
The emerging field of nanotechnology offers the development of new materials and methods for crucial neuroscience
applications namely (a) promoting survival and growth of the neurons, and (b) monitoring physiological signals
generated in the nervous system such as excitation, synaptic transmission, release of neurotransmitter molecules and
cell-to-cell communication. Such bio-devices will have several novel applications in basic science, laboratory
analysis and therapeutic treatments. Our goals in this field of research include (a) development of new biocompatible
substrates to guide and promote neuronal growth along specific pathways; (b) designing a neuron-friendly,
bio-molecule delivery system for neuroprotection; (c) monitoring of electrical activity from neuron and also from
neuronal networks; (d) determining the diffusion and intracellular localization of nanomaterial interacting with
neurons at high resolution; and (e) detection of release of neurotransmitter molecules by means of newly designed
nanosensors. Here we describe the fabrication and use of magnetic nanotubes and nanowire electrode arrays in studies
using a cell culture model of neuronally differentiating rat pheochromocytoma (PC 12) cells. The magnetic nanotubes
were fabricated by a template method yielding hematite (α-Fe2O3) nanotubes. These nanotubes were coupled with
nerve growth factor (NGF). Vertically aligned nanowires were fabricated on glass substrates using the
lithography-assisted template bonding (LATB) method. Rat pheochromocytoma (PC12) cells were cultured on these
nanotubes and polylysine coated nanowire electrodes. Our results showed that magnetic nanotube bound NGF was
available to PC12 cells as they showed significant differentiation into neurons. PC12 cells growing on nanowires in
the presence of NGF differentiated into neurons capable of synthesis and release of dopamine upon stimulation. The
neurons grew healthy neurites appearing to form synapses with other neurons in the dish. These results show that the
magnetic nanotubes were capable of delivering neurotrophic molecules and the nanowire electrodes are
neuron-friendly, promote cell to cell communication and can be used as bio-sensors in the nervous system.
KEYWORDS: Electrodes, Sensors, In vivo imaging, Gold, Scanning electron microscopy, Nanolithography, 3D surface sensing, Molecules, Nanowires, Oxidation
We investigated the use of a three dimensional, cylindrical nanocavity structure with two working electrodes for use in
dopamine sensing using redox cycling. This method of dopamine detection has been an active area of research for many
years, with sensor designs developing to smaller and smaller sizes, as detection limits approach those needed for an in
vivo dopamine detector. Toward that end, the nanocavity structure, based around a field of vertically oriented nanowires,
was conceived, fabricated, and tested for feasibility. Each nanowire serves as one of the working electrodes, while the
second is formed as a semi-enclosing cylindrical shell, with an inter-electrode spacing of .2um.
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