Thank you Paul thanks for the opportunity
to speak here today about my research

going to discuss the projects in some
detail one is regarding using nano belts

assembly to manufacturing and the other
one is an amino acid which we're trying

to miniaturize into a microfluidic
I have a microphone here but

maybe it is it switched on.

OK.

This is a picture of my research group and
the work I'm going to talk about this

morning is that of Ph D. candidates in my
group as paying who's done the work on

the bio sensor and
who is working on the nano devices

outline after introduction
the motivation for

this work like to describe the use
of dielectric grease is for

assembly of nano Why is onto substrates
this is a way to take advantage of some of

the fantastic properties available with
nano scale materials and it has mechanical

properties electrical properties or
biosensor related properties.

How do you put these materials on to
substrates to make useful devices where

using dielectric for a system which we can
generate and used in the material and then

an attractive force to a set of electrodes
on a substrate we've been studying by

simulation with a finite element modeling
package the generated on the particles or

the Nano will as a function of
the properties and the surrounding fluid.

Then I'll talk about a magnetic beat I'm
you know I say this is a collaboration

with Kathy Keller at the C.D.C. and

here we'd like to miniaturize
an existing side up.

You know what I say and
put it into a microfluidic format so

she's providing the antibodies
from an existing assets.

And then we're attaching them to magnetic
dates which we can introduce into

a microfluidic platform for
the Beat capture and

experimental results for
the bias sensor response.

Well the motivation for carrying out

this is to take advantage of some of
these new materials like carbon and.

They can be used for
actuated novel sensors and

even for high density interconnects we can
take advantage of these materials that

often synthesised at high temperatures
by chemical they put that position.

So unless you use a seeding
method to direct the growth

exactly where you'd like to form the Nano.

Then we need to look at ways to
assemble them onto a substrate.

So in this work.

We're using a set of electrodes either
platinum defined on a substrate and

then the electric field generates and
used in the Nano and

that dipole is used for
assembly onto the substrate.

Let me briefly describe the principle
of dielectric for a service.

This is based on the electric
field generated within the medium.

We have and you'll notice that
the asymmetric So one has a smaller

radius of curvature this generates
a field gradient which induces a dipole

in the particle because of this asymmetry
there's a net attractive force from

the particle to the electrode so we can
take advantage of this to pull the wire or

the nanoparticle towards the electrode
this depends on the difference between

the dielectric properties of the particle
and those of the surrounding medium.

So in some cases you can get negative.

Which would be a repulsive force would
push the particle away from the electrode.

In fact if the dielectric properties
are a function of frequency if we

had a dispersion relation.

Then we would see different behavior
different excitation frequencies to

actually one example where this work has
been quite successful is sorting out cells

with different properties
which in a biological sample.

The dielectric force can be
calculated using a dipole

approximation in this case we want to
replace the particle with the equivalent.

In the medium remove the particle it
had we calculate the electric field and

take the product to the field in
the field gradient using the a factor for

the magnitude of the dipoles that's
indicated here the closest must study fact

to be Kate's then the magnitude of
this induced dipole as a function

of the dialect properties of the particle
and those of the surrounding fluid for

a nano belt which is a larger

dimension we expected to extend through
a region electric field gradient so

dipole approximation may not be accurate
in predicting the attractive force.

So we're using a Maxwell stress tensor you
can think of this like a if you inflating

it plating a balloon and the balloon
is in an electric field gradient.

There's a stress a force on the surface of
the balloon and this will generate both

a took a net and
a net force that can then push the object.

The advantage of using Maxwell
stressed tensor is that it

doesn't depend on any assumptions
about the field gradient or

the dimension of the object
to the electrode gap.

So with the Finite Element modeling
package we're able to calculate

the electric fields and feel gradients and

then evaluate the Maxwell stress
tensor integrate over the surface

of the particle or the Nano wire and
then that will give us the.

Forces acting on the particle.

Well the first thing to do is to indicate
what kind of belts we're working with they

were very grateful for his a professor
in the Materials Science and

Engineering Department to access
to novel nanomaterials including.

The tin oxide nano belts a single crystal
material synthesized high temperature and

tin oxide is a well known any type
Semiconductor which is being very

widely applied to gas sensing and

so one of the things we've done with these
nano belts once they are assembled onto

an electrode is measure the conduct of it
as a function of the exposure to different

reducing gases like we can measure
ammonia down a ppm level concentrations.

But other nanomaterials are being
synthesize with very exciting properties

including zinc oxide which
is a electric material.

So you can use that as a actuator
has published some very innovative

looking work in using these materials for
nano electric generators.

So let me briefly describe how
the simulation takes place with com So

this is a schematic diagram indicating
the Jumma tree for the electrodes so

these regions are conductive
electrodes on an insulating substrate.

And this is a circle part
of one micron in diameter

with different dielectric properties
to the surrounding medium.

So the first thing that we'd like to do is
compare the generated on this particle as

a function of the frequency and
dielectric properties of the particle and

see if this is in agreement with a dipole
approximation compare the Maxwell stressed

calculation to the dipole
approximation calculation.

I should point out that the X.
axis runs in this direction.

So when we get a positive force in the X.

direction that would represent
a potion from the electrode.

Negative force would represent
attraction to the electrode.

Is a comparison indicating
the dipole dipole electric

generated as a function of frequency
in Hertz and particle convertibility

meter and you can see there's good
agreement between the dipole approximation

replacing the particle with the equivalent
of the force and the Maxwell

stress tensor where we've integrated
the force over the area of the particle.

So Maxwell stressed and so
looks like a good method for

calculating the forces
on these small objects.

I now let's look at the belt behavior
similar electrode dimensions and

then a belt extends over a region
of the electric field gradient.

So we need to then integrate over this
region to find the net force generated

on this surface and you notice
there's a shell so rounding this belt.

So the shell allowed us to
do a differential meshing So

we have a very tight mesh over the net
about it's only two hundred nanometers

in thickness compared to the spacing
which is twenty microns.

And then we can have a through
the volume of this analysis.

This simulation is carried out with a P.C.

computer in the lab a thirty two bit
something like a four gig of memory and

this shows you the convergence
of the calculation.

Basically as a function of time as we go
through different values of conduct for

the Nobel So we initially we converge and
we use that solution.

As the initial condition for
the subsequent calculations so

each time we change the kind of to Vittie
we use that as a new initial condition to

the next iteration to
calculate the Maxwell stress.

Then on the net as a function of the
convertibility of the of the Nano belt.

The conative of T.V.
varied over this range and

we picked this range based on covering
both Belconnen tippity a turn oxide and

connectivity measurements
made on our belts.

When they've been captured onto
a set of four electrodes so

we can make a four point probe type
electrical conduit conduction measurement.

This is the primitivity from
the literature and then the conative of

the ethanol and then the tutti we can
you measure the ethanol connotative T.

using a solar Tron impedance analyzer.

And this shows the dialect of
Fred Explorer generated on the nano belt

where the Belconnen to the T.
is greater than the conative a to happen.

And so here we see a negative force
in the X. direction so that then

represents an attractive Director Freeh
says would then a belt to the electrode.

And as we go up in frequency because of
the change in the dielectric properties of

the particle we see that the force is
changing one hundred killer Hood's.

Now it is attractive force
is very interesting and

useful but actually in the experiments
what we find is the Nano belt

is repaired old at low frequencies but
attracted at the higher frequency range.

So it's something different then
we've estimated in this model.

So let's make a kind of two prettier than
that a belt less then the conduct of a T.

The ethanol and he we see again the force
is in the X. Y. Z. direction and

total magnitude of the force the force
in the X. direction is now positive.

So this represents then repulsion

from the electrode which is in agreement
with what we see in the experiment.

So we think that the continuity
that we measure on the nano why or

the current If you can measure on that.

Why when it's dry for
the first calculation.

There's not as to make
correctly the force generator.

Whereas when the Nano belt is in the
ethanol solution we see a change in for

us that represents the kind of typically
the night a belt is different.

Has been modified by putting
the belt into the ethanol solution.

So in effect we could make and

then a belt which is sensitive to the
concentration of ethanol in the medium.

Well this computer model is
quite powerful and very useful.

I'm just showing you some of the data
we can see the stress tends to

is calculated over the volume
over the surface of the belt and

you can see the maximum force is ten so
forces are generated close

to the end of the structure not very much
force is generated in the center and

so this is a region where we
have a larger field gradient.

In addition to the attractive force
we have a look which would rotate and

align the known about to the electrode.

And this shows the torque on the nano
belt where the Nobel kind of put it he

is again less than the ethanol connotative
so we can get talk about the X.

axis which would rotate it would
rotate it relative to the picture I

showed you in the previous slide to
align it actually with the electrodes.

So we get a lot of useful information.

In fact we could think about
animating this procedure so

that once we've calculated
the force on then a belt.

We could move against that was
because forces of the fluid.

Then we could re calculate the force for

the new location when we get
the trajectory then about vs time as it's

attracted thru the field
gradient towards the electrode.

Well the graduate student working on this
once and some point to finish his Ph D.

So we have to get off the modeling
simulation at some point but

he's been able to demonstrate
these interesting the havior

in terms of the attractive
force generated at the hive.

And the repulsive force generated at low
frequency where we see the Nano Bell

connectivities being modified by the
presence of the ethanol in the surrounding

medium one I'd like to go out and

talk about collaboration with
Kathy Keller at the C.D.C.

We're interested in making
a microfluidic format on a chip

is to be extremely useful and could be
generally applied to many different asset.

In particular.

She's interested in carrying out acids
would be relevant to every infection so

we could look at the breath condensate and
identify cytokines in the breath.

So this is taking an existing
antibody antigen.

Which are using an enzymatic label and
color metric detection and

a standardized system.

Except we're putting our primary antibody
onto a pad Magnetic the magnetic bead

to attract the antibody antigen complex
close to the detecting electrodes so

as to ways of enhancing the performance
of this type of sensor is

by manipulating the primary antibody on
a magnetic beads so we can distribute

it through the sample and then bring it
close to the detecting electrodes and

the second issue is taking advantage of
the enzyme label on the secondary antibody

So we have the cytokine present
we form the complex and

by minimizing this role where
the measurement is made.

We can enhance the local concentration
close to the detecting electrodes

in this case we're using
electro chemical detection.

So the end sematic substrate has to
be if we docs active molecule and

this redux active molecule can undergo
cycling by having a pair of electrodes

a generator and collector electrodes so we
can get additional metric signal generated

as the enzyme generates the product
the enzyme is beta collect Also days.

The power of magnetic beads
commercially available from

one micron in diameter and
they have functionalized it in so

we can attach the primary antibody
without it in by a binding.

I mean just a few words about
the electric Himachal detection electro

electro chemical detection
requires of course.

Well control conditions
clean clean electrodes and

a control of the PH in the solution.

And we needed electro active product
generated by the end sematic reaction.

Well we can oxidize this product and
produce a but

by adding an additional generator
electrode we can reduce it again and

providing these electrodes are close
together we can get regeneration of

the magic generated label.

So this is being studied in
some detail actually the early

work was also carried out by Bill
Heinemann at the University of Cincinnati.

So taking advantage of
his initial measurements

with these types of electrodes
by minimizing the electrode gap.

You can see that we can increase the
diffusion limited current and by scaling

down the dimensions of the electrodes
then into the nano scale we can increase

the diffusion limited current and thereby
the limit of detection for the system.

So that's a great advantage
of working here Georgia Tech.

We had access to electron beam
with obviously facility and

in my collect Tronics Research Center.

So we're able to build
electrodes with two hundred four

hundred eight hundred
nanometers spacing and

look at the cycling advantages as
a function of electro geometry.

Let me just show you briefly
a comparison I think this is for

a one micron electrode for
cyanide solution.

This is real time.

Gram measured without recycling and
then when we turn on the counter

electrode we can see additional hand
spent in the diffusion limited.

So that will lower a minimum
limit limit of detection for

the system by enhancing the signal to
noise ratio and other words in the system.

Well the Redux molecule has to
be reversible also Day generates

a lot feed all and this can be oxidized.

And then this is reversible some
reversible under the right ph conditions.

So we can take advantage of this for

the detection and
substrate then for the enzyme.

Why mention we use a magnetic The to
bring the label material close to

the electrode and
Graham just indicates the advantage of

concentration that can be
carried out with a magnetic beat

here if the labeled antibody is
distributed through the solution.

The measurement would depend on diffusion
to the interface which would be

a signal then if the magnetic
field labeled material

close to the detecting electrodes and then
we just had to fusion of some of the ends

of matter product away from the interface
which may decrease our signal.

So the magnetic forces
generated on the beat can be

calculated based on the magnetic
field intensity and

the gradient of the magnetization of
the beads these commercial beads actually

a soft magnetic material ferrite
embedded within the be would it

would be interesting also to study other
magnetic materials that are large and

magnetic moments that you could generate
so to capture the beads at the surface.

We've used a set of soft
magnetic electrodes

combined with the platinum electrodes.

Detection.

So this again is using common sense to
model a magnetic field intensity close to

the electrode surface
the substrate magnet is behind

generating magnetic field that magnetizes
the soft magnetic nickel ion and

this nickel I am kind
of focus is the field.

So if we look at the field intensity as a
function of distance into the microfluidic

channel going up to four and
eight micro meters above the electrode or

a we can see a larger field
gradient is generated

with the presence of these nickel features
and so these field gradients would

generate the force to trap
the particles close to the electrode.

So can we arrange the Nicholai and

features to locally attract
the particles to labor particles

closer tech to electrodes and
therefore enhance the signal.

Well let me briefly describe
the fabrication for this chip

as I mentioned we're using electron
beam to define both the nickel features

and the platinum electrodes and
so process is carried

out in the sea clean room to define the
nickel eye on a satellite medical layer.

We have an insulating silicon dioxide or

we've also used the technique for
insulation and thin.

Insulation layer and then electron beam
authority to define with lift off.

We lift the photo resist off the substrate
the platinum electrode features.

So these can be in the two hundred four
hundred eight hundred nanometers scale

dimensions.

Now of course we don't want to nickel
iron to be in contact with a solution

that would just generate corrosion.

So the oxide film is protecting the nickel
and features these these things here and

then the platinum electrodes
need to be exposed.

So we can carry out the electric
chemical measurements.

I think these are for
eight hundred ninety to electrodes.

And electrodes introduced into the.

Into the microfluidic system.

There's a P.B.S.
soft molded channel to inject with

the magnetic beads we can place the magnet
here generate the fuel gradient

trap the magnetic particles
with the enzyme label and

then measure the current from the Into
did you take it directly in addition we

need a silver chloride reference electrode
and an exit for the electro chemical

measurements and this is a picture
showing the showing the device electrical

wiring his the his and
his an electrode array.

This is actually a larger dimensional
array in this in this particular picture.

But here the result trapping the particles
act to the nickel ion features

I can see that this magnetic field
gradient has really enhanced capture of

the particles relative to
placement on the oxide surface

in earlier measurements we really had
a random arrangement of particles So

here we've been able to enhance close to
the detecting electrodes which is really

the objective to measure
the enzyme particles and

here is an arrangement where
the soft magnetic features

scanning electron microscope pictures
show you then the details of

the substrate the nickel ion features
underneath the platinum electrodes and

here the nickel line features
of the platinum electrodes

have been captured by the nickel and
features.

Now we ideally like to trap future and
not have them on top of the platinum

electrodes where they could block
some of the diffusion limited current

We need to measure and see that
localized field gradients has helped.

To capture these particles into way and

we can measure the signal from
the paint this is just injecting

P A P A different situations without
the president presence of the enzyme So

we have an increased current as a function
of the concentration of the P.H.P.

And then finally injecting the particles
with the bay to collect also the label so

there's no antibody engine complex in
this but I meant I can see that we get

a signal from the generator and
which are complementary and

we have a signal plotted in that I am for
this is where we have

a large increase in signal as a function
of the number of beads present So

this with respond to the amount of
labor material present in the ass.

This is fifteen hundred be
read increase with time and

or seven hundred fifty measuring
not the diffusion limited but

the rate of increase in current with time
that indicates how much of the enzyme

we have present because we have an
oversupply of the ends of magic substrate.

So I think this is a very promising
direction to explore study

studying this for his Ph D. research
both in terms of examining the electrode

spacing in the Redux cycling
the what level this can be used on

to the electrode ray to get good
placement and avoid any electrode.

Now ultimately you'd like to multiplexes
to make it really useful I mentioned to

but we have antibodies for six and eight.

So we really are building arrays of three
measurement electrodes in a channel.

So we can get a multiplexed system and
this we're

doing this work actually in collaboration
with Joseph multiplexing aspect.

So I like to acknowledge the faculty and
students.

We were involved in this research
in the dielectric free source work.

Wang has supplied material
not to gallivant has assisted

in the in the visualization
of the nanowires assembly

work with a behind him and
at the University of Cincinnati.

I'd like to thank for
assistance at the University of Georgia

in the Agricultural Engineering Kathy
Keller of course and Paul Joseph for

his help and support the clean
room has been really crucial

to making all of these devices and
financial support has come from

both the fellowships and
some seed grants from the C.D.C..