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Guigen Zhang, Ph.D.
Bioengineering, Electrical & Computer EngineeringInstitute for Biological Interfaces of Engineering
Clemson UniversityClemson, SC, USA
OECD Conference on Potential Environmental Benefits of nanotechnology: Fostering Safe Innovation Led GrowthJuly 15-17, 2009, Paris, France
Introduction The need to bridge the nano world to the real world
Bridging the two worlds through the world of micro technologies
Integrated micro/nano structures as electrodes for electron transfer devices
Example applications: bioconversion and remediation
Future perspectives
Bridging the Nano World to the Real World Nanotechnology is now at a crossroad in terms of being
relevant, or bringing tangible benefits, to the real world we live in.
One of the major players in the world of nanotechnology thus far is nano particles, and they have brought mixed results in terms of benefits and consequences.
The need for bridging the nano world to the real world without causing unintended consequences is urgent.
Linking the Nano and Micro Worlds Since our daily life is surrounded by micro technologies,
our approach to integrating the nano and real worlds is through the ubiquitous micro world.
Technological niche: 3D skyscraper nanopillar structures with microfabrication processability
A network of connected micro dots
A pair of interdigitated electrodes
Zoom-in view
Zoom-in view
Zoom-in view
Close-up top view
Close-up
side view
Lesson from Gecko’s feet To increase the surface area; not just the end area,
the side area too
Physiology of Gecko’s feet Lamellae: rows of setae
Setae: micro-bundles (100 μm / 5 μm ) of nano-spatulae
Spatulae: nano-fibers (200 nm) with spatula heads
We use this lesson for a different purpose High surface area for interfacing and
electron-transfer purposes, instead of, for dry adhesives
Why 3D Nanopillar Structures
SEM images by Kellar Autumn & Ed Florance
Potential (mV vs Ag/AgCl)
-0.5 0.0 0.5 1.0 1.5
Curr
ent
( A
)
-2500
-2000
-1500
-1000
-500
0
500
1000
Flat electrode (RF=1)
Nano A (RF=20.0)
Nano B (RF=38.8)
Nano C (RF=63.4)
A B C
Nanostructures possess high surface area with respect to their volume. Of all the nanostructures, vertically aligned nanopillars offer a higher surface area at a fixed footprint area (in a “skyscraper” metaphor)
Substrates with 3D Skyscraper Nanopillars
For r = 150 nm, h = 6 μm and p = 75%:
75.60)2
1(/ 0 pr
hSS
22 3/2 arp
)2
33/()63(/ 22
0 arhrSS
ha rr
0S
%91,2/ par
Many Dry 3D Nanostructures Look Great3D nanostructures made by a dry vapor method (PVD, CVD, etc.)
3D nanostructures made by an aqueous ECD method
EDL 3)(
The flexure rigidity of these nanopillars can be adjusted by tuning their aspect ratio
Aspect ratio < 20
Aspect ratio >25
Use of 3D Skyscraper Nanostructures
EDL 3)(
Aspect ratio < 20
Aspect ratio >25
Photovoltaics, Javey et al., 2009
Energy Storage, Dunnn et al., 2008
SERS Substrates, Moskovits et al., 2006
Zhang et al., USPTO patent application No. 12,232,152, 2008; No. 12,382,860, 2009. Zhang et al., USPTO patent application No. 12,382,861, 2009.
Food and water safety and bio-security
Benefits of Integrated Micro/Nano Structures Robust structures with microfabrication processability Both the nano and micro scale features can be tailored Large surface area for interfacing and electron-transfer purposes Ease of implementation and ease of integration with the real world Posing no harm to human health and the environment Cost-effective structures and endless applications
Microtubule
Microtubule
Actin
Actin
Cells on a flat substrate
Cells on a 3D nanopillar substrate
A PC12 cell on a 3D nanopillar substrate
Beyond the Physical World: Interfacing with the biological world
3D Electrodes in Electron Transfer Devices
Gluconic_acid
+ 2H+ + 2e-
Glucose
CatE WE
CatE: catalytic electrodes; WE: working electrodes
Electrolyte Gold Platinum
4e4H2H 2
4H+ 2H2
4e-
Porous nanotube
An electron transfer device is one in which electron exchanges occur at the surface of its electrodes
Almost all chemical reactions involve electron transfer, thus all energy conversion, biomass process and sensing phenomena require certain types of electron transfer devices
3D electrodes add a new dimension to these devices
Zhang et al., USPTO patent application No. 12,232,152, 2008; No. 12,382,860, 2009. Zhang et al., USPTO patent application No. 12,382,861, 2009.
Example Applications Monitoring the bioconversion processes
Meeting the need for real-time measurement of carbon energy source in various bioprocesses
Biomass conversion for renewable energy sources
Fermentation bioprocess for value added bioproducts
Remediation of volatile organic compounds (VOCs)
Cost-effective catalysts for oxidizing VOCs in the environment from agricultural processes
Monitoring the Bioconversion Processes A robust sensor for glucose, the most widely used carbon
source, that will operate for the length of a bioprocess without failing or losing accuracy is not available
What is needed for many bioprocesses is a sensor with a wide detection range (~ 0–20 g/L), which a typical diabetic glucose sensor having a narrow detection range of 0.40–2.50 g/L, cannot provide
Ideally, a real time on-line (probe inserted into the reactor) measurement of glucose is necessary
Functionalization of 3D Nano Electrodes As sensing electrodes, these inorganic nanostructures have
to be functionalized for biological interaction purposes
Self assembled monolayer (SAM) of alkanethiols offer easy formation of well ordered and stable molecules for anchoring the enzyme – glucose oxidase (GOx) – for catalyzing the desired reactions
Short chain: 3-mercaptopropionic acid (MPA):
HS-(CH2)2-COOH
Long chain: 11-mercaptoundecanoic acid (MUA):
HS-(CH2)10-COOH
SAM formation and characterization 3D electrodes placed in ethanol containing 10 mM of MPA or MUA Voltammetric measurements: from -0.2 to 0.6 V at 100 mV/s Impedance measurements: from 0.1 Hz to 100 KHz, 0.1 M PBS pH7, 2 mM
Fe(CN)63-/4- (ferri : ferro = 1 : 1)
Percent defect in the SAM molecules Reduction peak associated with the uncovered area CV in 0.1 M H2SO4, from -0.5 to 1.5 V at 100 mV/s
Surface coverage of the SAM molecules Г=Q/nFA , Q=total charge, n=1, F=96485 C/mol, A=0.04 cm2
CV in 0.1 M NaOH, from -1.6 to -0.2 V at 100 mV/s
Immobilization of glucose oxidase Activating the carboxyl group in the SAMs
The electrodes placed in 0.1 M PBS containing 1 mg/mL of the GOx with constant stirring for 2 hours
Functionalization: SAM + GOx
O
HO
SAu
O
O
SAu
O
O
N
EDC/NHS H2N-AVIDIN
O
HN
SAu
AVIDINE
Au
MUA
O
HN
SAu
BIOTIN
BIOTIN
Au
(gold nanorods)
O
HO
SAu
O
O
SAu
O
O
N
EDC/NHS H2N-AVIDIN
O
HN
SAu
AVIDINE
Au
MUA
O
HN
SAu
BIOTIN
BIOTIN
Au
(gold nanorods)
Impedance Results
Potential (V vs. Ag/AgCl)
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8
Cu
rren
t (
A)
-150
-100
-50
0
50
100
150
200
Bare
MPA
MUA
A
|Z'| (k
0 10 20 30 40 50 60 70
|Z''|
(k
0
20
40
60
80
MPA
MUA|Z'| (k)
0 1 2 3 4 5 6 7
|Z''|
(k
)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Bare
MPA
B
Electrodes Rs (ohm) Ret (ohm)
Bare 227.0 (2.0%) 589.5 (5.0%)
MPA 256.6 (0.9%) 6281.0 (1.7%)
MUA 229.0 (1.0%) 209370 (4.3%)
The resolved Rs and Ret values based on the Randles circuit (fitting errors given in parentheses)
Potential (V vs. Ag/AgCl)
-0.5 0.0 0.5 1.0 1.5
Cu
rren
t (
A)
-1200
-1000
-800
-600
-400
-200
0
200
400
600
800
1000
Bare
MPA
MUA
A
Voltage (V vs. Ag/AgCl)
-1.8 -1.6 -1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0
Cu
rren
t (
A)
-800
-600
-400
-200
0
200
Bare
MPA
MUA
SAM desorption peaks
B
A: CV for the 3D electrodes in 0.1 M H2SO4
Au-oxide reduction peak at 0.78 V From bare nano/flat, roughness ratio: RR = 45
B: CV for the 3D electrodes in 0.1 M NaOH Au-S bond cleavage for alkanethiols
From -0.6 to -0.9 V for n=2 to 6 From -1.o to -1.2 V for n=11 to 18.
Г=Q/nFA , Q=total charge, n=1, F=96485 C/mol, A=0.04 cm2
Cyclic Voltammetry (CV) Results
Time (s)
0 200 400 600 800
Cu
rre
nt
(A
)
0.5
1.0
1.5
2.0
2.5
3.0
MPA
MUA
2.5 ml
Concentration (mM)
2 4 6 8 10 12 14
Cu
rren
t (
A)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
MUA
MPA
y = 0.1072x - 0.01430
y = 0.003633x + 0.01232
Glucose Detection Results
Detection Sensitivity(μAmM-1cm-2)
Nano(RR=45)
Flat(RR=1)
MPA 2.68 0.47
MUA 0.09 0.052
For nanopillar electrodes, the longer MUA SAM produced a higher electron transfer resistance and lower percent defect than the shorter MPA SAM, but the shorter MPA SAM led to higher sensitivity in glucose detection than the longer MUA SAM.
Potential (mV vs Ag/AgCl)
-0.5 0.0 0.5 1.0 1.5
Cu
rre
nt
( A
)
-2500
-2000
-1500
-1000
-500
0
500
1000
Flat electrode (RF=1)
Nano A (RF=20.0)
Nano B (RF=38.8)
Nano C (RF=63.4)
A B C
Concentration (mM)
0 2 4 6 8 10 12 14 16
Cu
rre
nt
( A
0
1
2
3
4
5
6
Flat Electrode
Nano A
Nano B
Nano C
R2=0.998
R2=0.996
R2=0.996
R2=0.990
B
Surface Area / Sensitivity Comparison Although these nanopillars increase the electrode surface area, their
close proximity limits the electrical current enhancement due to overlap of the diffusion fields of individual nanopillars, or the diffusion limit
Surface area increase: ~ 60-fold Sensitivity increase: ~ 12-fold (nano C: 3.13 μAmM-1cm-2, Flat: 0.26 μAmM-1cm-2)
A micro fluidic sensor with a four-electrode electrochemical setup
Each inlaid electrode is incorporated with 3D skyscraper nanopillars
The enzyme electrode catalyzes the oxidation of glucose and the working electrode collects electrons resulting from the glucose oxidation.
A New Sensing Paradigm:Adding convection to diffusion
y = 35.960x + 23.681R² = 0.984
0
20
40
60
80
100
120
0 1 2 3
Lim
itin
g C
urr
en
t (µ
A/c
m2)
Glucose Concentration (mM)
InletOutlet
1 2 3 4
Micro fluidic device
Electrodes: 1 – reference, 2 – counter3 – working, 4 - enzyme
A sensor with 2D electrodes Sensitivity value of 7.5 μAmM-1cm-2
Km= 11.7 mMA sensor with 3D electrodes
Sensitivity value of 35.9 μAmM-1cm-2
Km= 1.035 mM
2e-
Glucose
Gluconic_acid
+ 2H+ +
CatE WE
CatE: catalytic electrodes; WE: working electrodes
-300
-200
-100
0
100
200
-400 -200 0 200 400 600 800 1000 1200 1400
Potential/V
Cu
rren
t/10
-6A
Platinum oxide reduction Au oxide
reduction
Hydrogen desorption
Hydrogen adsorption
A
B
-400
-300
-200
-100
0
100
200
300
400
-400 -200 0 200 400 600 800 1000 1200 1400
Potential (mV)
Cu
rre
nt
(10
-6A
)
Pt-oxidePt-oxide Au-oxide
Au-oxide
2H2O+2e->H2+2OH-
Time (sec)
0 100 200 300 400 500
Curr
ent (n
A)
0
200
400
600
800
2.5 mM
Concentration (mM)
0 4 8 12 16 20 24
Curr
ent
(nA
)
0
200
400
600
800
1000y = 38.036x + 62.924
R2 = 0.9915
pH Value2 4 6 8 10
Curr
ent
( A
)
0
2
4
6
8
10
12
Inset-1
Inset-2
Making the Sensor Long-lasting: Going Nonenzymatic Gold surfaces (nanoscale) are catalytically active for directly oxidizing glucose
without using an enzyme Platinum coating can further increase the catalytic activity
Au nanopillarsPt coated Au nanopillars
Remediation of VOCs
Fuel
combustion
6%
On-Road
Vehicle
28%
Non-road
vehicles
16%
Miscellaneous
5%
Industrial
Processes
45%
- Petrochemicals - Semiconductors- Paints and cleaners- Wastewater- Animal husbandry
-Poultry Rendering
Data from Federal Highway Administration, USDOT, 2002
Industrial operations are major contributors of volatile organic compounds (VOCs)
Grinding Cooking
Processing ofcooked meat
Off gastreatment
Byproducts
Fertilizers, protein complexes
Feathers, bones, gut, etc.
www. Storkfoodsystems.com
Odorous VOCs150°C, 300 kPa
Poultry Rendering Generates Odorous VOCs
Current Remediation Method:Catalytic oxidation of VOCs using activated carbon
W
Xy
RT
PQr
C
CCX
T
inlet
outletinlet
0
%100
-Differential reactor -Isothermal (25ºC)-Isobaric (1 atm)-Constant flow (6 LPM)-Measured X-Calculated rate of oxidation
15’’
Active carbon:- Inexpensive and renewable- Known to posses catalytic properties- High surface area (500-1500 m2/g)
VOC: Propanal- Straight chain aldehyde:- Odorous- Recalcitrant
Oxidant: Ozone
Removal of Propanal by Activated Carbon
Propanal concentration (ppmv)
40 60 80 100 120 140 160 180 200 220
r pro
pa
nal
(x 1
09 m
ol/
g-s
)50
100
150
200
250
300
350
R2 = 0.97
6 LPM, 1500 ppmv ozone, 2 g active carbon
Improving the Activity of AC:Iron Modified Activated Carbon
Propanal concentration (ppmv)
0 50 100 150 200
-rp
rop
an
al (x
10
9o
l/g
-s)
0
50
100
150
200
250
300
350
Active carbon (control)
AC + ozone + iron + DIW
AC + iron + acetone
AC + iron +DIW
6 LPM, 1500 ppmv ozone, 2 g catalysts, 25°C
Iron oxide on AC in acetone Iron oxide on AC (ozone treated)
AC (original) Iron oxide on AC in DI water
Electrodeposition of Cobalt and Nickel nano structures onto activated carbon
Cobalt: Bath: 5 mM CoSO4, 0.1 M Na2SO4 and 0.1 M boric acid
adjusted to a pH of 5.0
Voltage: 1.6V, 4 min @ 25°C
Nickel: Bath: NiSO4. 6 H2O (300 g/L), NiCl2. 6 H2O (45 g/L), and
boric acid (40 g/L), pH of 4.8
2 amps/dm2 for 10 min @ 80°C
Calcined @ 300°C for 1-hr
Improving the Activity of AC:Nano Structure Modified Activated Carbon
SEM-EDS CharacterizationQuantitative results
Weig
ht%
0
20
40
60
80
100
Fe Co Cu Au
Quantitative results
Weig
ht%
0
10
20
30
40
50
60
O Cl Ni Ta Au
Cobalt and Nickel Modified Activated Carbon
Propanal concentration (ppmv)
0 50 100 150 200 250 300
-rp
rop
an
al
(x1
09 m
ol/
g-s
)
0
100
200
300
400
500
AC (control)
Nickel on ACElectrochemical
Cobalt on ACElectrochemical
Iron on ACDry impregnation
6 LPM, 1500 ppmv ozone, 25°C
The endless utilities of the 3D integrated micro/nano structures have yet to be explored
Further manipulation of sizes, dimensions and spacing of nanopillars for enhanced surface area and unique surface (catalytic) activities
Novel nano-structuring and nano-engineering for highly efficient electron-transfer properties (bioconversion processes and biological sensors) and non-electron-transfer properties (energy storage)
Scale-up production for even more cost-effective mass productions
Because of their metallic nature, they can be easily recycled and reused, thus posing no harms or new adverse effects to human health and the environment
Future Perspectives
Invention is not innovation
Invention is a technical
Innovation is technical, social and economic
To generate economic growth, the technological advancement has to meet a social need
Don’t search for applications for nanotechnologies
Search and research nanotechnologies for answers to our social (health, environmental, economic, etc.) problems
Innovation and Economic Development
Acknowledgement National Science Foundation
Department of Biological and Agricultural Engineering, University of Georgia
Institute for Biological Interfaces of Engineering, Clemson University
Kolar P, Anandan V, Gangadharan R, Jayaraju N, Rao Y, Yang X and Haq F
Thank You.For more information, please contact: Guigen Zhang, Professor of BioengineeringClemson University, Clemson, SC, [email protected]