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, 29634guigen@clemson.edu