Chemical and biochemical sensing

with silicon nanostructures

Professor Michael J. Sailor

UC San Diego

Dept. of Chemistry and Biochemistry

msailor@ucsd.edu

http://chem-faculty.ucsd.edu/sailor/

OECD Conference on Potential Environmental

Benefits of Nanotechnology:

Fostering Safe Innovation-Led Growth

Paris, France, July 2009

1

Environmental sampling

Samples collected in the field are

transported back to the laboratory for

more detailed analysis. The delay

reduces the effectiveness of

remediation efforts. Santa Margarita Ecological Reserve, Aug 2002

Sensor miniaturization

BAWS III

100 mm

Nature Materials 2002, 1, 39-41.

Miniaturization provides:

Lower cost

Redundancy

Highly distributed devices

At a price:

Lower sensitivity

Lower specificity

There is a great need for functional nanostructures

photonic crystal

microsensor

4

Sensor Networks using Smart DustKris Pister, UCB (1996)

Advantages of wireless

sensor networks:

• Highly distributed, fine

granularity gives faster,

more redundant

response to toxin

release

• Lower cost, smaller

infrastructure

• Readily moved or

reconfigured

Small Sensors-Applications

Wireless sensor networks

• Indoor air quality

• Industrial process monitors

• Environmental monitoring

• Water quality

Volume-constrained environments

• Portable instrumentation

• Gas masks

• On-body chemical hazard monitors

Medical

• In vivo diagnostics

• Point-of-care (blood, saliva, breath)

• Biomedical research

5

Sailor, M. J., “Color Me Sensitive: Amplification and Discrimination in Photonic Silicon

Nanostructures.” ACS Nano 2007, 1, (4), 248-252.

“The promise of nanotechnology is that it can

allow us to design some of the key sample

preparation, processing, and signal conversion

steps directly into the sensor element.”

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Challenges for nanosensors

•Specificity: Identification and amount of a chemical or

biological compound in a complex mixture

•Fouling: Accumulation of impurities leads to degradation of

sensitivity

•Zero Point Drift: From sensor to sensor; from day to day

•Sample collection:

•Air: Need efficient collector or sensor network with fine

granularity

•Water: Bioassays are sample volume limited--need high

sensitivity, need to reject most of the matrix

Sailor, M. J., ACS Nano 2007, 1, (4), 248-252.

7

Etching porous layers in silicon

20 m

Porosity (index) ~ current density

Thickness ~ etch time

Pore size: (1 nm - 1 m) ~ current, [F-]

2Si + 6 HF + 2 h + Si

H

Porous Si Surface

+ H2SiF6 + 2H+ + 1/2 H2

8

Etching porous layers in silicon

20 m

Porosity (index) ~ current density

Thickness ~ etch time

Pore size: (1 nm - 1 m) ~ current, [F-]

0

100

200

300

400

500

600

0 10 20 30 40 50 60 70

Curr

en

t D

ensity,

mA

/cm

2

Time, s

layer 1

layer 2

9

Pepsin-loaded reactor detects

cleavage of -casein

9.10 103

9.12 103

9.14 103

9.16 103

9.18 103

9.20 103

9.22 103

9.24 103

15.90 103

15.92 103

15.94 103

15.96 103

15.98 103

16.00 103

16.02 103

-50.0 0.00 50.0 100 150 200

2nL

, n

m

2nL

, nm

Time, min

Layer 2

Layer 1

Orosco, M. M., et al. Nature Nanotech. 2009, 4, 255 - 2581

10

1-D Photonic Crystals

PARKER, A. R., et al., J. Exper. Biol. 1998 201, 1307-1313.

Calloodes grayanus

2 mm

1 mm

Orosco, Manuel and Oakes, Melanie

Porous Si multilayers

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Modulation of pore dimensionsusing current modulation

2Si + 6 HF + 2 h + Si

H

Porous Si Surface

+ H2SiF6 + 2H+ + 1/2 H2

Silicon

Background: Lehmann, V. Electrochemistry of Silicon

(Wiley-VCH, Weinheim, Germany, 2002).

HF/Ethanol

Pt

AC

Current

TimePorosity

Depth

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Porous photonic crystal sensor

air ethanol

Analyte-induced

color change:• Visual detection

• Sensitive

• Specific?

Sailor, M. J.; Link, J. R. Chem. Commun. 2005, 1375-1383.

13

Porous photonic crystal sensor

Si

SiSi

Si

Si

O

OH

OO

SiSiSi

14

Surface chemistry and nanostructure control infiltration

• Detection of

protease activity in

water, the

environment, and

patient samples

• red shift in 1-D

photonic crystal

spectrum when

enzyme is present

• Presence of protease

is amplified.

• 2 pmol detection limit

45 pmol

23 pmol

0 pmol

1 mm

pepsin

concentration

Orosco, M. M., Pacholski, C., Miskelly, G. M. & Sailor, M. J. Adv.

Mater. 2006,18, 1393-1396.

Protease Biosensor15

“Smart Dust” sensor on an optical fiber16

Films, microparticles, and

nanoparticles of porous Si

2Si + 6 HF + 2 h + Si

H

Porous Si Surface

+ H2SiF6 + 2H+ + 1/2 H2

17

Porous Si microparticles18

Smart Dust:Optical sensors for chemical pollutants

19

“Smart Dust” particles as remote

sensors

Schmedake, T. A.; Cunin, F.; Link, J.

R.; Sailor, M. J. Adv. Mater. 2002, 14,

1270-1272

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Advantages•Highly distributed, rapid

response

•Environmentally degradable

•Low cost

Challenges•Sensitivity

•Specificity

Toxicity: Chemical composition, form, dose, and availability

Hazards of nanotechnology

UW Asbestos Management

Program: Heating/Chilling

Plant Furnace/Boiler

Asbestos (crocidolite): Na2O.Fe2O3

.3FeO.8SiO2.H2O

50 mm

US EPA: Attic Containing

Asbestos-Laden Vermiculite

Insulation

Electron Microscope Image of

Asbestos Fibers

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3 Laws of NanoRobotics*

1. The structure must not self-

replicate

2. The structure must degrade

3. The degradation products must

not be harmful

Are the chemical constituents toxic?

Is it going to end up in the environment?

*apologies to Isaac Asimov

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36

How does Si degrade?

Studies in Simulated Human Plasma. L T Canham, Adv Mater 7, 1033, (1995)

“…thin, high porosity and high surface area mesoporous layers were observed to be completely removed…within a day or so.”

S H C Anderson, H Elliott, D J Wallis, L T Canham, J J Powell. Phys Stat Solidi (a) 197, 331 (2003)

“porous silicon films release Si(OH)4 in aqueous solutions in the physiological pH range…high and very high porosity films showed the greatest dissolution”

Si + O2 SiO2

SiO2 + 2H2O Si(OH)4

Nanostructure determines dissolution rate

subcutaneous

implant in

Guinea pig.

pSiMedica, inc.

0 weeks

4 weeks

12 weeks

Biodegradable silicon quantum dots

Etching in HF

210mA/cm2, 150s

Lift-off

Ultrasonic fracture H2O, 24h

Si substrate (P++) Porous Si Free-standing film

Microparticles

Filtering

200nm pores

Nanoparticles

Activation

Luminescent

Nanoparticles

Park, J.-H. et al. Nature Mater. 2009, 8, 331-336.

•Si nanoparticles injected via tail vein

•Localize to MDA-MB-435 tumor

•Fluoresce @ 850 nm

•Degrade and clear in 3 d

In vivo degradation of porous Si

nanoparticles

Color map of fluorescence intensity @ 850 nm

Park, J.-H. et al. Nature Mater. 2009, 8, 331-336.

Conclusions

•Silicon electrochemistry provides

programmed nanostructures with built-in

sample and signal processing features

•Nanotechnology can enable higher fidelity,

smaller and lower cost microsensors

•Silicon and silica nanostructures can be

degraded in the environmentally (or in

vivo)

•Degradable nanomaterials are needed

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Michael J. Sailor, Department of Chemistry and Biochemistry

Funding: NSF, NIH, NIOSH, Hitachi Chemical Research

Center, Elintrix, Cellular Bioengineering, inc.

AcknowledgementsCoworkers:

Manuel Orosco, Claudia Pacholski, Anne Ruminski, Brian King, Jamie Link,

Luo Gu, Thomas Schmedake, Elizabeth Wu

Collaborators:

Dr. Jay Snyder, NIOSH

Prof. Sangeeta N. Bhatia, Geoff von Maltzahn (MIT Bioengineering)

Prof. Erkki Ruoslahti (Burnham Institute at UCSB)

Dr. Frederique Cunin, Prof. Jean-Marie Devoisselle (CNRS Montpellier, FR)Prof. Gordon Miskelly, Corrina Thompson (University of Auckland, NZ)

Prof. Yukio H. Ogata, T. Sakka, M.S. Salem (Kyoto University)

Dr. William Freeman, Dr. Lingyun Cheng (UCSD Jacobs Retina Center)

Prof. Kenneth Vecchio (UCSD Nanoengineering)

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