Chemical and biochemical sensing with silicon nanostructures Professor Michael J. Sailor UC San Diego Dept. of Chemistry and Biochemistry [email protected]http://chem-faculty.ucsd.edu/sailor/ OECD Conference on Potential Environmental Benefits of Nanotechnology: Fostering Safe Innovation-Led Growth Paris, France, July 2009 1
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Chemical and biochemical sensing with silicon nanostructures
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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
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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.
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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
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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
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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
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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.
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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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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)