Detecting Danger at Nanoscale

Detecting Danger at Nanoscale
Organic Nanowires for Trace Vapor Sensing of Explosives and Other Threatening Chemicals
Organic Semiconductor: competitive for silicon
nanodevices, optoelectronic sensors, lasers, etc.
1D self-assembly through molecular π−π stacking
Ideal sensor for vapor detection
• High sensitivity or low detection limit: stand-off detection (>
50 m, ideally 100 m), trace TNT (40 ppt) over buried
landmines.
• Fast response: seconds, porous structure and continuous
channel both enhancing the penetration of gaseous molecules
into the film, strong chemical interaction (sticking) at interface
improving the accumulation of target molecules within the
film.
• Stability: thermal damage, photobleaching, thick film desired
for improved stability, sustainability, reliability and
reproducibility.
• Selectivity: against environment interferences.
• Cost effective: cheap for materials and processing, flexible for
materials modification and improvement, adaptable to
various substrates for device fabrication --- all can be satisfied
with organic materials.
Accounts of Chemical Research, 41 (2008) 1596-1608.
Electron delocalization
leads to a sensor for
reducing reagents
Efficient fluorescence sensing of explosives vapor
Selectivity against ambient interference
Enhanced
sensitivity
Potential Interference from Cosmetics (10 s exposed to sat. vapor)
1. TNT (5 ppb); 2. Pantene Pro-V Mousse; 3. Loreal Studioline Hair Spray;
4. Head&Shoulders 2 in1 shampoo; 5. Pond's dry skin cream;
6. Olay UV moisturizing lotion; 7. Neutrogena men face lotion SPF 20;
8. Colgate Total toothpaste; 9. Chanel Allure perfume;
10. Fendi Theorema perfume.
Before exposure
After exposure
100
TNT (5 ppb)
Materials covering both n-type and p-type:
• n-type: electron accepting  sensing for
reductive (e-donating) molecules, e.g., amines.
• p-type: electron donating  sensing for
oxidative (e-accepting) molecules, e.g., nitroaromatics.
80
CH 3
O 2N
NO2
60
NO 2
40
TNT
20
0
1
J. Am. Chem. Soc. 2007, 129, 6978-6979
Efficient fluorescence sensing of amines vapor
High stability for
repeated use
2
3
4
5
6
7
8
9
10
Quenching efficiency independent on film thickness
--- easy for manufacturing
Long-range
exciton migration
+
Cross-film diffusion
of explosives
Thickness independence
100
80
Quenching (%)
Long-range exciton migration
enables amplification of
fluorescence quenching
• Amplified emission
quenching;
• Continuous porosity 
expedient diffusion of
gaseous molecules;
• Large surface area 
increased adsorption
I / I0 % (corr. for 2% photobleaching)
Optical and Electrical Sensing
J. Am. Chem. Soc. 2005, 10496-10497, 2006, 6576-6577, 7390-7398, 2007, 6354-6355, 6978-6979, 7234-7235.
60
CH 3
O 2N
CH 3
NO2
NO2
40
NO 2
20
NO 2
TNT
DNT
0
15
30
45
Vapor Sensing of Aniline
Ultrathin nanowires for increased surface area and more confined exciton diffusion and charge transport
Quenching efficiency (1-I/Io)
40 nm
nanofiber
0.1
350 nm
nanofiber
0.1 ppb
1 ppb
0.01
1E-3
1E-4
1E-3
5 ppb
5 ppt
Detection limit down to a
few ppt
0.01
0.1
1
10
100
1000
Vapor concentration (ppb)
Electrical sensing of hydrazine vapor
Acknowledgments
Freshly deposited nanobelt
+ PTCDI nanowire glass
Bare nanowire
J. Am. Chem. Soc. 2007, 129, 6354-6355.
90
Ultimate fine nanowires: cross-section of just one molecule!
1
amine
75
Film Thickness / nm
Nano Lett. 2008; 8, 2219-2223.
e-
60
Broken after high current
Zang Group:
Kaushik Balakrishnan
Aniket Datar
Tammene Naddo
Jialing Huang
Steve Loser
Meagan Hatfield
Randy Oitker
Ryan Rakher
Jay Moon
Ryan Martin
Dr. Xiaomei Yang
Dr. Yanke Che
Dr. Jianhua Gao
Dr. Chengyi Zhang
Collaborators:
Group of Jeff Moore, UIUC
Group of NJ Tao, ASU
Group of Jim Zuo, UIUC
Dr. David Tiede at Argonne National lab
Mater. Tech Center of SIU
$$Support $$ :
• MTC Grant, 2004, 2005;
• CARS program;
• K.C. Wong Foundation (Hong Kong);
• Argonne National Lab;
• NSF: CMMI, CAREER, CBET, MRI;
• ACS-PRF;
• FHWA-State DOT Partnership (07-10);
• NSFC;
• Department of Homeland Security;
• USTAR, UU-MSE.
Instrumentation Support:
UU Nanofab, Microfab, NMR of Chemistry, Argonne, APS; UIUC, DOE-CMM.
The Zang Research Group, Department of Materials Science and Engineering
Tel. 801-587-1551, Email: [email protected], Web: www.eng.utah.edu/~lzang