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Sensor Materials
Pelagia-Irene (Perena) Gouma
State University of New York, Stony Brook, NY, 11794-2275
US-Japan Workshop
Choosing Metal Oxide Crystals for Selective Gas Sensing
Gas sensing by Semiconducting Metal Oxides is possible:
• Because changes in electrical conductivity of oxide result from catalytic re-dox reactions at oxides’ surfaces
• Reactions are controlled by electronic structure, chemical composition, crystal structure, and relative orientation of the surfaces of the oxide exposed to gas detected
• Variations in gas sensing response of a given oxide are strongly related to the crystallographic modifications of the oxide during processing/testing
Oxide Phase (Polymorph)-Gas Selection Map (to achieve gas sensor specificity)
Group A of oxides with the rutilestructure: The rutile structure is tetragonal; TiO2, SnO2, CrO2, IrO2, β-MnO2, have stable rutile phases
Group B of oxides with the ReO3structure: The cubic ReO3 structure is closely related to the perovskite;WO3, β-MoO3, UO2 exist in this form
Group C of oxides with a weakly bonded layered structure:The α-MoO3 2D layered structure, h-WO3, etc.
Reducing Gases:Type I gases include CO and volatile organic compounds, such as methane, propylene, etc.
Type II gases include NH3and amines
Oxidizing gases: Type IIIType III refers to O2, NO, NO2
(from Gouma, Rev.Adv. Mater. Sci., 5, pp. 123-138, 2003)
CASE STUDY: Ammonia Sensor for Selective Catalytic Reduction Catalyst System
Sensing Response of NanostructuredSputtered Films
• 10min pulses of NH3 concentrations from 490-10ppm
• 10min interval of 0ppm concentration
• 10% background O2 concentration
• balance of N2 gas
60nm
(110) Orthorhombic MoO3
Relative Selectivity of the Ammonia Response
concentration (ppm)0 100 200 300 400 500
R(
Ω)
1e+5
1e+6
1e+7
1e+8
NH3
NO2
NOC3H6
H2
• Plotted are resistance values at the end of each 10min pulse
• Decrease in resistance was greatest for NH3, followed by C3H6
• Fractional response (R0-ppm/Rgas) for C3H6 only 1/17th of that for NH3
• Greatest selectivity for ammonia
(from Gouma et al, Thin Solid Films, 436, pp. 46-51, 2003; & Sensors &Actuators B, 9, pp. 25-30, 2003)
R (Ω)
Effect of voltage applied to the sensing response of MoO3 to a variety of gases
Effect of background oxygen concentration on the sensing response to ammonia
400 ppmNH3 pulses
elapsed time (min)0 50 100 150 200
R(
Ω)
1.0e+4
1.0e+5
1.0e+6
1.0e+7
1.0e+8
10% O2
5%
2%
1%0.5%
15% 20%R (Ω)
Comparison of the sensor response at 438°C to a 10-minute, 400-ppm NH3pulse for several values of the accompanying O2 ranging from 0.5% to 20%
244 240 236 232 228 224
244 240 236 232 228 224
binding energy (eV)
244 240 236 232 228 224
244 240 236 232 228 224
Intensity(arb.)
Intensity(arb.)
XPS Studies Reveal the Sensing Mechanism (a) The Mo 3d spectra after exposure to 1000ppm NH3 in 10% O2; (b) The Mo 3d spectra after exposure to 10% O2 only; (c) After exposure to 1000ppm NH3 in 0.5% O2 ; (d) After 1000ppm C3H6 in 10% O2
For the case of 1000ppm NH3 in 0.5% O2 only about 30% of the surface Mo remained as Mo+6, with the rest in the range of Mo+5 to Mo+4
MoO3 : Main Polymorphs
[011]
[010]
[001]
Oxide Crystallography and Sensing Properties
• The β-phase of MoO3 is isostructural with the orthorhombic phase of WO3 (cubic ReO3-type structure)
• When the material contains both α and β phases of MoO3 the sensor is not selective to ammonia in the presence of NO2
Sensing Response of Sol-gel films annealed for 8 hours at 500°C
100 nm
(421) O(040) O(031) O(220) O
(242) O(501) O
Selective NO2 Sensing Element based on WO3
( from Gouma et al, J. Mat. Sci, (21), pp. 4347-4352, 2003
10-9
10-8
10-7
1
10
100
1000
800 840 880 920 960 1000 1040 1080
WO2MO2MO1
NO2 [ppm]
NH3 [ppm]
CO2 [ppm]
Isoprene [ppm]C
ondu
ctan
ce [S
]
Concentration [ppm
]
Time [min]
Sensor Arrays for Trace Gas Analysis
P. Gouma, E. Comini, and G.Sberveglieri, Proc. SPIE’s Int. Symp. on “Microelectronics, MEMS and Nanotechnology”,Perth Australia, Dec. 9-12, 2003, in press.
2-sensor array based on binary MoO3
2-Sensor Array Reliability
Combined effects of phase and temperature
Set of Selective Sensor Array
Monoclinic MoO3
Operating Temp:400°C
Methanol Sensor
Orthorhombic MoO3
Operating Temp:500°C
Monoclinic and Orthorhombic MoO3
Operating Temp:450°C
Ammonia SensorIsoprene Sensor
Electrospinning: A Novel Nanomanufacturing Technique
for Molecular Sensing Probes• A simple, non mechanical method used to produce non-woven composites
with nanoscale components
• A viscous polymer solution is used and electrostatic charge is applied to it so as to create a single jet moving towards a metal target
The Electrospinning Process• An external electrostatic field is applied to a fluid -a charged
semi-dilute polymer solution or a charged polymer melt-and a suspended conical droplet is formed
• Electrostatic atomization occurs when the electrostatic field is strong enough to overcome the surface tension of the liquid
• The liquid droplet then becomes unstable and a tiny jet is ejected from the surface of the droplet
• As it reaches a grounded target, the jet stream can be collected as an interconnected web of fine sub-micron size fibers
• It was first developed by Zeleny in 1914 and patented by Formhals in 1934
Advanced Materials
LaboratoryCharacterization
Processing of bio-composite membranes
Power supply
Collector
Pump Needle
Advantages of the Electrospinning Process
• It produces porous non-woven fabrics of ultrafine fibers
• Fibers sizes may be in the nanometer diameter range (nanofibers)
• It is a one-step process and does not require further treatment to induce porosity
• We were able to form 1D nanostructures of metal oxides (nanowires) using this technique
• Incorporation of biomolecules to polymer membranes was also demonstrated by our group
Metal Oxide (MoO3, WO3) Nanowires
• Decomposition of the polymer matrix resulted in formation of oxide nanowires of high aspect ratio
• These were single crystals of nearly stoichiometric MoxOy composition
200nm
Sol-gel vs E-spun thin films of WO3
• E-spun nanowires showed faster response, higher sensitivity and lower detection limit for NO2detection
• p-type semiconducting behavior was observed for the oxide in both cases
• Cross-sensitivity tests have shown that ReO3-type phases are selective to oxidizing gases
Sol-gel film
10.00
12.00
14.00
16.00
18.00
0 4 8 12 16 20 24 28 32 36 40Time (min)
Resi
stan
ce (M
Ω)
500 ppm 400 ppm
300 ppm200 ppm
100 ppm
Electrospun film
10.00
12.00
14.00
16.00
18.00
0 4 8 12 16 20 24 28Time (min)
Res
ista
nce
(MΩ
)
500 ppm400 ppm
300 ppm200 ppm
100 ppm
50 ppm
Sensitivities Comparison
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
50 100 200 300 400 500
Concentration (ppm)
Sens
itivi
ty
Sol-GelElectrospun
Novel Materials and Applications of Electronic Noses and Tongues
Perena Gouma and Giorgio Sberveglieri, Guest Editors
Abstract This introductory article describes the content of the October 2004 issue of MRSBulletin focusing on novel materials and applications of electronic noses and tongues. The articles in this issue review the state of the art in materials, devices, and data processing algorithms used in electronic olfaction and taste systems. The most common gas-and liquid-phase analyte detection tools are presented and compared with traditional chemical analysis instrumentation such as gas chromatography/mass spectroscopy systems. Metal oxides, polymer/polymer composites, and dyes are covered in these articles as key sensing materials. Resistive, optical, electrochemical, and other types of electronic nose and tongue systems are reviewed, and their use in diverse applications, including environmental and food-quality monitoring and medical diagnostics, is discussed.
Keywords: biosensors, chemical detectors, electronic noses, electronic tongues,medical diagnostics, sensor arrays.
Exhaled human breath & non-invasive disease monitoring
• Volatile organic compounds in exhaled breath that may be used to study the mechanisms of human metabolism fast and efficiently, thus enabling the early identification of diseases such as asthma, SARS, or lung cancer
• Currently, there are no direct measures for these diseases in clinical practice, only invasive procedures
• Non-invasive monitoring may assist in differential diagnosis of pulmonary diseases, assessment of disease severity and response to treatment.
“Signalling Gases”
Trends in the change of disease markers
There is a need to monitor more than one gases at once for disease diagnoses purposes
↑↑↑↑↓CF
↑↑↑↑↑COPD
↑↑↑↑↑↑Asthma
8-isoprostaneCONO
From : S.A. Kharitonov and P.J. Barnes, Am. J. of Resp. & Critical Care Med.,
Vol 163, pp. 1693-1722, 2001
“Biological Warfare Canaries”
• Bacteria, viruses, toxins that spread deliberately in air, food or water can cause diseases
• Examples include: bacillus anthracis (anthrax), yersinia pestis (plague), variola major (smallpox), botulinum toxin (poison)
• DNA and antibody tests require prior knowledge of the bio-agent, and require long testing times
• The future biosensors are Gas Detection Systems
• Urea (carbonyldiamide) can be found in all body fluids
• When human body digests amines, urea becomes the waste product
• Elevated urea levels can indicate kidney and liver function problems
• Urease (urea amidohydrolase) may facilitate the removal of urea in kidney failure patients through haemodialysis (specif. 1-13mM urea)
• Due to its loss of activity when introduced to trace amounts of heavy metals, urease has also been used to analyze heavy metal contaminations and other pollutants
Advanced Materials
LaboratoryCharacterization
http://health.allrefer.com/pictures-images/kidney-anatomy.html
Urea Biosensor-A Model Enzyme-based System
CO(NH2)2 + H20 UREASE CO2 + 2NH3
• Urease E.C.3.5.1.5 acts
as a catalyst in urea hydrolysis
• It can increase the rate of reaction by 1014
• The two Ni atoms in the center allow
this reaction to occur
• Due to its specificity the most important application for urease is urea detection
http://www.biochem.ucl.ac.uk/bsm/pdbsum/1fwb/main.html
Advanced Materials
LaboratoryCharacterization
I. Bio-gels as bio-detectors
• Enzymes and other types of proteins are able to bind specific substrates with high specificity
• Excellent candidates for chemical detection and biosensingreceptors
• Enhanced oxide crystallization due to binding with enzyme
• Chemical reactions between proteins and analytes produce biochemical signals that are converted to electrical signals by gas sensitive transducer
Sol-Gel Processed Films MoO3 gas sensing films
Sensing data at 462°C
Reaction of urea with urease releases ammonia that is sensed by MoO 3 porousfilm(H2N)2CO ——in the presence of urease 2NH4
+ + HCO3-
where 2NH4+ + OH- 2NH3 + H2O
and HCO3- + H2 CO2 + H2O
poresureaseurea
sensor substrate electrodes
MoO3
Proposed Resistive Type Urea Sensing
Urease encapsulation in MoO3 sol-gel matrix
Research Challenges
• Using sol-gel metal oxide matrix other than SiO2 that iswidely studied for optical biodetection
• Use oxides that are selective to ammonia or CO2 and verify that are good hosts of urease
• Assess the stability and activity of urease in the bio-doped sol-gel
• Assess its urea sensing properties / ammonia gas detection limit
Bio-doped sol gel synthesis
0.3910gMoly-isopropoxide 2 ml PbS buffer
1 ml Urease sol.
7 ml butanol
Ultrasound mixing for 2hrs
Left to settle for 2 daysIn refrigerator
Structural characterization of bio-composite oxides
Clusters of intermixed nanocrystallineoxide and urease particles were observed in the TEM
Low Temperature Crystallization Effects of Bio-doping
Enzyme clustersOxide crystals
200nm 75nm
• The enzyme biomolecules were entrapped within the gel structures
• Their presence induced oxide crystallization at temperatures as low as 200 degrees C.
200degC, 4hr
200degC, 8hr
Undoped
500degC, 8hr
Enzyme activity assessment
1 ml sol-gel 10ml urea sol. 1 ml buffer
Mixing for 5 minsin a covered beaker
Activity measurement using thermo orionammonia electrode
Electrochemical testing data-proof of principle
Conclusions-Bio-doped Gels
• Successful processing of urease-doped MoO3 bio-gels was demonstrated
• The enzyme maintained its activity in the sol-gel matrix•• Urea detection in concentrations higher that 0.5mM was
possible using electrochemical sensing techniques
• The observed crystallization of the bio-doped oxide matrix at low temperatures suggests that resistive-sensing might be possible and is currently explored
KatarzynaSawickaStony Brook UniversityUndergraduate Category
Urea biosensing material prepared by electrospinning(Nanotech biosensor)
“Sawicka’s invention uses nanotechnology to create a novel type of biosensor. She created sub-microscopic polymer fibers containing a biological reagent that
detects the presence of urea. Improper levels of urea in the blood or urine can signify problems with the liver or kidney. Her invention could eventually be used
to create improved biological detectors needed to safeguard the health of patients.” “
II. Electrospun Bio-Composites
Power Supply
Syringe and Needle Collector
High Voltage
Fiber Jet
Synthesis of biocomposite membranesUrease: PVP (Mw=1,300,000)
16,000 units/g * .0986g = 1577.6units 4.615*10-5M in ethanol
Dissolved in 10mL of .1M PBS buffer pH 7.4
Solution I Electrospinning
3.5ml (70%) PVP in ethanol Flow rate: 15ul/min
1.5ml (30%) Urease in buffer Voltage: 20kV
Volume:0.4ml
Advanced Materials
LaboratoryCharacterization
Advanced Materials
LaboratoryCharacterization
The spherical aggregates of urease molecules varied in diameter from 10nm to 800nm. They are seen here covered with cubic salt crystals precipitated from the buffer.
Nanofiber Size Distribution
0
5
10
15
20
25
7 11 14 21 29 36 43 57 71 86
Diameter (nm)
Freq
uenc
y (%
)
Advanced Materials
LaboratoryCharacterization
(1)
0
20
40
60
80
100
0 5 10 15 20
Time (min)
Am
mon
ia C
once
ntra
tion
(ppm
)
(2)
0
5
10
15
20
25
30
35
40
0 5 10 15 20
Time (min)
(3)
0
2
4
6
8
10
12
0 5 10 15 20
Time (min)
.5mM
1.5mM
2.0mM
2.5mM
Ammonia concentration versus time when urea solutions reacted with: (1) 0.2ml of urease in PBS buffer(2) 0.2ml 30% urease in buffer/70% PVP in ethanol solution(3) 0.1ml of urease/PVP nanofiber mat
Sensing Data
Advanced Materials
LaboratoryCharacterization
020406080
100120140160180
0 2 4 6 8 10
Urea Concentration (mM)
Cha
nge
in P
oten
tial (
Urea Concentration vs Change in Potential
.005mM – 10.0mM urea solutions reacted with 3*8 cm mat
Advanced Materials
LaboratoryCharacterization
02468
1012
0.005 0.025
SolutionMat
Urea Concentration (mM)
Change in
Potential
(mV)
Comparison of response from a piece of mat to solution of equal number of units
Conclusions-Bio-composite Membranes
• Electrospinning has been used to successfully incorporate enzymes (urease) in polymeric matrices (e.g. PVP)
• The non-woven composite membrane forms were used as receptors to detect urea concentration, a substance which signals liver function problems
• Future work will study further the catalytic and aging effects of enzyme encapsulation in nanostructured fibrous membranes
• Bio-fuel cell devices, protective clothing, tissue engineering scaffolds may be developed using these bio-nano-composites
For further information about this work link to:http://www.matscieng.sunysb.edy/gouma/NIRT/ or [email protected]
Related published work:• P.I. Gouma, “Nanostructured Polymorphic Oxides for
Advanced Chemosensors”, Rev. Adv. Mater. Sci, 5:123, 2003.• K.M. Sawicka, P. Gouma, and S. Simon, “Electrospun
Biocomposite Nanofibers for Urea Biosensing”, Sensors Act. B, 2004, in print.
• P. Gouma and G. Sberveglieri, “Novel Materials and Applications of Electronic Noses and Tongues”, MRS Bull.29(10):697, Oct. 2004
• P. Gouma, “ Nanostructured Oxide-based Selective Gas Sensor Arrays for Chemical Monitoring and Medical Diagnostics in Isolated Environments”, Habitation: Int. Journal of Human Support Research, 2005.
Future Work: Detection of drug-induced gas release incancerous cell cultures (in-vitro studies)
0.0
10.0p
20.0p
30.0p
40.0p
50.0p
0 10000 20000 30000 40000 50000
0
10
20
30
40200300400500
1/R
Con
cent
ratio
n (P
PM)
NO2 CO NH3 Ethanola Ethanol Isoprene RHL
Time (s)
0.65g PVP/ 0.1625g LEB-PANI 1/12/05
0.0
500.0p
1.0n
1.5n
2.0n
2.5n
0 10000 20000 30000 40000 50000
05
10152025303540
300450
1/R
Con
cetra
tion
(PP
M) NO2
CO NH3 Ethanola Ethanol Isoprene RHC
Time (s)
0.65gPVP/01.625g LEB-PANI 1/12/05
Future Work: Use gas sensitive polymer matrices for RT sensing(Polyaniline / Polyvinylpyrrolidone Electrospun Fibers)
LEB-PANI/ PVP hybrid fibers are produced by electrospinning and exposed to NO2,
an oxidizing gas which ionizes LEB-PANI causing an increase in the materials conductivity
0 1 0 0 0 0 2 0 0 0 0 3 0 0 0 0 4 0 0 0 0 5 0 0 0 0
0 .0
1 0 .0 p
2 0 .0 p
3 0 .0 p
4 0 .0 p
5 0 .0 p
5 0 0 .0 p
1 .0 n
1 .5 n
2 .0 n
2 .5 n
1/R
T im e ( s )
P V P /P A N I T e s t A P V P /P A N I T e s t B
Acknowledgments
• This work has been partially supported by the National Science Foundation (NIRT and SGER awards), the Sensor CAT and Biotech CAT, and a WISC grant.
• The support of Prof. R. Gambino and Prof. S. Simon (from SUNY Stony Brook) and Prof. G. Sberveglieri and Dr. E. Comini (From Univ. of Brescia) is gratefully acknowledged
• The following students have contributed to this work: K. Sawicka, P. Jha, A. Prasad, and M. Karadge.