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

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25

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35

40

0 5 10 15 20

Time (min)

(3)

0

2

4

6

8

10

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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 emailpgouma@notes.cc.sunysb.edu

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.