Electronic Nose Applications in
the Fragrance Industry
Rachel M. Bukowski, Ph.D.
Outline
• Presentation Goals and Objective
• Background
• Current E-Nose Technology
– Evolution and present applications
• Molecular Imprinting Technology
– Xerogels
– Fluorescence-based sensors
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Previous results
Data Acquisition and Analysis Methods
Applicability to Fragrance Industry
Conclusions
Presentation Goals
and Objective
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•
•
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Definition of an E-nose
Review of current available technologies
Benefits of fluorescence-based MIPs
How can a fluorescence-based MIP E-nose
platform be applied to the fragrance industry?
• Benefits of E-nose over human sensory
evaluation
What is an E-Nose?
• Electronic nose: a device intended to detect,
identify and quantify odors and flavors
• Consists of three major parts:
– Sample delivery system: generates headspace
and injects sample into detection system
– Detection system: react to presence of VOCs,
undergo chemical change and produce useable
signal
– Computing system: combines the responses of
individual sensor elements and generated sample
information
Background
• Optically-based electronic noses are most
common (vapor phase)
• Generally consist of an array of sensors
– Wealth of research and experience for a diverse
set of applications
– Although it is difficult to copy the mammalian nose,
a sensor array system most closely resembles it
• Current products consist of combinations of
various technologies
Current Applications
• Food/beverage safety and security
• Food quality
– Olive oil
– Wine
– Coffee/Tea
• Homeland security
– Explosives detection
– Bio/Chem WMD detection
– Drug detection
• Medical screening and diagnostics
Signal
Array-Based E-Noses
Raw data
acquisition
Sample
Sensor
Array
Feature extraction and
pattern recognition
[Analyte]
- Generally, combinations of signals from several
different sensor elements allow the user to obtain the
identity of a sample
Optical Sensor Systems
• Optical sensor: sensor based on the emission of
photons, which are detected and converted into a
useable signal
• Most closely resemble the sensor array systems
– Various methods can be exploited
• Changes in photon properties
• High number of available technologies for light sources
and detectors
Other Systems
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•
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Mass Spectrometry
Ion Mobility Spectrometry
Gas Chromatography
Infrared Spectroscopy
• These technologies, although preferable to
use in many applications, generally fall short
of the advantages offered by an opticallybased detection system.
Current Products
• Alpha MOS Gemini
– Smell and VOC analyzer
– Automated headspace sampling
– 6 pre-selected sensors according to customer
applications
• Chemsensing Colorimetric Array
– Sensor array of chemically reactive dyes
– Sensitive to presence of VOCs and changes in
VOC concentration
– Application-specific arrays can be developed
Current Products
• GSG MOSES II
– Takes a “fingerprint” of a particular odor without
separating the individual components
– Useful for objective odor comparison
– Modular system design
• Sacmi EOS Ambiente
– Uses electrochemical sensors to take a fingerprint
of an odor and identify its concentration
– Initially developed to measure concentrations of
environmental and industrial plant malodours
– Highly sensitive and robust
Recognition Chemistry
Transducer
Xerogel Technology
• Hydrolysis:
• Si(OR)4 + nH2O  Si(OR)4-n(OH)n + nROH
• Condensation:
• ≡Si-OH + HO-Si≡  ≡Si-O-Si≡ + H2O
• ≡Si-OR + HO-Si≡  ≡Si-O-Si≡ + ROH
• Polycondensation:
• x(≡Si-O-Si≡)  (≡Si-O-Si≡)x
≡Si =
Si
Xerogels as Sensor Platforms
• The sol-gel process applied to analyte sensing:
– Sensor elements (fluorophores, dyes, indicators,
proteins, etc.) introduced into sol-gel matrix.
– Sensor element is entrapped within the xerogel matrix.
– Sensor element maintains its functionality and
accessibility.
1
2
3
4
Anal. Chem. 1994, 66, 1120A
Molecular Imprinting Technology
• Modeled after enzyme-like recognition of
molecules by receptor sites
– “Lock-and-key”
• Involves using the target analyte (TA) or
derivative of the TA to create recognition sites
within a porous polymer matrix
• Since the TA is used to create these sites,
they are highly selective towards the analyte
of interest
Fluorescence-Based MIPs
• Involves the installation of a chemically
responsive fluorophore at or near the
templated site
• Upon binding of TA, change in fluorescent
properties is observed and quantified
– Emission maxima, emission wavelength,
fluorescent lifetime, etc.
• Highly selective
• More sensitive than electrochemical methods
Simplified Schematic:
Fluorescence-Based MIP
Previous Results:
Edminston et. Al.
• Drawback to molecular imprinting
techniques:
– Molecules had to be small with at least two
polar functional groups to create templated
sites
– Edminston created a MIP for fluorene
– High sensitivity and selectivity
– Irreversible
– Opens the door for MIPs for aroma
chemicals
Previous Results:
Bright et. Al.
• Created first fluorescence-based MIP
with selective reporter installation
– Fluorescent reporter molecule is selectively
installed in the templated site
– Upon binding, target analyte is very close
to reporter molecule
– Higher sensitivity to target analyte
achieved
Applications to the
Fragrance Industry
• Strong drive to apply E-nose technology
to olfaction
– Toxic nature of some aroma chemicals
• Sensitization of the perfumer
• Odor fatigue
• Irritation
– Current technology is time-consuming and
costly
• ie: human test panels
Malodour Detection
and Identification
• Common malodorous molecules include:
– Indole, skatole, methanethiol: toilet and animal
malodours
– Piperidine, morpholine: urine
– Pyridine, triethylamine, diamines: kitchen and
garbage odors (fish)
– H2S, nicotine, pyrroles: cigarette smoke
– Short chain fatty acids: axilla malodours
• Malodours are small molecules with polar
functional groups
– Ideal for molecular imprinting applications
Possible Detection Scheme
for Example Malodour
React with
functional
monomers
Lauric Acid
Entrap in
polymer
Remove
TA
Selectively install
reporter
Reintroduce
TA
Change in
signal from
reporter
Malodour Counteractants
• Various approaches have been used to
counteract malodors:
– Masking via a more pleasant odor
– Blocking malodour olfactory receptors
– Elimination or absorption of malodour via chemical
reaction
– Association and complexation
– Physical absorption of malodour into other
materials
– Malodour suppression
– Malodour formation inhibition
Counteractant Effectiveness
• Electronic noses can be used to measure
malodor counteractant effectiveness
• MIPs could provide an excellent platform
– Robust
– Selective
– Sensitive
• Must be application-specific
– Example 1: determine the effectiveness of a
malodour-eliminating candle on typical household
odors (skatole, indole, amines)
– Example 2: quantify the effectiveness of deodorant
on axillary malodour (short chain fatty acids)
Counteractant Effectiveness (II)
• Direct measurement
– Measure the amount of malodour present
prior to testing, at various points during
testing, and at conclusion of testing
• Indirect measurement
– In the case of counteractants reacting with
malodour to eliminate malodour molecules,
measure the rate of decay of counteractant
molecules
Sample Platform
Volitile Sulfur
Compound Sensor
No counteractant
5 min. after
counteractant
introduced
- H2S
- CH3SH
- Allyl mercaptan
- Methanethiol
- Dimethyl sulfide
30 min. after
counteractant
introduced
Conclusions
• There is a need for a robust, consistent and
economically practical electronic nose system
in the fragrance industry
– Quality Assurance
– Research and Development
• The electronic nose system cannot be a
“black box”
– Must be application specific
• Malodour counteractant effectiveness
assessment presents a feasible application
for electronic nose technology
Acknowledgements
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Maesa Home
Dr. Ron Newman (Maesa Home)
Jill Belasco (Maesa Home)
Steve Herman (Fairleigh Dickinson
University)
• Udo Weimar (University of Tuebingen )