Electronic Nose Applications in the Fragrance Industry

Electronic Nose Applications in
the Fragrance Industry
Rachel M. Bukowski, Ph.D.
• Presentation Goals and Objective
• Background
• Current E-Nose Technology
– Evolution and present applications
• Molecular Imprinting Technology
– Xerogels
– Fluorescence-based sensors
Previous results
Data Acquisition and Analysis Methods
Applicability to Fragrance Industry
Presentation Goals
and Objective
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
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
– Computing system: combines the responses of
individual sensor elements and generated sample
• 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
Array-Based E-Noses
Raw data
Feature extraction and
pattern recognition
- 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
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
• 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
– 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
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 =
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
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
– Molecules had to be small with at least two
polar functional groups to create templated
– Edminston created a MIP for fluorene
– High sensitivity and selectivity
– Irreversible
– Opens the door for MIPs for aroma
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
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
• ie: human test panels
Malodour Detection
and Identification
• Common malodorous molecules include:
– Indole, skatole, methanethiol: toilet and animal
– 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
Lauric Acid
Entrap in
Selectively install
Change in
signal from
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
– Association and complexation
– Physical absorption of malodour into other
– 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
Sample Platform
Volitile Sulfur
Compound Sensor
No counteractant
5 min. after
- H2S
- Allyl mercaptan
- Methanethiol
- Dimethyl sulfide
30 min. after
• 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
Maesa Home
Dr. Ron Newman (Maesa Home)
Jill Belasco (Maesa Home)
Steve Herman (Fairleigh Dickinson
• Udo Weimar (University of Tuebingen )