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

• Previous results• Data Acquisition and Analysis Methods• Applicability to Fragrance Industry• Conclusions

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

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

Array-Based E-Noses

Sig

nal

[Analyte]Feature extraction andpattern recognition

Raw data acquisition

Sample

SensorArray

- 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

Sample Y

Sample X

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 optically-based 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

InterfaceImmobilization

OrientationChemistry

LuminophoreAnalyte

Association

Dissociation

Figure 1-1: Simplified schematic of an optically-basedchemical sensor system. The analyte of interest interactswith the RE and elicits a luminescent response.

InterfaceImmobilization

OrientationChemistry

LuminophoreAnalyte

Association

Dissociation

Figure 1-1: Simplified schematic of an optically-basedchemical sensor system. The analyte of interest interactswith the RE and elicits a luminescent response.

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

• 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

Molecular Imprinting Technology

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 withfunctionalmonomers

Lauric Acid Entrap inpolymer

RemoveTASelectively install

reporter

ReintroduceTA Change in

signal fromreporter

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

- Allyl mercaptan- Methanethiol- Dimethyl sulfide

- H2S- CH3SH

No counteractant

5 min. aftercounteractant

introduced

30 min. aftercounteractant

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

• Maesa Home

• Dr. Ron Newman (Maesa Home)

• Jill Belasco (Maesa Home)

• Steve Herman (Fairleigh Dickinson University)

• Udo Weimar (University of Tuebingen )