novel materials for development of optical sensors
DESCRIPTION
Materials for Sensors; Determination of organic pollutants. attenuated total reflection; fibre optic sensors; metal ion sensing.TRANSCRIPT
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Material Design for Optical Sensor Applications
Fiona Regan School of Chemical SciencesDublin City University
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Outline
Sensors and their applicationsPrinciples of ATR-FTIR spectroscopyUV-Visible sensingExamples of materials for sensingAnalytes determined using polymer-based sensorsNew materialsChallenges
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Design of a sensor for a particular application:
Dictated by the nature and requirements of that application.
Ideally adequate sensitivity broad dynamic rangeHigh selectivity towards the species of interestImmunity to sample-matrix interferences should also exist. Suitable for multicomponent measurement, have fast and
reversible responseexcellent long-term stability. The ideal sensor robust, reliable, simple, economical to
fabricate, of small size and with self-calibration capabilities.
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Sensor principle
The active surface of a chemical sensor contains the detection component e.g. a polymer layer
Interaction between the active layer and the analyte (s) being measured that is detected by the transducer.
The change in the transducer due to the active surface event is expressed as a specific signal.
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Principle of ATR spectroscopy
Infrared light propagating in a crystal of high refractive index is internally reflected.
Some of the light penetrates into the sample region outside the crystal in the form of an evanescent wave.
Analyte absorption spectra can therefore be recorded
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Evanescent wave
ZnSe crystal
Radiation from IR source To
detector
CHC
Evanescentwave
Aqueous phase containing CHC
~5 m
Figure
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Evanescent field sensing (EFS)
EFS with optical fibres is an extension of the established spectroscopic measurement ATR.
Routinely applied to the measurement of aqueous systems / analytes.
IR radiation is coupled to an ATR element (fibre/crystal) which is non-absorbing and has a higher refractive index than the surrounding medium.
The medium is a thin film or the absorbing analyte.
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Polymer-ATR spectroscopy
Removal of background water absorption is required to enable the detection of weaker signals at very low concentrations of analyte.
This can be overcome by coating the internal reflection element (crystal or fibre) with a hydrophobic polymer.
The polymer also serves to enrich the analytes within the penetration depth.
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Role of the polymer
PIB film
ZnSe crystalFrom IR source
To detector
CHC
Evanescentwave
Aqueous phase
Penetration depth
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Fibre optic evanescent wave sensor - FEWS
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Polymer selection criteria
No, or only weak, intrinsic polymeric IR bands in the region of interest;
Substances to be analysed must be reversibly absorbed in the film;
The time constant for the enrichment process should be low; The polymer should be easily prepared and be chemically
inert with respect to the analyte components; The polymer material must be resistant against water and
organic compounds; Must adhere well to the internal reflection element.
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Example 1: Teflon AF
window
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Teflon
Regan et al. Vibrational spectroscopy 14 (1997) 239-246
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FEWS - Effect of film thickness on analyte diffusion rates
0 200 400 600 8000.000
0.001
0.002
0.003
0.004
90% Saturation (T 90)
2.4 m
1.4 m
Abs
orba
nce
Time / seconds
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Teflon sensor reproducibility
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FEWS - Simultaneous analysis of 6 chlorinated hydrocarbons
0
.005
.01
950 900 850 800 750
Wavenumbers cm-1
Abs
TCE
TeCE
TCE TCB
TeCE
Cf
DCB
CB
10 mins enrichment time, 32 scans, 60 ppm each standard.
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Direct aqueous analysis using Teflon-coated ATR crystal (stopped flow)
Compound LOD/ppm
TCE 5
TeCE 1
Cf 10
CB 5
1,2-DCB 2
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Real sample analysis - Tolka River, Dublin
0
.001
.002
.003
.004
950 900 850 800 750
Abs.
Wavenumber cm-1
Real sample
60 ppm TCE standard
935 cm-1
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Example 2: PVC - plasticised
A. Adipic acid derivatives (1, 3,5,6,7,10,26,27)B. Azelaic acid derivatives (2,4,8,9)C. Epoxy derivatives (11,22)D. Lauric acid derivatives (12)E. Mellitates (13,14)F. Palmitic acid derivatives (15,16G. Phthalic acid derivatives (17,30)H. Sebaic acid derivatives (18,19)I. Stearic acid derivatives (20,21)J.Oleic acid derivatives (24)K. Linoleic acid derivatives (29) L. Isophthalic acid derivatives (28) M. Isobutyrate derivative (25)
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Pesticide determinations
Walsh et al. Analyst 121 (1996) 789-792
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Regan et al. Anal. Chim. Acta 334 (1996) 85-92
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Plasticisers
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Plasticisers
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Determination of BTEX compounds
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Xylene isomers
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Multicomponent analysis
Individual MixtureAnalytes t 90 (mins)Absorbance t 90 (mins) AbsorbanceBenzene 2.7 0.178 3.375 0.21Toluene 5.4 0.23 8.775 0.289Ethylbenzene 1.35 0.495 11.475 0.322o-xylene 2.7 0.495 20.25 0.463m-xylene 2.025 0.584 18.9 0.28p-xylene 1.35 0.466 20.25 0.385
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0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 1 2 3 4 5 6 7 8 9 10 1112131415161718192021222324252627282930
Plasticiser
t 90
(min
s)
TolueneTeCE
Comparison of enrichment time for TeCE and toluene into 30 plasticised PVC
phases (65% plasticiser)
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Example 3: Poly (isobutylene)
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Gas-flow system for analysis of aqueous samples by sparging over PIB coated ATR crystal
ZnSe crystal
PIB film
Steel air-flowcell (Volume = 1 ml)
Gas out
Gas in
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Sparging system for aqueous analysis
Why ?Aqueous solutions have proven to have deleterious
effect on polymer films. Ingress of water causes a shift in baseline thereby
lowering sensitivity due to increased noiseWater -OH bands interfere with measurements in the
fingerprint region even if hydrophobic polymers are used.
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Instrumental set-up for direct sparging method of analysis
Zero-grade air
Flow meter
CHC solution
Steel gas-flow cell
Sorbenttube
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Multi-component analysis by spargingSparging @ 50oC, 0.02 L/min, 6 minutes enrichment.
(Concentrations from 2-12 ppm)
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Analysis of solvent residues in pharmaceuticals using sparging
Chloroform
Tablet sample batch analysis for chloroform residuesTablets crushed, dissolved in water, sparged
Sparging @ 18oC, 1 L/min
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Example 4: Ethylene propylene copolymer
(CH CH) X
CH
(CH CH ) Y (CH CH) N
CH
CH
O Si
CH
CH
Ethylene-propylene co-polymer(E/Pco)
Poly(isobutylene)
Poly(dimethylsiloxane)(PDMS)
2 2
3
3
3
2 2
3
3
(PIB)
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Binary Studies
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Optical sensing materials for metal ion determinations
Azo DyeIonophorePlasticiserPVCSolvent
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Dyes for PVC Films
N N
Br
NN(C2H5)2
OH
OH
CH3
COOH
Cl Cl
SO3H
O
CH3
COOH
C
BrPADAP
CAS
Figure 3.8 Structure of KTCPB
B
Cl
Cl Cl
Cl
K+
-
Ionophore
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Visible spectrum for metal-dye (BrPADAP) complex
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Metal-CAS sensing
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Real Sample Analysis – Pb(II) determination
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Reversibility of metal films
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Selective responses
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Effect of pH on sensing films
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Principal component Analysis (PCA)
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New materials based on molecular imprinting
Molecular imprinting: Sensor materials Solid phase extraction materials HPLC packed columns Imprinting process
Functional monomerCross linkerTemplateInitiator
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MIP for caffeine
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NMR Mole ratio plot
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Ibuprofen - MIP
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Novel Antifouling CoatingsPVC compositesWhy PVC?Optically transparentLow bacterial adhesion Can be spin coatedDecided to study effect of using
different plasticizers on antifouling properties of PVC
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PVC and PlasticizersPlasticizers used to improve the flexibility
of the material. These molecules form secondary bonds
to the polymer chains and thus, spread them apart. (ester group has van der Waals interaction with H-Cl bond in PVC, linear chain acts as buffer between the polymer chains)
This results in increased permeability of the polymer
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PublicationCritical ReviewJ. Environ. Monit., 2006, 8, 880 - 886, DOI: 10.1039/b603289cAntifouling strategies for marine and
riverine sensors
Aine Whelan and Fiona Regan
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Assessment of FoulingThe change in mass of coated slides was
recorded after removal from tank.
The change in absorbance of films was recorded after removal from tank.
The quantity of biofilm on slide was determined by staining method reported by Tsai et al.
SEM images of the films were recorded after removal from tank.
Ref. C.L. Tsai, D.J. Schurman, R. Lane Smith, J. Orthopaedic Research, 1988, 666.
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Characterisation
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
200 300 400 500 600 700 800
w avelength(nm)
abso
rban
ce
UV-Vis spectrum of films prior to exposure
Type of film Contact Angle
PVC/Tridecyl adipate
84.6±2
PVC/Diethyl succinate
78.4±10
PVC/Ethyl hexyl sebacate
83.9±3
PVC/Diisononyl adipate
84.9±2
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PVC/Tridecyl adipate PVC/Ethyl hexyl sebacate
PVC/Diisononyl adipate PVC/Diethyl succinate
SEM Images of Films
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Optical density of biofilm on coated slides after exposure to river water (14 days)
00.2
0.40.60.8
11.2
1.41.6
type of coating
optic
al d
ensi
ty
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Change in mass of PVC/plasticizer coated slides after exposure to sea water (14 days)
0
2
4
6
8
10
12
14
16
18
20
Ethylhexylsebacate
Diethylsuccinate
Diisononyladipate
Tridecyl adipate Glass
type of coating
perc
enta
ge c
hang
e in
mas
s
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Change in absorbance of PVC/plasticizer coated slides after exposure to sea water
0
100
200
300
400
500
600
700
800
900
1000
Glass Diethylsuccinate
Ethylhexylsebacate
Diisononyladipate
Tridecyladipate
type of coating
perc
enta
ge c
hange a
bsorp
tion
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Conclusions
In the case of the river water, there was no clear difference in the antifouling performance of the different PVC films.
In the case of sea water, the PVC/tridecyl adipate film showed the best antifouling performance.
This plasticizer has the highest molecular weight and is expected to be less easily leached from PVC. It is proposed that this allows the PVC film to retain flexibility and toughness for longer.
It is interesting that for biofilm assay, in river water and sea water, PVC/tridecyl adipate performed best. Perhaps, tridecyl adipate has greater biocidal properties than the other plasticizers.
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PVC and plasticizers and surfactant
Add CTAB to polymer film (0.1% w/v)Why CTAB?Quaternary ammonium compounds
are widely employed as disinfectants due to their antimicrobial properties
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ConclusionsAs for PVC/plasticizer films, there was no clear
difference in the antifouling performance of the PVC/plasticizer/CTAB composites.
However, for Sea Water, the PVC/ethyl hexyl sebacate/CTAB film showed best antifouling performance.
Perhaps the PVC/ethylhexyl sebacate/CTAB film is more porous than other films, hence, CTAB can be more easily leached.
Porosity measurements are being undertaken at present.
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Acknowledgements
Funding: Strand I, Enterprise Ireland Strategic Grant & Basic Grant
Researchers: Eoin O’Donoghue Ambrose Hayden Kathleen O’Malley Fiona Walsh Keith Farrington
Collaboration with:Prof Boris Mizaikoff and Dr Edmond MagnerMSSI & NCSR