Thickness and viscosity of organic thin films probed by combined surface acoustic Love wave and surface plasmon resonance J.-M Friedt & al Introduction
Thickness and viscosity of organic thin films probed by combined surface acoustic Love wave and surface plasmon resonance
Experimental setup Experimental results
J.-M Friedt1 , L.A. Francis2 , S. Ballandras
1
Data modelling Conclusion
1
FEMTO-ST/LPMO (Besan¸con, France), 2 IMEC MCP/TOP (Leuven, Belgium)
slides available at http://jmfriedt.free.fr
16 septembre 2005
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Thickness and viscosity of organic thin films probed by combined surface acoustic Love wave and surface plasmon resonance J.-M Friedt & al
Direct detection biosensor Aim : detect DNA hybridation, antibody/antigen interaction without labeling (fluorescence, radiolabeling ...)
Introduction Experimental setup Experimental results Data modelling Conclusion
• in-situ measurement (not in dry state) : microfluidics ... • time resolution '1 s for kinetics measurements
⇒ detect mass bound to the surface : acoustic method (QCM, SAW) ⇒ detect optical index change (ellipsometry, SPR) ⇒ detect surface topography change due to adsorption (SPM) • Acoustic methods beyond Sauerbrey : density, thickness, viscosity • Optical methods : thickness, optical index • Scanning probe microscopies : molecule conformation, density of
molecules, thickness Modelling is required for extracting quantitative information on the physical properties of the adsorbed layer
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Thickness and viscosity of organic thin films probed by combined surface acoustic Love wave and surface plasmon resonance J.-M Friedt & al
Various solvent concentrations From QCM-D measurement we know that collagen and fibrinogen provide challenging properties :
Introduction
• S-layer, IgG : behaves as a rigidly bound mass (Sauerbrey)
Experimental setup
• collagen : displays a behaviour consistent with a predominantly
Experimental results
viscous interaction • fibrinogen : intermediate situation ...
Data modelling Conclusion
Analyte (bulk concentration, µg/ml) S-layer CTAB collagen (30µg/ml) collagen (300µg/ml) fibrinogen (46µg/ml) fibrinogen (460µg/ml)
√ ∆fn / n (Hz) QCM NO NO 1000 1200 110±5 NO
∆fn /n (Hz) QCM 45=900 8=160 NO NO 55±5' 1110 100=1700
∆D (×10−6 ) QCM 3-5 0.2-0.5 100 >120 4-10 8-10
J.-M. Friedt et al., J. Appl. Phys. 95 (4) 1677-1680 (2004) C. Zhou et al., Langmuir 20 (14) 5870-5878 (2004) 3 / 10
Thickness and viscosity of organic thin films probed by combined surface acoustic Love wave and surface plasmon resonance
SAW/SPR combination
J.-M Friedt & al Introduction Experimental setup Experimental results Data modelling Conclusion
• Objective : identify physical properties of protein films. • Acoustic methods are sensitive to layer thickness, density and
viscosity, but provide only insertion loss and phase variations. • Combine with optical method : optical index and thickness. • Assume that density and optical index vary linearly with solvent content ⇒ 3 unknowns and 3 measurements. Pt CE Cu RE PDMS or SU8+glass
Au WE
rotating mirror: +/−2.5 o
ST quartz substrate
Al IDT glass prism
670 nm laser diode
SAW
reflected laser incoming laser (670 nm)
linear CCD array + temperature sensor
rough optical allignement screw RF cables to network analyzer
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Thickness and viscosity of organic thin films probed by combined surface acoustic Love wave and surface plasmon resonance J.-M Friedt & al Introduction Experimental setup Experimental results Data modelling
Data collected with combined SAW/SPR setup • Globular protein (IgG, BSA, S-layer), fibrilar protein (collagen,
fibrinogen) and polymers (pNIPAM) adsorption have been investigated. • Globular proteins display a mostly rigid behaviour • pNIPAM displays a behaviour dependent on temperature
Conclusion
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Thickness and viscosity of organic thin films probed by combined surface acoustic Love wave and surface plasmon resonance J.-M Friedt & al Introduction Experimental setup
Data modelling approaches (acoustics) Two complementary approches for modelling the acoustic data : • transmission line model v L/2
L/2
Experimental results
C
Data modelling
T
Conclusion
G
dr
• harmonic admittance computation based on the Bl¨ otekja¨er-model
extended to include the viscous contribution of a newtonian fluid (linear response) Tij = − P + jω
2 η − ζ Skk δij + 2ωηSij 3 6 / 10
Thickness and viscosity of organic thin films probed by combined surface acoustic Love wave and surface plasmon resonance
Data modelling predictions (acoustics : Bl¨otekja¨er)
J.-M Friedt & al
Parameters are : the layer thickness, its viscosity and density x 10
−0.02
−1 ∆f (Hz)
Experimental results
0
ρ=1.40
5
0 −0.5
∆f0 (MHz)
Introduction Experimental setup
−1.5 −2
Data modelling
−3
−0.06 −0.08 −0.1 −0.12
−2.5
Conclusion
−0.04
−0.14 0
5
10
15
20
25 30 viscosity (cP)
35
40
45
50
55
50
100
150
200
layer thickness (nm)
250
300
2
1.2 1
∆IL (dB)
0.6 0.4
η=2.30
1
η=1.60
0.5 η=1.00
0.2 0
350
η=3.00
1.5
0.8 ∆IL (dB)
0
0 0
5
10
15
20
25 30 viscosity (cP)
35
40
45
50
55
0
50
100
150
200
layer thickness (nm)
250
300
350
Varying the viscosity Varying the thickness An insertion loss drop of -6 dB cannot be modelled by a newtonian fluid+rigid mass interactions. 7 / 10
Thickness and viscosity of organic thin films probed by combined surface acoustic Love wave and surface plasmon resonance
Data modelling predictions (acoustics : TLM)
J.-M Friedt & al
Experimental results
0
−10
−20
−30 0
20
40
60
80
100
120
140
160
Data modelling
4 3
−0.04
η=1.7
−0.06 η=2.4
−0.08 −0.1
η=3.1 δ
−0.12
180
layer thicknesss (nm)
Conclusion
η=1.0
−0.02
∆f0 (MHz)
Experimental setup
0
∆ φ (degrees)
Introduction
−0.14
0
20
40
60
80
100
layer thickness (nm)
120
140
160
2 1 0 0
η=3.1
dotted: ρ=1.40 solid: ρ=1.10
1.5
∆IL (dB)
∆ IL (dB)
2
180
η=2.4
experimental 1 value for 460 µg/ml fibrinogen adsorption 0.5
η=1.7
η=1.0
20
40
60
80
100
120
140
160
180
layer thicknesss (nm)
Transmission line model (η=[1, 1.5, 2, 3])
0
0
20
40
60
80
100
120
140
160
180
layer thickness (nm)
Bl¨ otekja¨ er (harmonic admittance computation)
Here (left) we find a possible set of parameters for the fibrinogen data : a viscosity around 2.6 cP and a thickness around 22.4 nm assuming a density of 1.4. Additional work requires sweeping the density parameter to extract water content. 8 / 10
Thickness and viscosity of organic thin films probed by combined surface acoustic Love wave and surface plasmon resonance J.-M Friedt & al
Data modelling results (SPR) 2D model of reflected intensity of a laser by a stack of planar interfaces : requires optical index of all layers at a given wavelength+incident angle
Introduction
x=1
1000
Experimental results
x=0.5
x=0.4
x=0.3
x=0.1
1000
x=0.08
x=0.07 o
=70.2297
900
900
800
800
700
x=0.2
600
500
400
x=0.06
x=0.05
700
SPR ∆θ (mo)
SPR ∆θ (mo)
Data modelling Conclusion
x=0.7
o
=70.2297
Experimental setup
x=0.04
600
500
x=0.03 400
x=0.1 300
200
x=0.05
100
0
x=0.02
300
200
x=0.01 100
x=0.0 0
5
10
15
layer thickness (nm)
20
25
0
x=0.00 0
50
100
150
200
250
300
350
layer thickness (nm)
Acoustic frequency shift+insertion loss and SPR angle shift → density ρ, optical index n, viscosity and water content x assuming ρ = x × ρprotein + (1 − x) × ρwater & n = x × nprotein + (1 − x) × nwater → with a thickness of 22.4 nm, SPR (755 mo ) tells us x'0.25 i.e. ρ '1.10 and iterate ... 9 / 10
Thickness and viscosity of organic thin films probed by combined surface acoustic Love wave and surface plasmon resonance
Conclusion and perspectives
J.-M Friedt & al Introduction Experimental setup
• Experimental measurement of thin film adsorption by acoustic and •
Experimental results Data modelling
•
Conclusion
• •
optical means Simultaneously monitor using both techniques the same area in liquid with time resolution Implementation of models for the predictions of SPR angle shift and acoustic frequency shift and insertion loss as a function of adsorbed layer properties Models are incomplete : cannot justify large insertion loss decrease upon collagen adsorption Possible extension : add Maxwellian liquid behaviour (complex : non-linear, delayed effects, incompatible with transmission line model)
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