Diffraction Gratings as a Chemical Sensing Platform

Transcription

1 Diffraction Gratings as a Chemical Sensing Platform Gordon T. Mitchell Center for Process Analytical Chemistry Department of Chemistry University of Washington

2 Grating Light Reflection Spectroscopy Refractive Index: n (T,λ) GLRS simultaneously measures Attenuation Index: K (T,λ) Scattering + Absorbance Speed of Light Analyte concentration Universal Detector for LC Mixing applications Concentration and size of particles Emulsions Pigments Cosmetics Drug Attrition Milling Heterogeneous Slurries Concentration of Chromophore UV Aromatics conc. Vis Dye conc. Near-IR Water conc.

3 GLRS Mechanism Polychromatic light Reflected orders Air ε (0) Grating Substrate ε (1) Evanescent field θ d Diffracted orders λ cr when θ d =90 o 650 nm 600 nm 550 nm 500 nm 450 nm 400 nm Sample ε (2) Transmitted orders

4 GLRS Theory Reflectance Reflected Spectra n=1.33 λ cr n= Wavelength (nm) Critical wavelength depends on the refractive index. Reflected intensity depends on the attenuation (absorption and scattering). Derivative of Reflectance No scattering or absorption. Some scattering or absorption. Lots of scattering or absorption. 1 st Derivative Spectra n=1.33 n= Wavelength (nm)

5 GLRS Theory δ m Re ( ε ) sinθ + Water (+) 3 rd Order Substrate (+) 3 rd Order Incidence Angle, θ Water (-) 1 st order Substrate (-) 1 st order mλ a Water (+) 2 nd order 2 Substrate (+) 2 nd order Wavelength, nm The critical wavelength corresponds to the transition between a traveling wave and an evanescent field. This occurs when δ m =0. Anderson, B. B.; Brodsky, A. M.; Burgess, L. W. Physical Review E 1996, 54,

6 GLRS Theory R ( 2) 2 ( ) ( ) 1 ε δ + C 2 2 Im δ + ε 1 2 C1 + C2 δm + m 3 m Im ( ) + δ = m Reflected intensity exhibits a strong dependence on Im (ε) near δ m =0. C 1, C 2, and C 3 are related to interfacial properties such as phase and polarization of incident light. C 2 and C 3 also depend on the optical contrast between grating and substrate or sample. C 2 +C 3 -C 2 -C 3 -C 2 +C 3 C 2 -C 3

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8 Applications of GLRS Naproxen Attrition Milling Second Derivative of Reflected Intensity Theoretical monodisperse spectra 3 x µm Decreasing 100 nm Wavelength (nm) Particle Zero Crossings Size 500 nm 300 nm Second Derivative of Reflected Intensity Observed polydisperse spectra x 10-4 Largest Particle Samples -1 39,270 25, , Smallest Particle Samples Wavelength (nm) Hamad, M.L.; Kailasam, S.; Brodsky, A.M.; Han, R.; Higgins, J.P.; Thomas, D.; Reed, R.A.; Burgess, L.W. Appl. Spectrosc. 2005, 59.

9 Applications of GLRS

10 Applications of GLRS Nanoparticle Analysis Analyzed a series of dendritic oligomers in nanometer sampling volumes. Particles detected down to 0.75 nm diameter Able to discriminate between particles with sub-nanometer differences in diameter. λ Run Number GH3a Injection Smith, S.A.; Brodsky, A.M.; Vahey, P.G.; Burgess, L.W. Anal. Chem. 2000, 72, Wavelength(nm)

11 U.S. Department of Energy Pacific Northwest National Laboratory Ultrasonic Diffraction Grating Spectroscopy Diffraction grating is formed by parallel triangular-shaped grooves on flat surface of stainless steel half-cylinder. Transducers one to transmit and one to receive ultrasound are pointed at the the diffraction grating. UDGS can be used to measure speed of sound in liquid or slurry particle size of slurry 30 degree flats Receive transducer Send transducer Grating surface Transducers Grating

12 GLRS Mechanism Polychromatic light Reflected orders Air ε (0) Grating Substrate ε (1) Evanescent field θ d Diffracted orders λ cr when θ d =90 o 650 nm 600 nm 550 nm 500 nm 450 nm 400 nm Sample ε (2) Transmitted orders

13 Hydrogen Sensing with GLRS Hydrogen adsorbs to palladium, causing a phase transition and changes in the dielectric function. A palladium-coated GLRS sensor should be an efficient hydrogen detector. Pd H phase diagram

14 Hydrogen Sensing H 2 H 2 H 2 H 2 Palladium H. H. H. H. Chromium grating on fused silica substrate -C 2 +C 3 C 2 +C 3 ` Reflection Transmission

15 Hydrogen Sensing Transmission intensity response to 100% hydrogen Pd mirror response Pd-coated grating response Transmitted Intensity (%) Transmitted Intensity (%) H 2 grating singularity Grating - substrate singularity Wavelength (nm) Wavelength (nm)

16 Hydrogen Sensing Time-resolved spectral response to hydrogen ~5 s cycle time

17 Hydrogen Sensing Pd mirror residual response after H 2 exposure Pd grating residual response after H 2 exposure Transmitted Intensity (%) cycles 1 cycle 2 cycles 3 cycles 4 cycles 5 cycles 6 cycles Transmitted Intensity (%) Residual spectral features caused by changes to surface morphology Wavelength (nm) Wavelength (nm)

18 Spectroelectrochemistry Potentiostat + Grating / Working electrode Reference electrode Counterelectrode

19 Spectroelectrochemistry Gold Coating Chrome Fused Silica Substrate Grating (working electrode) Ag reference electrode Pt counter electrode Grating (1.0 µm period) Electrochemical Cell To Lock-in amplifier Laser nm To Lock-in amplifier Turning Mirror 2 Optical Chopper Beam Pick-Off Si PIN Photo detector Turning Mirror 1 Layout Precision Rotation Stage To Lock-in amplifier Si PIN Photo detector GLRS Electrochemical Cell Kelly, M. J.; Sweatt, W. C.; Kemme, S. A.; Kasunic, K. J.; Blair, D. S.; Zaidi, S. H.; McNeil, J. R.; Burgess, L. W.; Brodsky, A. M.; Smith, S. A. In Sandia Report, 2000.

20 Spectroelectrochemistry Meldola s Blue detection limits: 50 ppb Chromophore near critical wavelength TNT detection limits: 50 ppm Transparent near critical wavelength 8.60 Cyclic voltammagram of Meldola s blue using EGLRS cell Zero order reflectance (a.u.) Meldola's Blue Concentration ppm 2.7 ppm Time (s) Modulation parameters extracted from curve fit: R= m1 + m2 *[Sin(m3 * time + m4)]

21 Spectroelectrochemistry Electrochemical Modulation of Methylene Blue at ITO-Cr Grating Cyclic Voltammagram of 100 ppm Methylene Blue Electrical Modulation of Grating Water 10 ppm Methylene Blue R e fle c te d In te n s ity (A Potential (V) Time (s)

22 Spectroelectrochemistry 2 V

23 Spectroelectrochemistry

24 Acknowledgements Scientific Support Dr. Lloyd Burgess Dr. Anatol Brodsky Dr. Mazen Hamad Joe Dragavon Technical Support UW Center for Nanotechnology Financial Support NIH (MLSC) DOE

25 GLRS Publications B. B. Anderson, A. M. Brodsky, and L. W. Burgess, Phys. Rev. E 54, 912 (1996). B. B. Anderson, A. M. Brodsky, and L. W. Burgess, Anal. Chem. 68, 1081 (1996). B. B. Anderson, A. M. Brodsky, and L. W. Burgess, U.S. Patent 5,502,560 (1996); U.S. Patent 5,610,708 (1997). B. B. Anderson, A. M. Brodsky, and L. W. Burgess, Langmuir 13, 4273 (1997). A. M. Brodsky, L. W. Burgess, and S. A. Smith, Appl. Spectrosc. 52, 332A (1998). Kelly, M.J.; Sweatt, W.C.; Kemme, S.A.; Kasunic, K.J.; Blair, D.S.; Zaidi, S.H.; McNeil, J.R.; Burgess, L.W.; Brodsky, A.M.; Smith, S.A. Sandia Report, April S. A. Smith, A. M. Brodsky, P. G. Vahey, and L. W. Burgess, Anal. Chem. 72, 4428 (2000). M.S. Greenwood, A.M. Brodsky, L.W. Burgess, and L.J. Bond, Rev. Prog. Quant. Nondest. Eval. 22B, 1637 (2002). M. S. Greenwood, A. Brodsky, L. Burgess, L.J. Bond, and M. Hamad, Ultrasonics, 42, 531 (2004). M.L. Hamad, S. Kailasam, A.M. Brodsky, R. Han, J.P. Higgins, D. Thomas, R.A. Reed, and L.W. Burgess, Appl. Spectrosc., 59, 16 (2005).