adaptive optical biocompact disk for molecular recognition leilei peng, manoj m. varma, fred e....
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Adaptive optical Adaptive optical biocompact disk for biocompact disk for
molecular recognitionmolecular recognitionLeilei Peng, Manoj M. Varma, Fred E. Leilei Peng, Manoj M. Varma, Fred E.
Regnier, David D. NolteRegnier, David D. NolteApplied Physics Letters, May 2005Applied Physics Letters, May 2005
Purdue UniversityPurdue University
Journal Club – 11-03-05Journal Club – 11-03-05
Emre ÖzkumurEmre ÖzkumurElectrical and Computer Engineering DepartmentElectrical and Computer Engineering Department
Boston UniversityBoston University
outlineoutline
Background for phase sensitive interferometric Background for phase sensitive interferometric detectiondetection
Details of how the method worksDetails of how the method works Phase modulation with a BioCDPhase modulation with a BioCD Conversion of phase modulation to amplitude modulationConversion of phase modulation to amplitude modulation Fabrication of the BioCDFabrication of the BioCD
ResultsResults SensitivitySensitivity Background for bio-detection; specific, non-specific bindingBackground for bio-detection; specific, non-specific binding Molecular dataMolecular data
Phase sensitive interferometryPhase sensitive interferometry
djeE
2
1
djneE
2
2
dd
εε11
εε22
)1(
2cos0
22
2
2
1 nd
IIeEeEIdjndj
MeasurMeasure d(n-1)e d(n-1)
Phase sensitive interferometry_2Phase sensitive interferometry_2II
ØØ00 22ππππ/2/2
Most sensitive Most sensitive region: region: quadrature quadrature
Satisfied when Satisfied when d(n-1)=d(n-1)=λλ/4/4
or…or…
by having a by having a time-time-independent independent ππ/2 /2 phase difference phase difference between between reference and reference and signal beams signal beams
Phase modulation with a BioCDPhase modulation with a BioCD
• 4” diameter4” diameter
• 1024 wedged-1024 wedged-spoke pattern of spoke pattern of biomoleculesbiomolecules
• spun at 50Hz, spun at 50Hz, pattern is pattern is transferred to transferred to probe beam as probe beam as phase phase modulation at modulation at 51.2kHz51.2kHz
Phase modulation -> Amplitude Phase modulation -> Amplitude modulationmodulation
EE11
EE22
EE22’’
EE22
””EE11’’
EE11””
Phase modulated probe and reference beams are Phase modulated probe and reference beams are sent into a Photorefractive Quantum Well devicesent into a Photorefractive Quantum Well device
PRQWPRQW
- Fringes change the effective refractive index - Fringes change the effective refractive index of the materialof the material
- Because of the periodic change in “n”, - Because of the periodic change in “n”, device acts as a diffraction gratingdevice acts as a diffraction grating
Why use PRQW?Why use PRQW?
2)1)((
2)(exp)0()()0(),( 2121
0
ntdiEEeLEE P
i
Photorefractive Photorefractive phase shiftphase shift
Excitonic Excitonic spectral shiftspectral shift
)( P
- - Quadrature condition is satisfied by adjusting the excitonic Quadrature condition is satisfied by adjusting the excitonic spectral shift by changing the applied voltage to PRQW and spectral shift by changing the applied voltage to PRQW and wavelength of the beamwavelength of the beam
- Grating can adapt to slowly varying phases, but not to rapid - Grating can adapt to slowly varying phases, but not to rapid changes => low frequency variations (environmental & changes => low frequency variations (environmental & mechanical disturbances) of the phase compansated, high mechanical disturbances) of the phase compansated, high frequency pass without changingfrequency pass without changing- - Resultant intensity amplitude modulated with 51.2kHz; total Resultant intensity amplitude modulated with 51.2kHz; total intensity is measured and sent to a spectrum analyzer or lock-in intensity is measured and sent to a spectrum analyzer or lock-in amplifieramplifier
Fabrication of the BioCDFabrication of the BioCD
- Ink gel stamping - Ink gel stamping methodmethod
Sensitivity of the systemSensitivity of the system To test the system sensitivity, a phase modulator was To test the system sensitivity, a phase modulator was
used instead of BioCDused instead of BioCD Phase modulator was used to calibrate the data, to Phase modulator was used to calibrate the data, to
extract the height informationextract the height information
Sensitivity of the systemSensitivity of the system Phase modulator created ØPhase modulator created Øpppp=2.1*10=2.1*10-2-2 rad, rad,
corresponding to:corresponding to:
(optical thickness for (optical thickness for λλ=830nm)=830nm)
Patterned Bovine serum albumin (BSA) optical Patterned Bovine serum albumin (BSA) optical thickness measured to be:thickness measured to be:
d(n-1)=0.6nm d(n-1)=0.6nm for which AFM measured 2.5±0.7nm for the height for which AFM measured 2.5±0.7nm for the height difference, confirming the refractive index of BSA to difference, confirming the refractive index of BSA to be n=1.2±0.1nmbe n=1.2±0.1nm
nmnd pp 8.22
)1(
Signal-to-NoiseSignal-to-Noise
2
22
2
NEOT
d
NN
d
N
S
PL
NEOT: noise equivalent optical NEOT: noise equivalent optical thicknessthickness
NNLL: Noise contribution of the local : Noise contribution of the local oscillatoroscillator
NNPP: Phase noise from the disk: Phase noise from the disk
At 51 kHz modulation frequency NAt 51 kHz modulation frequency NPP dominates, dominates,
NEOT=0.3nmNEOT=0.3nm
Higher sensitivity can be achieved by narrowing Higher sensitivity can be achieved by narrowing the detection bandwidth (3kHz) the detection bandwidth (3kHz)
Background for bio-detection dataBackground for bio-detection data
BioCD was implemented for an antigen-BioCD was implemented for an antigen-antibody molecular recognition experimentantibody molecular recognition experiment
For simplicity:For simplicity: Label “mouse IgG antigen” = MLabel “mouse IgG antigen” = M Label “anti-mouse IgG antibody” = mLabel “anti-mouse IgG antibody” = m Label “rabbit IgG antigen” = RLabel “rabbit IgG antigen” = R Label “anti-rabbit IgG antibody” = rLabel “anti-rabbit IgG antibody” = r
System should be able to detect the System should be able to detect the bindings of interest (specific bindings) bindings of interest (specific bindings) which are M-m, R-r, and should ignore non-which are M-m, R-r, and should ignore non-specific bindings such as M-r or R-m specific bindings such as M-r or R-m
Preperation of the samples on Preperation of the samples on CDCD
First, First, M-antigen M-antigen 1024-1024-spoke pattern was spoke pattern was printed on the diskprinted on the disk
Free surfaces (unprinted Free surfaces (unprinted areas) were covered areas) were covered with BSAwith BSA
Then the disk was Then the disk was divided 4 annular tracks divided 4 annular tracks (A-D)(A-D)
Molecular data_1Molecular data_1
Non-specific binding was tested by Non-specific binding was tested by incubating track C with r-antibodyincubating track C with r-antibody
Specific binding was tested by incubating Specific binding was tested by incubating both tracks B and C with m-antibodyboth tracks B and C with m-antibody
Molecular data_2Molecular data_2 This time, after M-antigen 1024 spoke pattern was printed on This time, after M-antigen 1024 spoke pattern was printed on
the cd, R-antigen was used as free-surface saturating reagent the cd, R-antigen was used as free-surface saturating reagent instead of BSAinstead of BSA
Tracks B and C exposed to R-antibody, whereas tracks C and D Tracks B and C exposed to R-antibody, whereas tracks C and D exposed to M-antibodyexposed to M-antibody When no antibody agents present, the homodyne signal is When no antibody agents present, the homodyne signal is
the same as noisethe same as noise When both antibodies bind in track C, homodyne signal When both antibodies bind in track C, homodyne signal
diminishes, meaning that the heights cancel each other diminishes, meaning that the heights cancel each other
ConclusionConclusion
First adaptive interferometric BioCD First adaptive interferometric BioCD for molecular recognition was for molecular recognition was demonstrateddemonstrated
Sensitivity = 0.3nmSensitivity = 0.3nm
Higher sensitivity can be achieved Higher sensitivity can be achieved byby
Narrowing the detection Narrowing the detection bandwidthbandwidth
Shifting to a reflection geometry Shifting to a reflection geometry that will not be sensitive to density that will not be sensitive to density fluctuations in the glassfluctuations in the glass
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