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