1 Cyttron Cyttron NSOM Lecture A Surface Imaging Method Prof. Ian T. Young Quantitative Imaging Group Department of Imaging Science & Technology Delft University of Technology
Dec 21, 2015
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Cyttron NSOM Lecture
A Surface Imaging Method
Prof. Ian T. Young
Quantitative Imaging Group
Department of Imaging Science & Technology
Delft University of Technology
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Theory: Optical resolution is limited
Ernst Abbe, 1873
500 nm
200 nm
Methods that are based on lenses have limited spatial resolution
Where does this result originate?
d =1.22λ2nsinθ
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Christiaan Huygens – Treatise on Light
Basic Concepts - Wave Optics
•Interference
•Diffraction QuickTime™ and aAnimation decompressor
are needed to see this picture.
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Numerical Aperture & Resolution I
The NA is one of the most important parameters of an optical microscope.
It determines:
• The amount of collected light
•The optical resolution
•But where does it originate?
NA=nsin(θ)
I ∝NA2
d≈0.61λNA
2aθ
θ
z
Note: tanθ =az
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•What is the intensity distribution for a 2-D aperture I(x, y, z)?
•Sketching the result:
I (x, y, z) = E(x,y,z) 2 = sinckxaz
⎛⎝⎜
⎞⎠⎟
⎡
⎣⎢⎤
⎦⎥
2
sinckybz
⎛⎝⎜
⎞⎠⎟
⎡
⎣⎢⎤
⎦⎥
22a
2b
Intensity on screen
: 1
b
: 1
a
Note: sinc q( )=sinqq
Numerical Aperture & Resolution II
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•Where are the zeroes of the intensity function?
•Adding one final substitution & approximation:
•Gives:
•For air, n = 1:
tanθ =az
for small θ ⇒ sinθ ≈tanθ =az
x̂ =λz2a
=λ
2sinθ=
n• λ2NA
square aperture round aperture
x̂ =0.5λNA
x̂=0.61λNA
x̂ =πzka
=λz2a
sinckxa
z⎛⎝⎜
⎞⎠⎟
Numerical Aperture & Resolution III
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•A point of light as object produces an Airy disk as the 2-D image
•Two points of light produce two Airy disks
•The size of the Airy disk(s) depends on the NA and λ
r [nm] with NA = 0.3, λ = 500 nm
Numerical Aperture & Resolution IV
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•A point of light as object produces an Airy disk as the 2-D image
•Two points of light produce two Airy disks
•The size of the Airy disk(s) depends on the NA and λ
r [nm] with NA = 0.3, λ = 500 nm
Numerical Aperture & Resolution IV
QuickTime™ and aAnimation decompressor
are needed to see this picture.
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Numerical Aperture & Resolution V
•A point of light as object produces an Airy disk as the 2-D image
•Two points of light produce two Airy disks
•The size of the Airy disk(s) depends on the NA and λ
r [nm] with NA = 1, λ = 500 nm
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Typical Values
•A round aperture produces an Airy disk on the screen
•The size of the Airy disk(s) depends on the NA and λ
•Rayleigh criterion says resolution is:
R=.61λNA
Magnification NA
16x 0.45 542 nm 813 nm20x 0.7 349 nm 523 nm40x 1.3 188 nm 282 nm63x 1.4 174 nm 261 nm100x 1.3 188 nm 282 nm
Resolution [nm]λ = 400 nm
[ ]Resolution nmλ = 600 nm
r [nm] with NA = 0.3, λ = 500 nm
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~250 nm
~180 nm
~100 nm
~30 nm
~30 nm
Garini et al, Curr Opin Biotech 2005. 16, 3-12
Practice: High-resolution optical methods
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How can we overcome the diffraction limit??
Completely different approach:
NEAR FIELD
High intensity
Low intensity
~50 nm
Measure VERY CLOSE to tip ~10 nm
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Near Field Microscopy
But how does it work?
It can only detect one small point.
Need to scan the surface
need scanning mechanism with ~10 nm resolution
It uses piezoelectric elements (expand with voltage)
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Piezoelectric motors
Material (example):
Perovskite-type lead zirconate titanate (PZT).
Different schemes:
single/multi layers
high/low voltage
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tip
laser
collection optics
detector
sample
optical fiber
psdlaser
Piezo 3-axis motor
Near-field scanning optical microscope
(NSOM or SNOM)The tip must be ~10 nm from the sample
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Total Internal Reflection Microscopy
Principle: Happens when light hit a surface
θ>θc & n1>n2
Calculation of θc for n1=1.5, n2=1.36 → Use Snell’s law:
n1 sinθ1 =n2 sinθ2 ⇒ θ1 =arcsinn2
n1
⎛
⎝⎜⎞
⎠⎟≈650
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Total Internal Reflection Fieldcreates evanescent field
z
I z =I 0e−z d
d=λ
4π n12 sin2 θ1 −n2
2
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Why is TIRF interesting?
Provides high resolution along z – overcomes wide-field limit
Limitation: only measures the surface,
Still important for various applications.
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TIRF History• Hirschfeld (1977):
• When light is reflected from a perfect mirror, a small amount of light (the evanescent wave) goes through to the other side of the mirror.
• The thickness of the wave on the “other side” is about λ/20, e.g. 25 nm.
Virometer: An Optical Instrument for Visual Observation, Measurement and Classification of Free Viruses, Hirschfeld T, Block M, Mueller W, J. Histochemistry & Cytochemistry, 25:719-723 (1977).
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virometer Brownian diameter
electron microscope diameter
TIRF History II
• What can we measure in this thin excitation field?
• Dynamic movement of labeled biomolecules
Protein dynamics
Vesicle–actin dynamics
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Right: Overlay of images. Green: wide field, red: TIRFGregg Gundersen, Columbia University
TIRF examples Cells labeled (tubulin) imaged with wide-field (Center panel) and TIRF illumination.
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Advanced TIRF for single molecule
detection Setup:Interference
Calibration by moving the slide
Cappello, G. Physical Review E 68, 2003.
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Hyper-spectral microscopy
Garini (1996): Using chromosome-specific probes & markers
• Multicolor spectral karyotyping of human chromosomes, Schrock E, duManoir S, Veldman T, Schoell B, Wienberg J, FergusonSmith MA, Ning Y, Ledbetter DH, BarAm I, Soenksen D, Garini Y, Ried T, Science 273:494-497 (1996).
DAPI
400 450 500 550 600 650 700 750 800
EXCITATION and EMISSION SPECTRA
EXCITATION
EMISSION
Cy2 SpectrumGreen FITC
Cy3 Rhodamine SpectrumOrange
Texas Red Cy3.5
Cy5 Cy5.5
INTENSITY [arb. units]
WAVELENGTH [nm]
5 dyes are sufficient for 24 chromosomes
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Hyper-spectral microscopy II
objective
sample
light source
filter cube
CCD detector
Sagnac interferometer
collimating lens • For every pixel (x,y) on the CCD camera a complete spectrum is generated
• This permits classification on the basis of color
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Hyper-spectral microscopy III
• This, in turn, permits spectral karyotyping
And the detection of genetic abnormalities…
And recognition…
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FLIM
Arndt-Jovin (1979):
• Fluorescence Decay Analysis in Solution and in a Microscope of DNA and Chromosomes Stained with Quinacrine, Arndt-Jovin DJ, Latt S, Striker SA, Jovin TM, J. Histochemistry & Cytochemistry, 27:87-95 (1979).
n = 1
2
3
4
t ≈ 10 ns fluorescence lifetime
• There is a distribution of times associated with the return of an electron to the ground state and the emission of a photon
• The biochemical environment (e.g. pH, O2, Ca2+) of the fluorescent molecule can affect this fluorescence lifetimeBodipy TR =
4.85 nsNile Red = 2.71 ns
0%
20%
40%
60%
80%
100%
0 2 4 6 8 10
time [ns]
excited electrons [%]