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Transcript
Biophotonics
www.postech.edu/~hjcha/jelyfish.jpg
Electromagnetism
• Its all described by Maxwell’s equations
(a Scott, 1831-1879)
(you need to know maths to do physics …)
Total internal Reflection
Total internal Reflection
• Snells law of refraction (contained in Maxwell’s Equations)
na sin( a )  nb sin( b )
na  1.5
a
a
medium a: na
nb  1.2
medium b: nb
nb  2
b
nb  1.3
nb  2
nb  1
Demonstration Prism
Use in technology
• Optical fibres – all high speed
telecommunication
Demonstration water jet
• Light concentrators for solar cells
Demonstration fluorescent tube
• Back-illumination for LCD TVs ~
- lightguides
Demonstration glass plate & paint
Use in sensing
• There is an evanescent wave close to the
surface, which can be used for sensing of
material close (<100nm) to the surface
100nm
Whispering Gallery at St Pauls
Whispering Gallery mode sensors
Use total internal reflection and circular orbits
nsphere>nmedium
Constructive interference condition
gives discrete set of optical modes:
resonances
Resonance shift used for sensing
reflection
Light orbit in microsphere by
quasi-total internal reflection.
Demonstration WGM, Resonance
frequency
Use of Optical Biosensors
Sensitive detection of viruses,chemicals,bacteria, proteins etc.
• Healthcare (Drug Development, Diagnosis)
• Defense (Detection of Explosives, chemical
and biological weapons)
• Police (Forensics)
• Research (Protein interactions – the
machinery of life)
Fluorescent Proteins
• Genetic code (DNA) describes fluorescent proteins
• Green Fluorescent Protein (GFP) extracted from Jellyfish,
and incorporated into other organisms by “genetic
engineering”
• A virus can add a code segment to your DNA
GFP
DNA
4 nanometer
10000 atoms
1/10000 of a hair
GFP Variants
• Genetic code engineered for different colour
Bacteria expressing different FPs
http://www.conncoll.edu/ccacad/zimmer/GFP-ww/tsien.html
Painting the Brain – The5mm
Brainbow
NMR Tomography
200mm
5cm
confocal two-photon microscopy
photography
Better transmission in the red (longer
wavelength
Two-Photon Microscopy
• Uses two photons, i.e. a light overtone. Needs high intensities
• excites only in the focus
• less scattering due to doubled wavelength
a neuron in the brain
imaged with two-photon
flourescence
Femtosecond Laser sources
1 fs = 10-15 s
100fs pulses are only 30mm thick
(This is the distance light is travelling in 100fs)
10ns
Power concentration
Pav = 1mW (like a laser pointer)
Ppeak = 1mW × 10ns/100fs = 1mW × 105 = 100W!
t
A two-photon microscope
femtosecond laser
How to see cell composition without paint
• Listen to the molecular vibration !
Complex
molecule
Water (H2O)
Sound slow-motion
118 THz
1 Billion to one
(1 second vibrations in 30 years audio)
95 THz
Methane
(CH4)
115 THz
92 THz
49 THz
47 THz
41 THz
Drive the vibration with light
• Green light has a frequency of 600THz, 10 times higher than molecular
vibrations
• Use interference of two light waves to drive vibration by the difference in
frequency
field amplitude
990Hz
1000Hz
time
990+1000Hz (10Hz difference)
999+1000Hz (1 Hz difference)
Finally: CARS Microscopy on Cells
HepG2 (Human liver) living cells in a soft-agar 3D matrix
Fat distribution in small droplets
Human Hair on this scale
Photography
Scanning Electron
Microscopy
50mmx50mmx20mm
CARS on uni-lamellar vesicle
(small soap bubble in water)
Any Questions ?