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

Demonstration Prism

Total internal Reflection• Snells law of refraction (contained in Maxwell’s Equations)

medium : n

medium : n

)sin()sin( nn

5.1n

2n

3.1n

2n

2.1n

1n

Use in technology

• Optical fibres – all high speed telecommunication

• Light concentrators for solar cells

• Back-illumination for LCD TVs ~- lightguides

Demonstration glass plate & paint

Demonstration fluorescent tube

Demonstration water jet

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 sensorsUse total internal reflection and circular orbits

Constructive interference condition gives discrete set of optical modes:

resonances Resonance shift used for sensing

Light orbit in microsphere by quasi-total internal reflection.

nsphere>nmedium

frequency

refle

ctio

n

Demonstration WGM, Resonance

Use of Optical Biosensors

• Healthcare (Drug Development, Diagnosis)

• Defense (Detection of Explosives, chemical and biological weapons)

• Police (Forensics)

• Research (Protein interactions – the machinery of life)

Sensitive detection of viruses,chemicals,bacteria, proteins etc.

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

4 nanometer10000 atoms1/10000 of a hair

DNA

GFP

GFP Variants

• Genetic code engineered for different colour

http://www.conncoll.edu/ccacad/zimmer/GFP-ww/tsien.html

Bacteria expressing different FPs

Painting the Brain – The BrainbowNMR Tomography

confocal two-photon microscopy5cm

5mm200m

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 brainimaged with two-photonflourescence

Femtosecond Laser sources1 fs = 10-15 s

100fs pulses are only 30m thick(This is the distance light is travelling in 100fs)

t10ns

Power concentrationPav = 1mW (like a laser pointer)

Ppeak = 1mW × 10ns/100fs = 1mW × 105 = 100W!

femtosecond laser

A two-photon microscope

How to see cell composition without paint

• Listen to the molecular vibration !

92 THz 47 THz

115 THz118 THz 49 THzSound slow-motion1 Billion to one(1 second vibrations in 30 years audio)

Water (H2O)

Methane (CH4)

95 THz 41 THz

Complexmolecule

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

990+1000Hz (10Hz difference)

999+1000Hz (1 Hz difference)990Hz 1000Hz

time

field amplitude

Finally: CARS Microscopy on CellsHepG2 (Human liver) living cells in a soft-agar 3D matrix

Fat distribution in small droplets

50mx50mx20m

Human Hair on this scale

Scanning Electron Microscopy

Photography

CARS on uni-lamellar vesicle (small soap bubble in water)

Any Questions ?