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Biophotonics

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).

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Biophotonics

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  1. Biophotonics www.postech.edu/~hjcha/jelyfish.jpg

  2. Electromagnetism • Its all described by Maxwell’s equations (a Scott, 1831-1879) (you need to know maths to do physics …)

  3. Total internal Reflection

  4. Total internal Reflection • Snells law of refraction (contained in Maxwell’s Equations) a a medium a: na medium b: nb b Demonstration Prism

  5. Use in technology • Optical fibres – all high speed telecommunication • Light concentrators for solar cells • Back-illumination for LCD TVs ~- lightguides Demonstration water jet Demonstration fluorescent tube Demonstration glass plate & paint

  6. 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

  7. Whispering Gallery at St Pauls

  8. 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 Light orbit in microsphere by quasi-total internal reflection. reflection Demonstration WGM, Resonance frequency

  9. 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.

  10. 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

  11. GFP Variants • Genetic code engineered for different colour Bacteria expressing different FPs http://www.conncoll.edu/ccacad/zimmer/GFP-ww/tsien.html

  12. Painting the Brain – The Brainbow 5mm NMR Tomography 200mm 5cm confocal two-photon microscopy photography

  13. Better transmission in the red (longer wavelength

  14. 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

  15. t 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!

  16. A two-photon microscope femtosecond laser

  17. How to see cell composition without paint • Listen to the molecular vibration ! Complex molecule Water (H2O) Sound slow-motion 1 Billion to one (1 second vibrations in 30 years audio) 118 THz 115 THz 49 THz 95 THz 92 THz 47 THz 41 THz Methane (CH4)

  18. 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 time 990+1000Hz (10Hz difference) 990Hz 1000Hz 999+1000Hz (1 Hz difference)

  19. 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

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

  21. Any Questions ?

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