Biophotonics

Electromagnetism Its all described by Maxwell’s equations (a Scott, ) (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   

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 sensors Use 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. n sphere >n medium frequency reflection 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 nanometer atoms 1/10000 of a hair DNA GFP

GFP Variants Genetic code engineered for different colour Bacteria expressing different FPs

Painting the Brain – The Brainbow NMR Tomography confocal two-photon microscopy 5cm 5mm 200  m 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 = s 100fs pulses are only 30  m thick (This is the distance light is travelling in 100fs) t 10ns Power concentration P av = 1mW (like a laser pointer) P peak = 1mW × 10ns/100fs = 1mW × 10 5 = 100W!

femtosecond laser A two-photon microscope

How to see cell composition without paint Listen to the molecular vibration ! 92 THz47 THz 115 THz118 THz49 THz Sound slow-motion 1 Billion to one (1 second vibrations in 30 years audio) Water (H 2 O) Methane (CH 4 ) 95 THz41 THz Complex molecule

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 Hz (10Hz difference) Hz (1 Hz difference) 990Hz1000Hz time field amplitude

Finally: CARS Microscopy on Cells HepG2 (Human liver) living cells in a soft-agar 3D matrix Fat distribution in small droplets 50  mx50  mx20  m Human Hair on this scale Scanning Electron Microscopy Photography

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

Any Questions ?