Psst: Looking for a really sensitive in Vivo sensor? – talking papers series, #3
The whisper is that IPAS are looking to work with people who need to measure proteins or other bio-molecules “in-Vivo” thanks to a new sensing architecture demonstrated in the paper “Highly efficient excitation and detection of whispering gallery modes in a dye-doped microsphere using a microstructured optical fiber”
Work led by Alexandre Francois shows that whispering gallery modes (WGM) can be excited and detected in dye doped micro spheres via a microstructured optical fibre (MOF). By sticking a tiny sphere to the end of a very thin fibre and running a series of experiments Alex & Kris have demonstrated a new architecture for sensors that not only works but provides a substantial increase in excitation & collection efficiency. The overall efficiency of this robust architecture is 200 times greater than that of more conventional schemes.
The curiously named “whispering gallery mode” refers to a special kind of resonance that occurs when light is trapped within a resonator by total internal reﬂection. I remember sitting in an IPAS seminar in which Kris Rowland eloquently and with much wit described WGMs using a picture like the one below:
To quote Kris from that presentation “A whispering gallery mode is said to exist when a light wave bouncing around the perimeter of a resonator returns in phase. This means that after one round trip, when the wave “catches its tail”, the wave overlaps itself identically.”
So, exactly how does one precisely position a tiny (10 micrometer) polystyrene sphere on the end of a very thin (130 micrometer) glass fibre? To get those dimensions in perspective, consider that a human hair is typically around 18-80 micrometre in diameter. It turns out that after a bit of ‘playing around’ (quite literally so, according to this audio grab from IPAS director, Prof Tanya Monro) the sphere tends to centre itself on one of the three holes in the MOF and stick there by a combination of electrostatic and surface forces. The end result – a compact and robust architecture for applications such as localized in-vivo/vitro biosensing.
Which leads us to the future…
IPAS are now actively looking for researchers with questions that can (only) be answered by “in vivo” measurement of bio-molecules. There is rich medical information that we cannot currently measure by taking measurements of externally accessible bodily fluids or with existing sensing technologies. This new technique opens up the possibility of increasing out understanding of the origins of disease and our response to treatment at a local level inside our bodies. Imagine, for example, being able to measure the response of a tumor to a new cancer treatment in real time ( “in vivo” and “in situ”). It is hoped that the development of specific sensors based on this new architecture will be extremely useful.
To paraphrase Tanya from the audio interviews that accompany this story:
“one day clinicians may have a little kit of spheres that have been functionalised to detect all their favorite bio markers and make a clinical decision on which ones to pick up on the end of a fibre and stick into the patient”.
Mike Seyfang for IPAS “talking papers” series