The word biophotonics deserves a definition page on this blog.  I’ll get to that presently.  Before I do here is a site that takes a similarly broad view of the field to my own.  The University of Surrey’s Advanced Technology Institute has a biophotonics initiative that includes the following fields:

* optical molecular motors (+ overview of computational biophotonics) (E. Gehrig and O. Hess)
* ultrafast imaging, spectroscopy and control (J. Allam)
* two-photon imaging (J. McFadden)
* applications related to wide band gap materials (D. Lancefield)
* application of optical-fibre techniques in biomedicine (A. Rogers)
* solvent effects in protein folding (?) (D. Faux)
* VCSELs for high power applications in medicine and sensing; tuneable devices for in-situ spectrometers. (S. Sweeney / T. Sale)
* ultrafast circular dichroism for biomolecular spectroscopy (B.Murdin)
* photodynamic therapy (S. Sweeney)
* new nanofabrication facilities (D. Cox)

The fourth one down encompass all those articles I have posted on butterflies and diatoms.

ATI Biophotonics page

In a previous entry I have pointed out the biophotonic possibilities in butterfly wings. A recent article in the Journal of Experimental Biology provides an extensive survey of wing scale optical properties. There had been no less than four different methods proposed by which butterfly wing scales could reflect colored light, this study found that only one method is at work.

The … analyses … of colour producing butterfly scales document that all species are appropriately nanostructured to produce visible colours by coherent scattering, i.e. differential interference and reinforcement of scattered, visible wavelengths.

They also found that the blue pigment of one Papilio species is not an incoherent Tyndal scattering phenomenon but rather the result of a fluorescent blue pigment. The take home message is that whether the nanostructuring is external or internal the method of filtering is the same.

JEB Abstract

Secondary harmonic generation (SHG) is when the frequency of light that impinges on the surface of a material is doubled by some physical characteristic of the material.  The shifted light is emitted with a very different color than the input light.  These starch crystals from rice are showing SHG of incident red light.  The cool thing about this biomimetic generator is that the light can impinge over a wide range of angles.

Image info

An explanation of SHG

Two researchers from Arizona State University have applied for a patent on a method for integrating photonic systems with living tissue. The exact nature of the invention is well concealed by patent, but the research likely falls out of Pizziconi’s research on chlorosomes of cyanobacteria. I will peruse the primary literature for further news.  

One application of the proposed invention is the enhancement of well-known photoactive semiconductor devices, such as Si photovoltaic cells using nanoscale biophotonic constructs that are either acquired, harvested or otherwise manipulated in their natural or adapted state using the method and apparati described herein to achieve desired FoM performance characteristics

Patent Application

The Innos R&D company announced its first nanoscale patterning breakthrough at the Southhampton University nanofab facility..  Darren Bagnall has patterned silicon after the structure of a night flying moth cornea.  The moth cornea allows very little light to escape making it an excellent anti-reflective coating. 

Press release

Bagnall’s Homepage

Blue is a color seldom achieved through dye, at least in nature. Bowerbirds get their iridescent blue the same way most insect and fish blues are generated, through trapping of light between thin layers of disparate material. This biophotonic filter allows only light of a specified wavelength to escape the surface. In the case of the satin bowerbird this light is UV-blue. This type of coloration, known as structural coloration, is quite common in bird feathers and is usually the result of many thin layers of keratin and melanin. with an air interface at the surface. The bowerbird however has only a single pair of layers, one of keratin and a melanin layer just a few granules thick.  Researchers at Auburn and Queen’s University (Canada) have successfully modeled this simple biophotonic system and can account for the variation in the color as the observers position changes. As predicted from our thin-film model, measured hues shifted to shorter wavelengths at increasing angles of incidence and reflectance. Moreover, we found that individual variation in barbule nanostructure can predict measured variation in both hue and UV-chroma. Thus, we have characterized the microstructure of satin bowerbird barbules, uncovered the mechanisms responsible for producing ultraviolet iridescence in these barbules, and provided the first evidence of a nanostructural basis for individual variation in iridescent plumage color.

Link to Summary

We have previously mentioned cases where a man-made solution to a problem is later discovered to use a similar approach to what is found in nature. Here is another example.

The BBC picks up on one of the articles in the current issue of Science that I mentioned below. The article highlights the research of Peter Vukusic and Ian Hooper at the University of Exeter who determined that the wing scales of African swallow tail butterflies (and keep your Monty Python references to yourselves) bear a striking resemblance to two dimensional photonic crystals used in the creation of high-efficiency LEDs.

Like its counterpart in a high emission LED, it prevents the fluorescent colour from being trapped inside the structure and from being emitted sideways.

The scales also have a type of mirror underneath them to upwardly reflect all the fluorescent light that gets emitted down towards it. Again, this is very similar to the Bragg reflectors in high emission LEDs.

“Unlike the diodes, the butterfly’s system clearly doesn’t have semiconductor in it and it doesn’t produce its own radiative energy,” Dr Vukusic told the BBC News website “That makes it doubly efficient in a way.

“But the way light is extracted from the butterfly’s system is more than an analogy - it’s all but identical in design to the LED.”

Thomas Fuhrmann of the University of Kassel in Germany has been looking at the micropatterning of diatom cell walls as possible photonic crystals and photonic lasers. In a previous post I ointed out one of Furhmann’s articles. This web page has a few nice visuals with proof that it is possible to dope the silica cell wall with laser dyes then excite them to emit particular color light with a laser. Furhmann is at the exciting stage of both cataloging the diversity of naturally occurring photonic waveguides and band gap materials in the diatom cell wall and exploring the flexibility of the system. Parts of this project are in what I have called the manipulative phase while some of the other research is in the investigative phase. Since diatoms are so easy to culture and so uniform in their properties I would be unsurprised to see this project make a serious leap towards commercialization in the next couple years

Website

I hope that by now anyone looking at silica based skeletons is wondering about the optical potential. Diatoms are unicellular algae that produce silicaceous cell walls in a stunning variety of shapes. The microstructure of the cell wall has that nanoscale serially repeated structure familiar to physicists studying photonic crystals. In this case the growing diatoms are exposed to laser dyes which are then incorporated into the skeleton. When excited by a laser the dyes emit light which is then filtered by the photonic crystal waveguide that is the cell wall.

Article

In the research described at this website the structural basis for a sexually dimorphism in butterfly wing color is described as a biophotonic crystal. Butterflies in the genus Polyommatus live in lowlands and highlands of Eastern Europe and the Middle East . At lower elevations the males have vibrant blue flash coloration similar to the Morpho genus of the Amazon.  At higher elevations the male is far more drab.  The reason for this difference is probably that the drabber coloration allows males at higher elevation (and lower ambient temperature) to absorb more sunlight in order to get heated up for the day.  The basis for the difference is shown to be a ‘pepper pot’ morphology in the fine structure of the wing.  As the SEM at the top of this article shows, there is a honeycomb of tiny holes that serve as a photonic band gap material. This structure is missing in the high altitude species. Geteza I. Mark of the Nanostructures Laboratory in Budapest has modeled the surface of the wing as a series of chitin layers. His results show the same high reflectance of blue light seen in the lowland forms. Website