Developing new bio-inspired sensors: breakthroughs from butterflies
Hello Earth !
We are very enthusiastic about our new DARPA Program to develop innovative bio-inspired nanostructured sensors that would enable faster, more selective chemical detection. This program is a collaborative effort of GE Global Research with the Air Force Research Laboratory, State University of New York at Albany, and the University of Exeter and includes for several important tasks as shown in the graphic to the left. Three years ago, we discovered (Nature Photonics 2007, 1, 123-128.) that nanostructures from wing scales of butterflies exhibited acute chemical sensing properties. Since then, we have been developing a dynamic, new sensing platform that replicates these unique properties.
The main focus of our new very challenging program is to eliminate the serious limitation of existing sensors – their poor selectivity – and to demonstrate selective detection of analytes of interest in the presence of several closely related interferences. One can argue that to meet this goal is impossible and it is “science fiction”. We would fully support this statement if one were using conventional sensing approaches based on univariate sensor responses or combining individual sensors in arrays. The philosophy of sensor arrays brings one only to a certain level of improved performance of an array over an individual sensor, without the ability for accurate, reliable, and dynamic sensing in complex realistic situations.
Conventional gas sensors do not compete for the resolution and selectivity with sophisticated high-end laboratory instrumentation that is designed to identify and quantify unknowns down to ppb-ppt levels in complex mixtures containing hundreds or thousands of volatiles. Nevertheless, gas sensors attempt to compete with other fieldable microanalytical instruments. Over the recent years, these instruments have become more portable, more energy-efficient, and less costly. For example, advances in miniaturization and ionization sources in mass spectrometry are bringing micromachined mass-spectrometry devices to the point of operating at ambient atmospheric pressure without vacuum pumps. Advances in miniaturization in ion mobility spectrometry are bringing these devices to the form factors and power requirements similar to conventional packaged sensor systems. Advances in miniaturization in gas chromatography are establishing the ability to detect and quantify a dozen of volatiles in less than a minute with cell-phone-sized micro-gas analyzers.
While we and other proponents of gas sensor technologies continue to bring the old arguments of low sensor cost and its small size, these arguments, one by one, become less valid when comparing to the state-of-the-art, fieldable microanalytical instruments based on competing detection concepts.
Our DARPA-funded program will detonate this status quo and will demonstrate how to selectively detect numerous gases with a single sensor. I would like to point out that about 100 years ago, Clyde W. Mason studied the effects of liquids of different refractive index on the color of the reflected light when these liquids were applied onto wings of iridescent butterflies. Our demonstrations of these effects are shown below. Here are Color changes of a Morpho butterfly upon exposure to liquids of different refractive index. On the left is a butterfly before exposure to liquids and on the right are the results of exposure of the left forewing to ethanol (n = 1.362) and left hindwing to toluene (n = 1.497).
In our research at GE, we have learned how to take this knowledge of the natural optical responses of nanostructures of butterfly scales to pure solvents of different refractive index and to expand this optical phenomena into the selective detection of numerous gases and their mixtures with a single bio-inspired photonic structure as shown in the figure below.
How many gases can we detect with a single bio-inspired nanostructure? Stay tuned for our reports on 2, 5, maybe 10, and maybe even 20 gases with a single sensor. Science fiction or science? Stay tuned and you will be the first to say “wow”….
