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”….

Hello Earth!

When we received a notification from the National Institute of Environmental Health Sciences (NIEHS) about the award for our proposal “Wearable Organic Electronic Film RFID Sensors for Monitoring of Airborne Toxicants”, our team was excited as never before – for the recognition of our idea by NIEHS, for the job well done during the proposal writing, and for this new two-year program that we wanted to launch ASAP.

Stepping back a couple of years before this proposal submission, at technical conversations with colleagues and business leaders, at scientific conferences, during visits of national labs and universities, and at many other occasions, I have been asked numerous times “What’s so special about your sensors that you are working on?”

To answer this key question, it is critical to recognize that there are numerous excellent sensors already available for measurements of physical, chemical, and biological parameters on interest. For example, there are available physical sensors for measurements of air pressure in automotive tires, body temperature of patients, and sudden fall motion of portable electronic devices. Numerous chemical sensors are also readily available, for example, humidity sensors in microwave ovens, carbon monoxide sensors in underground garages, nitrogen oxides sensors in exhausts of automobiles, and sensors for pH and other ions in industrial water. Lastly, more and more biological sensors are becoming available as well, for example a pregnancy test strip based on the color change produced by biofunctionalized gold nanoparticles upon their aggregation. Thus, available sensors provide information important to the end-user with high accuracy and without false readings.

However, there are numerous other practical situations, where existing sensors fall short in meeting the demanding measurement needs. Our research team focuses of the development of such new sensors for chemical and biological detection in complex environments where existing sensors will have too many false positive responses while our new sensors will provide desired accurate readings. Examples of such complex environments can be ambient air at a workplace, in an urban environment, and in a battlefield, samples of exhaled air from medical patients, and air in packaged food containers. For these and many other demanding applications, existing sensors suffer from responses to not only chemicals of interest in the air but also to numerous interferences that are present at much higher concentrations that the chemical of interest.

The two-year program that is funded by NIEHS capitalizes on recent achievements of our team and will provide innovations in three key areas:

1. A new battery-free radio-frequency identification (RFID)-based transducer platform will be leveraged from recent work by our team and will employ low cost passive RFID sensors for chemical monitoring of diverse populations. By measuring simultaneously several parameters of the complex impedance from such an RFID sensor coated with a sensing film and applying multivariate statistical analysis methods, the team will identify and quantify the non-polar and polar toxic volatile organic compounds (VOCs) with a single RFID sensor in presence of variable ambient humidity and other interferences.

2. New sensing materials will be developed that will be able to detect vapors with improved selectivity toward uncontrolled fluctuations in ambient relative humidity. The evaluation process of new sensing materials candidates will be performed using previously developed high-throughput screening infrastructure dramatically reducing the required characterization time, simplifying data manipulation, and allowing for efficient data mining for the rational downselection of materials and their further improved design. Thus, the detailed analysis of interactions of vapors with sensing materials will provide the foundation for a better understanding of the materials parameters that affect sensor selectivity and long-term stability and for the development of more quantitative and practical sensor models.

3. A prototype of wearable wireless sensor system will be developed and demonstrated that will contain replaceable passive RFID sensors. Developed sensors will be interrogated by a small-sized, wearable sensor reader that will relate the findings to a local base station.

This program promises to provide a significant impact to the modern sensing technology.

Stay tuned for more news from GE Research!

Hello Earth! I am very excited to share our results on the development of new general battery-free radio-frequency identification (RFID) sensing platform that selectively detects multiple individual chemicals with a single sensor.

Chemical sensing based on responsive materials goes back to times when the Romans used papyrus impregnated with an extract of acorns for selective colorimetric determinations of iron sulfate and copper sulfate and times when Lewis used litmus paper for detection of acids and alkalis in the late 18th century. In modern times, many types of chemical and biological sensors exist that involve electronic, optical, thermal, gravimetric, and other methods of sensing.

One of the most important parameters of sensor’s performance is its selectivity. There are many applications where sensors should be very selective because the quality of its signal is critical for further decision-making. Highly selective sensors are needed to detect pathogenic bacteria in water, the presence of many harmless species, to detect very low concentrations of toxic fumes in indoor and outdoor air in presence of many other odors, and to detect food spoilage or contamination. For these and many other reasons, existing sensors need a significant improvement in their selectivity.

I have realized that existing wireless sensors do have a significant deficiency of selectivity in their response. To solve this problem, I focused our diverse team of scientists such as analytical chemists, RF engineers, polymer scientists, and microfabrication engineers on conventional passive RFID tags that already have many but not all capabilities for performing chemical and biological sensing. As a result of our work, the technical innovation in our sensor development leverages a ubiquitous concept of asset tracking with conventional battery-free (passive) RFID tags and allows these tags to serve also as reliable and cost effective selective chemical and biological sensors.

The accomplishments of our team in RFID sensing are in the area of detection of toxic gases such as toxic industrial chemicals (TICs), volatile organic compounds (VOCs), and chemicals and bacteria in liquids. In gas-detection applications, the presence of uncontrolled amounts of water vapor in air is the biggest practical challenge for existing sensors because of the many orders of magnitude concentration difference between water vapor and gases of interest in air. The team developed these RFID sensors that overcome this critical limitation of existing sensors. These new RFID sensors detect trace concentrations of toxic gases in the presence of variable levels of relative humidity in air. The proper combination of antenna geometry and a sensing material on top of the antenna resulted in the achieved detection limit of toxic gases down to ~ 100 part per billion concentration. Detection of chemicals in liquids as well as measurements of several physical parameters is under development for applications where the low cost of these sensors and its battery-free operation are critical to making these sensors disposable. Bacterial growth detection has been demonstrated with biological RFID sensors.

This RFID sensors technology will enable capability for mass production of cost-effective sensors; detection selectivity in the presence of background interferences; zero power consumption; and implementation of a well-organized method of tracking sensor distribution over large areas and in large numbers. These passive, battery free RFID sensors are attractive when there is a need for the smallest sensor size, when a sensor is deployed for a long-term application, when a high power RF transmission is prohibited (e.g. on the manufacturing floor, in hospitals), or when the sensor should be low cost for disposable applications. These finding could lead to the design and manufacture of such RFID sensors for diverse chemical and biological detection applications ranging from healthcare, to security, food packaging, and pollution prevention.

Stay tuned for more news from GE Research!

Happy coming holidays!

Thank you all for the comments on our sensing results with iridescent butterfly scales. We recently learned about a story “Butterflies inspire GE’s sensor research” that ran this week on the Associated Press newswire. Check it out!

We are starting a next phase in our experiments that will help us gain further knowledge to move on in fabricating our own intricate nanostructures.

I just have seen that GE.com features our recent work with tropical butterflies that we have published in Nature Photonics. We have discovered that nanostructures of butterfly wing scales selectively respond to different vapors. This selective response is observed as very stable slight changes in iridescent colors of butterfly wings.

Numerous times after our paper was published, I was asked how did I come up with this idea? It is simple and can be summarized in several key steps: (1) to know your field of research; (2) to understand clearly the unmet needs; (3) to know the solutions that were tried and worked in the past; (4) to be open to non-traditional, disruptive solutions; (5) to understand other scientific areas and imagine how the observations or solutions from those areas can be applied to your unmet need.

My concept of using scales of tropical butterflies for vapor sensing came from understanding the principles of photonic sensors. While these photonic sensors based on structural color can be more attractive that those based on organic dyes (organic dyes tend to photobleach), the unmet need in photonic sensors is their poor selectivity – one still needs to have an array of such sensors for more selective vapor detection. Accidentally, I came across an image of a tropical butterfly at a very high magnification where the details of butterfly wings were at the nanoscale range. It became clear to me that these features can be used for vapor sensing and we may be able to get more selective vapor responses because of the well-organized hierarchical nanostructure of the butterfly wing scale.

Overall, my approach surprisingly matches with a quote from Dave Grusin, composer and jazz musician, that I have seen on a paper coffee cup: ‘In my career I’ve found that ‘thinking outside the box’ works better if I know what’s ‘inside the box.”

Our research team studied vapor responses in great detail and characterized the butterfly scales with great nano-characterization tools we have at GE Global Research. Our corporate team did a great job explaining on GE web page the vapor-sensing concept and putting an animation together.

Tropical Morpho butterflies are famous for their brilliant iridescent colors, which arise from ordered arrays of scales on their wings. In our paper, my team shows that the iridescent scales of the Morpho sulkowskyi butterfly give a different optical response to different individual vapors, and that this optical response dramatically outperforms that of existing nano-engineered photonic sensors. The reflectance spectra of the scales provide information about the nature and concentration of the vapors, allowing us to identify a range of closely related vapors-water, methanol, ethanol and isomers of dichloroethylene when they are analyzed individually. By comparing the reflectance as a function of time for different vapors, we deduce that wing regions with scale structures of differing spatial periodicity give contributions to the overall spectral response at different wavelengths. Our optical model explains the effect of different components of the wing scales on the vapor response, and could steer the design of new man-made optical gas sensors.

My research into butterfly wings was inspired by the review article written by Pete Vukusic and J. Roy Sambles in Nature in 2003 [see Nature 424,852 -855 (2003)]. In that article, the authors described the nanometer-scale photonic structures in the wing scales of the Morpho butterfly and the striking blue iridescence that they generate. Imagining a combination of this new to me knowledge with the optical sensing principles that I was practicing already, I realized that the underlying physics of this iridescence should be strongly influenced by the gas environment surrounding the nanostructures. After my initial careful experiments, it was clear that the underlying optical properties exhibited by the nanostructures on butterfly wings could offer a promising route to highly selective chemical sensing capabilities. I was fortunate to attract interest from several scientists to carry out together this small research further. The assembled research team that explored further the origin and details of this unique selective vapor response of butterfly wing scales. The team included Professor Helen Ghiradella from the Department of Biological Sciences, University at Albany; and Alexei Vertiatchikh, Katharine Dovidenko, Eric Olson, and James Cournoyer from GE Global Research.

Our next step is to find a way to mimic nature and to design acute and robust chemical sensors that will offer new attractive sensing solutions in the marketplace. That is what we are focused on solving. If successful, it could launch a new direction in the design of highly selective chemical sensors with straightforward colorimetric readout that could replace current complicated sensor arrays. We foresee that this kind of sensor could be in the market within the next five years. Of course this depends on the advances in fabrication technologies and further detailed testing.

Stay tuned for more news from GE Research!