March R&D Round Up

E-mail Melanie Martella

This month's collection of intriguing sensor research and development projects includes a sterilizable flexible transistor, a very speedy radiation sensor, and a low-cost sensor designed to assess how your immune system is doing.

A Sterilizable, Flexible Transistor
When it comes to tucking an embedded system into the human body, there are a number of barriers to success; it has to be biocompatible, it has to be a low-voltage device, and it needs to be sterile (and ideally sterilizable). If it's a wearable medical device, it should be comfortable to wear. A newly developed flexible organic transistor, developed by an international research team, may make these endeavors easier. Dr. Takao Someya, a professor at the University of Tokyo led the research, collaborating with Associate Professor Tsuyoshi Sekitani of the University of Tokyo and Professor Yueh-Lin (Lynn) Loo of Princeton University. They worked with the Max Planck Institute for Solid State Research, NIST, Hiroshima University, and Japan's Nippon Kayaku Co. and what they produced was an organic transistor that can be readily manufactured on a biocompatible polymeric film, has a driving voltage of 2 V, and can survive the standard 150°C heat treatment used to sterilize medical devices without suffering electronic degradation.

The team used densely packed self-assembled monolayer (SAM) films to create a gate insulator film on a biocompatible polymeric film, which was then coupled with an encapsulation layer of organic/metal composite materials and organic semiconductors that are both highly thermally stable and have high mobility. The resulting transistor is bendy, biocompatible, and boilable! For more technical details, I'd advise you to either read the full study published online in Nature Communications or the shorter summary article written for by Karen McNulty Walsh and Peter Genzer, titled "The world's first sterilizable flexible organic transistor."

A Novel Speedy X-Ray Sensor
SINTEF scientists working at the Micro and Nano Laboratory in Oslo's Gaustadbekkdalen have developed a silicon drift diode (SDD) that acts as a highly sensitive X-ray detector capable of revealing material compositions in a fraction of a second. the device uses X-ray spectroscopy to work its material identification magic and it's created by slowly and carefully building up a physical nanostructure on both sides of a silicon wafer, then doping the structure with charged atoms. (Since it takes 8 weeks to make and a single grain of dust can destroy all your hard work, I'm guessing a certain amount of breath-holding is also entailed.) The X-ray beam goes through the object being examined, enters the window side of the sensor, and then the device essentially measures the number and energy levels of the photons and uses the differences in absorption energy of the component elements to differentiate between materials. It's a tiny little piece of freakishly clever genius and you can read more about it in the article, "Nano-level detective."

Immune System Sensor
What's cheap, glass, and can count both the number and type of white blood cells in a patient's blood or fluid sample? The answer is the integrated microfluidics-waveguide sensor (say that three times fast) developed at the Stanford University School of Medicine. The device is the brainchild of Dr. Manish Butte who was looking for a better way to screen newborns for severe combined immunodeficiency, a condition in which a child lacks most of his or her immune system. As he quickly realized, lots of other conditions could benefit from an analysis of the white blood cells present in a fluid sample.

The sensor itself is a small rectangle of glass, impregnated with a strip of potassium ions to act as a waveguide. The fluid sample is mixed with antibodies specific to the type of white blood cell to be measured and each antibody is attached to a tiny bead of magnetic iron. Any white blood cells of the desired type will bond with the antibodies. The general idea is to shine laser light through the waveguide and measure how much light makes it to the far end. The tiny iron beads attached tot the white blood cells of interest reduce the amount of light that makes it through, giving you a measurement of how many white blood cells are present in the sample. You can read the full news release, "New Stanford immune-system sensor may speed up, slash cost of detecting disease," here.