Not all sensors are electronic, or at least if you expand the scope of sensor technology, measurement techniques (which is what sensor technology is about) can also be chemical or physical, among other things. In this case, the sensor is built from DNA and it’s called a DNA nanosensor.
The idea behind this particular nanosensor came from study of natural biosensors within cells. All living things monitor their condition, from the largest scale of organs to the smallest nanoscale chemistry of individual cells. At the level of the cell, there are billions of specialized proteins or RNA that perform the task of a sensor by reacting to the presence of very specific molecules. For example there are many loops or cyclical chemical pathways, where a certain condition, say a need for energy, triggers a chemical and physical change in one sensor protein. It in turn signals for production of more energy. When enough energy is produced, another sensor protein accumulates to the point where it turns off energy production.
Scientists at the University of California, Santa Barbara (USA) and the University of Rome Tor Vergata wanted to emulate this natural sensor-signal process with a specific target in mind. As published in the Journal of the American Chemical Society [04 August 2011, paywalled, Transcription Factor Beacons for the Quantitative Detection of DNA Binding Activity] they developed a sensor made from DNA that becomes luminescent (glows) when it encounters a particular protein of the type called a transcription factor. These are proteins used by cells to control the production of molecules (usually other proteins). There are literally thousands of transcription factors, but when scientists ‘reprogram’ cells for example in stem cells; they often change only a handful of factors. The trick is to know whether the reprogramming has worked properly or not. That’s where the nanosensors come in.
There are many techniques for reading transcription factors; most of them require laborious separation of specific proteins and examination either under microscopes or with chemical detectors. As one of the researchers put it, “With the new sensors, we just mash the cells up, put the sensors in, and measure the level of fluorescence of the sample.”
The sensors are built by re-engineering three natural DNA sequences, each set to recognize a different transcription factor, by adding a molecular switch that becomes fluorescent when activated. Eventually this technique can be extended to thousands of transcription factors. In turn, the technique can help scientists and doctors monitor the level of drug activity, screen for certain kinds of cancer signaling proteins or any other application where transcription factors might reveal an underlying biological condition. In short, this technique could be very useful and practical.
The technique also seems relatively simple, but it will ultimately compete with many other technologies (sometimes called assay technology) that read the presence of transcription factors and other protein signaling molecules. It’s a burgeoning field of cell biology and of sensor technology-in-the-very-small.