Sensing single molecules

Concept art of a molybdenum disulfide field-effect transistor based biosensor demonstrated by UCSB researchers with ability to detect ultra-low (femtomolar) concentrations with high sensitivity that is 74-fold higher than that of graphene FET biosensors. Credit: University of California at Santa Barbara

Researchers at the University of California, Santa Barbara, have been able to demonstrate a sensors that can detect single molecules, a holy grail for preventive medicine. Imagine being able to detect since cancerous cells ...

This has been possible by using MoS2, molybdenum disulfide, of which I posted a news just few days ago in relation to photon - electrons conversion.

A completely new generation of sensors is being studied, based on nanotechnology. Graphene has been demonstrated as an effective substrate for developing sensors and at Santa Barbara they have shown that MoS2 can be much better than graphene as a sensing substrate, over 70 times better!

When you are dealing with sensor what you are looking for is to create a discontinuity, like an increase of decrease in conductivity, whenever the substance you are looking for is present. The less substance is needed to activate this discontinuity the more "sensitive" your sensor is.

MoS2 has what the scientists call a big band-gap, that is there is quite a difference in energy needed to trap electrons where they are (no conductivity) and the one needed to let they roam freely (conductivity). In turns, this difference not only makes it clear when there is conductivity or insulation, it is also blocking undesired currents (leakage) that may blur the interpretation of the signal from the sensor. 

Graphene, on the contrary, has a zero band gap, is an ideal conductor and in order to use it as a semiconductor (like a FET transistor) you need to add specific doping. The problem with that is the leakage currents. Being such a wonderful conductor these currents more than happily move around with the result of blurring the signal. Hence its lower sensitivity with respect to MoS2.

Being able to create MoS2 sensors would open up application in health care as well as in other sectors, like environment monitoring. By working at the nano level we can also use an infinitesimal amount of power and that in turns would allow dissemination of these sensors every where eventually changing the way we look at the world and ourselves.

Author - Roberto Saracco

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