TNT Cages
The nanosensors are comprised of two main components: metal-organic polyhedral (MOP) molecular cages, and silicon nanowire (SiNW)-based field effect transistors (FETs). The coordination of the two components is what allows for the sensing of 2,4,6-trinitrotoluene (TNT).
Let’s start with the MOPs. Picture a tiny chemical cage with just enough space inside to accommodate a single molecule, such as TNT. Beyond getting the size right, you also have to make sure the target molecule will match up with the cage—kind of like a puzzle piece. Researcher Louis de Smet explains:
“In the case of relatively small molecules, as with explosives, the challenge is to ensure that the cage structure is not only the right size but that it also has the right anchor points so that the molecule can click into place—thus rendering it detectable.”
But trapping TNT molecules in MOP cages is only the first step. You need some way to determine if you’ve caught one—that’s where the SiNW-based FETs come into play. When there’s a local change in charge density on these devices, the current flowing through the SiNW channel is altered. The change in charge density is induced by the binding of an ion or a molecule.
Therefore, by placing several MOP cages on top of a SiNW chip, you create a system that will reliably respond to your target analyte. “The presence of [TNT molecules] causes the electrical conductance of the underlying silicon nanowires to change in a very characteristic way,” said de Smet. “We can measure this and thus confirm that we have actually found TNT molecules from an explosive.”
Done with Detection Dogs
Furthermore, by adjusting the properties of the MOPs, the sensor can be tuned to detect more than just TNT. In this way, the research offers a new method for designing and developing sensors to accommodate different target molecules.
For more nanosensor news, read Nanosensors Could Help Diagnose and Treat Cancerous Tumors.