Moscow: Researchers have developed an ultra sensitive detector based on black silicon that can be applied to identify the majority of explosives, or highly toxic pollutants for medical and forensic analysis.

The study, published in the journal ACS Sensors, noted that the new device can detect trace amounts of nitroaromatic compounds which make up most of the explosives.
The researchers, including those from Far Eastern Federal University (FEFU) in Russia, said the sensor is made from black silicon which has an ultrasmall, nanoscale spiky surface exhibiting unique optical properties.

They said this surface is covered with a single layer of complex organic molecules called carbazole to impart the substrate with certain important functions such as the ability to bind and concentrate nitroaromatic compounds on the surface.

The carbazole layer makes the device sensitive to widely spread nitroaromatic substances such as trinitrotoluene, commonly called TNT, an explosive.

However, the researchers added that the sensor does not react to the presence of other molecules like benzene, methanol, ethanol, and so on.

“Nitroaromatic compounds can be found in the waste waters of paint plants or military facilities and are extremely dangerous for the environment. Moreover, they are parts of many explosives as well. Their detection in trace concentration represents an important and complex practical task,” said study co-author Alexander Kuchmizhak from FEFU.

The study noted that the sensor identifies the presence of nitroaromatic compounds by registering the changes in the way the carbazole layer reacted to light.

“Combination of unique morphological and optical properties of black silicon being combined with easy-to-implement methods of surface chemistry used to functionalize silicon surface with carbazole molecules allowed to achieve unprecedented sensitivity,” explained study co-author Alexander Mironenko from FEFU.

He said the sensor can detect nitroaromatic compounds at concentrations down to a part per trillion.
“Extremely broad dynamic measurement range is caused by the unique spiky morphology of black silicon that provides uneven local concentration of carbazole molecules creating surface sites with different sensitivity,” Mironenko said.