‘Fastest ever’ responsive humidity sensor by organic nanofibers

Humidity sensing is of paramount importance in the control systems for industrial processes. For example, humidity sensing is vital in chemical, food and textile industries. Most of the currently available humidity sensors are based on ceramic materials as sensing element. They are expensive because of their production methods. Organics based sensors are attractive alternative as they can be prepared by low cost methods. However, the performance of organic material as sensing material has so far been unstable. But here come nanofibers …

To overcome the unstable performance, Prof. Giridhar U. Kulkarni and his team from Jawaharlal Nehru Centre for Advanced Scientific Research, India selected a new class of organic materials, namely ‘supramolecular system’ where molecules built via non-covalent interactions as sensing material, demonstrated a novel breath sensor by transferring the organic system into nanofibers and used as active humid sensing material to monitor the respiration rate.

Prof. Giridhar U. Kulkarni
Prof. Giridhar U. Kulkarni

The team designed supramolecular system in nanofiber morphology mainly because the nanofiber structure provides low scattering conducting pathsand easy alignment across the electrodes in field-effect transistor. The nanofibers of diameter in the range of 100–300 nm were prepared by the self-assembly of donor and acceptor molecules through charge transfer in water. The as-prepared nanofiber film enhanced charge transfer interaction and hence the conductivity and worked well in the ambient conditions.

The integrated device was tested for monitoring humidity in the exhaled breath from many volunteers undergoing exercise and alcohol induced dehydration. The nanofiber based humid sensor monitored the relative humidity (RH) present in nasal breath more accurately. The film of nanofibers exhibited high sensitivity (≈104), and nanofibers showed ultrafast response (≈10 ms), suggesting that the device could be implemented meritoriously for continuous monitoring of humidity in human breath. The fabricated devices were found to be stable over 8 months. As the sensing element was a simple organic system from solution processes, this sensor is essentially of low cost and also environment friendly.

In brief, the ultra-fast, wide range, highly sensitive resistive humidity sensor made of supramolecular (organic) nanofibers opened up new insights into diagnosis through breath analysis.

Details of this research work was published in Scientific Reports (Nature Publisher), Feb 2014, which can be assessed here: http://www.nature.com/srep/2014/140217/srep04103/full/srep04103.html#affil-auth