Real-time monitoring of environmental emissions is key to unravelling the local and global trends and complicated side effects of air pollution. To support this work, there is an urgent need for miniature, low power and ultra-sensitive gas sensors.

Carbon nanotubes, thanks to their hollow geometry and large surface area to volume ratios, are excellent candidates for ultra-sensitive gas/chemical sensors. However, in spite of these promising properties, electronic-nose systems based on nanomaterials are often bulky, power hungry and expensive.

One of the drawbacks of current technology is the need for an external measurement unit for sensing, processing and recognition of the measured response. Long wires used for routing are prone to parasitics and noise coupling, and they also limit the number of nanosensors that can be packed on a single chip.

Monolithic integration

Creating nanosensors on a commercial foundry chip would enable the realization of miniaturized and high-performance nanosystems of the future. Another benefit of monolithic integration is the ability to perform signal detection, amplification, buffering, storage and recognition on a single chip and possibly wireless transmission (with on-chip coils).

Recently, researchers from Northeastern University, Boston, US, have reported a technique for the integration of ss-DNA-decorated SWNTs onto CMOS circuitry to form nanoscale chemical sensors. Carbon nanotube based sensors offer high sensitivity to volatile gases. What's more, their lack of selectivity can be enhanced by decoration of deoxyribonucleic acid (DNA) molecules.

Utilizing low-voltage electric field assisted assembly, the team has incorporated SWNTs onto CMOS circuitry without causing any damage to the host chip. After assembly, the SWNTs were successfully decorated with ss-DNA by exploiting non-covalent π-π stacking interactions.

High-performance package

SWNT-based chemical sensors with and without a DNA coating have been demonstrated on a functional CMOS chip. The gas-sensing response is expected to be DNA-sequence-dependent, which is one of the motivating factors to use DNA-decorated SWNTs as selective gas sensors. The scientists show that DNA decoration enhances the sensitivity of the SWNTs to methanol by ~300%. In addition, the sensors are reusable and have a very fast response time.

The integration approach put forward by the group is simple and versatile and could help to realize high-sensitivity and low-power nanosystems for environmental detection and health monitoring.

This work has been published in the journal Nanotechnology.