
524 Nanosensors: Physical, Chemical, and Biological
four-probe conductometric chemical sensors. They reported a detection limit
for NO
2
of 3 ppm with response/recovery times ∼ seconds. The change in the
electrical conductivity was observed even near room temperature. (ii) Fields
etal. (2006) developed a hydrogen sensor from single SnO
2
NBs, synthesized
via catalyst-free thermal evaporation. The sensitivity and response time of the
sensors were measured without any catalyst on the surface to 2% hydrogen at
temperatures between 25°C and 80°C. A sensitivity >0.3/(% H
2
), with a response
time of about 220 s and power consumption of only 10 nW a