Chemical sensors are useful for analyzing odors from food samples and detecting atmospheric gases.  The "electronic nose" was developed in 1988 to determine the quality and freshness of food samples using traditional sensors, but more recently the sensing film has been improved with nanomaterials. A sample is placed in a chamber where volatile compounds become concentrated in the gas phase, whereby the gas is then pumped through the chamber to carry the aroma to the sensor that measures its unique fingerprint. The high surface area to volume ratio of the nanomaterials allows for greater interaction with analytes and the nanosensor's fast response time enables the separation of interfering responses. Chemical sensors, too, have been built using nanotubes to detect various properties of gaseous molecules. Many carbon nanotube based sensors are designed as field effect transistors, taking advantage of their sensitivity. The electrical conductivity of these nanotubes will change due to charge transfer and chemical doping by other molecules, enabling their detection. To enhance their selectivity, many of these involve a system by which nanosensors are built to have a specific pocket for another molecule. Carbon nanotubes have been used to sense ionization of gaseous molecules while nanotubes made out of titanium have been employed to detect atmospheric concentrations of hydrogen at the molecular level. Some of these have been designed as field effect transistors, while others take advantage of optical sensing capabilities. Selective analyte binding is detected through spectral shift or fluorescence modulation. In a similar fashion, Flood et al. have shown that supramolecular host–guest chemistry offers quantitative sensing using Raman scattered light as well as SERS.