Monitoring Food Spoilage Based on a Defect-Induced Multiwall Carbon Nanotube Sensor at Room Temperature: Preventing Food Waste.

We have developed an electronic nose based on carbon nanotubes (CNTs) synthesized by using a plasma-enhanced chemical vapor deposition, aiming to be a convenient monitoring device for food spoilage. The prepared CNTs showed a crystalline structure and smooth surface with a diameter of 11.3 nm and a length of ∼10 μm. The Raman spectrum showed that the CNTs fabricated were multiwalled carbon nanotubes (MWCNTs). The characteristic graphite peak (G) observed at 1595 cm in the Raman spectrum showed low intensity as compared to the defect peak (D) observed at 1330 cm, which referred to defect-induced points in CNTs. The CNTs were used to fabricate a sensor for ethylene gas produced by banana fruits for in situ measurements at room temperature. The sensor demonstrated good performance toward detecting the produced gas. The gas sensing signal was used as early indicators of the spoilage to help prevent food waste. The calibration curve was shown for the sensor responses evaluated at ripening days over 5 days. The sensor showed a response of 3.2% on the first day and increased to ∼7.0% by the third day and then gradually decreased. This sensor is appropriate for detecting the spoilage of food because it shows a good sensing response to a low level of produced gas from a single banana. Insight into food spoilage status of a specific level of gas shows its potential to be applied for quality assurance of food. The sensor sensitivity toward ethylene produced by a banana was confirmed based on the sensor response toward chemical ethylene gas.