Fresh produce or meats which are either spoiled or unpalatable exhibit odors, colors or other sensory characteristics which can be easily discerned by consumers. 
When packaging materials prevent extensive sensory exposure, however, consumers must rely on sell-by dates, which are determined by producers based on a set of idealized assumptions about the way that the food is stored or transported. 
While the sell-by date for a carton of milk may indicate to a consumer that the product should be good for a period of two weeks, this date may no longer be applicable if that milk was stored above its optimal temperature for an hour, either in a delivery truck or in a warm automobile.
The unique chemical and electro-optical properties of nanoscale particles offer solutions to this problem. 
Through bottom-up engineering, nanomaterials can be devised which are able to detect the presence of gasses, aromas, chemical contaminants and pathogens, or respond to changes in environmental conditions. 
This not only is useful for quality control to ensure that consumers are able to purchase products which are at their peak of freshness and flavor, but it also has the potential to improve food safety and reduce the frequency of food-borne illnesses. 
Such technology would obviously benefit consumers, industry stakeholders and food regulators.
Some companies (e.g., Ripesense [http://www.ripesense.com] and OnVu [http://www.onvu.com/]) already market nanotechnology products that help consumers determine whether certain foods are likely to be palatable, but most of the work on nanosensors or assays for food-related analytes is still in the early stages of development. 
This section highlights some of the most recent and exciting work in this area.