The term small molecule describes a diverse range of chemical entities of less than 800Da. The molecule would not be a polymer, or have only a limited degree of polymerisation. Their size gives these molecules the potential to diffuse across the cell membrane. The term is usually reserved for the description of an organic compound which has some pharmacological activity, but the name can accurately be applied to any number of chemical species that lack biological activity, such as explosives or chemical contaminants.

Typical small molecules can include:

• Biologically active small molecules:

         - Naturally occurring compounds
         - Toxins
         - Legal pharmaceuticals (vitamins, caffeine, etc.)
         - Controlled drugs (cocaine, heroin, etc.)

• Synthetic compounds

         - Toxins
         - Legal compounds (ibuprofen, paracetamol, etc.)
         - Controlled compounds (MDMA, methamphetamine, etc.)

• Biologically inactive molecules

         - Explosives
         - Dyes
         - Chemical contaminants

Publications:
The following studies have examined the study of small molecules using a nanopore sensor:

Pharmaceuticals: Identification of the chiral nature of a common pharmaceutical species.

Stochastic detection of enantiomers. J. Am. Chem. Soc. 128 (33), 10684-10685 (2006)

Toxins: Single molecule detection of nitrogen mustards by covalent reaction within a protein nanopore.  J. Am. Chem. Soc. 130 (21), 6813-6819 (2008)