A method and apparatus for non-invasive extraction and/or detection of chemicals such as heavy metals, drugs such as cocaine and analytes such as blood glucose has been developed. A patch or hydrogel containing a reagent such as N-methyl pyrrole, or a similar compound, is used to extract the chemical...http://www.google.co.uk/patents/US6492180?utm_source=gb-gplus-sharePatent US6492180 - Non-invasive transdermal detection of analytes
