Patches have been demonstrated to be a promising detection platform for sweat diagnostics.  Simple, long-term collection devices which check for drugs of abuse or alcohol are already on the market and operate on the following principle: a user applies the patch which then collects sweat over a period of hours or days, then the patch is analyzed utilizing techniques such as GC-MS which are accurate but have the drawback of lack of continuous measurements and high costs.  For example, sweat diagnostic products for illicit drugs and alcohol are manufactured and supplied by PharmChek and AlcoPro, respectively. Recently several efforts have been made to develop low cost polymer based continuous perspiration monitoring devices and are in early stages of commercialization.
More recently, startup companies such as [http://www.Xsensio.com Xsensio] have begun developing products targeted towards the consumer, healthcare and athletics market for sweat diagnostics.  Ultimately, it is the hope that these devices will have the ability to detect changes in human physiology within minutes without the need for repeated sample collection and analysis.