Sweat testing is an excellent matrix for Drugs of Abuse testing. One organization has held the rights to the sweat patch for years. New technologies such as LC/MSMS have made sweat an even more appealing matrix. Due to the limited colume of sample to actually test with the sweat patch testing (2.4 mL of a buffer) a hierachy for confirming positive was necessary due to limited sensitivity by GC/MS. Interference was also a common occurance with the opiates. 10 years ago only Codeine, Morphine, 6-MAM and Heroin were examined. Hydrocodone interfered extensively with Codeine and Hydromorphone interfered with Morphine. LC/MSMS technology does allow for simultaneous testing of all 6 of the above PLUS Oxycodone and Oxymorphone. All of this can be done with less specimen, less sample prep time, less reagents and a shorter run time. In other words, it costs less to do a better analysis. The same is true for other drugs.
The downside to screening is the use of ELISA. This technique was very suspect. It is possible it was due to the age of the TECAN instrumentation used but manipulation of the screening samples was necessary to achieve acceptable control results.
Oral fluid has a very short detection window. Hair still has too many forensic questions, for example - How does one obtain true matrix standards and controls? As mentioned meconium is difficult to work with. Of the alternate matrices, it is my opinion that sweat is the best option IF handled correctly.