Forensic analysis of crime scene samples, contraband, and smuggled packages often has to cope with a complicated matrix of materials and only the tiniest sniff of the target analyte. Now, Christoffer Abrahamsson working in the laboratory of George Whitesides at Harvard University has developed a new tool based on density separation that can be tuned to detect all but the smallest concentrations of worrying drugs of abuses, such as the opioid fentanyl. [Abrahamsson, C.K. et al. Angew Chem Int Edn (2019); DOI: 10.1002/anie.201910177]

The tool, referred to as Magneto-Archimedes Levitation, and abbreviated, somewhat confusingly for those who know the transport original, as MagLev, separates powdered substances into levitating clouds of crystals based on their density. The team suggests the approach is lower cost, easier to use, more accurate and more sensitive than available portable forensic testing equipment. It can overcome the serious problem of false positives and negatives and detect the likes of fentanyl or carfentanil even if they are "cut" with other powders.

The equipment was tested in collaboration with chemist Joseph Bozenko of the US Drug Enforcement Administration. "We started out with fentanyl. That was our main target because it is one of the biggest problems right now, and it just worked directly, levitated directly," Abrahamsson explains. "It was almost too good to be true."

The MagLev system is as tall as one-liter drinks bottle. Two magnets rest above and below a cuvette, a clear, straight-sided container. A hydrophobic solution carries a gadolinium chelating agent. When a foreign substance is added the claw-like structure of the chelator grabs it, the magnetic gadolinium ion is then attracted, together with the chelated payload towards the magnetic fields from above and below displacing other substances that are present, such as glass, plastic, or other non-target drugs.

The up and down jostling allows the chelated analyte to hang in the solution at a level dictated by gravity, the strength of the magnets, and the density of the substance. "This is novel in the fact that it is an entirely different tool to work with," says Bozenko. There is no other field-testing technology that can separate compounds into neat clouds that can then be isolated for analysis. Current options, such as immunoassays and colorimetric tests, are relatively unsophisticated they pick up several analytes at once. The team has demonstrated that MagLev can separate up to seven different analytes simultaneously, it could separate more, but seven is as many as the team has tried so far.

But that max is based on the highest number the team has tested-they're confident their tool can handle far more. For forensic chemists and law enforcement, that ability is precious: Street drugs are often mixtures of multiple drugs-heroin, fentanyl, cocaine, methamphetamines-combined with cutting agents like caffeine, sugar, baking soda, powdered milk, lidocaine, or even rat poison. Ingredient isolation is especially valuable when a new drug pops up. Carfentanil, for example, is just fentanyl with a few chemical adjustments. A few more adjustments and a new-potentially even more dangerous-version could appear on the street. In 2018, the DEA discovered 22 previously unidentified substances; six of those were new types of fentanyl.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase.