DNA aptamer-based sensors can accurately detect traces of fentanyl, heroin and cocaine

Researchers from North Carolina State University have developed a new generation of high-throughput DNA aptamers and high-precision drug sensors for cocaine and other opioids. The sensors are drug-specific and can detect traces of fentanyl, heroin and cocaine – even when these drugs are mixed with other drugs or with cutting agents and adulterants such as caffeine, sugar or procaine. The sensors could have far-reaching benefits for healthcare workers and law enforcement agencies.

“This work may provide much-needed updates to tests currently in use, both in healthcare and law enforcement,” says Yi Xiao, associate professor of chemistry at NC State and corresponding author of two studies describing the work.

For example, drug tests currently used by law enforcement still rely on chemical tests developed a century ago that are poorly specific, meaning they react to compounds that may not it’s the medicine they’re looking for.”

Yi Xiao, associate professor of chemistry at NC State

“And the existing aptamer test for cocaine is not sensitive and specific enough to detect clinically relevant amounts of the drug in biological samples, such as blood. The sensors we developed can detect cocaine in blood at nanomolecular rather than micromolecular levels, which represents a 1,000-fold improvement in sensitivity.”

In a pair of studies appearing in Journal of the American Chemical Society (JACS) and JACS AuXiao led a team that developed aptamer-based sensors for cocaine, heroin, codeine, fentanyl, and other illicit drugs.

An aptamer is a small single strand of DNA or RNA that will bind to a specific molecule with high affinity, meaning it will not bind to other molecules than the one of interest. Researchers begin the search by adding the molecule of interest – cocaine, for example – to a mixture of hundreds of trillions of randomized DNA sequences. They then see which aptamer binds to the molecule.

“We refer to the process as ‘bio-panning,’ as it is very similar to sifting through river sediment to find gold,” says Obtin Alkhamis, an NC State graduate student and co-author of both papers. “Once we separate the target-bound clones from the unbound clones, we rigorously test this aptamer against other interfering compounds to ensure that it is specific only for the compound of interest.”

The researchers then tested the compound-specific aptamers against drug mixtures, tablets and blood to determine if they could identify certain drugs in the samples.

Xiao’s team used the cocaine aptamer to detect cocaine in blood serum at levels of 10 nanograms (equivalent to 30 nanograms per milliliter, or 30 parts per billion), a 1,000-fold improvement over the best previous aptamer test that could detect only 10 micromoles of cocaine in 50% serum.

Additionally, collaborators at the University of California Santa Barbara were able to incorporate the aptamer into an electrode that could measure the concentration of the drug in situ in the blood (in a vein) of rats in real time every 10 seconds over a two-hour period. This is the first study that can measure the pharmacology of a drug of abuse with a time resolution measured in seconds.

Opioid-specific aptamers were incorporated into colorimetric assays that can detect specific opioids such as heroin and oxycodone in solution at levels as low as 0.5 micromolar (µM). A colorimetric test is a test that changes color when the compound of interest is detected. These assays were also able to detect opioids in complex chemical matrices within seconds – including pharmaceutical tablets and drug mixtures.

By comparison, the Marquis test, a standard test used by law enforcement officials and forensic laboratories, could not detect opioids in chemical mixtures.

The researchers believe that these aptamer sensors have useful health and public safety applications.

“Aptamers can be mass-produced, have a long lifetime, and are easily chemically modified, which means they can be used for any type of sensor you develop,” says Xiao. “So they could be incorporated into test films for officers in the field, for use at home or for human patients in the doctor’s office.”

“Since they detect drugs at clinically relevant levels, you could potentially do a drop of blood test in the ER to immediately determine what a patient may have taken, without a full blood draw and lab testing,” says Alkhamis. “The potential uses are really exciting.”

The work was supported by the National Institute of Justice (awards 2019-DU-BX-0024 and 2022-GG-04440-RESS), the National Science Foundation (grant CHE-2135005), and the National Institutes of Health (grant R01DA051100). Nicole Emmons, Yuting Wang, Kevin Honeywell, Kevin Plaxco and Tod Kippin, all from the University of California Santa Barbara, contributed to the development of the aptamer-based electrochemical sensor for in vivo cocaine testing. NC State graduate students Juan Canoura, Yuyang Wu, Matthew Venzke and Phuong Ly also contributed to the opioid work.