Currently, drug testing relies heavily on techniques like liquid chromatography–tandem mass spectrometry (LC–MS/MS) and gas chromatography–mass spectrometry (GC–MS). While accurate, these methods are slow, expensive, and require complex laboratory setups. Faster options such as ELISA tests exist, but they often struggle to pick up very low concentrations of drugs.
The team’s approach, using carbon nanotube-based field-effect transistors (FETs), bridges this gap by combining high sensitivity and specificity with portability and affordability, making it well-suited for use outside the lab.
Why Sweat?
Opioids such as fentanyl, morphine, and heroin remain a major public health concern, and traditional testing methods based on urine, blood, or saliva carry drawbacks such as invasiveness and limited detection windows. Sweat, on the other hand, offers an attractive alternative: it can be collected easily and reflects both recent and longer-term drug exposure. This opens the door to more practical monitoring approaches.
Nanomaterials have helped move this vision forward. Single-walled carbon nanotubes (SWCNTs), in particular, are valued for their unique electrical properties and ability to detect molecules at extremely low concentrations. When functionalized with bio-recognition elements like antibodies, they can provide precise signals in response to target drugs. Building on earlier laboratory work with antibody-functionalized SWCNT FETs, the researchers advanced the technology into a multiplexed, automated sensor array that can track multiple opioids and their metabolites at once.
How the Sensor Works
The platform uses semiconductor-enriched SWCNTs decorated with gold nanoparticles (AuNPs). The nanoparticles amplify electrical signals and provide a surface for antibody attachment. These nanotubes are arranged on silicon substrates with pre-patterned electrodes, forming the channels of the FETs. Antibodies specific to norfentanyl, morphine, and 6-monoacetylmorphine (6-MAM) are then immobilized on the AuNPs, giving the sensors their selectivity.
When the device is exposed to sweat—whether artificial or real—a small bias voltage is applied. The presence of opioids changes the conductance of the nanotube channels, and those shifts are recorded for analysis.
To make the system practical for real use, the researchers also integrated the sensors into an automated platform that allows high-throughput screening. This ensures not only speed but also reproducibility, a critical factor for scaling the technology.
Key Findings
Testing showed the array could detect norfentanyl at concentrations as low as 34 pg/mL in artificial sweat. Responses were highly specific, with signal strength correlating linearly to drug concentrations over a broad range. Multiplexing allowed simultaneous detection of opioids and their metabolites, and the system even picked up cross-reactivity with structurally similar compounds, broadening its potential use. A simple washing step with diluted PBS helped reduce background interference from sweat, improving accuracy.
Still, the work is not without challenges.
Variability between sensors and issues with non-specific adsorption remain obstacles for real-world applications. The researchers note that automated fabrication and improved surface chemistries could help address these problems. Despite these hurdles, the automated system demonstrated consistent, repeatable results and strong potential as a portable monitoring tool.
Looking Ahead
Taken together, the findings highlight a nanoparticle-decorated SWCNT FET sensor array capable of ultra-sensitive, multiplexed opioid detection in sweat. By integrating antibody functionalization with automation and portability, the platform moves a step closer to point-of-care testing. With further refinement, it could play a key role in drug monitoring, compliance checks, and even overdose prevention.
The team sees future efforts focused on improving device stability, reducing variability, and expanding the range of detectable substances. Ultimately, the goal is to transition from laboratory prototypes to user-friendly clinical and field-ready devices.
Journal Reference
Shao W., Zeng Z. et al. (2025). Detection of opioids and their metabolites in sweat by carbon nanotube FET sensor array. npj Biosensing 2, 29. DOI: 10.1038/s44328-025-00051-0, https://www.nature.com/articles/s44328-025-00051-0