To address these highly potent compounds, researchers are developing advanced sensor technologies to quickly and accurately detect nitazenes in complex biological and environmental samples.
These innovations are key to improving clinical management, public health surveillance, and risk reduction strategies amid the ongoing opioid crisis.
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2-Benzylbenzimidazole opioid agonists, or nitazenes, were developed by the pharmaceutical company CIBA AG in the late 1950s.2 Despite demonstrating potent analgesic effects, none of the nitazene compounds received clinical approval from the global regulatory bodies due to their significant risk of severe respiratory depression and high potential for addiction. They were never released for human use.
Traditional opioids such as morphine are based on a phenanthrene framework, while fentanyl is classified as a meperidine analogue. However, nitazenes have a unique 2-benzylbenzimidazole core structure, fundamentally different from the chemical scaffolds of conventional opioids.2
This structural distinction has important pharmacological implications. Not only does it distinguish the opioids from others in the same class, but it also contributes to their unusual potency and pharmacological behavior.
Nitazenes are µ-opioid receptor agonists and produce psychoactive effects similar to established opioids such as morphine, oxycodone, and heroin.
Among the nitazenes, isotonitazene, which is a 5-nitro-2-benzylbenzimidazole derivative, gained notoriety as a street drug in Europe in 2019, leading to the rapid global proliferation of related analogues.3
By early 2020, another potent analogue, metonitazene, appeared in the recreational drug market. Many of these compounds have been reported to possess potencies several orders of magnitude greater than morphine and, in some instances, even exceed fentanyl in their toxicity and risk profile.3
Exposure to even minute quantities can cause severe intoxication and life-threatening respiratory depression. In 2024 alone, the number of deaths as a result of nitazene overdose in the UK was reported as 333 by the National Crime Agency. A recent study in Clinical Toxicology states that this number is in fact underreported due to the instability of nitazenes in post-mortem blood samples.4
Analytical Challenges in Nitazenes Detection and Their Consequences
Nitazene was first detailed to the UN Office on Drugs and Crime (UNODC) in 2019 – they have now catalogued 26 different nitazene substances. In September 2025, a pill-testing site in Canberra recorded the first known detection of isotocyanozene in Australia, a drug never before reported to the UNODC.
These different analogues, each with distinct structural features, make it especially hard to identify the opioid in samples.5
Standard detection approaches, including immunoassays and traditional gas chromatography-mass spectrometry, often do not provide the sensitivity or specificity needed to accurately identify emerging nitazene variants and their metabolites.
While advanced liquid chromatography-mass spectrometry-based technologies have proven highly effective, their high cost and resource requirements limit access for smaller laboratories, restricting broader implementation and widespread availability.5
Analytical limitations are particularly concerning given the increasing prevalence of nitazenes in illicit drug markets, which is correlated with a rise in hospital admissions and overdose-related fatalities.
With hundreds of deaths reported in the UK and additional deaths reported in the US, there is a need for sensor technology to match the scope of the problem.6
A New Biosensor to Detect Nitazenes and Their Metabolites
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Accurate detection of nitazenes requires the development of diagnostic assays that use biomolecular components with superior specificity and sensitivity. To meet this requirement, a recent study engineered the plant abscisic acid (ABA) receptor, PYR1, using it as an advanced biosensor.7
In its native configuration, PYR1 undergoes a highly regulated interaction with the phosphatase HAB1 upon ABA binding, a process governed by an allosteric gate-latch-lock mechanism.
This chemical-induced dimerization module incorporates an intrinsic transduction pathway, in which ligand binding causes conformational changes. This structural change can be exploited to generate diverse signal outputs for detection.
This binding reaction, known as a molecular ratchet, enables highly sensitive detection in the PYR1-HAB1 receptor, even when ligand-receptor affinity is limited.
Using computational protein engineering, the researchers modified the PYR1 binding pocket to create biosensors capable of detecting multiple nitazene derivatives and their metabolic byproducts.
The design process integrated deep mutational scanning, directed evolution, and computational modeling to produce a pan-nitazene sensor, which effectively recognizes compounds such as isotonitazene and its 4-hydroxy metabolite.7
For practical detection, researchers developed a luciferase-based in vitro assay. This assay is label-free, offers high sensitivity and speed, and is suitable for use with complex biological samples such as urine.
Read more about the recent paper in Clinical Toxicology, here.
Limitations and Future Directions of the PYR1-Based Biosensor Design
Despite the success of this study, there are limits to the deployment of the PYR1-based pan-nitazene sensor.7
Its reliance on combinatorial library strategies, for example, led to large mutant pools, making screening labor-intensive and time-consuming. Additionally, the design workflow was fragmented, with separate steps for binding pose generation and sequence variant creation, which further complicated optimization.
Nonetheless, the adoption of conformer generation and alignment sampling markedly improved the accuracy of binding pose prediction, key to preserving sensor function.
Recent advances in deep learning, including ProteinMPNN and AlphaFold2 filtering, offer significant advantages over traditional physically-based algorithms. Incorporating these state-of-the-art tools could enhance both the efficiency and precision of future PYR1 receptor engineering, with the potential for modular integration throughout the design process.
However, structural constraints still remain a challenge. This recent sensor cannot accommodate certain ligands such as ethylene nitazene and ethylene etonitazene due to steric clashes with the fixed PYR1 backbone, among other issues.
More flexible sensing mechanisms are still needed. Engineering de novo proteins that preserve the PYR1 transduction mechanism could be a promising workaround.
Advancements in computational modeling and experimental techniques to predict and evaluate protein conformational dynamics will be essential for expanding the platform's applicability to a broader range of target ligands.
With these developments, the PYR1-based biosensor platform and others like it hold significant potential for detecting the potent 'Frankenstein opioids' and for the next generation of sensitive, versatile diagnostic tools.
References and Further Reading
- Pereira, J. R. P. et al. Nitazenes: The Emergence of a Potent Synthetic Opioid Threat. Molecules 2025, 30(19), 3890. DOI:10.3390/molecules30193890, https://www.mdpi.com/1420-3049/30/19/3890
- Pergolizzi, J., Jr. et al. Old Drugs and New Challenges: A Narrative Review of Nitazenes. Cureus 2023, 15(6), e40736. DOI:10.7759/cureus.40736, https://www.cureus.com/articles/140595-old-drugs-and-new-challenges-a-narrative-review-of-nitazenes
- Wood, D. M. et al. Is nitazene-related mortality underestimated? Findings from an in vivo and ex vivo rat study and pharmacoepidemiological analysis of coroner-reported deaths. Clinical Toxicology 2025. DOI:10.1080/15563650.2025.2601141, https://www.tandfonline.com/doi/full/10.1080/15563650.2025.2601141
- Mandrioli, R. et al. Analytical approaches for the identification and quantitation of nitazenes: A review. Journal of Chromatography Open 2026, 9, 100305. DOI:10.1016/j.jcoa.2025.100305, https://www.sciencedirect.com/science/article/pii/S2667045225000305
- Holland, A. et al. Nitazenes – heralding a second wave for the UK drug-related death crisis? Lancet Public Health 2024, 9(2), e71–e72. DOI:10.1016/S2468-2667(24)00001-X, https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(24)00001-X/fulltext
- Leonard, A. C. et al. Computational design of dynamic biosensors for emerging synthetic opioids. Nature Communications 2026, 17(1), 1234. DOI:10.1038/s41467-025-67994-w, https://www.nature.com/articles/s41467-025-67994-w
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