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1. High concentrations of illicit stimulants and cutting agents cause false positives on fentanyl test strips

   https://doi.org/10.1186/s12954-021-00478-4  

   Lockwood, Tracy-Lynn E.; Vervoordt, Alexandra; Lieberman, Marya (December 2021, Harm Reduction Journal)

   Abstract Background The opioid epidemic has caused an increase in overdose deaths which can be attributed to fentanyl combined with various illicit substances. Drug checking programs have been started by many harm reduction groups to provide tools for users to determine the composition of their street drugs. Immunoassay fentanyl test strips (FTS) allow users to test drugs for fentanyl by either filling a baggie or cooker with water to dissolve the sample and test. The antibody used in FTS is very selective for fentanyl at high dilutions, a characteristic of the traditional use of urine testing. These street sample preparation methods can lead to mg/mL concentrations of several potential interferents. We tested whether these concentrated samples could cause false positive results on a FTS. Methods 20 ng/mL Rapid Response FTS were obtained from BTNX Inc. and tested against 4 different pharmaceuticals (diphenhydramine, alprazolam, gabapentin, and naloxone buprenorphine) and 3 illicit stimulants [cocaine HCl, methamphetamine, and 3,4-methylenedioxymethamphetamine (MDMA)] in concentrations from 20 to 0.2 mg/mL. The FTS testing pad is divided into 2 sections: the control area and the test area. Control and test area signal intensities were quantified by ImageJ from photographs of the test strips and compared to a threshold set by fentanyl at the FTS limit of detection. Results False positive results indicating the presence of fentanyl were obtained from samples of methamphetamine, MDMA, and diphenhydramine at concentrations at or above 1 mg/mL. Diphenhydramine is a common cutting agent in heroin. The street sample preparation protocols for FTS use suggested by many online resources would produce such concentrations of these materials. Street samples need to be diluted more significantly to avoid interference from potential cutting agents and stimulants. Conclusions Fentanyl test strips are commercially available, successful at detecting fentanyl to the specified limit of detection and can be a valuable tool for harm reduction efforts. Users should be aware that when drugs and adulterants are in high concentrations, FTS can give a false positive result. 

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2. Superhydrophobic 3D‐Assembled Metallic Nanoparticles for Trace Chemical Enrichment in SERS Sensing

   https://doi.org/10.1002/smll.202204234  

   Liu, Youhai; Zhang, Nan; Tua, Dylan; Zhu, Yingkun; Rada, Jacob; Yang, Wenhong; Song, Haomin; Thompson, Alexis C.; Collins, R. Lorraine; Gan, Qiaoqiang (October 2022, Small)

   Abstract The performance of surface‐enhanced Raman spectroscopy (SERS) is determined by the interaction between highly diluted analytes and boosted localized electromagnetic fields in nanovolumes. Although superhydrophobic surfaces are developed for analyte enrichment, i.e., to concentrate and transfer analytes toward a specific position, it is still challenging to realize reproducible, uniform, and sensitive superhydrophobic SERS substrates over large scales, representing a major barrier for practical sensing applications. To overcome this challenge, a superhydrophobic SERS chip that combines 3D‐assembled gold nanoparticles on nanoporous substrates is proposed, for a strong localized field, with superhydrophobic surface treatment for analyte enrichment. Intriguingly, by concentrating droplets in the volume of 40 µL, the sensitivity of 1 nmis demonstrated using 1,2‐bis(4‐pyridyl)‐ethylene molecules. In addition, this unique chip demonstrates a relative standard deviation (RSD) of 2.2% in chip‐to‐chip reproducibility for detection of fentanyl at 1 µg mL^–1concentration, revealing its potential for quantitative sensing of chemicals and drugs. Furthermore, the trace analysis of fentanyl and fentanyl‐heroin mixture in human saliva is realized after a simple pretreatment process. This superhydrophobic chip paves the way toward on‐site and real‐time drug sensing to tackle many societal issues like drug abuse and the opioid crisis. 

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3. Sub-Part-Per-Billion Level Sensing of Fentanyl Residues from Wastewater Using Portable Surface-Enhanced Raman Scattering Sensing

   https://doi.org/10.3390/bios11100370  

   Zhang, Boxin; Hou, Xingwei; Zhen, Cheng; Wang, Alan X. (October 2021, Biosensors)

   Detection of illicit drug residues from wastewater provides a new route toward community-level assessment of drug abuse that is critical to public health. However, traditional chemistry analytical tools such as high-performance liquid chromatography in tandem with mass spectrometry (HPLC-MS) cannot meet the large-scale testing requirement in terms of cost, promptness, and convenience of use. In this article, we demonstrated ultra-sensitive and portable surface-enhanced Raman scattering sensing (SERS) of fentanyl, a synthetic opioid, from sewage water and achieved quantitative analysis through principal component analysis and partial least-squares regression. The SERS substrates adopted in this application were synthesized by in situ growth of silver nanoparticles on diatomaceous earth films, which show ultra-high sensitivity down to 10 parts per trillion in artificially contaminated tap water in the lab using a commercial portable Raman spectrometer. Based on training data from artificially contaminated tap water, we predicted the fentanyl concentration in the sewage water from a wastewater treatment plant to be 0.8 parts per billion (ppb). As a comparison, the HPLC-MS confirmed the fentanyl concentration was below 1 ppb but failed to provide a specific value of the concentration since the concentration was too low. In addition, we further proved the validity of our SERS sensing technique by comparing SERS results from multiple sewage water treatment plants, and the results are consistent with the public health data from our local health authority. Such SERS sensing technique with ultra-high sensitivity down to sub-ppb level proved its feasibility for point-of-care detection of illicit drugs from sewage water, which is crucial to assess public health. 

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4. 2D NMR detection and quantification of heroin in a street sample

   https://doi.org/10.1016/j.forc.2025.100687  

   James, K M; Boni, S V; Gratton, K; Stopko, M J; Cipoletti, M; Gilbert, T; Goroncy, A K; Suyama, T L (July 2025, Forensic chemistry)

   Two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy was evaluated for the identification and quantification of compounds in an unknown street drug sample. Using 2D COSY and HSQC techniques, heroin was successfully quantified, and the presence of 6-monoacetylmorphine (6-MAM), xylazine, and caffeine was confirmed through partial structural elucidation. These methods demonstrated the ability to differentiate structurally similar opioid analogues without reliance on reference library databases. While gas chromatography–mass spectrometry (GC–MS) remains the standard in forensic laboratories, it has limitations in de novo structural analysis and in detecting emerging analogues absent from spectral libraries. In this study, heroin and fentanyl were quantified in both simulated and actual street samples at concentrations ranging from 0.97 to 1.80 mg/mL, with errors between 0% and 34% using a 400 MHz NMR instrument. A benchtop 60 MHz NMR system also detected and quantified 56 mg/mL of heroin with a 24% error in a simulated sample. These findings support the complementary role of 2D NMR spectroscopy in forensic drug analysis in light of the opioid epidemic and the evolving drug market. 

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5. PRADA: Portable Reusable Accurate Diagnostics with nanostar Antennas for multiplexed biomarker screening

   https://doi.org/10.1002/btm2.10165  

   Wen, Xiaona; Ou, Yu‐Chuan; Zarick, Holly_F; Zhang, Xin; Hmelo, Anthony_B; Victor, Quinton_J; Paul, Eden_P; Slocik, Joseph_M; Naik, Rajesh_R; Bellan, Leon_M; et al (May 2020, Bioengineering & Translational Medicine)

   Abstract Precise monitoring of specific biomarkers in biological fluids with accurate biodiagnostic sensors is critical for early diagnosis of diseases and subsequent treatment planning. In this work, we demonstrated an innovative biodiagnostic sensor, portable reusable accurate diagnostics with nanostar antennas (PRADA), for multiplexed biomarker detection in small volumes (~50 μl) enabled in a microfluidic platform. Here, PRADA simultaneously detected two biomarkers of myocardial infarction, cardiac troponin I (cTnI), which is well accepted for cardiac disorders, and neuropeptide Y (NPY), which controls cardiac sympathetic drive. In PRADA immunoassay, magnetic beads captured the biomarkers in human serum samples, and gold nanostars (GNSs) “antennas” labeled with peptide biorecognition elements and Raman tags detected the biomarkers via surface‐enhanced Raman spectroscopy (SERS). The peptide‐conjugated GNS‐SERS barcodes were leveraged to achieve high sensitivity, with a limit of detection (LOD) of 0.0055 ng/ml of cTnI, and a LOD of 0.12 ng/ml of NPY comparable with commercially available test kits. The innovation of PRADA was also in the regeneration and reuse of the same sensor chip for ~14 cycles. We validated PRADA by testing cTnI in 11 de‐identified cardiac patient samples of various demographics within a 95% confidence interval and high precision profile. We envision low‐cost PRADA will have tremendous translational impact and be amenable to resource‐limited settings for accurate treatment planning in patients. 

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