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1. An Amperometric Sensor with Anti-Fouling Properties for Indicating Xylazine Adulterant in Beverages

   https://doi.org/10.3390/mi15111340  

   Vinnikov, Arielle; Sheppard, Charles W; Wemple, Ann H; Stern, Joyce E; Leopold, Michael C (November 2024, Micromachines)

   Amperometric electrochemical sensing schemes, which are easily fabricated and can directly relate measured current with analyte concentrations, remain a promising strategy for the development of the portable, in situ detection of commonly employed adulterants. Xylazine (XYL) is a non-narcotic compound designed for veterinary use as a sedative known as Rompun®. XYL is increasingly being abused as a recreational drug, as an opioid adulterant and, because of its chemical properties, has found unfortunate prominence as a date rape drug spiked into beverages. In this study, a systematic exploration and development of fouling-resistant, amperometric XYL sensors is presented. The sensing strategy features layer-by-layer (LBL) modification of glassy carbon electrodes (GCEs) with carbon nanotubes (CNTs) for sensitivity and the engagement of cyclodextrin host–guest chemistry in conjunction with polyurethane (PU) semi-permeable membranes for selectivity. The optimization of different materials and parameters during development created a greater fundamental understanding of the interfacial electrochemistry, allowing for a more informed subsequent design of effective sensors exhibiting XYL selectivity, effective sensitivity, rapid response times (<20 s), and low estimated limits of detection (~1 ppm). Most importantly, the demonstrated XYL sensors are versatile and robust, easily fabricated from common materials, and can effectively detect XYL at <10 ppm in both common alcoholic and non-alcoholic beverages, requiring only minimal volume (20 µL) of the spiked beverage for a standard addition analysis. 

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2. Mechanistic Elucidation of Nanomaterial-Enhanced First-Generation Biosensors Using Probe Voltammetry of an Enzymatic Reaction

   https://doi.org/10.3390/bios13080798  

   Wemple, Ann H; Kaplan, Jamie S; Leopold, Michael C (August 2023, Biosensors)

   The incorporation of nanomaterials (NMs) into biosensing schemes is a well-established strategy for gaining signal enhancement. With electrochemical biosensors, the enhanced performance achieved from using NMs is often attributed to the specific physical properties of the chosen nanocomponents, such as their high electronic conductivity, size-dependent functionality, and/or higher effective surface-to-volume ratios. First generation amperometric biosensing schemes, typically utilizing NMs in conjunction with immobilized enzyme and semi-permeable membranes, can possess complex sensing mechanisms that are difficult to study and challenging to understand beyond the observable signal enhancement. This study shows the use of an enzymatic reaction between xanthine (XAN) and xanthine oxidase (XOx), involving multiple electroactive species, as an electrochemical redox probe tool for ascertaining mechanistic information at and within the modified electrodes used as biosensors. Redox probing using components of this enzymatic reaction are demonstrated on two oft-employed biosensing approaches and commonly used NMs for modified electrodes: gold nanoparticle doped films and carbon nanotube interfaces. In both situations, the XAN metabolism voltammetry allows for a greater understanding of the functionality of the semipermeable membranes, the role of the NMs, and how the interplay between the two components creates signal enhancement. 

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3. Green Synthesis of Gold Nanoparticles Using Upland Cress and Their Biochemical Characterization and Assessment

   https://doi.org/10.3390/nano12010028  

   Hutchinson, Noah; Wu, Yuelin; Wang, Yale; Kanungo, Muskan; DeBruine, Anna; Kroll, Emma; Gilmore, De’Jorra; Eckrose, Zachary; Gaston, Stephanie; Matel, Phoebe; et al (January 2022, Nanomaterials)

   This article belongs to the Special Issue Synthesis and Applications of Gold Nanoparticles) Rodolphe Antoine (Ed.)

   This research focuses on the plant-mediated green synthesis process to produce gold nanoparticles (Au NPs) using upland cress (Barbarea verna), as various biomolecules within the upland cress act as both reducing and capping agents. The synthesized gold nanoparticles were thoroughly characterized using UV-vis spectroscopy, surface charge (zeta potential) analysis, scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray diffraction (XRD). The results indicated the synthesized Au NPs are spherical and well-dispersed with an average diameter ~11 nm and a characteristic absorbance peak at ~529 nm. EDX results showed an 11.13% gold content. Colloidal Au NP stability was confirmed with a zeta potential (ζ) value of −36.8 mV. X-ray diffraction analysis verified the production of crystalline face-centered cubic gold. Moreover, the antimicrobial activity of the Au NPs was evaluated using Gram-negative Escherichiacoli and Gram-positive Bacillus megaterium. Results demonstrated concentration-dependent antimicrobial properties. Lastly, applications of the Au NPs in catalysis and biomedicine were evaluated. The catalytic activity of Au NPs was demonstrated through the conversion of 4-nitrophenol to 4-aminophenol which followed first-order kinetics. Cellular uptake and cytotoxicity were evaluated using both BMSCs (stem) and HeLa (cancer) cells and the results were cell type dependent. The synthesized Au NPs show great potential for various applications such as catalysis, pharmaceutics, and biomedicine. 

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4. Tailoring carrier dynamics in perovskite solar cells via precise dimension and architecture control and interfacial positioning of plasmonic nanoparticles

   https://doi.org/10.1039/c9ee03937f  

   Cui, Xun; Chen, Yihuang; Zhang, Meng; Harn, Yeu Wei; Qi, Jiabin; Gao, Likun; Wang, Zhong Lin; Huang, Jinsong; Yang, Yingkui; Lin, Zhiqun (January 2020, Energy & Environmental Science)

   Placing plasmonic nanoparticles (NPs) in close proximity to semiconductor nanostructures renders effective tuning of the optoelectronic properties of semiconductors through the localized surface plasmon resonance (LSPR)-induced enhancement of light absorption and/or promotion of carrier transport. Herein, we report on, for the first time, the scrutiny of carrier dynamics of perovskite solar cells (PSCs) via sandwiching monodisperse plasmonic/dielectric core/shell NPs with systematically varied dielectric shell thickness yet fixed plasmonic core diameter within an electron transport layer (ETL). Specifically, a set of Au NPs with precisely controlled dimensions ( i.e. , fixed Au core diameter and tunable SiO 2 shell thickness) and architectures (plain Au NPs and plasmonic/dielectric Au/SiO 2 core/shell NPs) are first crafted by capitalizing on the star-like block copolymer nanoreactor strategy. Subsequently, these monodisperse NPs are sandwiched between the two consecutive TiO 2 ETLs. Intriguingly, there exists a critical dielectric SiO 2 shell thickness, below which hot electrons from the Au core are readily injected to TiO 2 ( i.e. , hot electron transfer (HET)); this promotes local electron mobility in the TiO 2 ETL, leading to improved charge transport and increased short-circuit current density ( J sc ). It is also notable that the HET effect moves up the Fermi level of TiO 2 , resulting in an enhanced built-in potential and open-circuit voltage ( V oc ). Taken together, the PSCs constructed by employing a sandwich-like TiO 2 /Au NPs/TiO 2 ETL exhibit both greatly enhanced J sc and V oc , delivering champion PCEs of 18.81% and 19.42% in planar and mesostructured PSCs, respectively. As such, the judicious positioning of rationally designed monodisperse plasmonic NPs in the ETL affords effective tailoring of carrier dynamics, thereby providing a unique platform for developing high-performance PSCs. 

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5. Adsorptive Cathodic Stripping Analysis of Xylazine Within Fouling-Resistant and Nanomaterial-Enhanced Modified Electrode Sensors

   https://doi.org/10.3390/s25175312  

   Leopold, Michael C; Sheppard, Charles W; Stern, Joyce E; Vinnikov, Arielle; Wemple, Ann H; Edelman, Ben H (September 2025, Sensors)

   Xylazine (XYL), an FDA-approved veterinary tranquilizer, is being abused both as an opioid adulterant in a street-drug known as “Tranq-dope” and as a date rape drug. Given its now nearly ubiquitous use with fentanyl and fentanyl derivatives across the globe, XYL has become a primary target for researchers seeking to develop portable and cost-effective sensors for its detection. Electrochemical sensors based on the oxidation of XYL, while useful, have limitations due to certain interferents and inherent electrode fouling that render the approach less reliable, especially in certain sample matrices. In this work, modified electrode platforms incorporating layers of multi-walled carbon nanotubes for sensitivity along with semi-permeable polyurethane (PU) layers and host–guest chemistry using β-cyclodextrin for selectivity are deployed for XYL detection using complementary adsorptive cathodic stripping analysis. The modified electrode sensors are optimized to minimize high potentials and maintain fouling resistant capabilities and investigated to better understand the function of the PU layer. The use of adsorptive cathodic stripping differential pulse voltammetry indirectly indicates the presence and concentration of XYL within complex sample media (beverages and synthetic urine). When used in this manner, the modified electrodes exhibited an overall average sensitivity of ~35 (±9) nA/μM toward XYL with a limit of quantification of <10 ppm, while also offering adaptability for the analysis of XYL in different types of samples. By expanding the capability of these XYL sensors, this study represents another facet of tool development for use by medical professionals, first-responders, forensic investigators, and drug-users to limit exposure and help stem the dangerous and illegal use of XYL. 

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