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Reactive oxygen species (ROS) including the superoxide anion (O2•−) are typically studied in cell cultures using fluorescent dyes, which provide only discrete single-point measurements. These methods lack the capabilities for assessing O2•− kinetics and release in a quantitative manner over long monitoring times. Herein, we present the fabrication and application of an electrochemical biosensor that enables real-time continuous monitoring of O2•− release in cell cultures for extended periods (> 8 h) using an O2•− specific microelectrode. To achieve the sensitivity and selectivity requirements for cellular sensing, we developed a biohybrid system consisting of superoxide dismutase (SOD) and Ti3C2Tx MXenes, deposited on a gold microwire electrode (AuME) as O2•− specific materials with catalytic amplification through the synergistic action of the enzyme and the biomimetic MXenes-based structure. The biosensor demonstrated a sensitivity of 18.35 nA/μM with a linear range from 147 to 930 nM in a cell culture medium. To demonstrate its robustness and practicality, we applied the biosensor to monitor O2•− levels in human leukemia monocytic THP-1 cells upon stimulation with lipopolysaccharide (LPS). Using this strategy, we successfully monitored LPS-induced O2•− in THP-1 cells, as well as the quenching effect induced by the ROS scavenger N-acetyl-l-cysteine (NAC). The biosensor is generally useful for exploring the role of oxidative stress and longitudinally monitoring O2•− release in cell cultures, enabling studies of biochemical processes and associated oxidative stress mechanisms in cellular and other biological environments. 

Two-dimensional (2D) layered materials that integrate metallic conductivity, catalytic activity and the ability to stabilize biological receptors provide unique capabilities for designing electrochemical biosensors for large-scale detection and diagnostic applications. Herein, we report a multifunctional MXene-based 2D nanostructure decorated with enzyme mimetic cerium oxide nanoparticle (MXCeO2) as a novel platform and catalytic amplifier for electrochemical biosensors, specifically targeting the detection of oxidase enzyme substrates. We demonstrate enhanced catalytic efficiency of the MXCeO2 for the reduction of hydrogen peroxide (H2O2) and its ability to immobilize oxidase enzymes, such as glucose oxidase, lactate oxidase and xanthine oxidase. The designed biosensors exhibit high selectivity, stability, and sensitivity, achieving detection limits of 0.8 μM H2O2, 0.49 μM glucose, 3.6 μM lactate and 1.7 μM hypoxanthine, when the MXCeO2 and their respective enzymes were used. The MXCeO2 was successfully incorporated into a wearable fabric demonstrating high sensitivity for lactate measurements in sweat. The unique combination of MXenes with CeO2 offers excellent conductivity, catalytic efficiency and enhanced enzyme loading, demonstrating potential of the MXCeO2 as a catalytically active material to boost efficiency of oxidase enzyme reactions. This design can be used as a general platform for increasing the sensitivity of enzyme based biosensors and advance the development of electrochemical biosensors for a variety of applications. 

Abstract The presence of poly‐ and perfluoroalkyl substances (PFAS) in the environment is associated with adverse health effects but measuring PFAS is challenging due to the associated high cost and technical complexities of the analysis. Here, the reactivity of atomically precise metal‐oxo clusters is reported and the foundation for their use is provided as fluorescent nanosensors for PFAS detection. The material comprises crystalline, water soluble, hexanuclear cerium‐oxo clusters [Ce₆(µ₃‐O)₄(µ₃‐OH)₄]¹²⁺decorated with glycine molecules (Ce‐Gly) characterized by fluorescence emission at 353 nm. The Ce‐Gly fluorescence is found sensitive to long chain carboxylated PFAS of CF₃–(CF₂)_n–, where n ≥ 6, such as perfluorooctanoic, perfluorononanoic and perfluorodecanoic acids. This unique reactivity leads to a change in the emission spectra in a concentration dependent manner, enabling PFAS detection through ligand exchange and aggregation‐induced emission (AIE) enhancement. No significant cross‐reactivity from potentially co‐existing species, including sulfonated PFAS, octanoic and dodecanoic acids, humic acid, and inorganic ions is observed. With an optimal concentration of 3.3 µg mL⁻¹Ce‐Gly, the method demonstrated detection limits of 0.24 ppb for PFOA and 0.4 ppb for PFNA. These findings highlight the potential of fluorescence‐based detection strategies utilizing nanoscale probes such as Ce‐Gly as fluorescent probes and nanosensors for PFAS. 

Abstract The presence of contaminants of emerging concerns (CECs) such as pharmaceuticals and personal care products, endocrine disrupting compounds (EDCs), per/poly‐fluorinated substances (PFAS), pesticides, and nanomaterials poses significant challenges to the environment and human health. This review discusses the current status of electrochemical sensing methods and their potential as low‐cost analytical platforms for the detection and characterization of emerging contaminants. Recent developments in advanced materials and fabrication techniques such as electrophoretic deposition, layer‐by‐layer deposition, roll‐to‐roll and 3D printing techniques, and the scalable manufacturing of low‐cost portable electrochemical devices are discussed. Examples of detection mechanisms, electrode modification procedures, device configuration, and their performance along with recent developments in fundamental electrochemistry, particularly nanoimpact methods, are provided to demonstrate the capabilities of these methods for the environmental monitoring of CECs. Finally, a critical discussion of future research needs, detection challenges, and opportunities is provided to demonstrate how electrochemistry can be used to advance field monitoring of these chemicals. These methods can be used as complementary or alternative methods to the currently used laboratory‐based analytical instrumentation to facilitate large‐scale studies and manage risks associated with the presence of CECs in the environment and other matrices. 

Abstract Nanoelectrochemistry allows for the investigation of the interaction of per‐ and polyfluoroalkyl substances (PFASs) with silver nanoparticles (AgNPs) and the elucidation of the binding behaviour of PFASs to nanoscale surfaces with high sensitivity. Mechanistic studies supported by single particle collision electrochemistry (SPCE), spectroscopic and density functional theory (DFT) calculations indicate the capability of polyfluorooctane sulfonic acid (PFOS), a representative PFAS, to selectively bind and induce aggregation of AgNPs. Single‐particle measurements provide identification of the “discrete” AgNPs agglomeration (e.g. 2–3 NPs) formed through the inter‐particles F−F interactions and the selective replacement of the citrate stabilizer by the sulfonate of the PFOS. Such interactions are characteristic only for long chain PFAS (‐SO₃⁻) providing a means to selectively identify these substances down to ppt levels. Measuring and understanding the interactions of PFAS at nanoscale surfaces are crucial for designing ultrasensitive methods for detection and for modelling and predicting their interaction in the environment.