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Owing to unique physical and optical properties, fluorescent carbon dots (C-dots) are used in various biomedical applications. In this study, C-dots have been integrated as sensing agent on paper surface for colorimetric determination of clinically important analytes. Polyacrylamidebased C-dots coated C-dips showed visible color change from white to brown for iron (Fe2+, Fe3+) sample. Moreover, iron and copper (Cu2+) samples showed significant quenching of C-dots under UV. Images captured with/without UV were analyzed to study the relationship between different iron and copper concentrations and colorimetric intensity values. Color intensity and fluorescence showed a linear relationship with concentrations of iron and copper (Range: 1×10-4 to 1×10-2 M, Linearity: R² = 0.94). LOD from the paper sensor showed a sensitivity of 3.89×10-5 μM, 4.65×10-5 μM and 6.7×10-5 μM for Fe3+, Fe2+ and Cu2+ respectively, reflecting its reliability as low-cost sensing solution to analyze clinically relevant analytes as reported in current study. [ABSTRACT FROM AUTHOR]

2D MXenes have emerged as promising supercapacitor electrode materials due to their metallic conductivity, pseudo‐capacitive mechanism, and high density. However, layer‐restacking is a bottleneck that restrains their ionic kinetics and active site exposure. Herein, a carbon dots‐intercalated strategy is proposed to fabricate flexible MXene film electrodes with both large ion‐accessible active surfaces and high density through gelation of calcium alginate (CA) within the MXene nanosheets followed by carbonization. The formation of CA hydrogel within the MXene nanosheets accompanied by evaporative drying endow the MXene/CA film with high density. In the carbonization process, the CA‐derived carbon dots can intercalate into the MXene nanosheets, increasing the interlayer spacing and promoting the electrolytic diffusion inside the MXene film. Consequently, the carbon dots‐intercalated MXene films exhibit high volumetric capacitance (1244.6 F cm−3 at 1 A g−1), superior rate capability (662.5 F cm−3 at 1000 A g−1), and excellent cycling stability (93.5% capacitance retention after 30 000 cycles) in 3 m H2SO4. Additionally, an all‐solid‐state symmetric supercapacitor based on the carbon dots‐intercalated MXene film achieves a high volumetric energy density of 27.2 Wh L−1. This study provides a simple yet efficient strategy to construct high‐volumetric performance MXene film electrodes for advanced supercapacitors. [ABSTRACT FROM AUTHOR]

Metal oxide-based electrochemical sensors, despite their robust redox activity, lack sufficient conductivity to overcome their sluggish kinetics. Herein, we propose a unique self-assembled hybrid configuration based on redox-active Co3O4 hexagons (Co3O4-HX) and the highly conductive, few-layer-thick Ti3C2Tx sheets. The self-assembly approach enabled the compact interfacial formation and moderate intercalation of Ti3C2Tx sheets, allowing the Co3O4/Ti3C2Tx composite (Co3O4–MX) to exhibit a synergetic improvement in the charge-transfer rate and oxidation current response toward isoprenaline (ISPT), a neurotransmitter drug. The hybrid composite when devised as an electrochemical sensor gives rise to a 7.9-fold higher oxidation current response to 0.65 μM ISPT than its pristine Co3O4 counterpart. The improved charge kinetics and generation of a superior oxidation current emphasized the critical role of Ti3C2Tx as an interactive substrate in the Co3O4–MX hybrid. The analytical detection capability assessed via differential pulse voltammetry (DPV) confirmed the sensor's high selectivity and marked stability both in low and high concentration ranges of ISPT ((0.01 to 0.33 μM) and 0.5 to 0.9 μM) with a limit of detection (LOD) of 3 × 10–3 μM (for low concentrations). Importantly, the fabricated sensor could detect ISPT from harsh biological environments such as human urine samples with a recovery rate of 99%. Moreover, the sensor exhibited a stable working response during its prolonged storage of 30 days in an aqueous PBS system. The proposed route of using MXenes as a conductive substrate paves the way for developing a robust metal-oxide-based redox-active hybrid system for the sensitive detection of important therapeutic compounds. [ABSTRACT FROM AUTHOR]

MXenes-Ti3C2Tx, based on their versatile surface characteristics, has rapidly advanced as an interactive substrate to develop electrochemical sensors for clinical applications. Herein, Ni embedded Ti3C2Tx (MX−Ni) composites were prepared using a self-assembly approach where Ti3C2Tx sheets served as an interactive conductive substrate as well as a protective layer to nickel nanoparticles (Ni NPs), preventing their surface oxidation and aggregation. The composite displayed a cluster-like morphology with an intimate interfacial arrangement between Ni, Ti3C2Tx and Ti3C2Tx-derived TiO2. The configuration of MX−Ni into an electrochemical sensor realized a robust cathodic reduction current against methylmalonic acid (MMA), a biomarker to vitamin B12 deficiency. The synergism of Ni NPs strong redox characteristics with conductive Ti3C2Tx enabled sensitive signal output in wide detection ranges of 0.001 to 0.003 µM and 0.0035 to 0.017 µM and a detection sensitivity down to 0.12 pM of MMA. Importantly, the sensor demonstrated high signal reproducibility and excellent operational capabilities for MMA in a complex biological matrix such as human urine samples. [ABSTRACT FROM AUTHOR]

MXenes have emerged as promising electrode materials for supercapacitors based on their metallic conductivity, good hydrophilicity, rich surface chemistry, and excellent mechanical characteristics. However, the strong interlayer van der Waals forces induce significant layer restacking, which restrict complete exposure of MXenes' surface active sites, impeding electron/ion transport and resulting in poor electrochemical performances. Herein, a porous MXene/carbon nanotube (CNT) film was prepared through a simple alkali-induced process. The developed porosity and the introduction of CNTs can effectively suppress the restacking of MXene nanosheets, promoting the effective utilization of the surface active sites of the MXene and facilitating fast ion/electron transportation. Consequently, the porous MXene/CNT film exhibited a high specific capacitance of 401.4 F g-1 at 1 A g-1 and a sustained capacitance of 336.2 F g-1 at an ultrahigh current density of 1000 A g-1, corresponding to an 83.8% capacitance retention. Furthermore, the film electrode demonstrated outstanding cycling stability, with a capacitance retention of 99.0% after 20,000 cycles at 100 A g-1, showing its significant potential for supercapacitor applications. [ABSTRACT FROM AUTHOR]