A dual-analyte electrochemical platform was developed using RuS2-Fe nanodots and a multi-walled carbon nanotube (MWCNT) incorporated RuS2-Fe composite (RuS2/MWCNT-Fe) composites for the sensitive detection of xylazine hydrochloride (XLZ) and erythrosine B (ERY). Both the RuS2-Fe nanodots and RuS2/MWCNT-Fe composites were synthesized via hydrothermal method then used to develop sensors via drop casting on glassy carbon electrodes (GCE). The RuS2-Fe nanodots and RuS2/MWCNT-Fe composites greatly improved the redox capacity of the interfacial region and electron transfer to the surface of the electrodes. Theoretical density functional calculations also validated experimental evidence of charge redistribution within the iron centres of the complex, narrowing of the band gap, and preferential adsorption of both XLZ and ERY. In particular, RuS2-Fe/GCE exhibited unprecedented electrodes within the context of the XLZ analyte, achieving 0.249 nM LOD and a linear range of 0.005–2500 μM. In contrasting work, RuS2/MWCNT-Fe composites electrode obtained 36 nM LOD and ranged 0.05–100 μM towards ERY. Careful analysis of electrochemical impedance and control studies utilizing pristine RuS2 with variable Fe concentrations, alongside extensive durability analysis, elucidated the significant influence of trace Fe concentrations on catalytic activity enhancements. In the context of recent reports on MXene, CNT, and oxide hybrids, the RuS2/MWCNT-Fe system still exhibited ample confirmations on charge transfer resistance and sensitivity. Proposed oxidation mechanisms illustrate the influence of iron on interfacial electron-proton coupling. The versatility of RuS2-Fe nanodots set as a carbon-based electrocatalyst has now been expanded to the dual detection of veterinary sedatives and food colorants. Such a development can be translated as a new stride toward the development of portable food safety, pharmaceutical quality control, and clinical diagnostics devices.

Fe-Doped RuS2 nanodots/MWCNT electrodes for dual detection of xylazine and erythrosine: experimental and computational insights
    Abstract
    1 Introduction
    2 Experimental
        2.1 Synthesis of RuS2-Fe nanodots and RuS2/MWCNT-Fe nanocomposites
        2.2 Surface modification of GCEs using RuS2-Fe and RuS2/MWCNT-Fe for the study
        2.3 Electrochemical determination of XLZ using RuS2-Fe/GCE and ERY using RuS2/MWCNT-Fe/GCE
    3 Results and discussions
        3.1 Characterisation of RuS2-Fe nanodots and RuS2/MWCNT-Fe nanocomposite
            3.1.1 RuS2-Fe nanodots
            3.1.2 RuS2/MWCNT-Fe nanocomposite
    3.2 Electrochemical characterization of RuS2-Fe/GCE and RuS2/MWCNT-Fe/GC
    3.3 Electrochemical studies
    3.4 Computational study
        3.4.1 Structural evaluation
        3.4.2 Interaction mechanism for detection
    3.5 Correlation of electrochemical data with redox mechanisms
    3.6 Electrochemical parameters optimisation studies
    3.7 Effect of scan rate
    3.8 Proposed oxidation mechanism of XLZ at RuS2-Fe/GCE and ERY at RuS2/MWCNT-Fe
    3.9 Quantifying linear range
    3.10 Reproducibility, repeatability and stability
    3.11 Sensitivity and selectivity
    3.12 Real-life application
    3.13 Relation of Fe–RuS2/MWCNT performance to recent carbon-based sensors
    4 Comparison study
    5 Conclusion
    References

• Beena Saraswathyamma(Department of Chemistry, Amrita Vishwa Vidyapeetham, Amritapuri campus, Clappana P O, Kollam, Kerala 690525, India) Corresponding author
• Gopika Meenakumari Gopakumar(Department of Chemistry, Amrita Vishwa Vidyapeetham, Amritapuri campus, Clappana P O, Kollam, Kerala 690525, India, Department of Chemistry, Oregon State University, Corvallis, OR 97331, United States of America) Corresponding author
• S. Prince Makarios Paul(Department of Physics, Karpagam Academy of Higher Education, Coimbatore, Tamil Nadu 641021, India, Centre for Computational Physics, Karpagam Academy of Higher Education, Coimbatore, Tamil Nadu 641021, India)
• Ravi Trivedi(Department of Physics, Karpagam Academy of Higher Education, Coimbatore, Tamil Nadu 641021, India, Centre for Computational Physics, Karpagam Academy of Higher Education, Coimbatore, Tamil Nadu 641021, India, Department of Physics, Manipal University Jaipur, Jaipur, Rajasthan 303007, India)
• Mani Govindasamy(Innovative Technology of Biomedical Engineering & Medical Devices, Ming Chi University of Technology, New Taipei City, Taiwan, Research Center for Intelligent Medical Devices, Ming Chi University of Technology, New Taipei City 243303, Taiwan)