Role of Ni and Co Phosphate–MWCNT Interactions in Enhancing Morphine Electrosensing Performance

Morphine is a commonly utilized opioid medication with vital medical uses, but its frequent misuse and unlawful distribution require the creation of sensitive, durable, and dependable detection methods. Development of carbon-based electrochemical sensors has proven reliable for morphine detection due to their exceptional combination of high sensitivity, tunable surface architecture, increased surface area, high electrical conductivity, and ease of functionalization. Multiwalled carbon nanotubes (MWCNTs) are composed of multiple concentric single-walled nanotubes that have different diameters and are separated by an interlayer distance of approximately 0.34 nm, providing many active sites useful for creating nanocomposites. In this work, phosphates of nickel and cobalt and a dual-doped nickel-cobalt phosphate were successfully integrated with MWCNTs and comparatively investigated for ultrasensitive detection of morphine. The synthesized nanocomposites were characterized extensively by using FT-IR, XRD, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron microscopy techniques such as scanning electron microscopy (SEM) and TEM to elucidate their structural, compositional, and morphological features. The performance of electrochemical sensing was assessed using EIS (electrochemical impedance spectroscopy), CV (cyclic voltammetry), and DPV (differential pulse voltammetry). The nickel-cobalt phosphate-MWCNT nanocomposite exhibited superior electrochemical activity, demonstrating improved sensitivity accompanied by a reduced LOD of 0.1 μM under neutral conditions, significantly outperforming the single-metal phosphate counterparts. Furthermore, the modified electrode showed excellent applicability for real sample analysis using urine. Density functional theory (DFT) calculations were employed to analyze adsorption energy, charge transfer, and interfacial interactions between morphine and the composite surface, with the theoretical outcome strongly supporting the experimental observations. Overall, the findings highlight the crucial synergistic role of metal phosphate-MWCNT interfaces in enhancing the selectivity and sensitivity of electrochemical morphine sensors.