Niobium-based MXenes for electrochemical sensors: advances in analytical performance, sensing strategies, and future perspectives.

Niobium (Nb)-based MXenes have recently emerged as promising two-dimensional (2D) materials for electrochemical sensing applications. Although titanium (Ti) based MXenes such as titanium carbide (Ti3C2Tx) dominate the current sensing literature, Nb-based MXenes, particularly Nb2CTx and Nb4C3Tx, also exhibit distinctive electrochemical stability and strong interfacial activity which make them attractive for detecting biomolecules, pharmaceutical compounds, environmental pollutants, food contaminants, metal ions, pathogens, and disease biomarkers. This review discusses recent advances in Nb-based MXenes such as Nb2CTx and Nb4C3Tx for the construction of electrochemical sensors. Widely used synthesis strategies such as direct hydrofluoric-acid etching, fluoride-free chemical/electrochemical etching, in situ fluoride-generating salt/acid etching (including hydrothermal processing variants), and Lewis-acidic molten-salt etching have been briefly discussed. Furthermore, electrochemical sensors based on Nb MXenes are reviewed for the detection of dopamine (DA), ascorbic acid (AA), uric acid (UA), glucose, rifampicin, fluoxetine, sertraline, nitrite, hydrogen peroxide (H2O2), pesticides, heavy metals, hormones, bacteria, and cardiac biomarkers. Unlike broad MXene reviews, this review focuses on Nb2CTx and Nb4C3Tx as sensing materials. Subsequently, the analytical performance of reported sensors based on Nb MXenes and their hybrid composites is discussed. Finally, challenges and perspectives have been discussed.