A Review on the Effect of Transition and Rare Earth Metal Doping on the Color Change Property of Nanoparticles Used in Sensors

Abstract

Colorimetric sensing using nanoparticles has gained immense attention as a simple, rapid, and cost-effective analytical technique due to its capability for naked-eye detection without the need for sophisticated instrumentation. The incorporation of transition and rare earth metal dopants into nanoparticles has emerged as a strategic approach to tailor their structural, electronic, and optical properties, thereby enhancing their sensitivity and selectivity toward diverse analytes. Doping not only modifies the electronic band structure and defect states of the host nanomaterials but also influences particle size, morphology, and surface chemistry, which collectively govern their optical behavior. This review provides a comprehensive overview of the role of metal doping in modulating the colorimetric responses of nanoparticles under various environmental and chemical stimuli. Particular emphasis is given to the classification of dopant types, host nanoparticle systems (such as metal oxides, noble metals, and semiconductor nanomaterials), and their specific sensing applications, including detection of toxic gases, heavy metals, biomolecules, and pH variations. Furthermore, the mechanistic aspects of how doping alters localized surface plasmon resonance (LSPR), energy band transitions, and charge-transfer processes are critically analyzed. The review also highlights recent advances, challenges, and future prospects of doped nanoparticle-based colorimetric sensing platforms in the context of real-world applications. By systematically correlating doping strategies with particle size modulation and resultant optical properties, this study underscores the pivotal role of doped nanomaterials as next-generation colorimetric sensors with high sensitivity, selectivity, and potential for portable, point-of-care diagnostics.