Advanced carbon dot- and quantum dot-based sensors for lead ion detection: a comprehensive review

Lead ion contamination in water sources poses severe threats to the environment and human health owing to its high toxicity, long-term persistence and nonbiodegradability. Natural events as well as diverse industrial and unavoidable human activities such as battery manufacturing, metal plating, use of cosmetics, recycling of electronic waste, consumer products, volcanoes, and corrosion of service pipes are some common sources of lead ion contamination. It has been well established that exposure to any ionic form of lead causes severe systemic toxicity and carries carcinogenic risks. Therefore, the development of potent innovative technologies or methodologies for detecting toxic lead ions is necessary for the protection of human health and environmental monitoring. Recent developments have highlighted the advancement of innovative analytical methodologies for detecting lead ions, focusing on enhanced sensitivity, rapid detection, accuracy and sustainability. The emergence of carbon-based nanomaterials, particularly carbon dots, carbon quantum dots and graphene quantum dots, has established them as promising candidates for designing efficient sensing materials for the detection of lead ions because of their biocompatibility, superior photoluminescence, tuneable surface chemistry, low detection limits and high sensitivity. Along with these carbon-based nanomaterials, quantum dots have also been established as benchmark semiconductor nanomaterials for sensing applications because of their distinct electro-optical properties arising from quantum confinement effects. This review provides a comprehensive overview of the current developments in carbon dots, carbon quantum dots, graphene quantum dots, quantum dots and their composites as zero-dimensional nanosensors for the detection of Pb²⁺ ions, focusing on their functionalization techniques, synthesis methods, sensing mechanisms and analytical capabilities. Special attention is placed on "turn-on/turn-off" systems, ratiometric sensors and hybrid nanocomposites to enhance stability and selectivity for lead ion detection, highlighting their crucial role in safeguarding the environment and public health.