Fluorescent DNA biosensors for Pb(II) detection based on G-quadruplex formation

Pb(II) ions pose a grave concern due to their ability to inflict irreparable harm upon humans, even at exceedingly low concentrations. Conventional techniques have limitations due to the need for complex sample pre-treatment, specialized operation, and expensive equipment for widespread Pb(II) ion detection. Consequently, there is a burgeoning interest in developing a DNA biosensor that employs fluorescence methodology to detect Pb(II) ions. It offers heightened sensitivity, an impressive lower detection limit, and user-friendly operation, thus rendering it a focal point of contemporary scientific inquiry. One noteworthy observation is the Pb(II) ion's capacity to form remarkably stable G-quadruplex structures when paired with G-base-rich oligonucleotide sequences (GOS), surpassing the stability achieved with K(I) ions. This observation opens up exciting avenues and possibilities for detecting Pb(II) ions. In this review, we undertake a comprehensive classification and summarization of diverse fluorescent biosensors for Pb(II) ion detection, relying on the formation of G-quadruplex structures through both label-free and labeled methodologies. The categorization encompasses signal on-off/off-on models and enzymatic-assisted approaches within the label-free methods. In the labeling method, our scrutiny delves into various classes of quenching groups, including conventional quenchers, continuous G bases, and nanomaterials, offering a comprehensive discussion of their respective merits and applications. Moreover, this review endeavors to explicate the formation of G-quadruplex structures triggered by Pb(II) ions, thereby fostering a more explicit understanding among researchers of these intricate structures.