Cu2+-integrated carbon dots as an efficient bioprobe for the selective sensing of guanine nucleobase†

This present work aimed to craft copper (Cu²⁺)-doped carbon dots (CuCDs) for the selective and sensitive detection of a guanine nucleobase. By employing a hydrothermal method, we synthesized blue-emitting CuCDs having emission maxima at 423 nm. CuCDs were used as a fluorescence turn-on ratiometric probe to detect guanine, a critical purine base in DNA involved in energy transduction, cell signalling, and metabolic processes. In the presence of guanine, the fluorescence intensity of CuCDs significantly increased due to the stable non-covalent interaction between Cu²⁺ and guanine. CuCDs achieved a very low limit of detection (LOD) of 0.59 nM for guanine as a highly sensitive probe. CuCDs demonstrated selectivity for guanine with no interference from other nucleobases (adenine, thymine, and cytosine) and various biomolecules and metal ions commonly found in the cellular environment. In addition, CuCDs demonstrated a higher affinity for guanine-enriched oligonucleotide cMYC G 27-mer over dsDNA 26-mer devoid of a large guanine population. Furthermore, the fluorescence intensity of CuCDs increased in guanine-treated mammalian cells and G-quadruplex-enriched cancer cells compared with that in non-cancerous cells. Hence, we developed a highly sensitive ratiometric fluorescence probe, CuCDs, for the selective detection of guanine both in vitro and within mammalian cells via a “fluorescence turn-on mechanism”.