Site-specific recognition of DNA modification or the formation of noncanonical structures has important applications in molecular biology, disease diagnosis, and gene expression analysis. In this study, we introduce a guanine-guided sensing tool using a terbium(III)-platinum(II) complex (TPC) as a time-resolved luminescence probe to site-specifically recognize DNA modification and i-motif formation in aqueous solution. The probe is composed of a TbIII center as the luminescent reporter and two PtII units as the receptor for guanine (G) nucleobase. TPC exhibits remarkable reaction selectivity for guanine nucleotides over other nucleotides, giving rise to a significant increase in luminescence. The luminescence enhancement of TPC is mainly attributed to an energy transfer from G base to the TbIII center after the specific coordination of PtII with N7 of guanine (N7-G), which would be facilitated by the phosphates through promoting the departure of coordinated water and bringing G closer to TbIIIvia noncovalent interactions. Based on such sensing feature, the enhanced luminescence of TPC sensitized by G nucleotides can correspondingly decrease upon N7-G modifications of DNA or i-motif formation through constructing simple guanine-guided sensing tools. This probe would provide a useful strategy for site-specific recognition of DNA for extensive purposes.