A unique metal–organic framework with the formula [Cd₄(H₂L)₂(L)·H₂O]·3H₂O (H₄L = 5,5′-(1H-1,2,4-triazole-3,5-diyl)diisophthalic acid) was successfully constructed under solvothermal conditions. The frameworks with multiple free Lewis base sites and Lewis acid sites exhibited easily sensitized properties. After the encapsulation of Tb³⁺ cations, the as-synthesized Tb³⁺@Cd-MOF demonstrated strong luminescence induced by the efficient energy transfer from the bridging ligands to the Tb³⁺ cations, with the potential to serve as a chemical sensor. Interestingly, Tb³⁺@Cd-MOF was proven to be a very promising and highly selective and sensitive luminescent platform for the quantitative detection of arginine, which is the biomarker of cystinuria. The fluorescent probe presented high selectivity to arginine in urine with strong luminescence quenching. Furthermore, a convenient fluorescence-based test paper for the visual detection of arginine in applications was prepared. For the first time, arginine was quantified and monitored in urine by a highly efficient recyclable fluorescent sensor based on Tb³⁺-functionalized MOF hybrids, which may be a potential candidate for the further development of clinical diagnostic tools.