Urgent demand for the prevention and diagnosis of physiological diseases is driving the development of biomarkers and physiological temperature fluorometric sensors. In this paper, a rare trinuclear lanthanide metal-organic framework (MOF), [(CH3)2NH2][Eu3(μ3-OH)(2,6-NDC)3(HCOO)3]·(solv)x (Eu(2,6-NDC), where 2,6-H2NDC = 2,6-naphthalenedicarboxylic acid) was synthesized using reticular chemistry via reducing the symmetry of the organic ligand from axisymmetric 1,4-naphthalenedicarboxylic acid (1,4-H2NDC) to non-axisymmetric 2,6-H2NDC. Eu(2,6-NDC) shows exceptional chemical and thermal stability in acid-base solutions, PBS solution, and boiling water, and even under an air atmosphere up to 300 °C. As-synthesized Eu(2,6-NDC) exhibits ratiometric detection abilities for P1,P5-di(adenosine-5') pentaphosphate (Ap5A), for use as a biomarker of dry eye disease, with a limit of detection (LOD) of 0.031 μM, as well as excellent anti-interference properties. As far as is known, it is the first Ap5A sensor based on MOFs. In addition, the results show that the ratiometric parameters of co-doped Eu0.001Gd0.999(2,6-NDC) deliver a good linear luminescence response to physiological temperatures (20-60 °C) with high sensitivity.