The development of low-background, facile, and robust fluorescent nanoprobes for imaging and monitoring of intracellular mRNA changes remains a great challenge. Taking advantage of the high fluorescence quenching efficiency of core-shell gold@polydopamine (Au@PDA) nanocomposites and Ca-promoting DNA adsorption stability, a simple and universal bioconjugate strategy was designed to a construct fluorescent nanoprobe for highly efficient tumor-related mRNA imaging. The fluorescence of Cy5-labeled DNA was quenched up to 92.38% by the AuNP and PDA via nanometal surface energy transfer (NSET) and photoinduced electron transfer (PET), respectively. TK1 mRNA, a biomarker of tumor growth, initiates hybridization and results in fluorescence recovery, which built the foundation for identifying the expression level changes in living cells. More importantly, three kinds of tumor-related mRNA (TK1 mRNA, GalNAc-T mRNA, and C-myc mRNA) can be detected simultaneously with different fluorophore-modified recognition sequences, which can avoid false positive signals and improve the reliability of cancer diagnostic, holding great promise for cancer diagnosis, prognosis, and therapy.