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Sensitive on-line detection of Cu2+ in lubricating oil of marine power plant is important for displaying equipment wear status and fault pre-judgment in real time. However, there are few reports on in-situ, portable and highly sensitive Cu2+ detection devices in organic media before. In this report, CsPbBr 3 perovskite quantum dots (PQDs) are employed as fluorescence probe for Cu2+ detection in microfluidic chip. The size effect of the CsPbBr 3 QDs on the detection performances is firstly investigated. To obtain preferable sensitivity and detection limit, polymethyl methacrylate opal photonic crystals (PMMA OPCs) film is developed as microfluidic sensor substrate, which can tremendously improve the fluorescence intensity of PQDs as high as 26-fold. The enhancement effect can be attributed to the coupling between photonic crystal stopband effect and the excitation light field. Moreover, the use of photomultiplier module for fluorescence signal measurement enables the detection device to be portable. The novel strategy offers the advantages of higher sensitivity (8.62 μM–1) and lower detection limit (0.40 nM). Otherwise, this sensor also provides wide detection range and good selectivity, thus, it will have potential in oil quality in-situ detection and mechanical wear prediction in the future. Unlabelled Image • Opal photonic crystals substrate synthesized in microfluidic chip can effectively enhance the fluorescence intensity of perovskite quantum dots Cu2+ probe. • The coupling between photonic crystal stop-band effect and excitation light field results in enhanced fluorescence with a maximum enhancement factor of 26. • The enhancement effect can increase the sensitivity of microfluidic sensor by 104.8% and reduce the detection limit by 51.2% to detect Cu2+ in lubricating oil. [ABSTRACT FROM AUTHOR]