Paper-based microfluidic devices (mPADs) with phase-engineered CsPbI3 and CsPbBr3 PQDs, surface-modified with streptavidin and antibodies, enable simultaneous detection of lung cancer biomarkers carcinoembryonic antigen (CEA) and neuron-specific enolase (NSE) via sandwich immunoassay. The gene discussed is CEACAM5; the disease is lung cancer.