Highly sensitive and homogeneous detection of membrane protein on a single living cell by aptamer and nicking enzyme assisted signal amplification based on microfluidic droplets.

Membrane proteins play vital roles in numerous physiological functions. Recently, they have been considered as candidate biomarkers for cancer and recognized as major drug targets. So, accurate, sensitive, and high-throughput quantitative detection of the membrane proteins is crucial for better understanding their roles in cancer cells and further validating their function in clinical research. Here, we report a highly sensitive and homogeneous detection of membrane protein on single living cells by aptamer and nicking enzyme assisted fluorescence signal amplification in microfluidic droplets. The homogeneous reaction based on the membrane protein-triggered conformation alteration of hairpin probe can improve the detection accuracy with elimination of several washing and separation steps. The microfluidic system provides a high-throughput platform for the detection of a single cell, and the highly monodisperse droplet can function as an independent microreactor for the aptamer and nicking enzyme assisted fluorescence signal amplification, coordinating with the small volume of the confined space (a droplet), increased reaction rate, and highly sensitive detection of membrane protein on single cell can be reached.