LAUSR

Abstract Immunoassays are critical for clinical diagnostics and biomedical research. However, two major challenges remaining in conventional immunoassays are precise quantification and development of immunoassays for small‐molecule detection. Here, a two signal‐mode small‐molecule immunoassay containing an internal reference that provides high stability and reproducibility compared to conventional small‐molecule immunoassays is presented. A system is developed for quantitative monitoring of the digoxin concentration in plasma in the clinically relevant range (0.6–2.6 nm). Furthermore, the model system is integrated into a simple gravity‐driven microfluidic chip (G‐Chip) requiring only 10 µL plasma. The G‐Chip allows fast detection without any complex operation and can be recycled for at least 50 times. The assay, and the G‐Chip in particular, has the potential for further development of point‐of‐care (POC) diagnostics.