Ultrasensitive Ambient Mass Spectrometry Immunoassays: Multiplexed Detection of Proteins in Serum and on Cell Surfaces.

The sensitive and accurate determination of multiple protein biomarkers for clinical diagnosis is in high demand. Here, an ambient mass spectrometry immunoassay platform that possesses advantages of high sensitivity, multiplexed quantitation, low sample consumption and convenient operation was established. A series of extensible rhodamine-based mass tags that ensured quantification of multiple proteins with ultrahigh sensitivity through two-stage signal amplification were developed. Thrombin was detected at zeptomole sensitivity in 2 μL serum/plasma, as was free cancer antigen 125 (CA125). Three protein biomarkers (CA125, carcinoembryonic antigen, and epithelial cell adhesion molecule) were simultaneously detected in situ on ca. 20 cells. This platform is promising for multiple protein detection in a single drop of sample or at the single-cell scale for clinical diagnosis and therapy.