Ultrasensitive amplification-free detection of protein kinase based on catalyzed assembly and enumeration of gold nanoparticles.

A single-particle enumeration method based on phosphorylation-directed in situ assembly of gold nanoparticles is developed for the ultrasensitive sensing of cellular protein kinase A activity. In comparison to existing strategies, the proposed new method demonstrates five orders of linear range and improves the detection limit up to 10-to-1000 fold without the involvement of target amplification.