Rapid micromotor-based naked-eye immunoassay

A dynamic micromotor-based immunoassay, exemplified by cortisol detection, based on the use of tubular
micromotors functionalized with a specific antibody is described. The use of antibody-functionalized micromotors
offers huge acceleration of both direct and competitive cortisol immunoassays, along with greatly
enhanced sensitivity of direct and competitive immunoassays. The dramatically improved speed and sensitivity
reflect the greatly increased likelihood of antibody-cortisol contacts and fluid mixing associated with the
dynamic movement of these microtube motors and corresponding bubble generation that lead to a highly
efficient and rapid recognition process. Rapid naked-eye detection of cortisol in the sample is achieved in
connection to use of horseradish peroxidase (HRP) tag and TMB/H2O2 system. Key parameters of the
competitive immunoassay (e.g., incubation time and reaction volume) were optimized. This fast visual
micromotor-based sensing approach enables “on the move” specific detection of the target cortisol down to
0.1 μg mL−1 in just 2 min, using ultrasmall (50 μL) sample volumes.