Turbidimetric inhibition immunoassay revisited to enhance its sensitivity via an optofluidic laser.

Turbidimetric inhibition immunoassay (TIIA) is a classic immunodiagnostic method that has been extensively used for biomarker detection. However, the low sensitivity of this technique hinders its applications in the early diagnosis of diseases. Here, a new concept, optofluidic laser TIIA (OFL-TIIA), is proposed and demonstrated for sensitive protein detection. In contrast to the immunoreaction in traditional TIIA, in which the single-pass laser loss is detected, the immunoreaction in the OFL-TIIA method takes place in a laser cavity, which considerably increases the loss induced by antigen-antibody complexes (AACs) via the amplification effect of the laser. A commercial IgG TIIA kit was selected as a demonstrative model to characterize the performance of OFL-TIIA. A wide dynamic range of five orders of magnitude with an exceptional limit of detection (LOD) (1.8 × 10-10 g/L) was achieved. OFL-TIIA is a fast, sensitive, and low-cost immunoassay with a simple homogeneous and wash-free process and low-volume sample consumption, thus providing a new detection platform for disease diagnostics.