ABSTRACT
With the requirements of early diagnosis, biomarker development and functional definition, the challenge of sensitivity of immunoassay has become increasingly prominent. How to improve it to break the bottleneck has become a major challenge in the field of bioassays. Amplifying the immunosignal is the most direct method to improve detection sensitivity. Biotin-avidin system (BAS), tyramide signal amplification (TSA) and immuno-polymerase chain reaction (Im-PCR) are the most classic signal amplification techniques which significantly improved the sensitivity of immunoassays. In recent years, studies have confirmed that the sensitivity of immunoassays can be further increased by approximately three orders of magnitude with the invention of techniques including catalyzed reporter deposition-based signal amplification, nanotechnologies-based signal amplification and hybridization chain reaction-based signal amplification. Herein, we will summarize the techniques that have been developed in recent years for amplifying the signals of immunodetection and comparatively analyze their advantages and disadvantages in order to provide reference for the developed techniques transformed to clinical application and further research on ultrasensitive immunoassays.