Emerging strategies to develop sensitive AuNP-based ICTS nanosensors

Abstract Immunochromatographic strip (ICTS) nanosensors are one of the most popular point-of-care (POC) diagnostic devices currently available for rapid target screening. However, the widely used ICTS sensors based on 20–40 nm gold nanoparticles (AuNPs) as labels are limited by their low detection sensitivity due to their relatively weak color intensity. Moreover, the ever-increasing demand for high sensitivity is restricting the application of conventional AuNP-based ICTS methods. Improving the color signal intensity of AuNP nanoprobes can theoretically overcome the limitations encountered by traditional ICTS assays. In recent years, the design of various improved strategies for the enhanced detection sensitivity of ICTSs has received increasing interest. In this review, we systematically summarize the emerging amplification strategies used to enhance the detection sensitivity of conventional AuNP-based ICTS nanosensors. These strategies include 1) signal enhancement mediated by nanoparticle accumulation, 2) signal amplification induced by noble metal nanoparticle growth, 3) signal enhancement based on enzyme-mediated colored product deposition, and 4) signal amplification assisted by nanoparticle flow rate regulation on strips. Representative examples are selected to demonstrate the proof-of-concept and their potential applications in biosensing. The study focuses on elaborating the underlying mechanisms of each strategy for the enhanced colorimetric signal intensity of AuNPs on the test regions of a strip. Finally, we briefly discuss the current limitations and future perspectives in this field.