Digital Single Virus Immunoassay for Ultrasensitive Multiplex Avian Influenza Virus Detection Based on Fluorescent Magnetic Multifunctional Nanospheres.

The fluorescence method has made great progress in the construction of sensitive sensors but the background fluorescence of the matrix and photobleaching limit its broad application in clinical diagnosis. Here, we propose a digital single virus immunoassay for multiplex virus detection by using fluorescent magnetic multifunctional nanospheres as both capture carriers and signal labels. The superparamagnetism and strong magnetic response ability of nanospheres can realize efficient capture and separation of targets without sample pretreatment. Due to their distinguishable fluorescence imaging and photostability, the nanospheres enable single-particle counting for ultrasensitive multiplexed detection. Furthermore, the integration of digital analysis provided a reliable quantitative strategy for the detection of rare targets. Based on multifunctional nanospheres and digital analysis, a digital single virus immunoassay was proposed for simultaneous detection of H9N2, H1N1, and H7N9 avian influenza virus without complex signal amplification, whose detection limits were 0.02 pg/mL. Owing to its good specificity and anti-interference ability, the method showed great potential in single biomolecules, multiplexed detection, and early diagnosis of diseases.