Development of a rapid and sensitive method for infectious disease diagnosis is highly important to prevent the further spread of disease and to enable effective clinical treatment. Herein, an ultrasensitive colorimetric approach combining the advantage of immunomagnetic nanobeads and the enzyme mimic activity of gold nanoparticles has been developed. Two kinds of amplification processes are used to enhance the detection sensitivity. The increased surface area and the magnetic properties enable the magnetic nanobead to catch a large number of antibodies and target viruses, thus very small amounts of the virus can be easily detected. And the signal amplification of naonzyme causing the enhancing of the optical signal. This approach could avoid complicate instruments and allowed detecting Influenza virus only by naked eyes as well as microplate reader.
In addition, we introduced a novel practical approach to develop a robust sensing system, named magnetoplasmonic ELISA (magplas-ELISA), which collects and concentrates target antigen, and amplifies signal simultaneously. Gold nanoparticles (Au NPs) were decorated with the magnetic nanoparticles (MNPs) based on its ease of synthesis and bio-compatibility. It can replace peroxidase in colorimetric biosensor owing to its outstanding peroxidase-like activity. Our choice of MNP-Au NP has a triple function which is a capture probe, magnetic concentrator and signal amplifier in this system. Triple-functional- magnetoplasmonic NPs described here provides direct monitoring of biomarker in a clinical sample as urine and serum.