Emission Onset Time-Adjustable Chemiluminescent Gold Nanoparticles with Ultrastrong Emission for Smartphone-Based Immunoassay of Severe Acute Respiratory Syndrome Coronavirus 2 Antigen

Recently,our group reported a chemical timer approachto manipulatethe onset time of chemiluminescence (CL) emission. However, it isstill in the proof-of-concept stage, and its analytical applicationshave not been explored yet. Nanomaterials have merits of good catalyticeffect, large specific surface area, good biocompatibility, and easeof self-assembly, which are ideal for constructing analytical-interfacesfor bioassays. Herein, an emission onset time-adjustable chemiluminescentL012-Au/Mn2+ was synthesized for the first time by modifyingMn(2+) on the surface of L012-protected gold nanoparticle.By using H2O2 and NaHCO3 as coreactants,L012-Au/Mn2+ could not only generate an ultrastrong andlong-time CL emission but also its CL emission onset time could beadjusted by the addition of thiourea, which could effectively eliminateinterference from the addition of coreactants, shorten the exposuretime, reduce the detection background, and finally achieve high sensitivityCL imaging analysis. On this basis, a label-free CL immunoassay wasconstructed with a smartphone-based imaging system for high-throughputand sensitive determination of severe acute respiratory syndrome coronavirus2 nucleocapsid (N) protein. The CL image of the immunoassay with differentconcentrations of N proteins was captured in one photograph 100 safter the injection of H2O2 with a short exposuretime of 0.5 s. The immunoassay showed good linearity over the concentrationrange of 1 pg/mL to 10 ng/mL with a detection limit of 0.13 pg/mL,which was much lower than the reported CCD imaging detection method.In addition, it showed good selectivity and stability and was successfullyapplied in serum samples from healthy individuals and COVID-19 rehabilitationpatients.

Automated summary

Recently, a chemical timer approach to manipulate the onset time of chemiluminescence (CL) emission was developed. By modifying Mn(2+) on the surface of L012-protected gold nanoparticles, an emission onset time-adjustable chemiluminescent L012-Au/Mn2+ was synthesized, which could generate strong and long-time CL emission with adjustable onset time. This approach was applied to construct a label-free CL immunoassay for the high-throughput and sensitive determination of the severe acute respiratory syndrome coronavirus 2 nucleocapsid (N) protein, showing good linearity and low detection limit.