Low-molecular-weight microspheres with soft-shell characteristics for remarkable signal enhancement in LOCI applications

Light-Activated Oxygen Channel Immunoassay (LOCI) is very attractive in immunoassay due to its advantages of simplicity, sensitivity and automation. The preparation of donor/acceptor beads (DBs/ABs) in LOCI is crucial to the detection sensitivity. In this study, microspheres with “hard core-soft shell” structure were prepared by stepwise dosing with a chain transfer agent (CTA), 2,4-diphenyl-4-methyl-1-pentene (a-MSD). The soft-shell structure facilitated the penetration of the photosensitizer into the microsphere and was encapsulated at the shell layer, thereby significantly improving the activity of singlet oxygen (1O2, λ< 200nm) in LOCI. With the amount of a-MSD added increased to 20wt%, the molecular weight of the microspheres decreased to 7235, and the loading of the photosensitizer in the microspheres could be as high as 80.6%, which enhanced the signal of LOCI detection by about 12.77 times. When the addition of a-MSD was 10wt%, the optimal molecular weight and soft-shell structure were obtained, with the best signal-to-noise ratio (S/N) of 58.24. Compared with solid microspheres, the S/N was improved by about 4.22 times. These findings indicated that low-molecular-weight soft-shell microspheres have great potential in immune-medical applications, and the idea of soft-shell microspheres provides a new strategy for the preparation of immune-magnetic beads and immune-fluorescence microspheres.