Combining Porous Magnetic Ni@C Nanospheres and CaCO3 Microcapsule as Surface-Enhanced Raman Spectroscopy Sensing Platform for Hypersensitive C-Reactive Protein Detection.

In this work, we have designed an efficient and rapid surface-enhanced Raman spectroscopy (SERS) immunosensor for a supersensitive analysis of hypersensitive C-reactive protein (hs-CRP) with a label-free method by combining porous magnetic Ni@C nanospheres to aggregate together for simplifying the experiment operation and CaCO3 microcapsule to encapsulate rhodamine B as the Raman signal. The final solution containing the signal molecule was dropped on the Ag nanoparticle substrate, and the signal could be enhanced by Ag particles. First, rhodamine B was encapsulated in the CaCO3 microcapsule when it precipitated to form microcubes. Subsequently, the porous CaCO3 microcapsule was assembled layer by layer with poly(ether imide) (PEI) and a second antibody to obtain rhodamine B@CaCO3@PEI@Ab2. Then, the functionalized magnetic Ni@C nanospheres were prepared to immobilize the primary antibody (Ab1). Finally, the immunosensor was fabricated by the sandwiched antibody-antigen interactions. Compared to the DNA hydrogel, the low-cost CaCO3 microcapsule would be rapidly dissolved by ethylene diamine tetraacetic acid, releasing rhodamine B to produce a strong Raman signal for a rapid and efficient detection of hs-CRP. With the hs-CRP concentration ranging from 0.1 pg mL-1 to 1 μg mL-1, the SERS intensity of the platform has a linear relationship with the logarithm of hs-CRP concentration, and the detection limit was 0.01 pg mL-1. By this smart design, this work can give a direction for a rapid label-free SERS analysis.