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In this study, we report the Ag nanoparticles aggregated in the process of the labeling that use the crystal violet as the
Raman probe. After this process- immune nanoparticles aggregate with high SERS sensitivity and biological specificity
are created. We track and characterize the preparation by employing UV-Vi absorption spectra, Transmission Electron
Microscope (TEM) and SERS spectra. With the increase of crystal violet, the aggregate of the Ag nanoparticles also
increase, while the intensity of absorption peaks decrease. When the concentration of crystal violet reaches 1.0×10-4
mol/L, new peaks were found in the long wavelengths, and with the increase of the crystal violet, the intensity of the
new peaks increase as well. We observe from the TEM, that with the increase of crystal violet, the aggregation degree of
the Ag nanoparticles also increase and then they unite together. The SERS activity of the aggregates was directly related
to the aggregation degree. Detecting the SERS activity of Ag NPs aggregates labeled with different amount of crystal
violet, we found that with the increase of the crystal violet, the SERS signals of NPs aggregates enhanced. However,
when the amount of crystal violet exceeded 25μL in 1mL colloidal silver, the Ag NPs occurred agglomeration and
thereafter the next preparation of immune-label aggregates was hindered. Whereas, the probe labelled with 12μL crystal
violet exhibited a better stability, stronger SERS activity and higher biological specificity, and it may accomplish a
highly efficient SERS-based immunoassay. This immune probe was applied for detecting the expression of
carcinoembryonic antigen (CEA) in the colon cancer tissue slice. Results show that appropriate immune aggregates
labelled with optimum quantity of crystal violet present high stability, strong SERS activity and good immune specificity,
which are expected to be applied in the analysis of the protein expression in the tissue section and promising for
developing into a clinical tool for diagnosis.
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