Metal-enhanced fluorescent dye-doped silica nanoparticles and magnetic separation: A sensitive platform for one-step fluorescence detection of prostate specific antigen.

The world health organization figures show prostate cancer in developed countries has been the second primary cause of cancer mortality following lung cancer for the men. So, early and sensitive diagnosis of cancer is very important before it spreads out to the other organs of the body. It is well-known that prostate-specific antigen (PSA) is the most specific and efficient tumor marker for the diagnosis of prostate cancer. Herein, we successfully fabricated core-shell composite fluorescent nanoparticle Ag@SiO2@SiO2-RuBpy which provide a photoluminescence enhancement of up to ~3-fold when the separation distance between the surface of silver core and the center of the third RuBpy doped silica shell is about 10nm. These core-shell MEF-capable nanoparticles have obvious advantages. The interaction between the doped RuBpy molecules in the outer silica layer and the silver core, greatly improves the excitation efficiency and enhances the fluorescence intensity. Importantly, the presence of silica can reduce the self-quenching of RuBpy, which makes larger amounts of RuBpy incorporated into the silica shell. In addition, the shell protects the RuBpy against collisional quenching and irreversible photodegradation and provides abundant hydroxyl for easy conjugation. After that a highly sensitive, specific and reliable strategy based on metal-enhanced fluorescence and magnetic separation was applied for the detection of PSA in both buffer and serum. The process could be rapidly accomplished, in which the immunomagnetic nanospheres (IMNs) and immunofluorescent nanoparticles (IFNs) were used to capture and identify the target molecules simultaneously. A good linear relationship between the fluorescence intensity and the concentration of PSA (0.1-100ng/mL) with a detection limit 27pg/mL was obtained.