This
work describes a simple and novel biosensor for the quantitative
determination of Staphylococcus aureus (S. aureus) based on target-induced
release of signal molecules from aptamer-gated aminated mesoporous
silica nanoparticles (MSNs) coupled with surface-enhanced Raman scattering
(SERS) technology. MSNs were synthesized and then modified with amino
groups by (3-aminopropyl) triethoxysilane to make them positively
charged. Next, signal molecules (4-aminothiophenol, 4-ATP) were loaded
into the pores of MSNs. Then, negatively charged aptamers of S. aureus were assembled on the surface of MSNs through
electrostatic interactions. Upon the addition of S.
aureus, the assembled aptamers were specifically bound
to the bacteria. Consequently, the “gates” were opened,
resulting in the release of 4-ATP from the pores of MSNs. The released
molecules were measured by a Raman spectrometer, and the intensity
of 4-ATP at 1071 cm–1 was linearly related to the S. aureus concentration. A silver nanoflower silica
core–shell structure (Ag NFs@SiO2) was prepared
and it served as a SERS substrate. Under optimized experimental conditions,
a good linear relationship (y = 2107.93 + 1536.30x, R
2 = 0.9956) in the range
from 4.7 × 10 to 4.7 × 108 cfu/mL was observed
with a limit of detection of 17 cfu/mL. The method was successfully
applied for the analysis of S. aureus in fish samples and the recovery rate was 91.3–109%.