Porous SiO2-coated Au-Ag alloy nanoparticles for the alkyne-mediated ratiometric Raman imaging analysis of hydrogen peroxide in live cells.

We prepared an ultrathin porous silica shell-coated Au-Ag alloy nanoparticle (AuAg@p-SiO2NP) and developed it as a novel alkyne-based surface-enhanced Raman scattering (SERS) nanoprobe for the ratiometric Raman imaging of exogenous and endogenous H2O2 in live cells. The AuAg@p-SiO2NPs functionalized with 4-mercaptophenylboronic acid (MPBA) and 4-mercaptophenylacetylene (MPAE, 1986 cm-1) as internal standard were first incubated with dopamine (DA) to incorporate the bridging molecules through the formation of borate bond between DA and MPBA on the surface of nanoparticle. Then, the signaling alkyne molecules of 3-(4-(phenylethynyl) benzylthio) propanoic acid (PEB, 2214 cm-1) were conjugated to the surface of nanoparticle through the formation of amide bond between the carboxyl group on the PEB and the amino group on the DA, forming the ratiometric SERS nanoprobe. In the presence of H2O2, the alkynyl on the PEB is released from the surface of the Au-Ag alloy nanoparticle due to the boronate-to-phenol switch, decreasing the Raman signal at 2214 cm-1 significantly. Since the Raman signal of MPAE at 1986 cm-1 remains unchanged, quantitative analysis of H2O2 concentration can be achieved based on the ratiometric value of I1986/I2214. Under the optimized conditions, the plot of the ratiometric value of I1986/I2214 versus the H2O2 concentration in the range from 0.12 to 8 µM revealed a good linear response with a detection limit of 52 nM based on a signal-to-noise ratio of S/N = 3. The porous SiO2-coated Au-Ag alloy nanoparticle provides a novel SERS substrate with excellent biocompatibility, high stability, and effective anti-interference ability. Together with the alkynyl derivatives as internal standard, the SERS nanoprobe reported here allows the ratiometric detection of H2O2 in live cells and can be further applied to quantify many other biomolecules by using different signaling agents.