Fig. 2
Characterization of SiO2@Au–Ag NPs. a(i) UV–vis extinction spectra of SiO2 NPs, SiO2@Au NPs, and SiO2@Au–Ag NPs. a(ii) Color image of SiO2 NPs, SiO2@Au NPs, and SiO2@Au–Ag NPs in EtOH solution. b(i) Scanned color image of the spots formed on the NC membrane (6 mm) with 3 μL suspension containing A SiO2@Au–Ag NPs, B SiO2@Au NPs, and C colloid AuNPs at different dilutions (1, 1/4, and 1/16). (b(ii)) Signal intensity based on the scattering effect of corresponding-colored spots on the NC membrane. Error bars represent the standard deviations of the means for three batches of analyte measurements