Ultrasensitive Aptamer-based SERS Detection of Cancer Biomarker by Heterogeneous Core-Satellite Nanoassemblies

chromatography (HPLC) and suspended in deionized water from a Milli-Q device (18.2 MΩ, Millipore, Molsheim, France). Hydrogen tetrachloroaurate trihydrate (HAuCl 4 • 3H 2 O), sodium citrate, AgNO 3 were bought from Sigma-Aldrich and used as received. All glassware was soaked in aqua regia with 24 h for clearance, then rinsed at least three times with deionized water and dried in an oven. Gold@silver core-shell nanoparticle synthesis Using 17 nm Au NPs as seeds, Ag shell with 10 nm thick was deposited via the chemical reduction of Ag NO 3 with 700 μL of 0.1 M ascorbic acid. Au NPs with a uniform diameter of 17 nm were easily obtained, and larger NPs with perfect size and shape were difficult to obtain. The volume of ascorbic acid used was optimized according to the homogeneity of obtained core-shell nanoparticles, and more rod-shaped structures appeared when the amount of ascorbic acid was greater than 700 μL. Therefore, a total diameter of 37 nm Au@Ag NPs were selected as the SERS substrates, DNA functionalized nanopartilcles Aqueous dispersions (10 mL) of 10 nM NPs were stirred with excess BPS (40 mg/mL) at room temperature for 10 h. The dispersion was concentrated by centrifuging at 13,000 rpm for 10 min. The supernatants were removed and the resulting pellets were resuspended in 0.5×TBE buffer. The modification of DNA onto the NPs performed in a 100 μL reaction system, and the buffer solution used was 0.01 M Tris-HCl containing 50 mM NaCl (pH 7.4). The core NP was adjusted to the concentration of 2 nM, and the DNA aptamer at a final concentration of 60 nM was then added. The 10 nm Au NPs at a concentration of 20 nM were reacted with 40 nM complementary DNA. After incubation for more than 8 h, the excess DNA in the two types of NPs was removed by centrifugation (two times) at 6500 rpm and 10000 rpm, respectively. The particles were resuspended in 0.01 M Tris-HCl and characterized by dynamic light scattering (DLS) to determine the change in NP size following modification with DNA. The hydrodynamic size of the DNA-modified NPs increased, which demonstrated 3 that DNA was successfully conjugated to the surface of the particles and could be used for the subsequent assembly of core-satellite nanostructures (Fig. S3). Characterization Transmission electron microscopy images were obtained using a transmission electron microscope (TEM, JEOL JEM-2100) operating at an acceleration voltage …