8100 transmission electron microscope

Au colloids were prepared by the Katherine method with minor modifications by citrate reduction of HAuCl₄ (Sigma-Aldrich, USA) (Fig. 1). A typical solution of 20 nm diameter gold particles exhibited a characteristic surface plasmon band centered at 518–520 nm. Transmission electron microscopy (TEM) with a Hitachi 8100 transmission electron microscope was used to determine the size and monodispersity of the resulting nanoparticles (Fig. 2).Fig. 1

Preparation and characterization of Au nanoparticles

Fig. 2

TEM electron microscope image of gold nanoparticles

DNA probes were modified with a thiol group at its 3′ or 5′ end to facilitate their conjugation on the surface of the gold nanoparticles (GNPs). The probes were prepared by conjugating the thiol DNA probe and GNPs (Hill and Mirkin, 2006). The preparation of DNA was performed by PCR amplification of 16SrDNA. DNA hybridization was performed using two complementary 21-mer DNA molecules according to the method suggested by Gill et al. [22 (link)]. After DNA denaturation at 95 °C for 5 min and ice chilling for 5 min, the prepared single-stranded DNA was added to 100 μL of solution containing gold NP probes. In this solution, there was a final concentration of 3.6 pmol of each probe. After being mixed at 37 °C, the solution was immediately measured by colorimetric method using UV/visible spectrophotometer (Rayleigh UV 2100, China).