Fabrication and characterization and biosensor application of gold nanoparticles on the carbon nanotubes

•Introducing a simple method for the direct assembly of Au NPs on CNTs to reach a localized surface plasmon resonance (LSPR) biosensor chip.•The prepared biosensor chip was characterized by TEM, XRD, Raman spectroscopy and LSPR spectroscopy.•Raman and LSPR spectroscopy were employed to investigate charge transferring in interface of Au NPs and CNTs.•Au NPs@CNT LSPR chip sensors were applied to detect DNA primer at fM concentration by recording of LSPR peak without probe employing and label free. Gold nanoparticles (Au NPs) were synthesized by co-deposition of RF-sputtering and RF-PECVD from acetylene gas and Au target on the carbon nanotubes (CNTs). The CNTs were prepared by thermal chemical vapor deposition (TCVD) and Pd nanoparticles catalyst. TEM image shows that high-density and uniform distribution of Au NPs were grown on the CNTs. XRD analysis indicates that Au NPs have fcc crystal structure and CNTs have a good graphite structure. Raman spectroscopy results suggest that our sample includes double-walled CNTs. It is resulted that intensity of D-band reduces and G-band intensity raises and radial breathing mode (RBM) is changed by immobilizing of Au NPs on the CNTs. Raman results that the free electrons on the CNTs increase by immobilizing of Au NPs. Also localized surface plasmon resonance (LSPR) peak of Au NPs has red-shift and broadens when it is immobilized on the CNTs. The change in LSPR peak rises from decreasing of local electrons density on the Au NPs surface. Raman and LSPR spectroscopy suggest that there are charge transferring and chemical bonds between Au NPs and CNTs. We applied the prepared sensor chips of Au NPs@CNTs to detect DNA primer at femtomolar concentration based on the LSPR technique.