Surface Engineering for Microsensing

In the last years, the unique electronic properties of carbon nanotubes have generated a great excitement due to the possibility to tune their electrical and optical properties for specific applications. The possibility to couple functionalized carbon nanotubes with biomolecules, quantum dots and metal nanoparticles has opened the possibility to produce functional materials with specific characteristics. In this work we describe how carbon nanotubes may be utilized to fabricate an engineered surface for sensing applications. Multi-walled carbon nanotubes were first chemically cut by acid treatments and then functionalized with short thiol chains (2-aminoethanethiol). The carbon nanotubes were successively deposited on a gold film by simple chemical adsorption. In an alternative route the acid-treated carbon nanotubes were deposited on a 2-aminoethanethiol modified gold film by means of an external electric field. Gold nanoparticles were then bonded to the nanotubes to exploit their plasmon resonances in Raman spectroscopy. Reaction yields as well as the final products were analyzed by X-Ray Photoelectron Spectroscopy, Infra-Red Spectroscopy, Scanning Electron Microscopy and Atomic Force Microscopy. The result of this surface engineering process leads to a high density of gold nanoparticles on a carbon nanotube carpet with a very efficient intensification of the Raman spectra. Gold nanoclusters were also directly synthesized on thiol functionalized carbon nanotubes film and characterized by means of X-ray photoelectron spectroscopy. Detailed analysis of the Au 4f core line is used to study the chemical modifications occurring on the substrate, as well as to obtain information on the nanocluster size distribution after each reducing treatment. Interestingly, a solution of carbon nanotubes decorated with gold nanoparticles show a drastic increase of the photoluminescence respect to the carbon nanotubes without the gold nanoparticles. This effect, investigated with the optical spectroscopy, may be explained as a consequence of an electromagnetic energy transfer from the gold nanoparticles to the emitting sites of the carbon nanotubes.