A comparison between powders and thin films of single-walled carbon nanotubes for the adsorption behaviors of phenylalanine and glycine by XANES study

Abstract

We have compared the adsorption behaviors between single-walled carbon nanotube (SWCNT) powders and thin films with amino acids such as phenylalanine and glycine by using the X-ray absorption near edge structure (XANES) spectroscopy. On SWCNT powders very weak adsorption occurs as confirmed also by studies at high solution concentrations. The comparison of the adsorption behaviors with previous reports for thin films of SWCNTs shows that, due to their compact structure, thin films favor the adsorption of amino acids and represent themselves good candidate for a reliable evaluation of the interaction among amino acids and SWCNTs. carbon nanotubes, XANES, amino acids PACS: 88.30.rh, 61.10.Ht, 87.85.J-The study of the adsorption of biological molecules on nanostructures like SWCNTs attracts considerable attention because of increasing applications of nanometer scale biosensors and biomedical devices. Different methods for the functionalization of carbon nanotubes by the adsorption of biological molecules have already been reported, yet there is still insufficient understanding of the interaction between SWCNTs and simple biological molecules [1-9]. Heller et al. showed a transition of the DNA secondary structure from B to Z conformation modulated by the dielectric environment of SWCNTs [1]. Recently, the peptide/SWCNTs interaction and the adsorption of biological molecules with different aromatic structures on SWCNTs have been investigated [2][3][4]. Amino acids are building blocks of proteins (polypeptides) and then essential biological molecules whose interaction with SWCNTs is a fundamental issue to be fully understood.Short of the characterization methods at single-bond resolution, the adsorption mechanism of biological molecules on SWCNTs is still an open question. The X-ray absorption near edge structure (XANES) spectroscopy is an element-specific technique that provides the fingerprint of the chemical interaction and accurate electronic details at the interface of complex systems [10,11]. As the method is good for characterizing biological molecules/SWCNTs systems, it has been employed to study amino acids and simple polypeptides [12][13][14]. The adsorption of proteins on the surface of SWCNTs has been explored by XANES and the characteristic feature of the peptide C==O bonds in proteins was found to be affected by the graphene-like structure of SWCNTs [15]. Also the adsorption of amino acids on SWCNTs has been studied by XANES [16]. A clear energy