Mechanism Study Of Adsorption Of Aromatic Amino Acids Onto Single-walled Carbon Nanotubes

Single-walled carbon nanotubes(SWCNTs) exhibits many peculiar physical and chemical properties due to it's ideal one-dimensional structure, therefore are widely applied to biomedical fields, such as bio-electrochemical sensors, drug transport vector, tissue engineering materials. However, in these biomedical applications, there involve bio-nano interaction between SWCNTs and biomolecules. In this paper, two essential aromatic amino acids in vivo- phenylalanine (Phe) and tryptophan (Trp) are adsorbed on the SWCNTs, and Near Edge X-ray Absorption Fine Structure Spectroscopy (NEXAFS) and Synchrotron Radiation Photoelectron Spectroscopy (SRPES) were employed to investigate the adsorption mechanism of Trp and Phe onto the SWCNTs. At the same time, different concentrations of HNO3,concentrated HNO3/H2SO4 mixed acid were used to carboxylate SWCNTs, and Raman Spectroscopy was used to study the best Carboxylation conditions. The main results are listed as following.1.Mechanism study of adsorption of tryptophan onto single-walled carbon nanotubes. SWCNTs films were fabricated by vacuum-filtering, and were incubated in saturated Trp solutions for one hour. C, N ,O K-edge NEXAFS spectrum and C, N,O 1s SRPES spectrum of SWCNTs,SWCNTs adsorbed by Trp and Trp were measured.1) Upon adsorption, the peak at 288.2eV of C K-edge NEXAFS spectrum shifts towards to low energy by 0.6eV, and C1s binding energy of Carboxyl of C1s SRPES spectrum shifts to low energy by 0.5eV. All these show carbonxyl involved in the interface interaction.2) Upon adsorption, negligible changes of peak shape and energy position of N K-edge NEXAFS and N1s SRPES spectrum imply N atoms not to be involved interface interaction.3) Upon adsorption, the peak shape of O K-edge NEXAFS spectrum Combined O1s SRPES spectrum shows only O-atom of the C=O in the Trp molecule participates in the interface interaction. 2.Mechanism study of adsorption of phenylalanine onto single-walled carbon nanotubesSWCNTs films were fabricated by vacuum-filtering, and were incubated in saturated Phe solutions for one hour. C, N ,O K-edge NEXAFS spectrum and C, N,O 1s SRPES spectrum of SWCNTs,SWCNTs adsorbed by Phe and Phe were measured.1) Upon adsorption, the peak at 288.1eV of C K-edge NEXAFS spectrum shifts towards to low energy by 0.5eV, which shows a significant interaction in the interface between SWCNTs and adsorbed Phe2) Upon adsorption, an obvious change in pre-peak profile of O K-edge NEXAFS spectrum exhibits O atoms participating in the interface interaction. O1s SPPES spectrum reveals that only O atom in the C=O is the active bonding site.3) Upon adsorption, an obvious change in peak intensity of NK-edge NEXAFS spectrum imply that amino N atoms are also involved in the interface interactions.4) Upon adsorption, Changes in C1s SRPES spectrum states that O atoms in the C=O and amino N atoms are involved in the interaction interface3. The study of carboxylation condition of SWCNTsRaman spectrum was employed to investigate to carboxylation interaction under different carboxylation conditions. The peak changes of Radial breathing mode in Raman spectrum shows 15M HNO3 destroyed the majority of wall of SWCNTs and shows about 10 M HNO3 Should be in the best carboxylation conditions. Intensity changes in D peak and G peak further proved about the 10M HNO3 is the best oxidizing conditions.