We present changes in the first and second order Raman spectra of multiwalled carbon nanotubes ͑MWNTs͒ functionalized with oxygenated groups. The oxygen groups were introduced onto the nanotube surface through two strong acid purification routes: ͑1͒ reflux in concentrated ͑70%͒ HNO 3 acid for 4 h at 80°C and ͑2͒ ultrasonification in 3 HNO 3 ͑70% ͒ :1H 2 SO 4 ͑98%͒ for 8.5 h. Raman spectroscopy, using two laser excitation wavelengths ͑514.5 and 632.8 nm͒, x-ray photoelectron spectroscopy, and thermal gravimetric analysis were employed to study the evolution of the products. All the techniques revealed a higher degree of functionalization for scheme 2 compared to scheme 1. Charge transfer phenomena were manifested by a shift of the C1s core level towards higher binding energies. We found that the intensity of both the D and G energy Raman modes if normalized to the second order mode D * mode follows similar trends upon acid treatments. We interpret this result together with the observed dispersion of G mode as an indication that the G mode in carbon nanotubes is defect induced in a double resonant process. Both acid schemes cause an upshift of D and G Raman modes, due to intercalation of acid molecules, exerting pressure on the sp 2 structure and an electron transfer from the states in MWNTs to the oxygen atoms.
The performance of glassy carbon (GCE) and graphite pencil electrodes (PGE) modified with multiwalled carbon nanotubes (CNTs) are compared, based on the direct electrochemical detection of nucleic acids. This is accomplished by monitoring the differential pulse voltammetry changes of the guanine signal. CNT-modified PGE compares favorably to that of the commonly used CNT-modified GCE owing to the intrinsic improved performance of the supporting PGE. The better intrinsic characteristics of the PGE are related to its composite structure and higher level of porosity compared to GCE. The performance characteristics of the direct DNA hybridization on the disposable CNT-modified PGE are studied in terms of optimum analytical conditions such as probe concentration, target concentration, hybridization time, and selectivity. The new DNA biosensor described here has shown some important advantages such being inexpensive, sensitive, selective, and able to generate reproducible results using a simple and direct electrochemical protocol.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.