Effect of High Energy Carbon Beam Irradiation on Carbon Nanotubes Modified Glassy Carbon and Its Application in Sensing of Deoxyguanosine

The effect of high energy carbon ion beam as the modification tool for the multiwalled carbon nanotubes (MWCNT) modified glassy carbon (GC) has been studied. The change in the morphology, length and diameter of the carbon nanotubes upon irradiation is analyzed using Raman spectroscopy, Atomic force microscopy and FE-SEM. The irradiated MWCNTs had a diameter in the range of 3-27 nm which is much lower in comparison to the diameter of the tubes present in the pristine state. All the bands in the Raman spectra, corresponding to the irradiated MWCNT, shifted towards higher wave numbers by 4-5 cm^-1. The irradiated MWCNT/GCE has been further used as a sensor for the electrochemical investigation of deoxyguanosine and deoxyadenosine. A sharp oxidation peak with much enhanced peak current at ~930 mV, corresponding to the oxidation of deoxyguanosine, is observed at the irradiated sensor, whereas, no peak was observed at the bare GCE. A very small peak at ~ 975 mV is observed at MWCNT modified GCE. Thus, it can be concluded that irradiation leads to appreciable defects formation which promotes the electron transfer and leads to enhanced electrooxidation of deoxyguanosine on the irradiated sensor surface.

It was found that the peak potential of both deoxyguanosine and deoxyadenosine depends on the pH of the supporting electrolyte and shifted to more positive potentials with increase in pH. The linear relation between pH and the peak potential (E_p) can be expressed by the following equations:

E_p (Deoxyguanosine) = -52.96 pH + 1307.3       (R² = 0.9928)                                          

E_p (Deoxyadenosine) = -49.94 pH + 1560.4       (R² = 0.9990)                                           

From the linear current versus concentration relations, it can be seen that exposure of MWCNT to high energy carbon beam lead to ~ 7 times increase in sensitivity in the case of deoxyguanosine and ~ 2 times for deoxyadenosine. The limit of detection, calculated by 3σ/b where σ is the standard deviation of the blank solution and b is the slope of the calibration curve, is substantially changed on irradiation from 12 µM to 507 nM and 4.29 µM to 300 nM for deoxyguanosine and deoxyadenosine respectively.  The simultaneous determination of the two analytes was performed using the fabricated sensor and its practical utility was tested by analyzing DNA, extracted from herring sperm and MCF7 cell line, for the presence of deoxyguanosine and deoxyadenosine. The common biomolecules present in blood and urine did not interfere in the determination and the high stability and reproducibility of the sensor confirmed its successful application in real sample analysis.