Sensing of epigallocatechin gallate and tannic acid based on near infrared optical spectroscopy of DNA-wrapped single-walled carbon nanotube hybrids

Abstract

The optical responses of DNA-wrapped single-walled carbon nanotubes (DNA-SWNTs) caused by the addition of epigallocatechin gallate (EG) and tannic acid (TA) were investigated. Near infrared absorbance and photoluminescence spectra of pre-oxidized DNA-SWNTs were measured with and without EG and TA. Since both EG and TA have antioxidant abilities, the near infrared spectra changed after the addition of the chemicals. While detection of the antioxidant abilities of EG by DNA-SWNT hybrids has been previously reported, TA was employed for the first time. The changes in the absorbance caused by the addition of TA were found to saturate at 0.33 µM TA, although saturation was not observed even at 3.3 µM with the addition of EG. Oxidation of DNA-SWNT was suppressed by addition of TA or EG. The effects of TA were much greater than those of EG on the absorbance. The photoluminescence did not appear to saturate at 3.3 µM for either EG or TA. photoluminescence had a larger measurement capacity than NIR absorbance. Interestingly, the photoluminescence change caused by EG was much larger than that of TA at 3.3 µM, although the antioxidant property of TA was stronger at 0.33 and 0.033 µM, suggesting that the optical responses were not simple redox reactions. Peak shifts in the absorbance/photoluminescence spectra revealed unique differences according to the chirality of the SWNTs and the types of chemicals used. This suggests that the combination of absorbance/photoluminescence and peak intensity/peak shifts could detect multiple types of chemical information, not only redox reaction. A direct comparison between EG and TA was demonstrated for the first time in this novel study. In addition, sensing of EG and TA by near infrared spectra was made available using not only changes in intensity but also a variety of peak shifts of SWNTs.