Effect on near-infrared absorption spectra of DNA/single-walled carbon nanotube (SWNT) complexes by adsorption of a blocking reagent.

In this study, we investigated whether the adsorption or coating of single-walled carbon nanotubes (SWNTs) with a blocking reagent would prevent the oxidation and reduction of SWNTs. Blocking reagents are widely used in life sciences to protect coated molecules from adsorption by other molecules. A complex of dsDNA-SWNT complex (Complex A) was prepared by mixing SWNTs powder with dsDNA solution of deoxyribonucleic acid and sodium salt from salmon testes. Blocking reagent (DB1130) was added to Complex A to a final concentration of 1% to prepare a dsDNA-SWNT-DB1130 complex (Complex B). Complex B was sonicated to prepare a dsDNA-SWNT-DB1130-s complex (Complex C). Each complex was oxidized with 0.03 % hydrogen peroxide (HO), after which the catechin solution, which has an anti-oxidative effect, was added to the sample. For Complex A, the height of the absorption spectra peak decreased with the addition of HO, and was recovered with the addition of catechin. In Complex B, the magnitude of change in the absorption peak height was smaller than that in Complex A, and no significant change was detected in Complex C. These results indicate that DB1130 blocks the redox action of SWNTs, and this effect becomes stronger with increasing DB1130 adsorption. We found that while the difference in the levels of DB1130 adsorption did not affect the absorbance significantly, it induces in a large change in photoluminescence intensity. Furthermore, ultrasonic treatment caused the replacement of dsDNA by DB1130 in Complex B, resulting in an increase in the amount of adsorption, and increasing the diameter of SWNTs. This was also confirmed by Atomic Force Microscopy (AFM) measurements.