A high precision length-based carbon nanotube ladder

Abstract

Today, carbon nanotubes manufacturers as well as users such as molecular electronics, nanomedicine, nano-biotechnology and similar industries are facing a major challenge: lack of length uniformity of carbon nanotubes in mass production. An effective solution to this major issue is the use of a length-based ladder. We are, for the first time, presenting such a valuable tool to determine the length purity. Our length-based carbon nanotubes ladder, containing a series of carbon nanotubes markers with different lengths, is made based on three combined techniques - bio-conjugation, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and silver staining. Creating an indicator using conjugation of a biomolecule with carbon nanotubes to make a carbon nanotubes ladder is a novel idea and a significant step forward for length-based carbon nanotubes separation. The very sensitive silver staining technique allows a precise visualization and quantification of the gel. This ladder with a pending patent by Northeastern University is an effective quality control tool when bulk quantities of nanotubes with a desirable length are manufactured.

Fig. 1. SEM image of SWCNTs before and after conjugation. (a) SWCNTs before conjugation (b–d) SEM images of conjugated lysozyme–SWCNTs. (b) a magnification 1.50k, diameter of the SWCNT bundle ≈ 592 nm, (c) a magnification of 10k, (d) a magnification 30.0k, diameter of conjugated lysozyme–SWCNT ≈ 89.5 nm.

Fig. 2. TGA thermogram of pristine SWCNT ((a), blue) and functionalized SWCNT–COOH (b).

Fig. 3. X-ray diffraction (XRD) patterns of SWCNTs (red), lysozyme (dark blue), and conjugated lysozyme–SWCNTs (light blue).

Fig. 4. FTIR spectra showing amide bonds in the conjugated lysozyme–SWCNTs. FTIR spectrum for lysozyme (green), the SWCNTs (black) and conjugated lysozyme–SWCNT (red).

Fig. 5. SDS-PAGE electrophoresis and silver staining of lysozyme. (a), SWCNT (b), and ladder/conjugated lysozyme–SWCNT (c). Distribution and the lengths of SWCNT fragments (d).

Fig. 6. Three ladders produced from 3 (a), 7 (b), and 10 (c) min sonication time. It is clear the conjugated SWCNTs fragments are separated based on their lengths.

Fig. 7. Distribution and the lengths of SWCNT fragments in two methods (ImageJ, (a) through (c) & MATLAB, (d) through (f)) after sonication time at 3 min (a and d), 7 min (b and e), and 10 min (c and f).

Fig. 8. Length distribution of the conjugated SWCNTs after sonication time at 3 min (a), 7 min (b), and 10 min (c). The intensity of the CNTs at each ladder is plotted versus length of CNTs calculated from eqn (1).