The Impact of Sonication on the Surface Quality of Single-Walled Carbon Nanotubes

Dispersion State and Damage of Carbon Nanotubes and Carbon Nanofibers by Ultrasonic Dispersion: A Review

Dispersion of carbon nanotubes and carbon nanofibers is a crucial processing step in the production of polymer-based nanocomposites and poses a great challenge due to the tendency of these nanofillers to agglomerate. Besides the well-established three-roll mill, the ultrasonic dispersion process is one of the most often used methods. It is fast, easy to implement, and obtains considerably good results. Nevertheless, damage to the nanofibers due to cavitation may lead to shortening and changes in the surface of the nanofillers. The proper application of the sonicator to limit damage and at the same time enable high dispersion quality needs dedicated knowledge of the damage mechanisms and characterization methods for monitoring nano-particles during and after sonication. This study gives an overview of these methods and indicates parameters to be considered in this respect. Sonication energy rather than sonication time is a key factor to control shortening. It seems likely that lower powers that are induced by a broader tip or plate sonicators at a longer running time would allow for proper dispersions, while minimizing damage.

αVβ3-Targeted Delivery of Camptothecin-Encapsulated Carbon Nanotube-Cyclic RGD in 2D and 3D Cancer Cell Culture

Integrin αvβ3 is widely expressed in various types of human cancer lines and plays a key role in angiogenesis for tumor growth and metastasis. Delivery of therapeutics to αvβ3-expressing tumors can thus be a promising approach for treating cancer. For targeted delivery of anticancer therapeutics to αvβ3-expressing tumor cells, cyclic arginylglycylaspartic acid (RGD) peptide was covalently conjugated to the surface of carboxylic acid-functionalized carbon nanotubes (fCNTs), and the topoisomerase I inhibitor camptothecin (CPT) was encapsulated in the fCNTs (CPT@fCNT-RGD). CPT@fCNT-RGD was successfully delivered to αvβ3-expressing A375 cells, and compared with nontargeted CPT@fCNT, it provided 3.78- and 3.02-fold increases in the anticancer effect in 2D and 3D culture. Analysis of apoptosis-related gene expression shows that the expression levels of Bax, cleaved caspase-3, and nuclear factor kappa-light-chain-enhancer of activated B cells were significantly increased in A375 cells incubated with CPT@fCNT-RGD compared with those incubated with CPT@fCNT. These results suggest that cyclic RGD-conjugated CNTs encapsulating an anticancer therapeutic can be a promising platform for treating cancer.

Using a fluorescence quenching method to detect DNA adsorption onto single-walled carbon nanotube surfaces

Surface modification of single-walled carbon nanotubes (SWNTs) with DNA molecules has attracted much attention in recent years to increase SWNT solubility and make various SWNT-based nanobiodevices. Therefore, there is a critical need to quantify the interaction between DNA molecules and SWNT surfaces, particularly the intermediate structures during DNA adsorption. In this study, we demonstrate the ability to detect the adsorption of DNA oligomers on SWNT surfaces by fluorescence spectroscopy. Fluorescein-labelled, 30mer, thymine oligonucleotides (F-T30) were employed as a fluorescent probe to study the interaction of DNA with SWNTs. A clear quenching effect was observed when F-T30 was adsorbed onto SWNT surfaces. Using this method, the amount of DNA adsorbed onto the SWNT surfaces was measured under different sonication conditions to correlate adsorption efficiency with sonication strength and duration. When a bath-type sonicator was used, mild adsorption of F-T30 on SWNT surfaces was observed. Furthermore, a two-step adsorption was observed in this condition. In contrast, we observed rapid adsorption of F-T30 to SWNT surfaces at the higher sonication amplitude (60% maximal) using a probe-type sonicator, while only slight adsorption of DNA molecules was observed at the lower amplitude (20% maximal). Our data revealed that the quenching effect can be used to evaluate DNA adsorption onto SWNT surfaces. In addition, atomic force microscopy (AFM) and photoacoustic spectroscopy (PAS) were conducted to provide complementary information on the DNA-SWNT nanoconjugates.

Airway exposure to multi-walled carbon nanotubes disrupts the female reproductive cycle without affecting pregnancy outcomes in mice

BACKGROUND

The use of multiwalled carbon nanotubes (MWCNT) is increasing due to a growing use in a variety of products across several industries. Thus, occupational exposure is also of increasing concern, particularly since airway exposure to MWCNTs can induce sustained pulmonary acute phase response and inflammation in experimental animals, which may affect female reproduction. This proof-of-principle study therefore aimed to investigate if lung exposure by intratracheal instillation of the MWCNT NM-400 would affect the estrous cycle and reproductive function in female mice.

RESULTS

Estrous cycle regularity was investigated by comparing vaginal smears before and after exposure to 67 μg of NM-400, whereas reproductive function was analyzed by measuring time to delivery of litters after instillation of 2, 18 or 67 μg of NM-400. Compared to normal estrous cycling determined prior to exposure, exposure to MWCNT significantly prolonged the estrous cycle during which exposure took place, but significantly shortened the estrous cycle immediately after the exposed cycle. No consistent effects were seen on time to delivery of litter or other gestational or litter parameters, such as litter size, sex ratio, implantations and implantation loss.

CONCLUSION

Lung exposure to MWCNT interfered with estrous cycling. Effects caused by MWCNTs depended on the time of exposure: the estrous stage was particularly sensitive to exposure, as animals exposed during this stage showed a higher incidence of irregular cycling after exposure. Our data indicates that MWCNT exposure may interfere with events leading to ovulation.

The dispersion, solubilization and stabilization in “solution” of single-walled carbon nanotubes

Methods for the solubilization and dispersion of single-walled carbon nanotubes in water and organic solvents by physical and chemical methods have been reviewed.