# Biocompatible Dispersants for Carbon Nanomaterials
## 6 Biocompatible Dispersants
### Polymer Dispersants
The resulting system displayed excellent biocompatibility. However, the use of HA resulted in the nanocarriers concentrating in the digestive tract of zebrafish, an effect that could translate to other organisms during further in vivo usage [61]. More recently, [PERSON] et al. applied this approach to SWCNTs. Through the addition of HA-DMPE and doxorubicin (DOX), they produced a DOX/SWCNT/HA-DMPE hybrid system for intelligent, targeted drug delivery [6] (Table 5 (5)). This innovative system showed excellent biocompatibility, targeting of CD44\({}^{+}\) overexpressing cells and pH-triggered drug release. A range of different HA molecular masses was tested, and it was found that 200 kDa HA was the best for facilitating cellular uptake. Biomolecules may also act as polymer dispersants. For example, polydopamine (PD) has been reported as a dispersant for CNMs [67]. However, the biomedical use of PD dispersions has not been widely investigated. PD is a biocompatible and cost-effective coating for nanomaterials [68], and the plentiful catechol groups give it great hydrophilicity. The main problem with PD is that it tends to self-aggregate in solution [69]. One way around that is to utilise O\({}_{2}\) purging during the coating process [70] to produce a uniform, thin coating. [PERSON] et al. developed a PD/polyether amine surface coating for MWCNTs that allowed for tunable solubility by varying chain length and amine groups in the final coating [70] (Table 5 (6)). Deoxyribonucleic acid (DNA) is another amphiphilic biopolymer with surfactant properties. It can be cheaply obtained from animal/plant waste material [71]. There have been many examples of using DNA as a biocompatible dispersant to produce stable CNM dispersions. For instance, [PERSON] et al. produced graphene dispersions with concentrations of up to 2.5 mg/mL that were stable for several months [72]. They used single-strand DNA (ssDNA) as a dispersant. However, the method they employed required the use of hydrazine, which may negatively affect the biocompatibility of the final product [72] (Table 5 (7)). Since then, innovative ways have been developed to solubilise graphene using environmentally friendly techniques. [PERSON] et al. developed a method of producing non-covalently DNA-functionalised graphene using a ball-milling technique with graphite and DNA extracted from fish waste [71] (Table 5 (8)). The downside of this method is that ball milling is very rough on the CNMs. It also results in a small degree of covalent graphene modification [71]. Plenty of literature exists on using DNA to solubilise CNTs. [PERSON] et al. successfully functionalised SWCNT with DNA to produce stable aqueous dispersions. [PERSON] et al. have also achieved this using natural salmon testes DNA to disperse SWCNTs [73] (Table 5 (9)). They incorporated cisplatin and potassium tetra-chloroplatinate into these hybrid systems by covalently attaching them to the immobilised DNA. They also reduced the cisplatin molecules on the SWCNT surface to form platinum nanocrystals, successfully retaining the optical and electronic properties of the CNTs, the biological properties of the DNA and the chemical functionality of the platinum [74] (Table 5 (10)). In more recent studies, [PERSON] and [PERSON] demonstrated that ssDNA could be utilised to recognise and purify different SWCNT enantiomers by a surfactant substitution mechanism [20]. This discovery lays the foundations for using enantiomerically pure CNTs in various applications, such as bio-imaging and sensor technology (Table 5 (11)). Using DNA as a dispersant for CNMs has many advantages, as the DNA itself can additionally be used as a therapeutic, imaging, or targeting agent. For example, DNA can be utilised as a non-viral vector for animal gene therapy and plant genetic engineering [75]. These materials have many advantages over traditional viral vectors, such as increased payload capacity, lower toxicity concerns, high transfection efficiency, and increased targeting capabilities [75].