# Biocompatible Dispersants for Carbon Nanomaterials
## 6 Biocompatible Dispersants
### Polymer Dispersants
Another benefit of DNA is that tremendous work has been done on its chemistry to date--allowing for many options in terms of functionalisation and use in hybrid systems. DNA exhibits strong binding to CNMs due to \(\pi\)-\(\pi\) stacking interactions between the aromatic nucleobases and the surface of the CNM. This causes the hydrophobic inner DNA surface to orientate itself towards the CNM surface whilst the hydrophilic sugar-phosphate backbone orientates itself towards the aqueous solution, forming a hydrophilic layer around the CNM. CNTs can fit inside the spiral structure of the double helix, causing synergistic binding due to complementarity. For graphene surfaces, ssDNA forms globular aggregates on its surface [72], perhaps leading to less efficient dispersion due to unfavourable surface coverage, although this is yet to be investigated. A range of commercially available polymers that can disperse CNMs also exists. One example is Triton X-100, a phenolated polyethylene glycol derivative. This non-ionic surfactant is biocompatible, cheap, and widely studied as a dispersant for CNMs. [PERSON] et al. demonstrated the impressive efficiency and effectiveness of Triton X-100 as a dispersant for MWCNTs [22]--these dispersions consisted of individual MWCNTs (Table 5 (12)). There are examples of Triton X-100:CNT dispersions that are stable for up to two months [3]. The high efficiency of this surfactant stems from the presence of an aromatic ring in its hydrophobic region. This ring takes part in \(\pi\)-\(\pi\) interactions, leading to enhanced binding to the CNM surface. The hydrophilic polyethylene glycol chain orientates away from the CNM surface, into the solvent. This orientation provides steric repulsion with other dispersed CNMs and, to a degree, electrostatic repulsion between the polar oxygen atoms. Stable, biocompatible dispersions of CNOs using Triton X-100 have been described by [PERSON] et al. [56], and graphene dispersions using this surfactant have also been produced [3]. Overall, this dispersant is cheap, versatile, and biocompatible, making it an excellent choice in producing CNM dispersions for biomedical uses (Table 5 (13)). Biocompatible sugar-based polymer surfactants such as Montanov 82 (an alkyl polyglucose), and Surfhope 1216 (a sucrose based dispersant) also show promise [16]. These compounds are cheap and already approved for use in pharmaceutical, beauty, and food products [16]. [PERSON] et al. were able to produce stable aqueous MWCNT dispersions via a surfactant substitution method using Montanov 82, Surfhope 1216, gum Arabic (a natural gum consisting of polysaccharides and glycoproteins), and Tween 20 (a commercially available polymer surfactant) [16] (Table 5 (14)). Polymer surfactants are perhaps the most promising class of non-covalent CNM dispersants due to their versatility, effectiveness, biocompatibility, and stability of dispersions produced by polymer wrapping mechanisms. Block copolymers can be tuned to the specific CNMs to ensure high dispersing efficiency. Biopolymers such as DNA and PD offer negligible toxicity, low cost, and biorecognition/therapeutic properties. The addition of drug molecules, targeting ligands, and fluorophores to form composite polymers is a potential game-changer in the field of non-covalent CNM functionalisation. This approach will have many future applications; for example, these polymers could be used to produce targeted drug delivery systems, and the incorporation of fluorophores also allows for cellular tracking experiments to be performed. The main downside to polymer dispersants (particularly composite polymers), compared to small-molecule surfactants, is that they are difficult to prepare and characterise. They are not always commercially available either.