# Carbon Nanodots as Peroxidase Nanozymes for Biosensing
## 8 Advantages, Challenges and Future Perspectives  
In order to fully realize the potential of C-dots domain as POD nanozymes, it would be worthwhile to pinpoint their key advantages or favorable features over noble metal/metal oxide nanomaterials. Specifically, diversified synthesis, cost-effectiveness, excellent water-dispersibility, (photo)chemical stability, photoluminescence properties, low toxicity/biocompatibility, and most importantly, on-demand surface engineering are the remarkable advantages of C-dots, formulating them as the materials-of-choice for POD mimetics and biosensing applications. Despite this, in contrast to metal/metal oxide NPs or materials, C-dots suffer with certain disadvantages or challenges such as low product yield, difficulties associated with their purifications, which, in turn, do not allow their large-scale production, and the deficiencies in precisely controlling the uniform size of C-dots, a factor that may significantly influence the POD-like activity of C-dots. Not surprisingly, therefore, despite the overwhelming collection of reports on carbonaceous nanomaterials, in particular, 2D graphene with POD-like activities, the research progress on C-dots as POD nanozymes is still in its infancy, leaving a wide open space for future developments. Taking into account the recent advancements in the field as well as dictated by future applications, we speculate that the significant trends in C-dots-based POD mimic should follow the development of high performance synergistic nanocomposites, functional assemblies for cascade reactions, and a variety of doped C-dots. Manifestation of such improvements will possibly lead to the development of inexpensive, portable, and conductive to commercialization  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Nanoconjugate(s)/** & **Synthesis Method** & **Substrate(s)** & **Application(s)** & **LOD** & **Reference** \\ \hline GQDs/Au & Photo-Fenton reaction and covalent assembly & TMB & H\({}_{2}\)O\({}_{2}\) detection & 0.7 uM & [53] \\ \hline C-dots/cyt \(c\) & Thermal pyrolysis and electrostatic assembly & ABTS & Enzyme modulation & – & [54] \\ \hline C-dots/NiAl-LDH & Electrostatic assembly & TMB & H\({}_{2}\)O\({}_{2}\) detection & 0.11 uM & [55] \\ \hline GQDs-Fe\({}_{3}\)O\({}_{4}\) & Co-precipitation & TMB & Removal of phenolics & – & [56] \\ \hline ZnFe\({}_{2}\)O\({}_{4}\)-GQDs & Hydrothermal + photo-Fenton reaction & TMB & DNA detection & 62 uM & [57] \\ \hline CDs-Pt\({}^{\text{b}}\) & Hydrothermal + mechanical stirring & TMB & H\({}_{2}\)O\({}_{2}\) detection & 0.8 uM & [58] \\ \hline Au NPs@CDs\({}^{\text{b}}\) & MW-assisted synthesis + chemical reaction & TMB & – & – & [59] \\ \hline CNDs\({}^{\text{c}}\) & MW-assisted synthesis & TMB & H\({}_{2}\)O\({}_{2}\) detection & 0.4 uM & [60] \\ \hline \end{tabular} \({}^{\text{a}}\) GQDs, Graphene quantum dots; C-dots, Carbon nanodoids; LOD, Limit of detection; GQDs/Au, Covalently assembled GQDs on the Au electrode surface; TMB 3,3’,5’,5’-tetramethylbenzidine; yet \(c\), cytochrome \(c\); ABTS, 2,2’-azino-bis-(3-ethylbenzidine:6-sulfonic acid; C-dots/NiAl-LDH, Non-covalently assembled C-dots with positively charged NiAl-layered double hydroxide nanoplates; NPs, Nanoparticles; GQDs-Fe\({}_{3}\)O\({}_{4}\), GQDs integrated with iron oxide NPs; ZnFe\({}_{2}\)O\({}_{4}\)-GQDs, GQDs assembled on the magnetic ZnFe\({}_{2}\)O\({}_{4}\); _a_M, Attomolar (10\({}^{-18}\) M); CDs-Pt, C-dots-Pt NP composites; Au NPs@CDs, Core-shelled Au NPs@C-dots nanocomposites; MW, Microwave; CNDs, Carbon nitride dots; \({}^{\text{b}}\) CDs represent C-dots as per refs. [58,59]; \({}^{\text{c}}\) CNDs represent CN-dots as per ref. [60].  
\end{table}
Table 2: POD-like activity of GQDs/C-dots conjugates or nanocomposites and carbon nitride (CN) dots \({}^{\text{a}}\).  
C-dots-based test strips as practical kits for sensing purposes as well as may significantly influence the current biotechnology and bioanalytical chemistry in the context of point-of-care detection.