Nanocellulose-Based Passivated-Carbon Quantum Dots (P-CQDs) for Antimicrobial Applications: A Practical Review

Abstract

Passivated-carbon quantum dots (P-CQDs) have been attracting great interest as an antimicrobial therapy tool due to their bright fluorescence, lack of toxicity, eco-friendly nature, simple synthetic schemes, and possession of photocatalytic functions comparable to those present in traditional nanometric semiconductors. Besides synthetic precursors, CQDs can be synthesized from a plethora of natural resources including microcrystalline cellulose (MCC) and nanocrystalline cellulose (NCC). Converting MCC into NCC is performed chemically via the top-down route, while synthesizing CODs from NCC can be performed via the bottom-up route. Due to the good surface charge status with the NCC precursor, we focused in this review on synthesizing CQDs from nanocelluloses (MCC and NCC) since they could become a potential source for fabricating carbon quantum dots that are affected by pyrolysis temperature. There are several P-CQDs synthesized with a wide spectrum of featured properties, namely functionalized carbon quantum dots (F-CQDs) and passivated carbon quantum dots (P-CQDs). There are two different important P-CQDs, namely 2,2'-ethylenedioxy-bis-ethylamine (EDA-CQDs) and 3-ethoxypropylamine (EPA-CQDs), that have achieved desirable results in the antiviral therapy field. Since NoV is the most common dangerous cause of nonbacterial, acute gastroenteritis outbreaks worldwide, this review deals with NoV in detail. The surficial charge status (SCS) of the P-CQDs plays an important role in their interactions with NoVs. The EDA-CQDs were found to be more effective than EPA-CQDs in inhibiting the NoV binding. This difference may be attributed to their SCS as well as the virus surface. EDA-CQDs with surficial terminal amino (-NH₂) groups are positively charged at physiological pH (-NH³⁺), whereas EPA-CQDs with surficial terminal methyl groups (-CH₃) are not charged. Since the NoV particles are negatively charged, they are attracted to the positively charged EDA-CQDs, resulting in enhancing the P-CQDs concentration around the virus particles. The carbon nanotubes (CNTs) were found to be comparable to the P-CQDs in the non-specific binding with NoV capsid proteins, through complementary charges, π-π stacking, and/or hydrophobic interactions.

Keywords: antiviral therapy; carbon quantum dots; functionalization; microcrystalline cellulose; nanocrystalline cellulose; norovirus; passivation.

Figure 1

Formation of sulphated nanocrystalline cellulose (SNCCs): (a) SEM micrograph of anatomical structure of a typical wood tissue. (b) An optical image of macerated fibers. (c) The crystalline and amorphous domains within a microfibril. (d) SNCCs crystallite grafted by sulphated groups. (e) A monomeric molecule of SNCC. (f) TEM micrographs of SNCCs colony, and (g) Close-up image the SNCCs colony. (h) SEM micrographs of spreading and converging of the SCMCs. (i) A single colony with wider particles due to agglomeration. (j) SCMCs aggregation of single and multiball-shaped microcrystalline cellulose (SMCCs). (k) Desulphated cellobiose unit.

Figure 2

Schematic construction of surface modification of carbon quantum dots (CQDs): a surface passivation. (a) The spherical core and the thin layer shell of CQDs, (b) chemical structure of 2,2′-ethylenedioxy-bis-ethylamine (EDA) and 3-thoxypropylamine (EPA) which will be grafted on the CQD surface, (c) passivated CQDs, where MW is molecular weight of the surface molecule, TG is the terminal group of the surface molecule, FGY is fluorescence quantum yield, and PS is particle size. (d) 3D-ilustration schematic model for the grafted EDA and EPA, and (e) surface functionalization.

Figure 3

Scheme illustrating the different types of antimicrobial CQDs for biomedical and industrial applications.

Figure 4

The synthesis routes of carbon quantum dots (CQDs).

Figure 5

Schematic representation of deriving CQDs from macro-, nano-, and angstrom-structured cellulosic tissues.

Figure 6

Synthesis of CQDs from (a) MCC, and (b) NCC [11,16].

Figure 7

Synthesis of CQDs from carbon nanopowders.

Figure 8

Synthesis of chemically passivated-CQDs (P-CQDs): (a) EDA-CQDs, and (b) EPA-CQDs [15,32,33].

Figure 9

The potential role of the passivated-carbon quantum dots (P-CQDs) in detecting and inactivating human infection by noroviruses through targeted tagging and by blocking viral surface proteins.