Tiny Diamonds, Big Impact: Unlocking the Structure-Activity Relationship of Antimicrobial Nanodiamonds

Abstract

Nanodiamonds (NDs) have emerged as a highly promising nanomaterial due to their intrinsic biocompatibility and remarkable antimicrobial and anti-adhesive properties, which result from their unique surface morphology. NDs serve as an excellent platform for extensive functionalization with diverse chemical groups and complex bioactive molecules, including peptides, photosensitizers, antibiotics and polycations. The antimicrobial potential of NDs has gained considerable attention in recent years across numerous application areas, including drug-delivery platforms, wound dressings, dentistry, surface coatings, biomedical implants, the food industry and water treatment technologies. This article compiles and critically evaluates the current microbiological evidence on ND antimicrobial activity. However, translating these findings into practical guidelines remains challenging due to the wide variability in reported results and the limited diversity of bacterial strains employed. The antimicrobial mechanisms of NDs in the context of Gram positive, Gram negative, and flagellated bacteria are examined, and it is demonstrated that key factors, including particle size, surface charge, and the composition of testing media, profoundly influence experimental outcomes and underlie many apparent contradictions in the field. Moreover, this review summarizes the functionalization strategies available for NDs, their reported biomedical and industrial applications, and current knowledge regarding their cytotoxicity and biocompatibility. Collectively, the article provides an integrated view of the structure-activity relationship governing ND antimicrobial performance.

Keywords: antibacterial nanomaterials; biocompatibility; drug resistance; nanodiamonds; surface functionalization.

Graphical abstract

Figure 1

Graphical breakdown of surface functionalization possibilities. (i) Pristine NDs may be oxidated (O-NDs), approaches vary on method followed, most commonly via air oxidation. (ii) Pristine ND may be carboxylated (C-NDs), approaches vary on method followed, most commonly via acid treatment. (iii) O-NDs/C-NDs may be functionalised with antibiotics, most commonly via electrostatic interactions or hydrogen bonding, as well as amide bonds utilising linkers such as polyethylenimine (PEI). (iv) O-NDs/C-NDs may be functionalised with various amides via amide bond formation, most commonly done to enable further modifications. (v) O-NDs/C-NDs are usually functionalised with polycations via the initial amination of the NDs (vi) O-NDs/C-NDs may be functionalised with peptides/proteins, most commonly via electrostatic interactions, or covalent linkages utilising linkers such as benzotriazole (vii) O-NDs/C-NDs may be functionalised with photosensitizers such as phthalocyanine, most commonly via electrostatic interactions.

Figure 2

Schematic representation of the antibacterial mechanism of NDs against Gram-positive and Gram-negative bacteria.

Figure 3

Antimicrobial applications of nanodiamonds.