A bio-inspired approach for the synthesis of few-layer graphene using beetle defensive gland extract

Abstract

Graphene exhibits remarkable properties and holds substantial promise for diverse applications. Its unique combination of thermal, chemical, physical, and biological properties makes it an appealing material for a wide range of uses. But, the lack of an economical and environmentally friendly approach to synthesize good-quality graphene represents an immense challenge for the scientific community. What makes this research unique is the utilization of the defensive gland extract from the beetle species Luprops tristis (Order: Coleoptera, Family: Tenebrionidae) to synthesize a few layers of graphene (FLG). This innovative incorporation of natural resources and exploration of biologically inspired methods provides an eco-friendly and cost-effective alternative to conventional graphene production techniques. The exfoliated graphene displayed antimicrobial effects against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, with particularly potent bactericidal activity. Additionally, the cytotoxicity assay demonstrated the anti-cancer properties of biosynthesized graphene against Daltons Lymphoma Acetic (DLA) cells.

Fig. 1. Diagrammatic representation of the exfoliation of graphite using the defensive gland extracts of the beetle L. tristis. (A) The Mupli beetle, Luprops tristis and the defensive gland of the beetle exposed from the body of the insect. (B) Extraction of defensive gland. (C) Adding powdered graphite flakes into the defensive gland extract. (D) The reaction mixture, which includes graphite flakes, is located at the bottom of the Eppendorf tube. (E) Sonication of the immiscible mixture for one hour. (F) Exfoliated graphene after sonication.

Fig. 2. (A–C); (A) red coloured defensive extract of 60 beetles, (B) mixture of defensive gland extract and graphite solution (immiscible) before sonication and (C) the black dispersion formed after sonicating for 1 hour containing the exfoliated graphene. In the diagram: (a) reaction mixture containing the defensive secretion of 60 beetle and the graphite solution in deionised water. (b) The polyphenolic compounds present in the defensive secretion of the Mupli beetle. (c) Stalked graphene layers which constitute the bulk graphite (present in the graphite solution). (d) Adsorption of graphene layers on the surface & edges of graphite and weakening of the van der Waals forces. (e) Intercalation of polyphenolic compounds in between the graphene layers. (f) Separation of graphene layers.

Fig. 3. (A–C) TEM images of exfoliated graphene layers with dimensions of 50 nm, 20 nm, and 2 nm respectively, (D) electron diffraction pattern (EDP) of the exfoliated graphene layer (51 nm), (E) AFM profile of the exfoliated graphene. (F) Height of the exfoliated graphene obtained from AFM analysis, (G) Raman spectra of the exfoliated graphene. (H) FTIR data of N-doped graphene, (I–K) PS Spectra of N-doped graphene; (I) survey spectrum (J) C 1s deconvoluted spectrum and (K) N 1s deconvoluted spectrum of N-doped graphene.

Fig. 4. (A) Bar diagram showing the anti-bacterial assay of exfoliated graphene on both Gram positive & negative bacteria, (B) bar diagram showing the cytotoxicity of exfoliated graphene on DLA cells.