Exploiting Micrometer-Scale Replication of Fungal Biotemplates for Multifunctional Uses in Electrochemistry and SERS Substrates

Abstract

In this paper, filamentous fungi have been used as biotemplates to integrate gold nanoparticles (Au-NPs) into the cell wall. A new chemical mechanism has been proposed to elucidate the assimilation of Au-NPs by fungi, considering the ionic current that arises in the function of fungal metabolism. After biological components were eliminated, mycelium-like gold microtubes have been obtained using different fungal species as precursors. Mycelium-like gold microtubes replicate the biological shape of fungi, presenting inherent multifunctionality. This work presents two promising applications for this material: high surface area electrodes for electrochemical experiments and substrates for SERS detection of organic molecules such as Rhodamine 6G.

Figure 1

Schematic representation of the formation of mycelium-like gold microtubes. Initially, the fungi are cultivated in citrate-stabilized Au-NPs. Then, biohybrid material is harvested and dried using critical point drying to preserve its tubular morphology. In the last step, calcination of the fungus/Au-NPs biohybrid at 800 °C results in the formation of multifunctional mycelium-like gold microtubes.

Figure 2

(a) Schematic model of binding of citrate anions on the surface of Au-NP. (b) TCA cycle and some products of fungal anabolism/catabolism. (c) Schematic representation of transcellular ionic current generated during fungal hyphae growth. (d) Negatively charged Au-NPs may be attracted to the hyphal tip during polarized fungal growth, binding to functional groups of cell wall components.

Figure 3

(a) UV–vis spectrum of a citrate-stabilized Au-NPs solution. Inset: fresh colloidal solution of Au-NPs used in fungal cultivation. (b) Digital image of the mycelial tissue ofTalaromyces pinophilus/Au-NPs immersed in deionized water. (c) and (d) SEM micrographs of Aspergillus niger/Au-NPs biohybrid. (e) and (f) SEM micrographs of an isolated Phiolomyces macrosporus/Au-NPs biohybrid filament and its tip. (g) and (h) TEM micrographs of the transversal cross-sectioned region of an Aspergillus niger hypha after Au-NPs incorporation. (i) and (j) TEM micrographs of the longitudinal cross-sectioned biohybrid Trichoderma sp./Au-NPs.

Figure 4

Thermogravimetric analysis of native P. macrosporus and the as-produced P. macrosporus/Au-NPs biohybrids.

Figure 5

SEM micrographs of mycelium-like microtubes obtained from different fungal species exemplifying the 3D metallic network. a) Phialomyces macrosporus, b) Penicilliumsp. and c) Trichoderma sp. replicas. d–f) Aspergillus niger replicas.

Figure 6

Cyclic voltammograms of Fe(CN)₆ in a 1.0 mol·L^–1 H₂SO₄ electrolyte recorded using (a) a bulk gold electrode and (b) a mycelium-like gold electrode (A. niger replica), for different scan rates (10 to 250 mV·s^–1). Insets: cathodic peak currents versus square root of scan rates.

Figure 7

Raman spectra of Rhodamine 6G. SERS effect was observed in mycelium-like microtubes (P. macrosporusreplica) using 10^–8 mol L^–1 Rhodamine 6G solution (red line). Inset: 10^–2 mol L^–1 Rhodamine 6G solution droplet on a silicon wafer. Curves were adjusted through baseline remotion to facilitate comparison.