Biosynthesis of gold nanoparticles by fungi and its potential in SERS.

Surface enhanced Raman spectroscopy (SERS) by using gold nanoparticles (AuNPs) has gained relevance for the identification of biomolecules and some cancer cells. Searching for greener NPs synthesis alternatives, we evaluated the SERS properties of AuNPs produced by using different filamentous fungi. The AuNPs were synthesized utilizing the supernatant of Botrytis cinerea, Trichoderma atroviride, Trichoderma asperellum, Alternaria sp. and Ganoderma sessile. The AuNPs were characterized by ultraviolet-visible spectroscopy (UV-Vis) to identify its characteristic surface plasmon resonance, which was located at 545 nm (B. cinerea), 550 nm (T. atroviride), 540 nm (T. asperellum), 530 nm (Alternaria sp.), and 525 nm (G. sessile). Morphology, size and crystal structure were characterized through transmission electron microscopy (TEM); colloidal stability was assessed by Z-potential measurements. We found that, under specific incubation conditions, it was possible to obtain AuNPs with spherical and quasi-spherical shapes, which mean size range depends on the fungal species supernatant with 92.9 nm (B. cinerea), 24.7 nm (T. atroviride), 16.4 nm (T. asperellum), 9.5 nm (Alternaria sp.), and 13.6 nm (G. sessile). This, as it can be expected, has an effect on Raman amplification. A micro-Raman spectroscopy system operated at a wavelength of 532 nm was used for the evaluation of the SERS features of the AuNPs. We chose methylene blue as our target molecule since it has been widely used for such a purpose in the literature. Our results show that AuNPs synthesized with the supernatant of T. atroviride, T. asperellum and Alternaria sp. produce the stronger SERS effect, with enhancement factor (EF) of 20.9, 28.8 and 35.46, respectively. These results are promising and could serve as the base line for the development of biosensors through a facile, simple, and low-cost green alternative.

Influence of the fluoroethylene carbonate on the electrochemical behavior of Bi3Ge4O12 as Lithium-ion anode.

Systematic ex-situ X-ray diffraction (XRD) characterization and electrochemical study revealed the key roles that the cut-off voltage and fluoroethylene carbonate (FEC) additive play on improving electrochemical performance of the Bi3Ge4O12-based (BGO) electrode. The ex-situ XRD analysis revealed that BGO particles suffer multiphase transitions during the (dis)charge reactions, being observed some phases as Bi2O2.33, BiLi3, Li2O, Ge4Li15, Ge2Li7, Ge3Li7, Ge5Li22, Ge4Li9, Bi2O3 and GeO2. The electrochemical evaluation exhibited that the addition of 5 v/v% of FEC in 1.0 M lithium hexafluorophosphate (LiPF6) in ethylene carbonate and diethyl carbonate (EC: DEC) at an applied cut-off voltage (1.5 V vs Li/Li+) improves the specific capacity (29%, delivering 479 mAh g-1), capacity retention (12%) and rate capability (369 mAh g-1 at 1000 mA g-1) of the BGO-based electrode. Also, FEC promotes the formation of a stable solid-electrolyte interface (SEI) layer on the anode at a cut-off voltage of 1.5 V vs Li/Li+. It displays the lowest values of SEI and charge transfer (CT) resistances, and electrode polarization, improving the reversibility of the alloying reactions related to Ge-Li and Bi-Li and maintaining their redox activity after 100 cycles, according to dQ dV-1 data.

Bismuth germanate (Bi4Ge3O12), a promising high-capacity lithium-ion battery anode.

An unexplored promising lithiation-host anode material, Bi4Ge3O12, delivers a reversible specific discharge capacity of ∼586 mA h g-1 at 200 mA g-1 after 500 cycles with a coulombic efficiency of ∼99.8%. DFT calculations detected distorted [BiO6]9- octahedra, and the band structure of BGO revealed an indirect gap of 3.50 eV. A plausible reaction mechanism of storing lithium is proposed.