1-D Carbon Nano-Coils Derived from Almond Skin: Exhibiting Density of State, Diffusivity, Electron Transfer Rate, and Dopamine Redox Modulation Properties Akin to Graphene Oxide.

The quest to develop graphene-like biomass-carbon for advanced biomolecule redox modulation and sensing remains a challenge. The primary obstacle is the limited ability of biomass to undergo extensive graphitization during pyrolysis resulting in the formation of amorphous carbon materials with a small carbon-double-bond-carbon domain size (Lsp2), density of state (LDOS), ion diffusivity (D), and electron transfer rate constant (Ks). Herein, using almond skin (AS) the morphology of biomass is demonstrated as the key to overcoming these limitations. AS consists of 1D syringyl/guaiacyl lignin nano-coils which under H2/H2 annealing transform into pyrolytic 1D carbon nano-coils (r-gC). Spectroscopy and microscopy analyses reveal that the sheet layering structure, crystallinity, LDOS, and Lsp2 of r-gC mimic those of graphene oxide (GO). Moreover, its unique 1D morphology and profound microstructure facilitate faster charge transfer and ion diffusion than GO's planar structure, leading to better redox modulation and sensing of the neurotransmitter dopamine (DA) in physiological fluids. r-gC's DA detection limit of 3.62 nM is below the lower threshold found in humans and on par with the state-of-the-art. r-gC is also DA-selective over 14 biochemicals. This study reveals that biomasses with well-defined and compact lignin structures are best suited for developing highly electroactive graphene-like biomass carbon.

Engineering FeOOH/Fe2O3@Carbon Interfaces With Biomass-Derived Carbon Nanodot/Iron Colloids for Efficient Redox-Modulated Dopamine Voltammetric Detection.

The Fe2+/Fe3+ redox couple is effective for voltammetric detection of trace dopamine (DA). However, achieving adequate concentrations with high electroactive surface area (ECSA), DA affinity, and fast interfacial charge transfer is challenging. Consequently, most reported Fe-based sensors have a high nanomolar range detection limit (LOD). Herein, we address these limitations by manipulating the phase and morphology of FeOOH/Fe2O3 heterojunctions anchored on sp2-carbon. FeOOH/Fe2O3 is synthesized by variable temperature aging of unique Fe5H9O15/Fe2O3@sp2-carbon colloidal nanoparticles, which form via chelation between biomass-derived carbon nanodots (CNDs) and Fe2+ ions. At 27 °C and 120 °C, Fe5H9O15/Fe2O3@sp2-carbon transforms into ß-FeOOH/Fe2O3 nanoparticles and α-FeOOH/Fe2O3 nanosheet, respectively. The ß-FeOOH/Fe2O3 interface exhibits higher eg orbital electron occupancy than α-FeOOH/Fe2O3, thereby facilitating oxygen adsorption and the generation of Fe2+/Fe3+ sites near the polarization potential of DA. This facilitates interfacial electron transfer between Fe3+ and DA. Moreover, its nanoparticle morphology enhances ECSA and DA adsorption compared to α-FeOOH/Fe2O3 nanosheets. With a LOD of ~3.11 nM, ß-FeOOH/Fe2O3 surpasses the lower threshold in humans (~10 nM) and matches noble-metal sensors. Furthermore, it exhibits selective detection of DA over 10 biochemicals in urine. Therefore, the ß-FeOOH/Fe2O3@sp2-C platform holds promise as a low-cost, easy-to-synthesize, and practical voltammetric DA monitor.

Tailoring phases of ferrihydrite/α-Fe2O3@C nanocomposites using syringyl and guaiacyl-rich biomass-derived carbon nanodots for electrochemical application.

Biomass-derived carbon nanodots (CNDs) hold promise as effective reducing agents for metal oxide nanoparticles yet understanding the intricate interplay with CND structure remains challenging. This study explores the impact of lignin types, specifically syringyl (S), and guaiacyl (G) units in CNDs on metal oxide phases and their electrochemical activity toward dopamine oxidation. We design phases of ferrihydrite/α-Fe2O3@C nanocomposites, using hazelnut carbon nanodots (HS-CNDs (S-rich)) and beetroot carbon nanodots (BS-CNDs (G-rich)) via a one-pot hydrothermal technique. Our findings show S units in HS-CNDs promote α-FeOOH/α-Fe2O3@CHS, while G units in BS-CNDs favor α (ß)-FeOOH/α-Fe2O3@CBS. In contrast to α(ß)-FeOOH/α-Fe2O3@CBS, α-FeOOH/α-Fe2O3@CHS exhibits superior electrochemical performance in dopamine oxidation due to its larger electrochemical active surface area, higher absorbance capacity, and shortened electron transfer length. Moreover, α-FeOOH/α-Fe2O3@CHS nanocomposites demonstrate remarkable dopamine selectivity, achieving rapid detection response in 10 s with a low LOD of 4 nM within a broad linear range (0.05-0.3 µM), demonstrating impressive reproducibility (97.5 %), stability (96.4 %), and works in real-time human urine detection with a recovery rate of ranging from 94.57 % and 102.2 %. Therefore, the utilization of biomass-derived CNDs, particularly S and G units-rich CNDs, in tailoring the phases of ferrihydrite/α-Fe2O3@C nanocomposites for electrochemical dopamine detection is promising.