Charge transport dynamics and energy storage implications of nickel cobalt carbonate hydroxide interaction with the...

Nanomaterial-plant interactions have recently emerged as a promising approach for modulating charge transport and energy storage behavior in living plant tissues. In this study, we report the first-time application of Nickel Cobalt Carbonate Hydroxide (NCCH) nanostructures to modulate the electrical properties of Aloe vera leaves. Uptake of transition metal oxides (TMOs) has enhanced or reduced seed germination, shoot/stem growth, and physiological and biochemical activities. However, NCCH nanoparticles (NPs) show improved redox behaviour compared to TMOs. The presence of CO₃ ^2- ions increases the wettability and ion transport. Well-characterized NCCH nanostructures were introduced at varying concentrations (1, 5, and 10 mg L^-1), and their influence on the impedance behavior of the plant was systematically examined. Electrochemical impedance spectroscopy data were modelled using an equivalent circuit comprising a parallel combination of resistance and capacitance for both intracellular (grain) and intercellular (grain boundary) regions of the leaves. The results showed a concentration-dependent increase in resistance and a decrease in capacitance across both domains, highlighting the significant modulation of charge mobility on uptake of NPs. The grain resistance increased from 2.83 Ω (control) to 8.1 Ω (10 mg L^-1) and the grain boundary resistance from 95.9 Ω to 299.74 Ω. Meanwhile, the capacitance decreased from 5.75 × 10^-9 F to 2.15 × 10^-9 F (grain) and from 1.38 × 10^-10 F to 1.79 × 10^-12 F (grain boundary), indicating a lower stored energy density but for a longer time in spiked plants. Jonscher's power law analysis revealed reduced hopping frequencies and altered carrier dynamics, especially in the grain boundary region, where the exponent dropped sharply at low concentrations. Modulus spectroscopy further confirmed the relaxation behavior influenced by NCCH uptake, with distinctive changes in M' and M'' profiles reflecting shifts in localized conduction and energy dissipation processes. These findings provide critical insights into the electrical modulation of plant tissues due to the uptake of transition metal nanostructures. This study not only expands the scope of plant nanobionics but also opens potential avenues for understanding the mechanism of plant defence against the toxicity of NPs and sustainable bioelectronics.