Researchers in Brazil have turned an iconic Amazonian crop into a versatile nanotechnology platform. In a study published in Discover Chemistry, a team led by Jardel Ramos da Encarnação of the Universidade Federal do Amazonas used an aqueous extract of guaraná seeds (Paullinia cupana) to synthesize silver nanoparticles under mild conditions, then deployed the resulting materials in two very different arenas: electrochemical experiments involving a commercial deltamethrin insecticide formulation, and germination assays with gherkin and coriander seeds. The work stands out less for any single technique than for its integrative scope, linking sustainable nanoparticle synthesis, pesticide-relevant electrochemistry, and concentration-dependent biological effects within one framework.
The synthesis itself is strikingly simple. One gram of guaraná seed material was soaked in 100 milliliters of distilled water for 24 hours, filtered, and stored cold. When 50 milliliters of a dilute silver nitrate solution were mixed with a small aliquot of this extract, the reaction medium changed from colorless to yellowish-brown within minutes, the classic visual signature of colloidal silver forming. Ultraviolet-visible spectroscopy confirmed the transformation, revealing a surface plasmon resonance band at 418 to 420 nanometers, the optical fingerprint of silver nanoparticles. The plasmon intensity grew over the first two hours, indicating ongoing nanoparticle formation, before shifting slightly toward 410 nanometers, a change the authors interpret cautiously as evidence of evolving colloidal populations rather than proof of any specific particle shape.
Why guaraná? The seeds of P. cupana are rich in caffeine, phenolics, and other redox-active metabolites, compounds that previous phytochemical studies have identified in guaraná-derived matrices. The authors are careful to note that the extract was not chromatographically profiled in this study, so these constituents are cited as literature-supported candidate reducing and stabilizing agents rather than directly measured ones. Still, the chemistry is plausible: plant phenolics can reduce silver ions to metallic silver while simultaneously adsorbing onto particle surfaces, providing an organic corona that helps keep the colloid dispersed. After testing different temperatures and pH values, the team settled on pH 9.0 at 30 degrees Celsius as the optimal working condition for subsequent preparations.
Dynamic light scattering painted a nuanced picture of the resulting colloid. The mean hydrodynamic diameter came out at 429.5 plus or minus 14.0 nanometers, with a polydispersity index of 0.229, indicating a moderately polydisperse system rather than a uniform one. The intensity-weighted distribution actually contained two populations: a minor population centered at 21.7 nanometers accounting for roughly 2 percent of the scattered-light intensity, and a dominant population near 452 nanometers making up the remaining 98 percent. Because light scattering is intensity-weighted, larger entities dominate the signal even when they represent a small fraction of the particle count. The authors therefore interpret the large value as the hydrodynamic size of hydrated, associated colloidal entities, metallic domains wrapped in extract-derived organic material, rather than the size of individual silver cores. The zeta potential of minus 10.93 millivolts, modest in magnitude, suggests limited electrostatic repulsion, with steric stabilization from the organic corona likely helping the dispersion persist.
To make the nanoparticles electrochemically useful, the team immobilized the silver phase onto Vulcan XC-72R carbon black using two routes. In the in situ route, the carbon was present during nanoparticle formation; in the ex situ route, pre-formed nanoparticles were combined with carbon afterward. Ultraviolet-visible analysis of the supernatants showed a marked suppression of the plasmon band after contact with the support, consistent with retention of the silver-containing phase on the carbon surface. X-ray diffraction patterns were dominated by the broad carbon reflections at 24.5 and 43.7 degrees two-theta, with a weak additional reflection near 37.9 degrees assigned to a silver-containing phase, supportive but not exhaustive evidence of immobilization. Scanning electron microscopy showed that both materials preserved the particulate morphology of the carbon support, while energy-dispersive X-ray spectroscopy detected carbon, oxygen, and a low but detectable silver signal. Transmission electron microscopy in dark-field mode revealed high-contrast nanodomains distributed across the carbon matrix, tentatively associated with the silver phase.
Textural measurements added an important control dimension. Pristine Vulcan carbon displayed a specific surface area of 150.73 square meters per gram, while the in situ and ex situ composites measured 131.10 and 133.04 square meters per gram respectively, with pore diameters remaining in a narrow 2.03 to 2.18 nanometer range. The key insight is that the two supported materials are texturally almost identical yet electrochemically distinct, which means their different behaviors cannot be explained by gross porosity differences and likely reflect route-dependent interfacial organization, how the silver and organic residues are arranged at the surface.
The electrochemical experiments used the commercial emulsifiable concentrate Decis 25 EC, a Bayer product containing 25 grams per liter of deltamethrin, as the pesticide source. Deltamethrin is a synthetic pyrethroid widely used against insect pests, but its environmental persistence and potential effects on non-target organisms have raised toxicological concern, making detection methods valuable. The researchers deposited their AgNPs@C materials onto polished gold disk electrodes and ran cyclic voltammetry at scan rates from 0.01 to 0.30 volts per second in pH 8.0 phosphate buffer with potassium chloride. In blank electrolyte, the ex situ material showed a better-resolved anodic process around 1.0 volt and a corresponding cathodic process between 0.9 and 0.8 volts, tentatively associated with silver redox chemistry, while the in situ material gave a broader response with a stronger capacitive contribution.
In the presence of the deltamethrin formulation, both materials exhibited two irreversible cathodic processes. For the ex situ composite, the peaks appeared near 0.42 and 0.55 volts versus a normal hydrogen electrode, with currents of approximately minus 3.556 and minus 4.491 milliamperes. The in situ material showed peaks near 0.32 and 0.60 volts, with a substantially stronger first cathodic response of about minus 16.177 milliamperes. Regression analysis of peak current against scan rate and the square root of scan rate showed that the latter relationships were generally more linear, particularly for the second cathodic process, indicating diffusion-influenced transport rather than ideal surface-confined behavior. The authors stress an important interpretive caveat: because a commercial emulsifiable concentrate was used rather than analytical-grade deltamethrin, the voltammograms reflect the behavior of the whole formulation, coformulants included, in the presence of the electrode material. The study is therefore framed as a comparative behavior investigation at a fixed formulation concentration, not as analytical validation of a deltamethrin sensor.
The biological half of the study revealed a different kind of duality. In germination bioassays, gherkin (Cucumis anguria) and coriander (Coriandrum sativum) seeds were exposed to the aqueous guaraná extract and the biosynthesized nanoparticle dispersions at low (0.1 percent) and high (1.0 percent) concentrations, with distilled water and a Tween vehicle as controls. Each treatment comprised three replicates of 25 surface-disinfected seeds maintained for 14 days under a 12-hour dark and light photoperiod, with germination scored daily and root length measured at the end. The parameters tracked included germination percentage, mean germination time, mean germination rate, germination rate index, and mean root length, with statistical analysis by ANOVA followed by the Student–Newman–Keuls test.
The results were clearly concentration- and species-dependent. For gherkin, the low-dose nanoparticle treatment maintained high germination and a higher germination rate index than the extract treatments, while the high-dose nanoparticle treatment caused a marked reduction in final germination. Coriander followed a different pattern: the low-dose extract remained comparable to the controls, whereas both high-dose treatments were clearly inhibitory. Root growth data reinforced the trend, with the strongest negative effects associated with the highest nanoparticle concentration, especially for coriander. Notably, the low nanoparticle dose was in some cases compatible with a more favorable early response than the corresponding extract treatment alone. Because the dispersions were applied as complete systems, the authors interpret these effects as properties of the dispersions as applied rather than attributing them exclusively to an isolated nanoparticulate fraction. The findings align with a broader literature in which silver nanoparticles can either stimulate or impair germination depending on dose, particle properties, and plant species, ranging from biostimulation to phytotoxicity. Taken together, the study positions guaraná-mediated silver nanoparticles as green multifunctional materials, one part sustainable synthesis, one part pesticide-relevant electrochemistry, and one part dose-sensitive biology, while leaving open the question of which interfacial and molecular mechanisms underlie each response.
Subject of Research: Green synthesis of guaraná-mediated silver nanoparticles for electrochemical response to deltamethrin and effects on seed germination
Article Title: Green synthesized silver nanoparticles mediated by Paullinia cupana extract exhibit electrochemical behavior toward a commercial deltamethrin formulation and concentration related effects on seed germination
Article References: da Encarnação, J. R., Flores, S. M., da Silva, E. M., Ribeiro, C. R., de Souza, E. A., Neiva, E. G. C., Perotti, G. F., & Maia, P. J. S. (2026). Green synthesized silver nanoparticles mediated by Paullinia cupana extract exhibit electrochemical behavior toward a commercial deltamethrin formulation and concentration related effects on seed germination. Discover Chemistry, 3(1), Article 483. https://doi.org/10.1007/s44371-026-00946-5
Image Credits: AI Generated
DOI: 10.1007/s44371-026-00946-5
Keywords: silver nanoparticles, green synthesis, Paullinia cupana, guaraná, deltamethrin, electrochemistry, cyclic voltammetry, carbon black, seed germination, phytotoxicity, nanotechnology, pyrethroid
News Source: Bethany Barker. (October 9, 2026). Guaraná-Powered Silver Nanoparticles Detect Pesticide and Show Dose-Dependent Effects on Seeds. Scienmag.
