Green Routes to Metal Nanoparticles A PRISMA-Guided Meta-analysis of Plant Microbe- and Enzyme-Mediated Synthesizes

Abstract

The present research study addresses the fragmentation of the “green” nanoparticle literature by integrating 120 eligible reports into a single analytical framework. The study emphasizes route-level comparisons, heterogeneity, and small-study bias to identify what truly changes particle size versus what only fine-tunes it. This study compares head-to-head three biogenic routes-plant, microbe, and enzyme-on key practical outcomes that matter in use, such as particle size and dispersity (TEM/DLS), yield, crystallinity (XRD/SAED), and surface/capping chemistry (FTIR/XPS), linking these material characteristics to performance in catalysis, sensing, and antimicrobial assays. In parallel, we extract lab-ready guidance for greener scale-up by pinpointing which controllable knobs-precursor system, pH, temperature-time profile, and biomass/extract variability-reliably deliver reproducible nanoparticles with lower environmental and safety burdens, translating the evidence into process recommendations researchers can immediately adopt. The present study screened ~200 records and included 120 biosynthetic reports meeting predefined criteria. Data were extracted at the study-arm level and harmonized for TEM mean core size (primary outcome), with ζ-potential, PDI, pH, temperature, time, metal, and a reporting-quality score (NCM) as covariates. Random-effects models pooled sizes by route (enzyme, plant, microbe). Distributional evidence used box/violin plots. Global differences were tested by Kruskal–Wallis, with Mann–Whitney post-hoc tests and Bonferroni adjustment. Small-study bias was explored with funnel plots where k≥10. Variance-weighted meta-regression (weights = 1/Var(mean)) evaluated pH, temperature, time, and NCM. The results of the study: Sizes clustered by route, with enzyme < plant < microbe in central tendency. The global Kruskal–Wallis was significant with a large effect (ε²≈0.51), and post-hoc contrasts preserved the ranking after correction. Random-effects pooling reproduced the pattern and showed high heterogeneity (I² high across routes), consistent with variable chemistries and workflows. Meta-regression identified a small negative temperature coefficient (≈ −0.05 nm per °C; 95% CI narrowly below zero), while pH, time, and NCM showed no clear independent associations. Stability summaries indicated generally acceptable ζ-potentials and PDIs within each route. The Choice of biosynthetic route is the primary driver of particle size in green syntheses; within-route tuning offers modest, incremental control. Enzyme routes favour smaller and tighter size distributions; plant routes balance accessibility with moderate control; microbe routes suit applications tolerant of larger cores. Standardizing extract characterization, oxygen control, and purification/reporting would reduce heterogeneity and sharpen comparative inference.