A novel study on enhancing ascorbic acid colorimetric detection: Green synthesis-driven crystallinity, stability, and catalytic performance of iron oxide nanoparticles in Mo(VI)/FeNPs-based biosensors

The goal of this study is to investigate how the green synthesis influences the crystallinity, stability, and catalytic performance of green-synthesized iron oxide nanoparticles (FeNPs) in Mo(VI)/FeNPs-based biosensors for ascorbic acid (AA) colorimetric detection. By examining the correlation between total antioxydant capacity (TAC) and FeNPs' structural properties, phase composition, and defect levels, the study aims to establish how plant-mediated synthesis drives FeNPs' catalytic efficiency, ultimately enhancing biosensor sensitivity and lowering detection limits (LOD and LOQ). Statistical analyses, including ANOVA and Pearson correlation, are applied to validate the relationship between TAC and FeNPs' characteristics, reinforcing the role of green synthesis in enhancing biosensor performance. In this study, FTIR spectroscopy was employed to analyze unoxidized free AA groups, offering detailed insights into oxidation preferences across various Mo(VI)/FeNPs pairs. The results showed that AA was preferentially oxidized at the four biosensors with a consistent oxidation peak at 820 nm across all Mo(VI)/FeNPs pairs, with a linear correlation to AA concentrations from 0.05 to 100 mM. FTIR analysis of unoxidized AA supported these findings, revealing that AA oxidation was most efficient at Mo(VI)/ROS-FeNPs and Mo(VI)/ARM-FeNPs biosensors compared to Mo(VI)/JUN-FeNPs and Mo(VI)/MAT-FeNPs. Likewise, the highest sensitivity, reflected by the lowest LOD (0.01183 +/- 0.00116 mM and 0.01521 +/- 0.00187) and LOQ (0.0393 +/- 0.00386 mM and 0.0506 +/- 0.00623), was observed in Mo(VI)/ROS-FeNPs and Mo(VI)/ARM-FeNPs, whereas Mo(VI)/JUN-FeNPs and Mo(VI)/MAT-FeNPs exhibited higher LOD (0.03237 +/- 0.00318 mM and 0.03550 +/- 0.00348) and LOQ (0.107887 +/- 0.01058 mM and 0.11834 +/- 0.01159), confirming the impact of FeNPs' catalytic performance on detection sensitivity. One-way ANOVA analysis confirmed that these variations in LOD (F = 42.7, p < 0.0001) and LOQ (F = 58.3, p < 0.0001) were statistically significant (p < 0.05), indicating that intrinsic properties of FeNPs strongly influence the catalytic performance of the biosensors. Post-hoc Tukey's test revealed that FeNPs synthesized with extracts of higher TAC, such as Rosmarinus officinalis and Artemisia herba-alba, achieved significantly lower LOD and LOQ values compared to those prepared with Juniperus phoenicia and Matricaria pubescens extracts, signifying superior catalytic performance. The catalytic performances of FeNPs in AA oxidation are closely linked to their stability and crystallinity. XRD analysis revealed that higher-TAC extracts, like Rosmarinus officinalis and Artemisia herba-alba, yielded FeNPs with minor defects, with a greater percentage of the gamma - Fe2O3 phase, indicating enhanced stability and crystallinity. In contrast, extracts with lower TAC, such as Juniperus phoenicia and Matricaria pubescens, produced FeNPs with more defects, with a higher percentage of the alpha - Fe2O3 phase. Statistical analysis of ANOVA and Pearson correlation confirmed a significant influence of TAC on FeNPs' phase composition (F = 89.3, p = 0.002), with a strong positive correlation to gamma - Fe2O3 (r = 0.99, p = 0.004) and a negative correlation to alpha - Fe2O3 (r = -0.99, p = 0.004). These results highlight the role of TAC in promoting gamma - Fe2O3 formation, enhancing FeNPs' stability and crystallinity. This emphasizes that high TAC contributes to improved stability and crystallinity, and thereby enhances AA oxidation by driving FeNPs' catalytic performance in Mo(VI)/FeNPs biosensors.