Dextran-Gold Nanoparticle-Based Tablets and Swabs for Colorimetric Detection of Urinary H₂O₂

Diagnosis of oxidative stress is essential to avoiding serious life-threatening situations. Hydrogen peroxide (H 2 O 2 ) is a potential biomarker of oxidative stress. Herein, we introduce a reagent-free nanoscale approach for the colorimetric detection of urinary H 2 O 2 utilizing dextran-gold nanoparticles (dAuNPs). The plasmonic properties of these nanoparticles are central to their function, leveraging their high surface area and tunable optical characteristics for sensitive detection. We transformed the colloidal dAuNPs solution into two formats: as a tablet (dAuNPs-Tablet) or impregnated on a cotton swab (dAuNPs-Swab). The assay generates a hydroxyl radical (•OH) from H 2 O 2 via the Fenton reaction, followed by nanoscale-driven detection of H 2 O 2 using a plasmonic tablet and swab sensors. In the presence of H 2 O 2 in a sample, the red color of the tablet solution or plasmonic swab turns to blue due to salt-induced nanoparticles aggregation. The transition in color is observed due to •OH-assisted degradation of the dextran layer around dAuNPs, leading to the loss of colloidal stability and subsequent aggregation of dAuNPs. Sodium chloride acts as the aggregating agent, enhancing the nanoscale interactions. The detection limit in artificial urine is found to be 50 μM for the tablet sensor and 100 μM for the swab sensor. The plasmonic tablet is more stable as compared to a plasmonic swab which gradually loses stability, after one month, with approximately 40% degradation within three months. Interference studies demonstrate the high selectivity of both platforms for H 2 O 2 detection. Notably, we investigated the H 2 O 2 levels in human urine samples from healthy volunteers (both female and male) before and after green tea consumption. The observed decrease in the H 2 O 2 level in urine postgreen tea consumption suggests a potential role of green tea antioxidants in mitigating oxidative stress. The utilization of nanoprobes in our research not only enhances our understanding of oxidative stress dynamics but also drives advancements in point-of-care detection platforms, offering enhanced portability and ease of use of nanoprobes. These platforms open exciting avenues in healthcare diagnosis.