Green synthesis of ultra-stable silver nanoparticles modified with oxidized sodium alginate and high sensitivity detection of urine biomarkers

In this study, a surface-enhanced Raman scattering (SERS) substrate based on oxidized sodium alginate (OSA)-modified silver nanoparticles (Ag NPs) was developed for the highly sensitive detection of urine biomarkers. Compared to conventional citrate-reduced Ag NPs, the OSA-Ag NPs eliminate the need for additional reducing agents, offering cost-effectiveness and alignment with green chemistry principles. OSA acts as both a stabilizer and a binding site for Ag NPs, enabling uniform nanoparticle distribution and enhanced substrate robustness. This modification significantly improves the substrate's high-salinity stability, sensitivity, and reproducibility. Furthermore, the OSA-Ag NPs substrate exhibited remarkable storage stability, maintaining 92.49 % SERS intensity after 50 days under ambient conditions, which outperforms traditional Ag colloid substrates. The OSA-Ag NPs exhibited detection limits as low as 1.9 × 10 −4  M for urea, 2.4 × 10 −7  M for creatinine, and 2.7 × 10 −7  M for bilirubin, demonstrating high sensitivity and a wide linear range. In artificial urine, the OSA-Ag NPs with high accuracy and repeatability, confirming their practical utility. These results highlight the OSA-Ag NPs substrate as a promising tool for urine biomarker detection, particularly in high-salinity environments. Its ability to maintain performance in complex biological matrices suggests potential for rapid and precise diagnostics, advancing the field of biosensing.