Papain-mediated Synthesis of Silver Nanoparticles and Their Use in the Fluorescence-based Analysis of Folic Acid

Abstract

Silver nanoparticles (AgNPs) were synthesized using an aqueous extract of papain as a reducing and a stabilizing agent for the fluorescence-based sensing of the B-vitamin, folic acid.  The AgNPs obtained were spherical with diameters between 3-40 nm, with an average diameter of 11.4 ± 6.4 nm.  The AgNPs also exhibited surface plasmon resonance (SPR) at 420 nm and fluorescence upon excitation with UV light.  The addition of increments of folic acid caused the quenching of the AgNPs’ fluorescence which could be fitted to the Stern-Volmer equation. The limits of detection (LOD) and quantification (LOQ) of the AgNPs as folic acid sensors were 1.10 μg/mL and 3.31 μg/mL, respectively. Analysis of folic acid in selected over-the-counter vitamin and mineral supplements showed stark discrepancies between declared and experimental folic acid levels. Thus, it was inferred that other substances, such as metal ions and other vitamins, could interfere in folic acid analysis. While the use of papain-AgNPs as sensors seems promising, more work should be done for the improved selectivity and specificity of folic acid.