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

Silver nanoparticles (AgNPs) were synthesized using an aqueous extract of papain as a reducing and a stabilizing agent for use in 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 folate sensors were 1.510 μg and 5.033 μg, respectively. Analysis of folate in selected over-the-counter vitamin and mineral supplements showed stark discrepancies between declared and experimental folate levels. Thus, it was inferred that other substances, such as metal ions and other vitamins could interfere in folate analysis. While the use of papain-AgNPs as sensors seems promising, more work should be done for the improved selectivity and specificity for folate.