INTRODUCTION: Silver nanoparticles (AgNPs) are capable of producing a plasmonic effect, which can amplify the local electric field of certain materials, such as methylene blue (MB), resulting in fluorescence spectra with increased intensity. However, for this effect to occur, two conditions must be met: (i) spectral overlap between the extinction spectrum of the AgNPs and the absorption spectrum of MB, and (ii) an intermediate distance (10–20 nm) between the AgNPs and the material whose electromagnetic signal is to be amplified.

METHODOLOGY: Initially, AgNPs were synthesized using a bottom-up approach by reducing an Ag⁺ solution with NaBH₄, yielding nanoparticles with an extinction band overlapping the absorption band of MB. Subsequently, different volumes of AgNPs (10, 20, and 40 µL) were mixed with MB to obtain a final MB concentration of 10 µmol L⁻¹. A 10 µmol L-1 MB solution without AgNPs was used as a control. Spectrofluorimetric measurements were performed to evaluate the effects on the MB + AgNP systems and on MB alone.

RESULTS: Fluorescence measurements were carried out for each sample, revealing variations in fluorescence intensity relative to isolated MB. Upon the addition of 10, 20, and 40 µL of AgNPs, the fluorescence intensity increased by 5.7%, 2.5%, and 1.7%, respectively. These results indicate that higher volumes of AgNPs did not lead to the further enhancement of MB fluorescence intensity.

CONCLUSION: In conclusion, at the studied concentration, it is possible to achieve an amplification of the fluorescence signal of MB using the synthesized AgNPs; however, the optimal added volume was approximately 10 µL. These findings may contribute to the development of improved outcomes in treatments that employ phototherapy.