A low-cost and reliable detection of hydrogen peroxide is essential in the pharmaceutical, medical, and food industries, since H2O2 can cause irreversible cellular damage through the oxidation of biomolecules. This paper describes a sensitive luminescent sensor for H2O2 based on a dual fluorescence-colorimetric assay for determining the hydrogen peroxide using silver nanoparticles prepared with Plinia cauliflora extracts (PcAgNPs). Nanoparticles were characterized by UV???Vis, transmission electron microscopy, elemental analysis, Zeta potential, FTIR, and fluorescence. The average size of spherical particles was???~???14 nm. The photoreduction process and pH control improved the nanoparticle's photophysical properties and stability. With pH adjustment, the Zeta potential of PcAgNPs prepared with fruit extract changed from???~?????? 17 mV to???~?????? 30 mV. The behavior of the PcAgNPs SPR and fluorescence bands were studied in the presence of H2O2. The SPR band of PcAgNPs around 420 nm gradually decreased upon the increasing concentration of H2O2, while the PcAgNPs emission has an enhancement and a shift (from???~???470 to???~???440 nm) in the presence of hydrogen peroxide. A calibration curve was obtained in the range of 0???5 ??M, with a calculated detection limit of 0.15 ??M. The present biosensor can be applied as an alternative method for detecting hydrogen peroxide in medical care and environmental monitoring.Conselho Nacional de Desenvolvimento Cient??fico e Tecnol??gico (CNPq)CNPq: 303715/2017-0