Current study relates to the development of an electrical power-free, handheld microfluidic nanoparticle synthesizer for synthesis of uniform sized silver nanoparticles at room temperature. The synthesizer module consists of a custom designed microreactor and employs negative pressure based pumping mechanism for the electrical power free synthesis of metal nanoparticles. In order to realize a microreactor capable of on-site synthesis of monodisperse nanoparticles, optimization studies by bulk biosynthesis at varying ratios of the precursor and the reducing agent followed by UV-VIS absorption studies were performed to determine the appropriate mixing ratio. Later, a custom designed microfluidic micromixer was used to perform volumetric flow rate optimizations at the desired ratio using syringe pumps. From the knowledge of the precursor and reducing agent ratio and the flow rates, we modified the hydraulic resistance of micro-mixer inlets by varying the channel geometry to meet the optimized specifications leading to effective synthesis. The synthesized nanoparticles were characterized by UV-VIS spectroscopy, XPS, FTIR, EDS, HRTEM and SAED. The crystal lattice planes of 111] and 220] from the SAED pattern confirms the presence of silver nanoparticles. HRTEM study elucidates that the size of the synthesized nanoparticles is between 2 and 10 nm.