ORIGINAL PAPER Microfluidics based Handheld Nanoparticle Synthesizer S. C. G. Kiruba Daniel 1 • Lourdes Albina Nirupa Julius 1 • Sai Siva Gorthi 1,2 Received: 15 July 2016 Ó Springer Science+Business Media New York 2016 Abstract 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, opti- mization studies by bulk biosynthesis at varying ratios of the precursor and the reducing agent followed by UV–VIS absorption studies were performed to deter- mine the appropriate mixing ratio. Later, a custom designed microfluidic micro- mixer 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 nanoparti- cles. HRTEM study elucidates that the size of the synthesized nanoparticles is between 2 and 10 nm. S.C.G. Kiruba Daniel and Lourdes Albina Nirupa Julius have equally contributed. Electronic supplementary material The online version of this article (doi:10.1007/s10876-016-1120-x) contains supplementary material, which is available to authorized users. & Sai Siva Gorthi saisiva.gorthi@gmail.com; saisiva.gorthi@iap.iisc.ernet.in 1 Shanmukha Innovations Pvt. Ltd, First Floor, SID Building, IISc, Bangalore 560012, India 2 Department of Instrumentation and Applied Physics, Indian Institute of Science (IISc), Bangalore 560012, India 123 J Clust Sci DOI 10.1007/s10876-016-1120-x