An apparatus for continuous solvothermal synthesis of nanoparticles, comprising: an inlet section comprising a plurality of inlet portions for separately receiving at least a metallic precursor solution and a solvent; a reactor section extending from the inlet section, the reactor section enabling continuous mixing resulting in solvothermal reactions between the metallic precursor solution and the solvent, and further nanoparticles formation and nanoparticles growth, the reactor section comprising a spiral section having a plurality of spiral turns (122, 124,..), each spiral turn of the plurality of spiral turns having a helical channel followed by a counter-helical channel, wherein the metallic precursor solution and the supercritical fluid interchanges the flow direction for enabling mixing between the metallic precursor solution and the solvent, and wherein the mixing enables the solvothermal reactions between the metallic precursor solution and the solvent which yields a slurry comprising nanoparticles; a flexible quenching unit enclosing a set of spiral turns from amongst the plurality of spiral turns, the set of spiral turns configured in proximity to an exit portion of the reactor section, the flexible quenching unit capable of holding a quenching fluid for rapidly reducing temperature of the reactor section to a set temperature, further wherein the flexible quenching unit capable of adjusting a number of the set of spiral turns based on targeted particle characteristics of the nanoparticles; and an outlet section configured at an exit portion of the reactor section for collecting the slurry of nanoparticles. an inlet section comprising a plurality of inlet portions for separately receiving at least a metallic precursor solution and a solvent; a reactor section extending from the inlet section, the reactor section enabling continuous mixing resulting in solvothermal reactions between the metallic precursor solution and the solvent, and further nanoparticles formation and nanoparticles growth, the reactor section comprising a spiral section having a plurality of spiral turns (122, 124,..), each spiral turn of the plurality of spiral turns having a helical channel followed by a counter-helical channel, wherein the metallic precursor solution and the supercritical fluid interchanges the flow direction for enabling mixing between the metallic precursor solution and the solvent, and wherein the mixing enables the solvothermal reactions between the metallic precursor solution and the solvent which yields a slurry comprising nanoparticles; a flexible quenching unit enclosing a set of spiral turns from amongst the plurality of spiral turns, the set of spiral turns configured in proximity to an exit portion of the reactor section, the flexible quenching unit capable of holding a quenching fluid for rapidly reducing temperature of the reactor section to a set temperature, further wherein the flexible quenching unit capable of adjusting a number of the set of spiral turns based on targeted particle characteristics of the nanoparticles; and an outlet section configured at an exit portion of the reactor section for collecting the slurry of nanoparticles.