Systems and methods are disclosed that utilize metal nanostructures that are synthesized in situ along the internal surfaces of a microfluidic device. The nanostructures are formed by initial deposition of metallic seeds followed by flowing growth and reducing agent solutions into the capillaries/microfluidic channels to grow the nanostars. The nanostructures may optionally be functionalized with a capture ligand. The capture ligand may be used to selectively bind to certain cells (e.g., circulating tumor cells). The cells may be removed by a beam of light (e.g., laser beam) that induces localized heating at the surface location(s) containing the nanostructures. The plasmonic nature of the nanostructures can be used to heat the nanostructure(s) locally for the selective removal of one or certain cells. The nanostructures may be used to acquire Raman spectra of molecules or other small objects that are bound thereto for identification and quantification.