Single positively charged particle trapping in nanofluidic systems

•Contact-free passive trapping of positively charged single nano-objects•Geometry-induced electrostatic trapping of single nanoparticles•Surface functionalization of nanofluidic devices is performed.•Charge reversal of glass based nanofluidic devices using poly-(ethyleneimine)•Interference scattering detection (iSCAT) for single nanoparticle imaging

High-throughput and contact-free trapping of single nano-objects in an aqueous solution is of substantial interest for fundamental and applied research. One of the several trapping methods is geometry-induced electrostatic (GIE) trapping that allows for passive spatial confinement of single nanoparticles in nanofluidic devices. In aqueous environments (pH > 2) glass and silicon dioxide surfaces acquire a net negative surface charge density due to the self-dissociation of terminal silanol groups. Thus, with native glass/silicon-based GIE-trapping devices only negatively charged nano-objects can be trapped, limiting the applications of this method. In this work, we have performed surface modifications of glass-based GIE-trapping nanofluidic devices to enable the trapping of positively charged nanoparticles. For surface functionalization of the devices, a layer transfer of poly-(ethyleneimine) electrolytes were used which provides a net positive surface charge density. We demonstrate the successful confinement of positively charged 60 nm gold nanoparticles inside the functionalized devices, and present a comparison study between trapping of negatively- and positively charged particles in native and functionalized devices, respectively.

Graphical abstractDownload high-res image (336KB)Download full-size image