Soft electrostatic trapping in nanofluidics

Trapping and manipulation of nano-objects in solution are of great interest and have emerged in a plethora of fields spanning from soft condensed matter to biophysics and medical diagnostics.We report on establishing a nanofluidic system for reliable and contact-free trapping as well as manipulation of charged nano-objects using elastic polydimethylsiloxane(PDMS)-based materials.This trapping principle is based on electrostatic repulsion between charged nanofluidic walls and confined charged objects,called geometry-induced electrostatic(GIE)trapping.With gold nanoparticles as probes,we study the performance of the devices by measuring the stiffness and potential depths of the implemented traps,and compare the results with numerical simulations.When trapping 100 nm particles,we observe potential depths of up to Q≅24 k_(B)T that provide stable trapping for many days.Taking advantage of the soft material properties of PDMS,we actively tune the trapping strength and potential depth by elastically reducing the device channel height,which boosts the potential depth up to Q~200 k_(B)T,providing practically permanent contactfree trapping.Due to a high-throughput and low-cost fabrication process,ease of use,and excellent trapping performance,our method provides a reliable platform for research and applications in study and manipulation of single nano-objects in fluids.

Surface-modified elastomeric nanofluidic devices for single nanoparticle trapping

Our work focuses on the development of simpler and effective production of nanofluidic devices for high-throughput charged single nanoparticle trapping in an aqueous environment.Single nanoparticle confinement using electrostatic trapping has been an effective approach to study the fundamental properties of charged molecules under a controlled aqueous environment.Conventionally,geometry-induced electrostatic trapping devices are fabricated using SiOx-based substrates and comprise nanochannels imbedded with nanoindentations such as nanopockets,nanoslits and nanogrids.These geometry-induced electrostatic trapping devices can only trap negatively charged particles,and therefore,to trap positively charged particles,modification of the device surface is required.However,the surface modification process of a nanofluidic device is cumbersome and time consuming.Therefore,here,we present a novel approach for the development of surface-modified geometry-induced electrostatic trapping devices that reduces the surface modification time from nearly 5 days to just a few hours.We utilized polydimethylsiloxane for the development of a surface-modified geometry-induced electrostatic trapping device.To demonstrate the device efficiency and success of the surface modification procedure,a comparison study between a PDMS-based geometry-induced electrostatic trapping device and the surface-modified polydimethylsiloxane-based device was performed.The device surface was modified with two layers of polyelectrolytes(1:poly(ethyleneimine)and 2:poly(styrenesulfonate)),which led to an overall negatively charged surface.Our experiments revealed the presence of a homogeneous surface charge density inside the fluidic devices and equivalent trapping strengths for the surface-modified and native polydimethylsiloxane-based geometry-induced electrostatic trapping devices.This work paves the way towards broader use of geometry-induced electrostatic trapping devices in the fields of biosensing,disease diagnosis,molecular analysis,fluid quality control and pathogen detection.