(309a) 2-D Manipulation of Individual Nanoparticles Using Fluid Flow In a Microfluidic Device

In this work, we present a hydrodynamic flow-based method to manipulate, confine or isolate single nanoparticles in free-solution. We directly demonstrate two-dimensional micromanipulation of individual nanoparticles in a microfluidic device. Recent developments in trapping micro- and nanoparticles using optical, electrokinetic, magnetic and acoustic methods have enabled key questions in biological and nano-scale science to be addressed. Here, we present an automated method for “on-demand” trapping and 2-D manipulation of nanoparticles. We built a microfluidic device containing a cross-slot channel geometry in which two laminar inlet streams converge at a microchannel junction, thereby generating a planar extensional flow. Nanoparticles are effectively trapped at the stagnation point of the extensional flow by implementing an automated feedback-control mechanism, such that the location of the stagnation point is actively adjusted using an integrated “on-chip” metering valve. Importantly, hydrodynamic trapping is feasible for any particle with no specific requirements on the material composition or the chemical/physical nature (optical, magnetic, surface charge) of the trapped object. In addition, hydrodynamic trap enables confinement of nanoscale particles because the trapping force scales linearly with particle radius, whereas the trapping force for optical or magnetic traps scales with particle volume. Hydrodynamic trapping inherently enables confinement of a single target nanoparticle in a concentrated sample suspension, provides the ability to change the surrounding medium of a trapped nanoparticle in real time and enables fine-scale particle manipulation in free solution for extended time scales. Trap stiffness compares favorably to optical, magnetic and electrophoretic traps and depends on the strain rate and the feedback control parameters along each axis of manipulation. Overall, the hydrodynamic trap offers a new platform for observation of nanoparticles without surface immobilization. We anticipate that this microfluidic-based technique will enable new scientific studies in the fields of cellular mechanics, colloidal science and fluid dynamics.

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