We present a fabrication process to create bifunctional microparticles displaying two distinct proteins that are spatially segregated onto the surface hemispheres. Silica and polystyrene microparticles with 2.0 μm, 4.1 μm, and 4.7 μm diameters are processed with metal deposition to form two chemically distinct and segregated hemispheres. The surface of each hemisphere is then separately derivatized with biological proteins using different chemical conjugation strategies. These bifunctional Janus particles possess biologically relevant, native conformation proteins attached to a biologically-unreactive and safe substrate. They also display high densities of each type of proteins which may enable a range of capabilities that monofunctional particles cannot, such as improved targeting of drugs and bioimaging agents.
We have designed and built a microfluidic liquid cell capable of high-resolution atomic force microscope (AFM) imaging and force spectroscopy. The liquid cell was assembled from three molded poly(dimethylsiloxane) (PDMS) pieces and integrated with commercially purchased probes. The AFM probe was embedded within the assembly such that the cantilever and tip protrude into the microfluidic channel. This channel is defined by the PDMS assembly on the top, a PDMS gasket on all four sides, and the sample substrate on the bottom, forming a liquid-tight seal. Our design features a low volume fluidic channel on the order of 50 nl, which is a reduction of over 3-5 orders of magnitude compared to several commercial liquid cells. This device facilitates testing at high shear rates and laminar flow conditions coupled with full AFM functionality in microfluidic aqueous environments, including execution of both force displacement curves and high resolution imaging.
The objective of this paper is to design and fabricate a low stiffness cantilever with an enclosed nanofluidic channel. This paper addresses the primary challenge of current hollow cantilever design, and introduces the use of a thermally decomposable polymer as the enabling technology to form a reduced stiffness, and thus higher sensitivity, cantilever. A numerical stiffness model is first developed to identify the critical geometric parameters necessary for structural soundness and bendability. A new sacrificial material is then introduced to cantilever fabrication that uses a low temperature top coat layer of plasma enhanced chemical vapor deposition nitride. Experimental measurement of the film's internal stress and the resulting bending radius of a composite cantilever are used to characterize residual stress from film deposition as a new design parameter, unique to this method, which was mitigated by a thorough analysis of the combined effect of film properties and cantilever mechanics. A numerical model is developed for optimizing cantilever geometry and refining film process parameters to minimize the internal stress of the cantilever, whilst achieving a low stiffness, high sensitivity, and composite nanofluidic atomic force microscopy cantilever.
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