Patterning of quantum dot bioconjugates via particle lithography

Identification of Dewetting Stages and Preparation of Single Chain Gold Nanoparticle Rings by Colloidal Lithography

Massively parallel nanoparticle assembly was carried out by means of colloidal lithographic experiments over a silicon substrate supported (sub)microparticle Langmuir-Blodgett monolayer, using high purity aqueous solution of PEGylated gold nanoparticles. The size of the polystyrene template particles in the monolayer was varied between 608 nm and 2.48 μm, while gold nanoparticles with diameters between 18 and 65 nm were used. Thanks to the PEGylation of the gold nanoparticles, they could be used as tracer objects to follow the drying process. In this way, different dewetting stages could be identified in the confined space between and underneath the template polystyrene spheres. Depending on the concentration of the nanoparticles, the presented approach allows the preparation of single-particle width necklace structures composed of gold particles. At the same time, the high purity of the substrate as well as of the evolved particle rings is preserved and unwanted particle deposition on the substrate surface is minimized.

Fabrication of quantum dot microarrays using electron beam lithography for applications in analyte sensing and cellular dynamics

Quantum dot (QD) based micro-/nanopatterned arrays are of broad interest in applications ranging from electronics, photonics, to sensor devices for biomedical purposes. Here, we report on a rapid, physico-chemically mild approach to generate high fidelity micropattern arrays of prefunctionalized water-soluble quantum dots using electron beam lithography. We show that such patterns retain their fluorescence and bioaffinity upon electron beam lithography and, based on the streptavidin-biotin interaction, allow for detection of proteins, colloidal gold nanoparticles and magnetic microparticles. Furthermore, we demonstrate the applicability of QD based microarray patterns differing in their shape (circles, squares, grid-like), size (from 1 to 10 μm) and pitch distance to study the adhesion, spreading and migration of human blood derived neutrophils. Using live cell confocal fluorescence microscopy, we show that pattern geometry and pitch distance influence the adhesion, spreading and migratory behavior of neutrophils. Research reported in this work paves the way for producing QD microarrays with multiplexed functionalities relevant for applications in analyte sensing and cellular dynamics.

Independently controlling protein dot size and spacing in particle lithography

Particle lithography is a relatively simple, inexpensive technique used to pattern inorganics, metals, polymers, and biological molecules on the micro- and nanometer scales. Previously, we used particle lithography to create hexagonal patterns of protein dots in a protein resistant background of methoxy-poly(ethylene glycol)-silane (mPEG-sil). In this work, we describe a simple heating procedure to overcome a potential limitation of particle lithography: the simultaneous change in feature size and center-to-center spacing as the diameter of the spheres used in the lithographic mask is changed. Uniform heating was used to make single-diameter protein patterns with dot sizes of approximately 2-4 or 2-8 μm, depending on the diameter of the spheres used in the lithographic mask, while differential heating was used to make a continuous gradient of dot sizes of approximately 1-9 μm on a single surface. We demonstrate the applicability of these substrates by observing the differences in neutrophil spreading on patterned and unpatterned protein coated surfaces.

Large-area protein patterns generated by ordered binary colloidal assemblies as templates

We demonstrate the use of binary colloidal assemblies as lithographic masks to generate tunable Au patterns on SiO(2) substrates with dimensions ranging from micrometers to nanometers. Such patterns can be modified with different chemistries to create patterns with well-defined sites for selective adsorption of proteins, where the pattern size and spacing is adjustable depending on particle choice. In our system, the binary colloidal assemblies contain large and small particles of similar or different material and are self-assembled from dilute dispersions with particle size ratios ranging from 0.10 to 0.50. This allows masks with variable morphology and thus production of chemical patterns of tunable geometry. Finally, the Au or SiO(2) regions of the pattern are surface modified with protein resistant oligoethyleneglycol self-assembled molecules, which facilitates site selective adsorption of proteins into the unmodified regions of the pattern. This we show with fluorescently labeled bovine serum albumin.