Tunable two-dimensional array patterning of antibody annuli through microsphere templating

Lithographic patterning of antibodies by direct lift-off and improved surface adhesion

The inherent property of antibodies binding to their antigen with high specificity makes them a strong candidate for sensing and detection applications. Microscale patterning of antibodies is desired for the miniaturization of sensors and fundamental cell biology studies. However, existing methodologies to pattern antibodies at the microscale are multi-step. In this work, we demonstrate microscale patterning of antibodies on a glass coverslip in a single step photolithography process. The microscale features of the photoresist were generated on the coverslip using photolithography, and the antibody solution was incubated. Acetone lift-off of the antibody incubated photoresist, and subsequent washing by isopropanol (IPA), produced a micro-array of antibodies. The functionality of patterned primary antibody was confirmed using the corresponding antigen and strict controls. One of the striking features of this method of patterning is that the process steps and chemicals inherently improve the adhesion between the antibodies and glass without the need to functionalize the glass surface. We performed an ultrasonication test, detergent washing test, and Scotch tape test to show improved adhesion. Using appropriate controls, we show that the interaction taking place between the antibodies and the glass surface, after our process, is stronger than the simple physisorption taking place between the antibodies and the glass surface, without any treatment.

Nanometric protein-patch arrays on glass and polydimethylsiloxane for cell adhesion studies

We present a simple cost-effective benchtop protocol to functionalize glass and polydimethylsiloxane (PDMS) with nanometric protein patches for cell adhesion studies. Evaporation masks, covering macroscopic areas on glass, were made using improved strategies for self-assembly of colloidal microbeads which then served as templates for creating the protein patch arrays via the intermediate steps of organo-aminosilane deposition and polyethylene-glycol grafting. The diameter of the patches could be varied down to about 80 nm. The glass substrates were used for advanced optical imaging of T-lymphocytes to explore adhesion by reflection interference contrast microscopy and the possible colocalization of T-cell receptor microclusters and the activating protein patches by total internal reflection fluorescence microscopy. The selectively functionalized glass could also serve as template for transferring the protein nanopatches to the surface of a soft elastomer. We demonstrated successful reverse contact printing onto the surface of thin layers of PDMS with stiffness ranging from 30 KPa to 3 MPa.

Foam-film-stabilized liquid bridge networks in evaporative lithography and wet granular matter

Evaporative lithography using latex particle templates is a novel approach for the self-assembly of suspension-dispersed nanoparticles into ordered microwire networks. The phenomenon that drives the self-assembly process is the propagation of a network of interconnected liquid bridges between the template particles and the underlying substrate. With the aid of video microscopy, we demonstrate that these liquid bridges are in fact the border zone between the underlying substrate and foam films vertical to the substrate, which are formed during the evaporation of the liquid from the suspension. The stability of the foam films and thus the liquid bridge network stability are due to the presence of a small amount of surfactant in the evaporating solution. We show that the same type of foam-film-stabilized liquid bridge network can also propagate in 3D clusters of spherical particles, which has important implications for the understanding of wet granular matter.

Tunable two dimensional protein patterns through self-assembly nanosphere template

By the aim of constructing surfaces for multi-component and multifunctional bioassay, a microsphere lithography technique was employed to control the surface morphology. Two kinds of protein molecules (antibodies) were used as building blocks. As a result, dual-component biocompatible surfaces with alternate immunoglobulin micropatterns were fabricated. The employed antibodies included human Immunoglobulin G (IgG) and rabbit IgG, which composed nanometer scale surface arrays on the surfaces. The antibodies were identified specially by immunoreactions with labeled antigens of fluorescein isothiocyanate (FITC)-antihuman IgG and tetramethylrhodamine-5-(and 6)-isothiocyanate (TRITC)-antirabbit IgG. The immune responses were confirmed by confocal fluorescence (FL) microscopy. A study on the sensitivity and quantification was done by using surface-enhanced resonance Raman scattering (SERRS) spectroscopy. The obtained SERRS spectra showed satisfactory resolution in the multi-component detection objects. No interference was observed from inner- or interactions of detecting molecules. The detection limits for both of the antigens reached to as low as 1 ng/mL, which was comparable to FL method. Meanwhile, a good linear relationship between SERRS peak intensity and the logarithm of antigens' concentrations (from 1 ng/mL to 1 mg/mL) were observed. The results demonstrated that SERRS is a very promising detection technique for multi-component immunoassay, and has great potential applications in biotechnology and biochemistry.

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.