Electron-Beam Lithographic Grafting of Functional Polymer Structures from Fluoropolymer Substrates

Controlling orientation, conformation, and biorecognition of proteins on silane monolayers, conjugate polymers, and thermo-responsive polymer brushes: investigations using TOF-SIMS and principal component analysis

Control over orientation and conformation of surface-immobilized proteins, determining their biological activity, plays a critical role in biointerface engineering. Specific protein state can be achieved with adjusted surface preparation and immobilization conditions through different types of protein-surface and protein-protein interactions, as outlined in this work. Time-of-flight secondary ion mass spectroscopy, combining surface sensitivity with excellent chemical specificity enhanced by multivariate data analysis, is the most suited surface analysis method to provide information about protein state. This work highlights recent applications of the multivariate principal component analysis of TOF-SIMS spectra to trace orientation and conformation changes of various proteins (antibody, bovine serum albumin, and streptavidin) immobilized by adsorption, specific binding, and covalent attachment on different surfaces, including self-assembled monolayers on silicon, solution-deposited polythiophenes, and thermo-responsive polymer brushes. Multivariate TOF-SIMS results correlate well with AFM data and binding assays for antibody-antigen and streptavidin-biotin recognition. Additionally, several novel extensions of the multivariate TOF-SIMS method are discussed.

Graphical abstract

Spatiotemporal control of polymer brush formation through photoinduced radical polymerization regulated by DMD light modulation

Spatially arranged polymer brushes provide the essential capability of precisely regulating the surface physicochemical and functional properties of various substrates. A novel and flexible polymer brush patterning methodology, which is based on employing a digital mirror device (DMD)-based light modulation technique to spatiotemporally regulate a surface-initiated photoinduced atom transfer radical polymerization (photo-ATRP) process, is presented. Various characterization techniques confirm that the spatially and/or temporally controlled brush formation results in complex PEG-derived brush patterns in accordance with a customized digital image design. A series of step-and-exposure strategies, including in situ multiple exposure, dynamic multiple exposure and dynamic sequential exposure, are developed to implement spatiotemporal regulation of the photo-ATRP process, leading to complex patterned and gradient brushes featuring binary functionalities, pyramid nanostructures and radial directional chemical gradients. Moreover, tunable and radial directional concentration gradients of various biomacromolecules (e.g., streptavidin) are obtained through preparation of height gradients of azido-functionalized brushes and subsequent orthogonal chemical activation aimed at specific protein immobilization. Finally, a unidirectional concentration gradient of fibronectin, surrounded by non-fouling PEG brushes, is fabricated and applied for human umbilical vein endothelial cell (HUVEC) adhesion experiments, whose preliminary results indicate gradient-dependent cell adhesion behavior in response to the concentration gradient of fibronectin. The presented fabrication technique could be integrated with microfluidic devices for sensors and bio-reactors, paving the way for novel approaches for lab-on-a-chip technologies.