Abstract
A novel approach to local functionalization of plasmonic hotspots at gold nanoparticles with biofunctional moieties is reported. It relies on photocrosslinking and attachment of a responsive hydrogel binding matrix by the use of a UV interference field. A thermoresponsive poly(N-isopropylacrylamide)-based (pNIPAAm) hydrogel with photocrosslinkable benzophenone groups and carboxylic groups for its postmodification was employed. UV-laser interference lithography with a phase mask configuration allowed for the generation of a high-contrast interference field that was used for the recording of periodic arrays of pNIPAAm-based hydrogel features with the size as small as 170 nm. These hydrogel arrays were overlaid and attached on the top of periodic arrays of gold nanoparticles, exhibiting a diameter of 130 nm and employed as a three-dimensional binding matrix in a plasmonic biosensor. Such a hybrid material was postmodified with ligand biomolecules and utilized for plasmon-enhanced fluorescence readout of an immunoassay. Additional enhancement of the fluorescence sensor signal by the collapse of the responsive hydrogel binding matrix that compacts the target analyte at the plasmonic hotspot is demonstrated.
Highlights
IntroductionThe nanoscale patterning of responsive polymer materials is important to let them serve in diverse areas ranging from sensing,[14] optical components,[15] and catalysis[16] to tissue engineering[17] and cell biology.[18] Self-assembly represents a widely used method for the preparation of nano- and microstructures based on, for instance, block-copolymer that combines hydrophobic and hydrophilic segments.[19,20] In addition, casting of microstructures by polymerization in template cavities has been utilized for the fabrication of miniature responsive polymer objects actuated in aqueous solution.[21] To prepare structures that are attached to a solid surface, photolithography has been extensively used for various types of responsive polymer structures.[22] Shadow mask photolithography-based methods typically enable facile means for the patterning of microstructures over macroscopic areas
A variety of naturally occurring or synthetic biopolymers has been tailored for specific biomedical[1] and analytical[2] applications, and among these, stimuli-responsive polymers represent attractive “smart” materials capitalizing on their ability to undergo physical or chemical changes triggered by an external stimulus.[3−5] Such materials can be incorporated into architectures that are on-demand actuated by stimuli, including temperature, pH, or electric current.[6−8] A prominent example of a responsive polymer is the poly(Nisopropylacrylamide), which is well-known for its thermoresponsive behavior. pNIPAAm exhibits a lower critical solution temperature (LCST) with pronounced and fully reversible hydrophobic-to-hydrophilic transition close to the body temperature.[9] pNIPAAm has been utilized in drug delivery micro/nanogels,[10] for modulating cellular interactions,[5,11] biosensors,[12] and in opto-responsive coatings.[13]
The present paper reports on the local attachment of a 3D hydrogel binding matrix in the vicinity of well-ordered gold nanoparticles, which can be postmodified for specific affinity capture of target analytes and actuated for their compacting at the plasmonic hotspot
Summary
The nanoscale patterning of responsive polymer materials is important to let them serve in diverse areas ranging from sensing,[14] optical components,[15] and catalysis[16] to tissue engineering[17] and cell biology.[18] Self-assembly represents a widely used method for the preparation of nano- and microstructures based on, for instance, block-copolymer that combines hydrophobic and hydrophilic segments.[19,20] In addition, casting of microstructures by polymerization in template cavities has been utilized for the fabrication of miniature responsive polymer objects actuated in aqueous solution.[21] To prepare structures that are attached to a solid surface, photolithography has been extensively used for various types of responsive polymer structures.[22] Shadow mask photolithography-based methods typically enable facile means for the patterning of microstructures over macroscopic areas. This method is based on a transfer of a target motif carried by a stamp to a polymer layer by the subsequent polymerization[26] or photocrosslinking.[27]
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