Abstract
Hydrogel materials consisting of water-swollen polymer networks exhibit a large number of specific properties highly attractive for a variety of optical biosensor applications. This properties profile embraces the aqueous swelling medium as the basis of biocompatibility, non-fouling behavior, and being not cell toxic, while providing high optical quality and transparency. The present review focuses on some of the most interesting aspects of surface-attached hydrogel films as active binding matrices in optical biosensors based on surface plasmon resonance and optical waveguide mode spectroscopy. In particular, the chemical nature, specific properties, and applications of such hydrogel surface architectures for highly sensitive affinity biosensors based on evanescent wave optics are discussed. The specific class of responsive hydrogel systems, which can change their physical state in response to externally applied stimuli, have found large interest as sophisticated materials that provide a complex behavior to hydrogel-based sensing devices.
Highlights
The general term “gel” is defined as a viscoelastic solid-like but deformable material composed of a dispersion of a substantially diluted network in a continuous gas or liquid medium
The lower critical solution temperature (LCST) was varied from 25 °C for a poly(2-vinylpyridine)-poly(N-isopropylacrylamide) block copolymer to 43 °C for a poly(N,N-dimethylacrylamide-co-N-isopropylacrylamide) copolymer [37]. Another example of thermoresponsive hydrogel type is based on polyvinyl derivatives. This was shown for poly(N-vinylcaprolactam) hydrogel films immobilized on track-etched poly(ethylene terephthalate) membranes for temperature-dependent separation of dextrans of different molecular weight [49]
The specific capture of target analyte in the hydrogel with imprinted moieties alters its density and refractive index, which is subsequently optically detected by methods including surface plasmon resonance (SPR) or optical waveguide spectroscopy (OWS)
Summary
The general term “gel” is defined as a viscoelastic solid-like but deformable material composed of a dispersion of a substantially diluted network in a continuous gas or liquid medium. Owing to the highly open structure and large inner surface, hydrogels can accommodate large amounts of molecules with specific functions and are becoming irreplaceable materials in biosensing technology for detection of chemical or biological analytes [17,18,19,20,21,22]. Compared to other types of biointerfaces (e.g., based on 2D self-assembled monolayers—SAMs), the 3D nature of the hydrogel networks allows to accommodate orders of magnitude larger amounts of recognition elements [23], provides a more natural microenvironment for biomolecules that increases their stability [24] and offers routes to implement additional functionalities (e.g., separation of target analyte from other molecules in a sample) [25]. The chemical nature, particular properties and specific application in biosensing of surface-attached hydrogel films are discussed
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