Functionalized Polymer Microgel Particles Enable Customizable Production of Label-Free Sensor Arrays

Fabrication and Phase Behavior of Thermo- and/or pH-Responsive Polymer-Grafted SiO2 Nanoparticles

Three series of thermo- and/or pH-responsive polymer-grafted SiO2 nanoparticles, SiO2-graft-poly(oligo(ethylene glycol) methacrylate) (SiO2-g-POEGMA), SiO2-graft-poly(acrylic acid) (SiO2-g-PAA) and SiO2-graft-poly(oligo(ethylene glycol) methacrylate-state-acrylic acid (SiO2-g-P(OEGMA-stat-AA)), were prepared by grafting POEGMA and/or PAA onto the surface of silica nanoparticles through the surface-initiated atom transfer radical polymerization (SI-ATRP). The lower critical solution temperature (LCST) of SiO2-g-POEGMA (MOEGMA = 300 g/mol) was found to be 64 °C. For SiO2-g-PAA nanoparticles, at the pH range from 8 to 12, the hydrodynamic diameter of the nanoparticles increases with increasing pH, and the zeta potential of SiO2-g-PAA nanoparticles is negatively charged and decreases with increasing pH. Owing to the thermo- and pH-responsive, the hydrodynamic diameters of SiO2-g-P(OEGMA-stat-AA) nanoparticles increase with the increasing pH, and the LCSTs of those nanoparticles increase with the increase of POEGMA content.

The Bioanalytical and Biomedical Applications of Polymer Modified Substrates

Polymers with different structures and morphology have been extensively used to construct functionalized surfaces for a wide range of applications because the physicochemical properties of polymers can be finely adjusted by their molecular weights, polydispersity and configurations, as well as the chemical structures and natures of monomers. In particular, the specific functions of polymers can be easily achieved at post-synthesis by the attachment of different kinds of active molecules such as recognition ligand, peptides, aptamers and antibodies. In this review, the recent advances in the bioanalytical and biomedical applications of polymer modified substrates were summarized with subsections on functionalization using branched polymers, polymer brushes and polymer hydrogels. The review focuses on their applications as biosensors with excellent analytical performance and/or as nonfouling surfaces with efficient antibacterial activity. Finally, we discuss the perspectives and future directions of polymer modified substrates in the development of biodevices for the diagnosis, treatment and prevention of diseases.

Mechanoresponsive diselenide-crosslinked microgels with programmed ultrasound-triggered degradation and radical scavenging ability for protein protection

In the context of controlled delivery and release, proteins constitute a delicate class of cargo requiring advanced delivery platforms and protection. We here show that mechanoresponsive diselenide-crosslinked microgels undergo controlled ultrasound-triggered degradation in aqueous solution for the release of proteins. Simultaneously, the proteins are protected from chemical and conformational damage by the microgels, which disintegrate to water-soluble polymer chains upon sonication. The degradation process is controlled by the amount of diselenide crosslinks, the temperature, and the sonication amplitude. We demonstrate that the ultrasound-mediated cleavage of diselenide bonds in these microgels facilitates the release and activates latent functionality preventing the oxidation and denaturation of the encapsulated proteins (cytochrome C and myoglobin) opening new application possibilities in the targeted delivery of biomacromolecules.

Mechanoresponsive diselenide-crosslinked microgels undergo controlled ultrasound-triggered degradation and can be used for protein delivery due to their dual protection properties acting as radical scavengers and conformation stabilizers.

A Stable Biotin-Streptavidin Surface Enables Multiplex, Label-Free Protein Detection by Aptamer and Aptamer-Protein Arrays Using Arrayed Imaging Reflectometry

While label-free multiplex sensor technology enables “mixing and matching” of different capture molecules in principle, in practice this has been rarely (if ever) demonstrated. To fill this gap, we developed protocols for the preparation of mixed aptamer-protein arrays on the arrayed imaging reflectometry (AIR) sensing platform using streptavidin as a common attachment point for both biotinylated proteins and aptamers. Doing so required overcoming the noted instability of dried streptavidin monolayers on surfaces. After characterizing this degradation, stable surfaces were obtained using a commercial microarray product. Microarraying through the layer of stabilizer then provided mixed aptamer-antibody arrays. We demonstrate that sensor arrays prepared in this manner are suitable for several probes (thrombin and TGF-β1 aptamers; avi-tagged protein) and targets.

Convection-driven microfabricated hydrogels for rapid biosensing

A microscale biosensing platform using rehydration-mediated swelling of bio-functionalized hydrogel structures and rapid target analyte capture is described. Induced convective flow mitigates diffusion limited incubation times, enabling model assays to be completed in under three minutes. Assay design parameters have been evaluated, revealing fabrication criteria required to tune detection sensitivity.

Self-Assembled Microgels for Sensitive and Low-Fouling Detection of Streptomycin in Complex Media

In terms of detection of antibiotics within complex media, the nonspecific adsorption is an enormous challenge and antifouling sensing interfaces capable of reducing the nonspecific adsorption from complex biological samples are highly desirable. In this work, a novel antifouling electrochemical immunosensor was explored based on the self-assembly of two kinds of poly( N-isopropylacrylamide) microgels on the surface of graphene oxide for sensitive detection of streptomycin (STR). The microgels modified with glycidyl methacrylate (GMA) and zwitterionic liquid 1-propyl-3-vinylimidazole sulfonate (PVIS) were prepared. The microgels with GMA were used by combining specific recognition of anti-STR. The rapid specific binding of antigen and anti-STR resulted in a decrease of current density to generate electrochemical responsive signals. Zwitterionic liquid-modified microgels were used for antifouling, which can form stronger hydration and show excellent antifouling ability. As a result, we achieved efficient and sensitive detection of STR in the complex sample with evidently resisted nonspecific adsorption effect, the wide linear range toward STR was from 0.05 to 100 ng mL^-1, with a detection limit down to 1.7 pg mL^-1. The immunosensor based on the surface functionalization of microgels showed promising applications for the detection of antibiotics in complex media.

Chemical Design of Functional Polymer Structures for Biosensors: From Nanoscale to Macroscale

Over the past decades, biosensors, a class of physicochemical detectors sensitive to biological analytes, have drawn increasing interest, particularly in light of growing concerns about human health. Functional polymeric materials have been widely researched for sensing applications because of their structural versatility and significant progress that has been made concerning their chemistry, as well as in the field of nanotechnology. Polymeric nanoparticles are conventionally used in sensing applications due to large surface area, which allows rapid and sensitive detection. On the macroscale, hydrogels are crucial materials for biosensing applications, being used in many wearable or implantable devices as a biocompatible platform. The performance of both hydrogels and nanoparticles, including sensitivity, response time, or reversibility, can be significantly altered and optimized by changing their chemical structures; this has encouraged us to overview and classify chemical design strategies. Here, we have organized this review into two main sections concerning the use of nanoparticles and hydrogels (as polymeric structures) for biosensors and described chemical approaches in relevant subcategories, which act as a guide for general synthetic strategies.

Thermoresponsive Arrays Patterned via Photoclick Chemistry: Smart MALDI Plate for Protein Digest Enrichment, Desalting, and Direct MS Analysis

Sample desalting and concentration are crucial steps before matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) analysis. Current sample pretreatment approaches require tedious fabrication and operation procedures, which are unamenable to high-throughput analysis and also result in sample loss. Here, we report the development of a smart MALDI substrate for on-plate desalting, enrichment, and direct MS analysis of protein digests based on thermoresponsive, hydrophilic/hydrophobic transition of surface-grafted poly(N-isopropylacrylamide) (PNIPAM) microarrays. Superhydrophilic 1-thioglycerol microwells are first constructed on alkyne-silane-functionalized rough indium tin oxide substrates based on two sequential thiol-yne photoclick reactions, whereas the surrounding regions are modified with hydrophobic 1H,1H,2H,2H-perfluorodecanethiol. Surface-initiated atom-transfer radical polymerization is then triggered in microwells to form PNIPAM arrays, which facilitate sample loading and enrichment of protein digests by concentrating large-volume samples into small dots and achieving on-plate desalting through PNIPAM configuration change at elevated temperature. The smart MALDI plate shows high performance for mass spectrometric analysis of cytochrome c and neurotensin in the presence of 1 M urea and 100 mM NaHCO₃, as well as improved detection sensitivity and high sequence coverage for α-casein and cytochrome c digests in femtomole range. The work presents a versatile sample pretreatment platform with great potential for proteomic research.

Super-resolution optical microscopy resolves network morphology of smart colloidal microgels

We present a new method to resolve the network morphology of colloidal particles in an aqueous environment via super-resolution microscopy. The 3D structure of thermoresponsive microgels with different cross-linker content is resolved and compared to established models.

Hydrogel Based Sensors for Biomedical Applications: An Updated Review

Biosensors that detect and convert biological reactions to a measurable signal have gained much attention in recent years. Between 1950 and 2017, more than 150,000 papers have been published addressing the applications of biosensors in different industries, but to the best of our knowledge and through careful screening, critical reviews that describe hydrogel based biosensors for biomedical applications are rare. This review discusses the biomedical application of hydrogel based biosensors, based on a search performed through Web of Science Core, PubMed (NLM), and Science Direct online databases for the years 2000⁻2017. In this review, we consider bioreceptors to be immobilized on hydrogel based biosensors, their advantages and disadvantages, and immobilization techniques. We identify the hydrogels that are most favored for this type of biosensor, as well as the predominant transduction strategies. We explain biomedical applications of hydrogel based biosensors including cell metabolite and pathogen detection, tissue engineering, wound healing, and cancer monitoring, and strategies for small biomolecules such as glucose, lactate, urea, and cholesterol detection are identified.