Oxygen reduction reaction induced pH-responsive chemo-mechanical hydrogel actuators.

We describe and characterize elementary designs for electrochemical micro- and macro-scale chemomechanical hydrogel actuators. The actuation of a pH-sensitive cross-linked polyacrylic acid (PAA) hydrogel is driven in the model devices through the oxygen reduction reaction (ORR) occurring at the electrodes of an embedded Au mesh micro-electrochemical array. Proton consumption by the ORR at the cathode of the embedded electrochemical cell leads to the formation of a localized pH gradient that in turn drives the strain response in the composite actuators. The dynamics result from the ionization of the carboxylic acid moieties of the PAA network in the high pH region, yielding an osmotic pressure that drives a volumetric expansion due to water imbibition. This system actuates both stably and reversibly; when the electrochemically-induced ORR is halted, the localized pH gradient dissipates due to diffusive mixing, which in turn relaxes the induced strains. Two approaches to the fabrication of hydrogel actuators were examined in this work. The first method adopted a design based on small flagella (∼0.2 mm × 1.5 mm × 60 µm, width × length × height) in which the actuating PAA structures are molded atop a set of fixed electrodes mounted on a supporting substrate. These hydrogel actuators show fast, large-amplitude, and largely reversible responses in the ORR mediated chemomechanical dynamics. We also investigated larger hydrogel actuators (∼4.5 mm × 11 mm × 1 mm, width × length × height), based on an autonomous design that embeds an open mesh stretchable micro-electrode array within the hydrogel. The significant and design-dependent impacts of mass transfer on the chemomechanical dynamics are evidenced in each case, a feature examined to elucidate more efficient mesoscopic design rules for actuators of this form.

Electronically programmable, reversible shape change in two- and three-dimensional hydrogel structures.

Combining compliant electrode arrays in open-mesh constructs with hydrogels yields a class of soft actuator, capable of complex, programmable changes in shape. The results include materials strategies, integration approaches, and mechanical/thermal analysis of heater meshes embedded in thermoresponsive poly(N-isopropylacrylamide) (pNIPAM) hydrogels with forms ranging from 2D sheets to 3D hemispherical shells.

Bienzyme functionalized three-layer composite magnetic nanoparticles for electrochemical immunosensors.

The preparation, characterization and application of a three-layer magnetic nanoparticle composed of an Fe(3)O(4) magnetic core, a Prussian Blue (PB) interlayer and a gold shell (it can be abbreviated as Au-PB-Fe(3)O(4)) for an ultrasensitive and reproducible electrochemical immunosensing fabrication were described for the first time in this work. With the employment of the Au-PB-Fe(3)O(4) nanoparticle, a new signal amplification strategy was developed based on bienzyme (horseradish peroxidase and glucose oxidase) functionalized Au-PB-Fe(3)O(4) nanoparticles for an electrochemical immunosensing fabrication by using Carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP) as model systems, respectively. The experiment results show that the multilabeled Au-PB-Fe(3)O(4) nanoparticles exhibit satisfying redox electrochemical activity and high enzyme catalysis activity, which predetermine their utility in high sensitivity antibody detection schemes. Furthermore, this immunosensor could be regenerated by simply using an external magnetic field which ensured a reproducible immunosensor with high sensitivity.

Nanostructured conductive material containing ferrocenyl for reagentless amperometric immunosensors.

This work describes a two-step conjugate synthesis of a porous organometallic nanostructured materials composed of ferrocenemonocarboxylic (Fc-COOH) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and then a reagentless amperometric immunosensor prepared with positively charged gold nanoparticles (PGN) immobilized in this nanostructure conductive film is developed. This nanostructured material containing ferrocenyl (PTC-Fc) could easily form stable film on the electrode surface with efficient redox-activity and excellent conductivity. Furthermore, with the negatively charged surface, this film can be used as an interface to adsorbing the PGN, which was prepared in organic solvents at relatively high concentrations with improved monodispersity compared to those prepared in aqueous solution. The presence of PGN provided a congenial microenvironment for adsorbed biomolecules and decreased the electron-transfer impedance. Thus, with carcinoembryonic antibody (anti-CEA) as a model antibody, the proposed immunosensor showed rapid and highly sensitive amperometric response to carcinoembryonic antigen (CEA) with acceptable preparation reproducibility and stability.