Graphene@Poly(phenylboronic acid)s Microgels with Selectively Glucose-Responsive Volume Phase Transition Behavior at a Physiological pH

The selective response to glucose is possible by using a poly­(phenylboronic acid) microgel under a rational design. Such a microgel is made of graphene covalently immobilized in a microgel of poly­(4-vinylphenylboronic acid) cross-linked with <i>N</i>,<i>N</i>′-methylenebis­(acrylamide). Unlike the microgels reported in previous arts that would undergo volume phase transition in response to both glucose and other monosaccharides, the proposed microgels shrink upon adding glucose, whereas keep unchanged in the size upon adding other monosaccharides (with fructose, galactose, and mannose as models). Although the polysaccharides/glycoproteins (with dextran and Ribonuclease B as models) that contain many glycosyl residues can slightly absorb on the microgel surface and lead to a small impact on glucose-response, it can be addressed by further coating the microgel as a core with a thin nonglucose-responsive poly­(<i>N</i>-isopropylacrylamide) gel shell. This selectively glucose-responsive volume phase transition behavior enables “turn-on” photoluminescence detection of glucose in blood serum (a model for complex biosystems)

Synthesis and Characterization of Dextran–Tyramine-Based H₂O₂‑Sensitive Microgels

We report a type of polymer microgel that can undergo a rapid and highly sensitive volume change upon adding H₂O₂. Such a H₂O₂-sensitive microgel is made of dextran–tyramine and horseradish peroxidase (HRP), which are interpenetrated in chemically cross-linked gel networks of poly­(oligo­(ethylene glycol) methacrylates). Unlike the H₂O₂-sensitive microgels reported in previous arts that typically involve degradation processes related to H₂O₂-induced cleavability of specific bonds, the proposed microgels can shrink upon adding H₂O₂ owing to the HRP-catalyzed coupling reaction of tyramine residues via decomposition of H₂O₂. While a fast (<10 s) and stable shrinkage of the microgels can be reached upon adding H₂O₂ over a concentration range 50.0 μM–1.0 mM, the response time can be modulated by the dispersion temperature in a nonmonotonous way over 10–38 °C. With the microgels as probes, the H₂O₂ detection limit was approximately 6.8 μM. In a combined use of the microgels with glucose oxidase for glucose detection, the glucose detection limit was approximately 83.1 μM

Large Photocurrent Response and External Quantum Efficiency in Biophotoelectrochemical Cells Incorporating Reaction Center Plus Light Harvesting Complexes

Bacterial photosynthetic reaction centers (RCs) are promising materials for solar energy harvesting, due to their high ratio of photogenerated electrons to absorbed photons and long recombination time of generated charges. In this work, photoactive electrodes were prepared from a bacterial RC-light-harvesting 1 (LH1) core complex, where the RC is encircled by the LH1 antenna, to increase light capture. A simple immobilization method was used to prepare RC-LH1 photoactive layer. Herein, we demonstrate that the combination of pretreatment of the RC-LH1 protein complexes with quinone and the immobilization method results in biophotoelectrochemical cells with a large peak transient photocurrent density and photocurrent response of 7.1 and 3.5 μA cm^–2, respectively. The current study with monochromatic excitation showed maximum external quantum efficiency (EQE) and photocurrent density of 0.21% and 2 μA cm^–2, respectively, with illumination power of ∼6 mW cm^–2 at ∼875 nm, under ambient conditions. This work provides new directions to higher performance biophotoelectrochemical cells as well as possibly other applications of this broadly functional photoactive material

Hybrid Wiring of the Rhodobacter sphaeroides Reaction Center for Applications in Bio-photoelectrochemical Solar Cells

The growing demand for nonfossil fuel-based energy production has drawn attention to the utilization of natural proteins such as photosynthetic reaction center (RC) protein complexes to harvest solar energy. The current study reports on an immobilization method to bind the wild type Rhodobacter sphaeroides RC from the primary donor side onto a Au electrode using an immobilized cytochrome <i>c</i> (cyt <i>c</i>) protein via a docking mechanism. The new structure has been assembled on a Au electrode by layer-by-layer deposition of a carboxylic acid-terminated alkanethiol (HOOC (CH₂)₅S) self-assembled monolayer (SAM), and layers of cyt <i>c</i> and RC. The Au|SAM|cyt <i>c</i>|RC working electrode was applied in a three-probe electrochemical cell where a peak cathodic photocurrent density of 0.5 μA cm^–2 was achieved. Further electrochemical study of the Au|SAM|cyt <i>c</i>|RC structure demonstrated ∼70% RC surface coverage. To understand the limitations in the electron transfer through the linker structure, a detailed energy study of the SAM and cyt <i>c</i> was performed using photochronoamperometry, ellipsometry, photoemission spectroscopy, and cyclic voltammetry (CV). Using a simple rectangle energy barrier model, it was found that the electrode work function and the large barrier of the SAM are accountable for the low conductance in the devised linker structure

Primer specificity and amplicon size.

<p>(A) Agarose gel (2.0%) electrophoresis indicates amplification of a single PCR product of the expected size for 13 genes. (B) Melting curves of 13 genes show single peaks. M represents 100 bp DNA marker.</p

Median cycle threshold (C_T) values for each reference gene for all samples.

<p>The filled diamond symbol indicates median C_T values. The bars indicate standard deviation.</p

Average expression stability values (M₁) of 11 candidate reference genes calculated by geNorm.

<p>(a) drought stress, (b) salt stress, (c) heat stress, (d) waterlogging stress, (e) ABA treatment. Lower M₁ values indicate more stable expression.</p

Expression stability values for perennial ryegrass candidate reference genes calculated using BestKeeper under five treatments.

<p>Note: Expression stability and ranking of 11 candidate reference genes calculated with BestKeeper under drought, salt, heat, waterlogging stresses and ABA treatment. Eleven reference genes are identified as the most stable genes, as evaluated by the lowest values of the coefficient of variance (CV) and standard deviation (SD).</p

Agarose gel results of <i>SOD</i>, <i>POD</i>, <i>elF4A</i>, and <i>60S</i> PCR amplicons in perennial ryegrass leaves exposed to drought stress treatment.

<p>Agarose gel results of <i>SOD</i>, <i>POD</i>, <i>elF4A</i>, and <i>60S</i> PCR amplicons in perennial ryegrass leaves exposed to drought stress treatment.</p

Stability ranking of 11 candidate reference genes.

<p>Stability ranking of 11 candidate reference genes.</p