Construction of Three-Dimensional Hemin-Functionalized Graphene Hydrogel with High Mechanical Stability and Adsorption Capacity for Enhancing Photodegradation of Methylene Blue

A three-dimensional hemin-functionalized graphene hydrogel (Hem/GH) was prepared by a facile self-assembly approach. The as-prepared Hem/GH showed good mechanical strength with a storage modulus of 609–642 kPa and a high adsorption capacity to organic dye contaminants (341 mg g^–1 for rhodamine B). Moreover, Hem/GH could be used as a photosensitizer for the photocatalytic degradation of organic dyes and displayed superior photodegradation activity of methylene blue (MB). This result was better than that of counterparts such as graphene hydrogel (GH) and commercial catalyst P25. The excellent cycling performance of the Hem/GH was well maintained even after multiple cycles on adsorption process and photocatalytic reaction. Interestingly, after the photodegradation of MB, a light-induced pH change of the solution from alkaline pH 8.99 to acidic pH 3.82 was observed, and 10 wt % total organic carbon remained. The liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS) analysis confirmed the generation of acidic degradation products. The photocatalytic mechanism was further investigated by trapping experiments, which revealed that the MB degradation was driven mainly by the participation of O₂^•– radicals in the photocatalytic reaction. As an extended application, visually intuitive observation showed the as-prepared Hem/GH also had strong antibacterial properties. These results suggest that Hem/GH could be potentially used for practical application due to its high adsorption ability, excellent photocatalytic activity, and strong antibacterial properties

Application of Spectral Crosstalk Correction for Improving Multiplexed MicroRNA Detection Using a Single Excitation Wavelength

MicroRNAs (miRNAs) play crucial roles in the regulation of cellular activities and are next-generation biomarkers for early cancer detection. Simultaneous monitoring of multiplexed miRNA is very important for enhancing the accuracy of cancer diagnostics. Traditional fluorescence methods for multicomponent analysis were usually operated under multiple excitation wavelengths, because spectral crosstalk is very detrimental to detecting accuracy for multicomponent analysis. Herein, we present a fluorescence strategy for multi-miRNAs detection in plasma under a single excitation wavelength. Nucleic acid stain TOTO-1 and three labeled fluorescence dyes Cy3, Cy3.5, and Cy5 emit no fluorescence in their free state. Target miRNA hybridized the auxiliary and probe oligonucleotides into duplex nucleic acid. Intercalation interaction localized TOTO-1 and labeled dyes into the duplex nucleic acid. As a result, TOTO-1 emitted strong fluorescence and efficient Förster resonance energy transfer (FRET) happened. MicroRNAs miRNA-155, miRNA-182, and miRNA-197, which are significant for the early diagnosis of lung cancer, were simultaneously detected as models. Deviations from spectral crosstalk in the presence of other miRNAs were corrected by mathematical methods. Results demonstrated that, after spectra crosstalk corrections, every miRNA at high or low concentration in plasma was determined accurately in the presence of either high or low concentrations of the other two miRNAs. This new multiplexed assay for miRNAs is promising for clinical diagnosis, prognosis, and therapeutic monitoring of early-stage lung cancer

Visual, Label-Free Telomerase Activity Monitor via Enzymatic Etching of Gold Nanorods

Early diagnosis and life-long surveillance are clinically important to improve the long-term survival of cancer patients. Telomerase activity is a valuable biomarker for cancer diagnosis, but its measurement often used complex label procedures. Herein, we designed a novel, simple, visual and label-free method for telomerase detection by using enzymatic etching of gold nanorods (GNRs). First, repeating (TTAGGG)_<i>x</i> sequences were extented on telomerase substrate (TS) primer. It formed G-quadruplex under the help of Hemin and K⁺. Second, the obtained horseradish peroxidase mimicking hemin/G-quadruplex catalyzed the H₂O₂-mediated etching of GNRs to the short GNRs, even to gold nanoparticles (GNPs), generating a series of distinct color changes due to their plasmon-related optical response. Thus, this enzymatic reaction can be easily coupled to telomerase activity, allowing for the detection of telomerase activity based on vivid colors. This can be differentiated sensitively by naked eyes because human eyes are more sensitive to color variations rather than the optical density variations. As a result, telomerase activity can be quantitatively detected ranging from 200 to 15000 HeLa cells mL^–1. The detection limit was 90 HeLa cells mL^–1 (<i>S</i>/<i>N</i> = 3). Importantly, the application of this method in bladder cancer samples was in agreement with the clinical results. Thus, this method was considerably suitable for point-of-care diagnostics in resource-constrained regions because of the easy readout of results without the use of sophisticated apparatus

Reversible Assembly of Graphitic Carbon Nitride 3D Network for Highly Selective Dyes Absorption and Regeneration

Responsive assembly of 2D materials is of great interest for a range of applications. In this work, interfacial functionalized carbon nitride (CN) nanofibers were synthesized by hydrolyzing bulk CN in sodium hydroxide solution. The reversible assemble and disassemble behavior of the as-prepared CN nanofibers was investigated by using CO₂ as a trigger to form a hydrogel network at first. Compared to the most widespread absorbent materials such as active carbon, graphene and previously reported supramolecular gel, the proposed CN hydrogel not only exhibited a competitive absorbing capacity (maximum absorbing capacity of methylene blue up to 402 mg/g) but also overcame the typical deficiencies such as poor selectivity and high energy-consuming regeneration. This work would provide a strategy to construct a 3D CN network and open an avenue for developing smart assembly for potential applications ranging from environment to selective extraction

Three-Dimensional Macroporous Polypyrrole-Derived Graphene Electrode Prepared by the Hydrogen Bubble Dynamic Template for Supercapacitors and Metal-Free Catalysts

We report a general method for the fabrication of three-dimensional (3D) macroporous graphene/conducting polymer modified electrode and nitrogen-doped graphene modified electrode. This method involves three consecutive steps. First, the 3D macroporous graphene (3D MG) electrode was fabricated electrochemically by reducing graphene oxide dispersion on different conducting substrates and used hydrogen bubbles as the dynamic template. The morphology and pore size of 3D MG could be governed by the use of surfactants and the dynamics of bubble generation and departure. Second, 3D macroporous graphene/polypyrrole (MGPPy) composites were constructed via directly electropolymerizing pyrrole monomer onto the networks of 3D MG. Due to the benefit of the good conductivity of 3D MG and pseudocapacitance of PPy, the composites manifest outstanding area specific capacitance of 196 mF cm^–2 at a current density of 1 mA cm^–2. The symmetric supercapacitor device assembled by the composite materials had a good capacity property. Finally, the nitrogen-doped MGPPy (N-MGPPy or MGPPy-X) with 3D macroporous nanostructure and well-regulated nitrogen doping was prepared via thermal treatment of the composites. The resultant N-MGPPy electrode was explored as a good electrocatalyst for the oxygen reduction reaction (ORR) with the current density value of 5.56 mA cm^–2 (−0.132 V vs Ag/AgCl). Moreover, the fuel tolerance and durability under the electrochemical environment of the N-MGPPy catalyst were found to be superior to the Pt/C catalyst

Boosting Gas Involved Reactions at Nanochannel Reactor with Joint Gas–Solid–Liquid Interfaces and Controlled Wettability

The low solubility of gases in aqueous solution is the major kinetic limitation of reactions that involve gases. To address this challenge, we report a nanochannel reactor with joint gas–solid–liquid interfaces and controlled wettability. As a proof of concept, a porous anodic alumina (PAA) nanochannel membrane with different wettability is used for glucose oxidase (GOx) immobilization, which contacts with glucose aqueous solution on one side, while the other side gets in touch with the gas phase directly. Interestingly, it is observed that the O₂ could participate in the enzymatic reaction directly from gas phase through the proposed nanochannels, and a hydrophobic interface is more favorable for the enzymatic reaction due to the rearrangement of GOx structure as well as the high gas adhesion. As a result, the catalytic efficiency of GOx in the proposed interface is increased up to 80-fold compared with that of the free state in traditional aqueous air-saturated electrolyte. This triphase interface with controlled wettability can be generally applied to immobilize enzymes or catalysts with gas substrates for high efficiency