Graphitic Carbon Nitride Sensitized with CdS Quantum Dots for Visible-Light-Driven Photoelectrochemical Aptasensing of Tetracycline

Graphitic carbon nitride (g-C₃N₄) is a new type of metal-free semiconducting material with promising applications in photocatalytic and photoelectrochemical (PEC) devices. In the present work, g-C₃N₄ coupled with CdS quantum dots (QDs) was synthesized and served as highly efficient photoactive species in a PEC sensor. The surface morphological analysis showed that CdS QDs with a size of ca. 4 nm were grafted on the surface of g-C₃N₄ with closely contacted interfaces. The UV–visible diffuse reflection spectra (DRS) indicated that the absorption of g-C₃N₄ in the visible region was enhanced by CdS QDs. As a result, g-C₃N₄–CdS nanocomposites demonstrated higher PEC activity as compared with either pristine g-C₃N₄ or CdS QDs. When g-C₃N₄–CdS nanocomposites were utilized as transducer and tetracycline (TET)-binding aptamer was immobilized as biorecognition element, a visible light-driven PEC aptasensing platform for TET determination was readily fabricated. The sensor showed a linear PEC response to TET in the concentration range from 10 to 250 nM with a detection limit (3S/N) of 5.3 nM. Thus, g-C₃N₄ sensitized with CdS QDs was successfully demonstrated as useful photoactive nanomaterials for developing a highly sensitive and selective PEC aptasensor

A Cathodic “Signal-off” Photoelectrochemical Aptasensor for Ultrasensitive and Selective Detection of Oxytetracycline

A novel cathodic “signal-off” strategy was proposed for photoelectrochemical (PEC) aptasensing of oxytetracycline (OTC). The PEC sensor was constructed by employing a p-type semiconductor BiOI doped with graphene (G) as photoactive species and OTC-binding aptamer as a recognition element. The morphological structure and crystalline phases of obtained BiOI-G nanocomposites were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The UV–visible absorption spectroscopic analysis indicated that doping of BiOI with graphene improved the absorption of materials in the visible light region. Moreover, graphene could facilitate the electron transfer of BiOI modified electrode. As a result, the cathodic photocurrent response of BiOI under visible light irradiation was significantly promoted when a suitable amount of graphene was doped. When amine-functionalized OTC-binding aptamer was immobilized on the BiOI-G modified electrode, a cathodic PEC aptasensor was fabricated, which exhibited a declined photocurrent response to OTC. Under the optimized conditions, the photocurrent response of aptamer/BiOI-G/FTO was linearly proportional to the concentration of OTC ranging from 4.0 to 150 nM, with a detection limit (3<i>S</i>/<i>N</i>) of 0.9 nM. This novel PEC sensing strategy demonstrated an ultrasensitive method for OTC detection with high selectivity and good stability

Highly Selective Self-Powered Sensing Platform for <i>p</i>‑Nitrophenol Detection Constructed with a Photocathode-Based Photocatalytic Fuel Cell

A photocathode-based photocatalytic fuel cell (PFC) was fabricated and proposed as a self-powered sensor for <i>p</i>-nitrophenol (<i>p</i>-NP) detection. The PFC was comprised of a photocathode and an anode in separated chambers, which could generate suitable power output under photoirradiation to drive the sensing process. In this device, p-type PbS quantum dots-modified glass carbon electrode (GCE) served as the photocathode for the reduction of <i>p</i>-NP under photoirradiation while graphene-modified GCE was employed as the anode for the oxidation of ascorbic acid. In order to improve the selectivity of the PFC sensor, <i>p</i>-NP binding molecularly imprinted polymer (MIP) was introduced on the photocathode. Under optimal conditions, the open circuit voltage of the constructed PFC sensor was found to sensitively respond to <i>p</i>-NP in a wide concentration range from 0.05 μM to 20 μM. The proposed sensor exhibited high selectivity, good reproducibility, and stability, demonstrating the successful combination of MIP with photocathode in construction of high-performance PFC self-powered sensors for pollutant monitoring

One-Step Synthesis of CuO–Cu₂O Heterojunction by Flame Spray Pyrolysis for Cathodic Photoelectrochemical Sensing of l‑Cysteine

CuO–Cu₂O heterojunction was synthesized via a one-step flame spray pyrolysis (FSP) process and employed as photoactive material in construction of a photoelectrochemical (PEC) sensing device. The surface analysis showed that CuO–Cu₂O nanocomposites in the size less than 10 nm were formed and uniformly distributed on the electrode surface. Under visible light irradiation, the CuO–Cu₂O-coated electrode exhibited admirable cathodic photocurrent response, owing to the favorable property of the CuO–Cu₂O heterojunction such as strong absorption in the visible region and effective separation of photogenerated electron–hole pairs. On the basis of the interaction of l-cysteine (l-Cys) with Cu-containing compounds via the formation of Cu–S bond, the CuO–Cu₂O was proposed as a PEC sensor for l-Cys detection. A declined photocurrent response of CuO–Cu₂O to addition of l-Cys was observed. Influence factors including CuO–Cu₂O concentration, coating amount of CuO–Cu₂O, and applied bias potential on the PEC response toward l-Cys were optimized. Under optimum conditions, the photocurrent of the proposed sensor was linearly declined with increasing the concentration of l-Cys from 0.2 to 10 μM, with a detection limit (3S/N) of 0.05 μM. Moreover, this PEC sensor displayed high selectivity, reproducibility, and stability. The potential applicability of the proposed PEC sensor was assessed in human urine samples

Visible-Light Induced Self-Powered Sensing Platform Based on a Photofuel Cell

A self-powered sensing system possesses the capacity of harvesting energy from the environment and has no requirement for external electrical power supply during the chemical sensing of analytes. Herein, we design an enzyme-free self-powered sensing platform based on a photofuel cell (PFC) driven by visible-light, using glucose as a model analyte. The fabricated PFC consists of a Ni­(OH)₂/CdS/TiO₂ photoanode and a hemin-graphene (HG) nanocomposite coated cathode in separated chambers. Under visible-light irradiation, glucose in the anodic chamber is facilely oxidized on Ni­(OH)₂/CdS/TiO₂ while H₂O₂ in the cathodic chamber is catalytically reduced by HG, which generates a certain cell output sensitive to the variation of glucose concentration. Thus, a PFC based self-powered sensor is realized for glucose detection. Compared to the existing enzymatic self-powered glucose sensors, our proposed PFC based strategy exhibits much lower detection concentration. Moreover, it avoids the limitation of conventional enzyme immobilized electrodes and has the potential to develop high-performance self-powered sensors with broader analyte species

High Elastic Strain Directly Tunes the Hydrogen Evolution Reaction on Tungsten Carbide

Elastic strain provides a direct means to tune a material’s electronic structure from both computational and experimental vantage points and can thus provide insights into surface reactivity via changes induced by electronic structure shifts. Here we investigate the role of elastic strain on the catalytic activity of tungsten carbide (WC) in the hydrogen evolution reaction. WC makes an interesting material for such investigations as it is an inherently promising catalyst that can sustain larger elastic strains (e.g., −1.4 to 1.4%) than common transition-metal catalysts, such as Pt or Ni (e.g., −0.4 to 0.4%). On the basis of density functional theory calculations, a compressive uniaxial strain is expected to cause weakening of the surface–hydrogen interaction of 10–15 meV per percent strain, while a tensile strain is calculated to strengthen the surface–hydrogen interaction by a similar magnitude. Sabatier analysis suggests that weakening of the surface-hydrogen interaction would enhance catalysis. We prepared 20 nm thin films of WC supported on thick polymer substrates and mechanically subjected them to uniaxial tensile and compressive loading, while the films catalyze hydrogen evolution in an electrochemical cell. We report a systematic shift in the hydrogen evolution sweeps of cyclic voltammetry measurements: Compressive strain increases the activity, and tensile strain has the opposite effect. The magnitude of the shift was measured to be 10–20 mV per 1% strain, which agrees well with the computations and corresponds to 5–10% of the difference in the overpotentials of WC and Pt. These results were further substantiated through chronoamperometry measurements and highlight how strain can be used to systematically improve catalytic activity

Scalable and Multifunctional Polyurethane/MXene/Carbon Nanotube-Based Fabric Sensor toward Baby Healthcare

Continuous monitoring of physiological health status and effective protection against external hazards is an indispensable aspect of healthcare management for critically vulnerable populations, particularly for infants or babies. So, the exploration of all-in-one devices remains critical to avoiding their injury and illness. The integration of multiple properties such as sensing, electromagnetic protection, warming/cooling, and water/bacterial repellence into a common fabric is no doubt a promising solution to coping with diverse application scenarios. However, achieving simultaneous integration in an effective and durable fashion faces huge challenges. Herein, multifunctional fabric was achieved by sequentially coating MXene, carbon nanotubes (CNTs), and self-healing polyurethane (PU) onto cotton fabric. The outstanding conductivity of MXene and CNTs as well as the self-healing ability of PU synergistically enable a flexible, breathable, protective, and sensing fabric with a good durability. It could detect the body motions like bending of the finger, elbow, wrist, and knee, with a high gauge factor of 8.78 and fast response. Moreover, this sensing fabric could protect the wearers against electromagnetic waves and bacteria, delivering a minimum reflection loss of −57.6 dB at 7.6 GHz and high bacterial inhibition efficiency due to the incorporation of MXene and polyethylenimine. Besides, the electrothermal performance of carbonaceous materials enables them to act as a heater for body warmth. The synergistic design of this multifunctional textile offers a promising strategy for producing advanced smart textiles, holding great promise in infant or baby healthcare

Plasmon-Enhanced Photothermoelectric Conversion in Chemical Vapor Deposited Graphene p–n Junctions

Graphene p–n junctions grown by chemical vapor deposition hold great promise for the applications in high-speed, broadband photodetectors and energy conversion devices, where efficient photoelectric conversion can be realized by a hot-carrier-assisted photothermoelectric (PTE) effect and hot-carrier multiplication. However, the overall quantum efficiency is restricted by the low light absorption of single-layer graphene. Here, we present the first experimental demonstration of a plasmon-enhanced PTE conversion in chemical vapor deposited graphene p–n junctions. Surface plasmons of metallic nanostructures placed near the graphene p–n junctions were found to significantly enhance the optical field in the active layer and allow for a 4-fold increase in the photocurrent. Moreover, the utilization of localized plasmon enhancement facilitates the realization of efficient PTE conversion of graphene p–n junction devices under global illumination, which may offer an avenue for practical applications of graphene-based photodetectors and solar cells

Sulfur Cathodes with Hydrogen Reduced Titanium Dioxide Inverse Opal Structure

Sulfur is a cathode material for lithium-ion batteries with a high specific capacity of 1675 mAh/g. The rapid capacity fading, however, presents a significant challenge for the practical application of sulfur cathodes. Two major approaches that have been developed to improve the sulfur cathode performance include (a) fabricating nanostructured conductive matrix to physically encapsulate sulfur and (b) engineering chemical modification to enhance binding with polysulfides and, thus, to reduce their dissolution. Here, we report a three-dimensional (3D) electrode structure to achieve both sulfur physical encapsulation and polysulfides binding simultaneously. The electrode is based on hydrogen reduced TiO₂ with an inverse opal structure that is highly conductive and robust toward electrochemical cycling. The relatively enclosed 3D structure provides an ideal architecture for sulfur and polysulfides confinement. The openings at the top surface allow sulfur infusion into the inverse opal structure. In addition, chemical tuning of the TiO₂ composition through hydrogen reduction was shown to enhance the specific capacity and cyclability of the cathode. With such TiO₂ encapsulated sulfur structure, the sulfur cathode could deliver a high specific capacity of ∼1100 mAh/g in the beginning, with a reversible capacity of ∼890 mAh/g after 200 cycles of charge/discharge at a <i>C</i>/5 rate. The Coulombic efficiency was also maintained at around 99.5% during cycling. The results showed that inverse opal structure of hydrogen reduced TiO₂ represents an effective strategy in improving lithium sulfur batteries performance

Bronchosphere formation by sorted cells.

<p>A) Phase-contrast photomicrographs of bronchospheres (Bar = 100 µm). B) The diameter of all spheroid colonies in the wells which 5000 cells were seeded. Bar graph reveals average spheroid colony size (µm). (Mean ±S.D. p = 0.0048, Student t-test). C) Average spheroid colony number per well in serial diluted cells after one week sphere cell culture. D) Efficiency of sphere colony formation = total colony number/total seeded cell ×1000. Efficiency of sphere colony formation was higher in CCSP⁻ cells than that in CCSP⁺ cells (p<0.0001, Chi-square test).</p