Light-Activated Interface Charge-Alternating Interaction on an Extended Gate Photoelectrode: A New Sensing Strategy for EGFET-Based Photoelectrochemical Sensors.

Integration of extended gate field-effect transistors (EGFET) and photoelectrochemical (PEC) measurement to construct highly sensitive sensors is an innovative research field that was proven feasible by our previous work. However, it remains a challenge on how to adjust the interaction between the extended gate and the analyte and study its influence on EGFET-based PEC sensors. Herein, a new sensing strategy was proposed by a mutual electrostatic interaction. Three-dimensional TiO2 and g-C3N4 core-shell heterojunction on flexible carbon cloth (TCN) was designed as the extended sensing gate. Tetracycline (TC) was also used as a model analyte, and it contains electron-donating groups (-NH2 and -OH) with negative charge. The designed TCN-extended sensing gate was negatively charged in the dark by introducing carbon vacancies with oxygen doping in the g-C3N4 shell, while it was positively charged under illustration due to the aggregation of photogenerated holes on the surface. Therefore, a light-activated PEC sensing platform for the sensitive and selective determination of tetracycline (TC) was demonstrated. Such a PEC sensor exhibited wide linear ranges within 100 pM to 1 µM and 1-100 µM with a low detection limit of 0.42 pM. Furthermore, the sensing platform possessed excellent selectivity, good reproducibility, and stability. The proposed sensing strategy in this work can expand the paradigm for developing a light-regulated FET-based PEC sensor by mutual electrostatic interaction, and we believe that this work will offer a new perspective for the design of interface interaction in PEC devices.

An effective strategy for promoting charge separation by integrating heterojunctions and multiple homojunctions in TiO2 nanorods to enhance photoelectrochemical oxygen evolution.

It is important to achieve high photoelectrochemical (PEC) oxygen evolution performance in titanium oxide (TiO2) via the separation and transportation of photogenerated carriers. Herein, three-dimensional (3D) TiO2 nanorod arrays growing on flexible carbon cloth (CC) were decorated with graphitic carbon nitride (g-C3N4) to yield a 3D g-C3N4/TiO2/CC heterojunction composite (TCN). The photocurrent density of TCN is 10.6 times that of the bare TiO2 nanorod arrays, which can be attributed to the promoted separation and transportation of photogenerated carriers by the heterojunction. Then, a simple rapid cooling and heating (RCH) treatment was creatively introduced to form a gradient Ti3+ self-doping TiO2 multiple homojunction (GTSD-TiO2) in the bulk during the hydrothermal growth of the TiO2 nanorod array. This can further facilitate the separation and transportation of carriers in the bulk owing to the formation of a built-in electric field. The GTSD-TiO2 was decorated with g-C3N4 to form a core-shell heterojunction composite (GTSD-TCN). Notably, the photocurrent density of the GTSD-TCN core-shell heterojunction reached 1.23 mA cm-2 at 1.23 V (vs reversible hydrogen electrode (RHE)) under air mass (AM) 1.5 G illumination without the use of hole scavengers or cocatalysts; this was twice the photocurrent density of the TCN heterojunction (0.64 mA cm-2) and is one of the best values obtained from the previously reported TiO2 and g-C3N4 heterojunction. This performance may be ascribed to the enhanced charge separation and transportation efficiency of the heterojunction after the RCH treatment; the efficiency rises from 51 % (TCN) to 71 % (GTSD-TCN). We believe that the RCH treatment is a highly promising method towards fabricating unique multiple homojunctions by gradient self-doping. This simple and novel design provides a new route for the preparation of high-performance PEC photoelectrodes.

Laser-Induced Graphene-Based Wearable Epidermal Ion-Selective Sensors for Noninvasive Multiplexed Sweat Analysis.

Wearable sweat sensors are a rapidly rising research area owing to their convenience for personal healthcare and disease diagnosis in a real-time and noninvasive manner. However, the fast and scalable fabrication of flexible electrodes remains a major challenge. Here, we develop a wearable epidermal sensor for multiplexed sweat analysis based on the laser-induced graphene (LIG) technique. This simple and mask-free technique allows the direct manufacturing of graphene electrode patterns on commercial polyimide foils. The resulting LIG devices can simultaneously monitor the pH, Na+, and K+ levels in sweat with the sensitivities of 51.5 mV/decade (pH), 45.4 mV/decade (Na+), and 43.3 mV/decade (K+), respectively. Good reproducibility, stability, and selectivity are also observed. On-body testing of the LIG-based sensor integrated with a flexible printed circuit board during stationary cycling demonstrates its capability for real-time sweat analysis. The concentrations of ions can be remotely and wirelessly transmitted to a custom-developed smartphone application during the period in which the sensor user performs physical activities. Owing to the unique advantages of LIG technique, including facile fabrication, mass production, and versatile, more physiological signals (glucose, uric acid, tyrosine, etc.) could be easily expanded into the LIG-based wearable sensors to reflect the health status or clinical needs of individuals.

Photodepositing CdS on the Active Cyano Groups Decorated g-C3 N4 in Z-Scheme Manner Promotes Visible-Light-Driven Hydrogen Evolution.

g-C3 N4 /CdS heterojunctions are potential photocatalysts for hydrogen production but their traditional type-II configuration generally leads to weak oxidative and reductive activity. How to construct the novel Z-scheme g-C3 N4 /CdS counterparts to address this issue remains a great challenge in this field. In this work, a new direct Z-scheme heterojunction of defective g-C3 N4 /CdS is designed by introducing cyano groups (NC-) as the active bridge sites. Experimental observations in combination with density functional theory (DFT) calculations reveal that the unique electron-withdrawing feature of cyano groups in the defective g-C3 N4 /CdS heterostructure can endow this photocatalyst with numerous advantageous properties including high light absorption ability, strong redox performance, satisfactory charge separation efficiency, and long lifetime of charge carriers. Consequently, the resultant photocatalytic system exhibits more active performance than CdS and g-C3 N4 under visible light and reaches an excellent hydrogen evolution rate of 1809.07 µmol h-1 g-1 , which is 6.09 times higher than pristine g-C3 N4 . Moreover, the defective g-C3 N4 /CdS photocatalyst maintains good stability after 40 h continuous test. This work provides new insights into design and construction of Z-scheme heterojunctions for regulating the visible-light-induced photocatalytic activity for H2 evolution.

Functional Sensing Interfaces of PEDOT:PSS Organic Electrochemical Transistors for Chemical and Biological Sensors: A Mini Review.

Organic electrochemical transistors (OECTs) are promising devices for applications in in vitro and in vivo measurements. OECTs have two important sensing interfaces for signal monitoring: One is the gate electrode surface; the other is the channel surface. This mini review introduced the new developments in chemical and biological detection of the two sensing interfaces. Specific focus was given on the modification technological approaches of the gate or channel surface. In particular, some unique strategies and surface designs aiming to facilitate signal-transduction and amplification were discussed. Several perspectives and current challenges of OECTs development were also briefly summarized.