Ion migration and dark current suppression in quasi-2D perovskite-based X-ray detectors.

Cesium-based lead-free double perovskite materials (Cs2AgBiBr6) have garnered significant attention in the X-ray detection field due to their environment friendly characteristics. However, their substantial ion migration properties lead to large dark currents and detection limits in Cs2AgBiBr6-based X-ray detectors, restricting the detection performance of the device. In terms of process technology, ultrasonic spraying is more suitable than a spin-coating method for fabricating large-area, micron-scale perovskite thick films, with higher cost-effectiveness, which is crucial for X-ray detection. This work introduces a BA+ (BA+ = CH3CH2CH2CH2NH3 +, n-butyl) source into the precursor solution and employs ultrasonic spraying to fabricate quasi-two-dimensional structured polycrystalline (BA)2Cs9Ag5Bi5Br31 perovskite thick films, developing a low-cost, eco-friendly X-ray detector with low dark current density and low detection limit. Characterization results reveal that the ion migration activation energy of (BA)2Cs9Ag5Bi5Br31 reaches 419 meV, approximately 17% higher than that of traditional three-dimensional perovskites, effectively suppressing perovskite ion migration and subsequently reducing the dark current. The (BA)2Cs9Ag5Bi5Br31-based X-ray detectors exhibit high resistivity (about 1.75 × 1010 Ω cm), low dark current density (66 nA cm-2), minimal dark current drift (0.016 pA cm-1 s-1 V-1), and detection limit (138 nGyair s-1), holding considerable promise for applications in low-noise, low-dose X-ray detection.

Enantioselective formal total synthesis of dihydrospirotryprostatin B.

Spirotryprostatins are representative members of medicinally interesting bioactive molecules of the spirooxindole natural products. In this communication, we present a novel enantioselective total synthesis of the spirooxindole alkaloid dihydrospirotryprostatin B. The synthesis takes advantage of copper-catalyzed tandem reaction of o-iodoanilide chiral sulfinamide derivatives with alkynone to rapidly construct the key quaternary carbon stereocenter of the natural product dihydrospirotryprostatin B.

A Phase Field Approach to Two-Dimensional Quasicrystals with Mixed Mode Cracks.

Quasicrystals (QCs) are representatives of a novel kind of material exhibiting a large number of remarkable specific properties. However, QCs are usually brittle, and crack propagation inevitably occurs in such materials. Therefore, it is of great significance to study the crack growth behaviors in QCs. In this work, the crack propagation of two-dimensional (2D) decagonal QCs is investigated by a fracture phase field method. In this method, a phase field variable is introduced to evaluate the damage of QCs near the crack. Thus, the crack topology is described by the phase field variable and its gradient. In this manner, it is unnecessary to track the crack tip, and therefore remeshing is avoided during the crack propagation. In the numerical examples, the crack propagation paths of 2D QCs are simulated by the proposed method, and the effects of the phason field on the crack growth behaviors of QCs are studied in detail. Furthermore, the interaction of the double cracks in QCs is also discussed.

Silicon-Based 3D All-Solid-State Micro-Supercapacitor with Superior Performance.

The large-scale fabrication of high-performance on-chip micro-supercapacitors (MSCs) is the footstone for the development of next-generation miniaturized electronic devices. In practical applications, however, MSCs may suffer from a low areal energy density as well as a complicated fabrication strategy that is incompatible with semiconductor processing technology. Herein, we propose a scalable fabrication strategy for the realization of a silicon-based three-dimensional (3D) all-solid-state MSC via the combination of semiconductor-based electrode processing, chemical vapor deposition, and hydrothermal growth. The individual Si/C/MnO2 electrode shows a maximum specific capacitance of 223.74 mF cm-2, while the symmetric electrodes present a maximum areal energy density of 5.01 µWh cm-2 at the scan rate of 1 mV s-1. The full 3D Si/C/MnO2 MSC delivers a high energy density of 2.62 µWh cm-2, at a power density of 117.82 µW cm-2, as well as a long cycle life with capacitance retention >92% after 4000 cycles. Our proposed method enables the fabrication of 3D MSCs based on a thick silicon interdigitated electrode array, holding a great promise for the development of 3D on-chip microscale energy storage devices.

Combined metal/air fuel cell and electrocoagulation process: Energy generation, flocs production and pollutant removal.

Electrocoagulation (EC) which is characterized by in-situ generation of highly absorbable hydroxide flocs, is an environmentally friendly process for treating heavy metal ions and toxic organic wastewater. In order to decrease EC's energy consumption, a combined metal/air FC-EC process which contains two successive parts: metal/air fuel cell (FC) and electrocoagulation (EC) was studied with the consideration of hydroxide flocs production, pollutant removal and energy generation analysis. For the combined iron/air FC-EC process, the porous nickel cathode which has a good performance in high polarization zone was selected as the ideal air cathode. It was found that iron/air FC-EC with acid electrolyte condition has a high energy generation (as high as 20% EC energy consumption). The energy generation increases with iron/air FC time. Also energy generation increases with wastewater's conductivity. Beside the energy generation, the iron/air fuel cell generate extra coagulants Fe2+ for the subsequent EC process. The coagulants generated from iron/air FC and EC process together have further spontaneous hydrolysis reactions with the OH- to form hydroxide flocs, which are beneficial for a rapid adsorption and pollutant trapping. Compared with EC process, iron/air (or Al/air) FC-EC process shows lower energy consumption and high removal efficiency for treating acid wastewater.

A FRET-based ratiometric fluorescent aptasensor for rapid and onsite visual detection of ochratoxin A.

A color change observable by the naked eye to indicate the content of an analyte is considered to be the most conceivable way of various sensing protocols. By taking advantage of the Förster resonance energy transfer (FRET) principles, we herein designed a dual-emission ratiometric fluorescent aptasensor for ochratoxin A (OTA) detection via a dual mode of fluorescent sensing and onsite visual screening. Amino group-modified OTA's aptamer was firstly labeled with the green-emitting CdTe quantum dots (gQDs) donor. The red-emitting CdTe QDs (rQDs) which were wrapped in the silica sphere could serve as the reference signal, while the gold nanoparticle (AuNP) acceptors were attached on the silica surface to bind with the thiolated complementary DNA (cDNA). The hybridization reaction between the aptamer and the cDNA brought gQD-AuNP pair close enough, thereby making the FRET occur in the aptasensor fabrication, while the subsequent fluorescence recovery induced by OTA was obtained in the detection procedure. Based on the red background of the wrapped rQDs, the aptasensor in response to increasing OTA displayed a distinguishable color change from red to yellow-green, which could be conveniently readout in solution even by the naked eye. Since the bioconjugations used as the aptasensor can be produced at large scale, this method can be used for in situ, rapid, or high-throughput OTA detection after only an incubation step in a homogeneous mode. We believe that this novel aptasensing strategy provides not only a promising method for OTA detection but also a universal model for detecting diverse targets by changing the corresponding aptamer.

Preparation of graphene quantum dots based core-satellite hybrid spheres and their use as the ratiometric fluorescence probe for visual determination of mercury(II) ions.

We herein proposed a simple and effective strategy for preparing graphene quantum dots (GQDs)-based core-satellite hybrid spheres and further explored the feasibility of using such spheres as the ratiometric fluorescence probe for the visual determination of Hg(2+). The red-emitting CdTe QDs were firstly entrapped in the silica nanosphere to reduce their toxicity and improve their photo and chemical stabilities, thus providing a built-in correction for environmental effects, while the GQDs possessing good biocompatibility and low toxicity were electrostatic self-assembly on the silica surface acting as reaction sites. Upon exposure to the increasing contents of Hg(2+), the blue fluorescence of GQDs can be gradually quenched presumably due to facilitating nonradiative electron/hole recombination annihilation. With the embedded CdTe QDs as the internal standard, the variations of the tested solution display continuous fluorescence color changes from blue to red, which can be easily observed by the naked eye without any sophisticated instrumentations and specially equipped laboratories. This sensor exhibits high sensitivity and selectivity toward Hg(2+) in a broad linear range of 10 nM-22 µM with a low detection limit of 3.3 nM (S/N = 3), much lower than the allowable Hg(2+) contents in drinking water set by U.S. Environmental Protection Agency. This prototype ratiometric probe is of good simplicity, low toxicity, excellent stabilities, and thus potentially attractive for Hg(2+) quantification related biological systems.

Multiwalled carbon nanotube@reduced graphene oxide nanoribbon heterostructure: synthesis, intrinsic peroxidase-like catalytic activity, and its application in colorimetric biosensing.

In this study, multiwalled carbon nanotube@reduced graphene oxide nanoribbon (MWCNT@rGONR) core-shell heterostructures have been synthesized by the facile unzipping of MWCNTs and subsequent chemical reduction with hydrazine. MWCNTs with diameter <10 nm were selected as the starting material to maintain narrow ribbons <30 nm wide with a few-layer structure. The most important discovery is that the resulting MWCNT@rGONR heterostructures possess intrinsic peroxidase-like activity, 15.9 times higher than that of MWCNTs and 8.4 times higher than that of their unreduced form. The nature of the peroxidase-like activity of the MWCNT@rGONR heterostructures can be attributed to the acceleration of their electron-transfer process and the consequent facilitation of ˙OH radical generation. Kinetic analysis demonstrates that the catalytic behavior is in accordance with typical Michaelis-Menten kinetics and the obtained kinetic parameters indicate that the MWCNT@rGONR heterostructures display a higher affinity for both H2O2 and 3,3,5,5-tetramethylbenzidine than that of horseradish peroxidase. On this basis, we have employed the MWCNT@rGONR heterostructures as novel biosensing platforms to develop a simple, sensitive, and selective colorimetric biosensor for free cholesterol determination. This work will facilitate the formation of MWCNT@rGONR heterostructures with narrow ribbons and the utilization of their intrinsic peroxidase-like activity in biotechnology and medical diagnostics.

A facile label-free colorimetric aptasensor for acetamiprid based on the peroxidase-like activity of hemin-functionalized reduced graphene oxide.

A facile aptasensor has been developed for the colorimetric detection of acetamiprid by using the hemin-functionalized reduced graphene oxide (hemin-rGO) composites. The as-prepared hemin-rGO composites possessed both the ability of rGO to physically adsorb the aptamers and the peroxidase-like activity of hemin that could catalyse 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, to produce a solution with blue color. The well-dispersed hemin-rGO composites coagulated completely at the proper salt concentration; however, the coagulation of hemin-rGO was vanished when abundant aptamers were adsorbed on its surface because the attached negatively charged DNA backbone increased individual hemin-rGO electrostatic repulsion. In the detection scheme, acetamiprid with different concentrations was firstly incubated with the same amount of aptamer. The more acetamiprid in the tested solution, the less free aptamers were absorbed on the hemin-rGO surface, making the composites coagulate to a higher degree in the presence of the optimum NaCl concentration. As a consequence, the content of hemin-rGO in the supernatant was decreased after centrifugation, which catalysed oxidation of TMB in the presence of H2O2 to produce light blue color with a low absorbance. The color variation relavant to the acetamiprid concentration can be judged by the naked eyes and easily monitored by the inexpensive UV-vis spectrometer. Such designed aptasensor displayed a linear response for acetamiprid in the range from 100nM to 10µM with a detection limit of 40nM (S/N=3). This colorimetric aptasensing platform offers great advantages including the simple operation process, low-cost portable instrument, and user-friendly applications.

Enhanced non-enzymatic glucose sensing based on copper nanoparticles decorated nitrogen-doped graphene.

Copper nanoparticles (NPs) decorated nitrogen-doped graphene (Cu-N-G) was prepared by a facile thermal treatment, and further employed as a novel sensing material for fabricating the sensitive non-enzymatic glucose sensor. Compared with pure Cu NPs, the Cu-N-G showed enhanced electrocatalytic activity to glucose oxidation due to the integration of N-G, which exhibited the oxidation peak current of glucose ca. 23-fold higher than that of pure Cu NPs. The presented sensor showed excellent performances for glucose detection including wide linear range of 0.004-4.5 mM, low detection limit (1.3 µM, S/N=3), high sensitivity (48.13 µA mM(-1)), fast response time (<5 s), good selectivity to the general coexisted interferences, etc. Such properties would promote the potential application of the nitrogen-doped graphene as enhanced materials in fabricating sensors for chemical and biochemical analysis.