Single-atom Ni-N_(4) for enhanced electrochemical sensing

Single-atom catalysts(SACs)attract widespread attention in heterogeneous catalysis due to their maximum atomic utilization efficiency and unique physical and chemical properties.However,their applications in chemical sensing keep huge potential but remain unclear.Herein,a Ni-N_(4)-C SAC was synthesized for the trace detection of dopamine(DA)and uric acid(UA).The Ni-N_(4)-C SAC exhibited superior sensing performance compared to the Ni clusters.The detection range for DA and UA were 0.05–75μM and 5–90μM with detection limits of 0.027 and 0.82μM,respectively.Density functional theory(DFT)computations indicate that Ni-N_(4)-C has a lower reaction barrier during electrochemical process,indicating that the atomic Ni sites possess higher intrinsic activity than Ni clusters.Moreover,DA and UA show strong potential dependency on the Ni-N_(4)-C catalyst,indicating its applicability for their concurrent detection.This work extends the application of SACs in chemical sensing.

Black phosphorus-based field effect transistor devices for Ag ions detection

Black phosphorus （BP）, an attractive two-dimensional （2D） semiconductor, is widely used in the fields of optoelec- tronic devices, biomedicine, and chemical sensing. Silver ion （Ag＋）, a commonly used additive in food industry, can sterilize and keep food fresh. But excessive intake of Ag＋ will harm human health. Therefore, high sensitive, fast and simple Ag＋ detection method is significant. Here, a high-performance BP field effect transistor （FET） sensor is fabricated for Ag＋ detection with high sensitivity, rapid detection speed, and wide detection concentration range. The detection limit for Ag＋ is 10 l0 mol/L. Testing time for each sample by this method is 60 s. Besides, the mechanism of BP-FET sensor for Ag＋ detection is investigated systematically. The simple BP-FET sensor may inspire some relevant research and potential applications, such as providing an effective method for the actual detection of Ag＋, especially in wimessed inspections field of food.

Flexible organic electrochemical transistors for chemical and biological sensing

Chemical and biological sensing play important roles in healthcare,environmental science,food-safety tests,and medical applications.Flexible organic electrochemical transistors(OECTs)have shown great promise in the field of chemical and biological sensing,owing to their superior sensitivity,high biocompatibility,low cost,and light weight.Herein,we summarize recent progress in the fabrication of flexible OECTs and their applications in chemical and biological sensing.We start with a brief introduction to the working principle,configuration,and sensing mechanism of the flexible OECT-based sensors.Then,we focus on the fabrication of flexible OECT-based sensors,including material selection and structural engineering of the components in OECTs:the substrate,electrodes,electrolyte,and channel.Particularly,the gate modification is discussed extensively.Then,the applications of OECT-based sensors in chemical and biological sensing are reviewed in detail.Especially,the array-based and integrated OECT sensors are also introduced.Finally,we present the conclusions and remaining challenges in the field of flexible OECT-based sensing.Our timely review will deepen the understanding of the flexible OECT-based sensors and promote the further development of the fast-growing field of flexible sensing.

Nuclear Planetology:Especially Concerning the Moon and Mars

To approach basic scientific questions on the origin and evolution of plan- etary bodies such as planets, their satellites and asteroids, one needs data on their chemical composition. The measurements of gamma-rays, X-rays and neutrons emit- ted from their surface materials provide information on abundances of major elements and naturally radioactive gamma-ray emitters. Neutron spectroscopy can provide sen- sitive maps of hydrogen- and carbon-containing compounds, even if buried, and can uniquely identify layers of carbon-dioxide frost. Nuclear spectroscopy, as a means of compositional analysis, has been applied via orbital and lander spacecraft to extrater- restrial planetary bodies： the Moon, Venus, Mars, Mercury and asteroids. The knowl- edge of their chemical abundances, especially concerning the Moon and Mars, has greatly increased in recent years. This paper describes the principle of nuclear spec- troscopy, nuclear planetary instruments carried on planetary missions so far, and the nature of observational results and findings of the Moon and Mars, recently obtained by nuclear spectroscopy.

MoS_(2)core-shell nanoparticles prepared through liquid-phase ablation and light exfoliation of femtosecond laser for chemical sensing

Molybdenum disulfide(MoS_(2))-based nanostructures are highly desirable for applications such as chemical and biological sensing,photo/electrochemical catalysis,and energy storage due to their unique physical and chemical properties.In this work,MoS_(2)core-shell nanoparticles were first prepared through the liquid-phase processing of bulk MoS2by a femtosecond laser.The core of prepared nanoparticles was incompletely and weakly crystalline MoS_(2);the shell of prepared nanoparticles was highly crystalline MoS_(2),which wrapped around the core layer by layer.The femtosecond laser simultaneously achieved liquid-phase ablation and light exfoliation.The formation mechanism of the core-shell nanoparticles is to prepare the nanonuclei first by laser liquid-phase ablation and then the nanosheets by light exfoliation;the nanosheets will wrap the nanonuclei layer by layer through van der Waals forces to form core-shell nanoparticles.The MoS_(2)core-shell nanoparticles,because of Mo-S bond breakage and recombination,have high chemical activity for chemical catalysis.Afterward,the nanoparticles were used as a reducing agent to directly prepare three-dimensional(3D)Au-MoS_(2)micro/nanostructures,which were applied as surface-enhanced Raman spectroscopy(SERS)substrates to explore chemical sensing activity.The ultrahigh enhancement factor(1.06×10^(11)),ultralow detection limit(10-13M),and good SERS adaptability demonstrate highly sensitive SERS activity,great ability of ultralow concentration detection,and ability to detect diverse analytes,respectively.This work reveals the tremendous potential of 3D Au-MoS_(2)composite structures as excellent SERS substrates for chemical and biological sensing.

Swelling-Based Chemical Sensing With Unmodified Optical Fibers

We use distributed fiber optic strain sensing to examine swelling of the fiber’s polymer coating.The distributed sensing technique that uses unmodified low-cost telecom fibers opens a new dimension of applications that include leak detection,monitoring of water quality,and waste systems.On a short-range length scale,the technology enables“lab-on-a-fiber”applications for food processing,medicine,and biosensing for instance.The chemical sensing is realized with unmodified low-cost telecom optical fibers,namely,by using swelling in the coating material of the fiber to detect specific chemicals.Although generic and able to work in various areas such as environmental monitoring,food analysis,agriculture or security,the proposed chemical sensors can be targeted for water quality monitoring,or medical diagnostics where they present the most groundbreaking nature.Moreover,the technique is without restrictions applicable to longer range installations.

Recent advances in AIEgen-based crystalline porous materials for chemical sensing

Aggregation-induced emission-based luminogens(AIEgens)have aroused enormous interest due to their unique high fluorescence in a condensed state.To further explore their potential applications,such as chemical monitoring,immobilization of AIE molecules has been widely studied with a variety of supports.Crystalline porous materials,such as metal-organic frameworks,covalent organic frameworks,hydrogen-bonded organic framework,and organic cages,demonstrate well-controlled structures,large surface areas,and promising stabilities,thus providing a perfect platform for AIE agents loading.Outstanding chemical sensing performances are achieved based on these AIE-active crystalline porous materials,such as high sensitivity,short response time,selective identification,and high recyclability,which provide a new alternative to readily detect various hazardous molecules.Furthermore,precise structures of AIEgen-based crystalline porous materials offer an easy way to investigate detection mechanisms.This mini-review will provide a brief overview of AIEgen-based crystalline porous materials for detection and then address how to improve sensing performances remarkably.

Metal-organic frameworks as functional materials for implantable flexible biochemical sensors

Metal-organic frameworks(MOFs)exhibit attractive properties such as highly accessible surface area,large porosity,tunable pore size,and built-in redox-active metal sites.They may serve as excellent candidates to construct implantable flexible devices for biochemical sensing due to their high thermal and solution stability.However,MOFs-based sensors have only been mostly reported for in-vitro chemical sensing,their use in implantable chemical sensing and combination with flexible electronics to achieve excellent mechanical compatibility with tissues and organs has rarely been summarized.This paper systematically reviews the biochemical sensors based on MOFs and discusses the feasibility to achieve implantable biochemical sensing through MOFs-based flexible electronics.The properties of MOFs and underlying mechanisms have been intrcxluced,followed by a summarization of different biochemical sensing applications.Strategies to integrate MOFs with flexible devices have been supplied from the standpoints of matching mechanics and compatible fabrication processes.Issues that should be addressed in developing flexible MOFs sensors and potential solutions have also been provided,followed by the perspective for future applications of flexible MOFs sensors.This paper may serve as a reference to offer potential guidelines for the development of flexible MOFs-based biochemical sensors that may benefit future applications in personal healthcare,disease diagnosis and treatment,and fundamental study of various biological processes.

Smartphones for sensing

Simple, portable analytical devices are entering our daily lives for personal care, clinical analysis, allergen detection in food, and environmental monitoring. Smart- phones, as the most popular state-of-art mobile device, have remarkable potential for sensing applications. A growing set of physical-co-chemical sensors have been embedded; these include accelerometers, microphones, cameras, gyroscopes, and GPS units to access and perform data analysis. In this review, we discuss recent work focusing on smartphone sensing including representative electromag- netic, audio frequency, optical, and electrochemical sen- sors. The development of these capabilities will lead to more compact, lightweight, cost-effective, flexible, and durable devices in terms of their performances.

Sensitive and fast response ethanol chemical sensor based on as-grown Gd_2O_3 nanostructures

Well crystalline gadolinium oxide（Gd2O3） nanostructures were grown by annealing the hydrothermally as-prepared nanostructures without using any template. Microscopic studies of Gd2O3 nanostructures were recorded along the [111] direction due to the clearly resolved interplanar distance d（222）-0.31 nm of the cubic crystal structure Gd2O3. Sensing mechanism of Gd2O3 as efficient electron mediator for the detection of ethanol was explored. As-fabricated sensor demonstrated the high-sensitivity of -0.266 μAm/M/cm2 with low detection limit（-52.2 μmol/L） and correlation coefficient（r^2, 0.618）. To the best of our knowledge, this was the first report for the detection of ethanol using as-grown（at 1000 oC） Gd2O3 nanostructures by simple and reliable Ⅰ-Ⅴ technique and rapid assessment of the reaction kinetics（in the order of seconds）. The low cost of the starting reagents and the simplicity of the synthetic route made it a promising chemical sensor for the detection of various toxic analytes, which are not environmentally safe.

Chemical-sensitive graphene modulator with a memory effect for internet-of-things applications

Modern internet of things(IoTs)and ubiquitous sensor networks could potentially take advantage of chemically sensitive nanomaterials and nanostructures.However,their heterogeneous integration with other electronic modules on a networked sensor node,such as silicon-based modulators and memories,is inherently challenging because of compatibility and integration issues.Here we report a novel paradigm for sensing modulators:a graphene field-effect transistor device that directly modulates a radio frequency(RF)electrical carrier signal when exposed to chemical agents,with a memory effect in its electrochemical history.We demonstrated the concept and implementation of this graphene-based sensing modulator through a frequency-modulation(FM)experiment conducted in a modulation cycle consisting of alternating phases of air exposure and ethanol or water treatment.In addition,we observed an analog memory effect in terms of the charge neutrality point of the graphene,Vcnp,which strongly influences the FM results,and developed a calibration method using electrochemical gate-voltage pulse sequences.This graphenebased multifunctional device shows great potential for use in a simple,low-cost,and ultracompact nanomaterial-based nodal architecture to enable continuous,real-time event-based monitoring in pervasive healthcare IoTs,ubiquitous security systems,and other chemical/molecular/gas monitoring applications.

Engineered olfactory system for in vitro artificial nose

The engineered biomimetic sensors can not only realize the action of organs,but also combine functional materials as in vitro organs by simulating the response of biological organs to different environmental signals.Artificial nose is a concept proposed by imitating biological olfactory system,simulating olfactory nerve cells,olfactory bulb and olfactory cortex through different materials to realize olfactory function.The sensor array used to sense external gas stimulation can be analyzed based on different recognition principles through different original signals such as optics,electricity,electrochemistry and bioelectricity.Furthermore,combined with pattern recognition and microarray technology,artificial nose can be highly integrated with biocompatible and other important properties to achieve in vitro application.The design principle and necessary components of artificial nose are introduced in this paper including sensing structure,recognition system and functional module.At the same time,the potential development prospects of molecular recognition technology,polymer-based materials and microarray integration in artificial nose are prospected.

Human-Like Robot Sensing Mediated by Body Heat

This paper presents a novel robotic sensor system that can monitor volatile chemicals and airflow. The system is modelled on characteristics of the human body that are thought to have a significant influence on the human odour and airflow senses. In particular, the effect of buoyant airflow due to body heat acts to gather volatile chemicals over large areas of the human body and carry them to the nose. It is postulated that this effect increases the receptive area for human olfaction. In addition, the interaction between rising air heated by the body and external airflow produces a temperature distribution about head height that can be used to infer airflow direction and magnitude. A heated sensor system was constructed to investigate these effects and the resulting sensor was mounted on a mobile robot. The design of the sensor system is described. Results are presented which demonstrate its ability to measure airflow direction and detect chemical signals over a wider receptive field compared with an unheated sensor.

A fully electronic microfabricated gas chromatograph with complementary capacitive detectors for indoor pollutants

This paper reports a complete micro gas chromatography(μGC)system in which all the components are lithographically microfabricated and electronically interfaced.The components include a bi-directional Knudsen pump,a preconcentrator,separation columns and a pair of capacitive gas detectors;together,these form the iGC3.c2 system.All the fluidic components of the system are fabricated by a common three-mask lithographic process.The Knudsen pump is a thermomolecular pump that provides air flow to theμGC without any moving parts.The film heaters embedded in the separation columns permit temperature programming.The capacitive detectors provide complementary response patterns,enhancing vapor recognition and resolving coeluting peaks.With the components assembled on printed circuit boards,the system has a footprint of 8×10 cm^(2).Using room air as the carrier gas,the system is used to experimentally demonstrate the analysis of 19 chemicals with concentration levels on the order of parts per million(p.p.m.)and parts per billion(p.p.b.).The tested chemicals include alkanes,aromatic hydrocarbons,aldehydes,halogenated hydrocarbons and terpenes.This set of chemicals represents a variety of common indoor air pollutants,among which benzene,toluene and xylenes(BTX)are of particular interest.

Direct identification of HMX via guest-induced fluorescence turn-on of molecular cage

Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine(HMX) is one of the most widely used powerful explosives. The direct and selective detection of HMX, without the requirement of specialized equipment, remains a great challenge due to its extremely low volatility, unfavorable reduction potential and lack of aromatic rings. Here, we report the first chemical probe of direct identification of HMX at ppb sensitivity based on a designed metal-organic cage(MOC). The cage features two unsaturated dicopper units and four electron donating amino groups inside the cavity, providing multiple binding sites to selectively enhance host-guest events. It was found that compared to other explosive molecules the capture of HMX inside the cavity would strongly modulate the emissive behavior of the host cage, resulting in highly induced fluorescence “turn-on”(160 folds). Based on the density functional theory(DFT) simulation, the mutual fit of both size and binding sites between host and guest leads to the synergistic effects that perturb the ligand-to-metal charge-transfer(LMCT) process, which is probably the origin of such selective HMX-induced turn-on behavior.

In-situ monitoring of nitrile-bearing pesticide residues by background-free surface-enhanced Raman spectroscopy

In-situ monitoring of pesticide residues during crop growth or/and in related products is of great significance in avoiding the abuse of pesticides but remains challenging thus far.In this report,we proposed a background-free surface-enhanced Raman spectroscopy(bf-SERS)platform to non-destructively track the nitrile-bearing pesticide residues in soybean leaves with high sensitivity and selectivity.The outstanding feature of the assay stems from the dramatic Raman enhancement effect of the 50 nm-sized gold nanoparticles(AuNPs)towards the pesticides and simultaneously the background-free Raman signal of the nitrile group in the so-called Raman-silent region(1800-2800 cm^(-1)).This bf-SERS assay was applied to evaluate the penetration effects of nitrile-bearing pesticides and monitor their residues in soybean leaves after rinsing with various solutions,providing a reliable tool for guiding the safe use of nitrile-bearing pesticides in agriculture.