High-Performance Ni3(HHTP)2 Film-Based Flexible Field-Effect Transistor Gas Sensors.

Conductive metal-organic frameworks (MOFs) have received increasing attention in recent years and present high application potential as sensing elements in electronic sensors. In this study, flexible field-effect transistor (FET) sensors based on conductive MOF, i.e., Ni3(HHTP)2, have been constructed. This Ni3(HHTP)2 sensor has high sensitivity (detection limit of 56 ppb) as well as superior selectivity for NO2 detection at room temperature, which is demonstrated by accurate gas detection in a mixed gas atmosphere. Moreover, by employing six flexible substrates, i.e., polyimide (PI), tape (PET), facemask, paper cup, tablecloth, and take-out bag (textile), we successfully demonstrate the universality of the flexible sensor construction with conductive MOF as sensing film on various substrates. This study of conductive MOF-based flexible electronic sensors offers a new opportunity for a wide range of sensing applications with wearable and portable electronic devices.

Discriminative Analysis of NOx Gases by Two-Dimensional Violet Phosphorus Field-Effect Transistors.

Two-dimensional violet phosphorus (VP) has emerged as a new sensing material in various sensing applications due to its unique electrical properties and high stability among allotropes of phosphorus. Currently, the research of the VP-based analysis method is at the early stage. In this work, a VP nanosheet-based field-effect transistor (FET) sensor is reported for the detection of NO2 and N2O gases with extraordinary sensing performance. This sensor can achieve excellent sensitivity of up to ∼50% current change/ppm and a low detection limit of 5.9 ppb and enables the NO2 analysis in various mixed gases. Moreover, this sensor can effectively distinguish between NO2 and N2O gases, which is a big challenge for current FET or chemiresistor gas sensors. The different sensing behaviors of the VP sensor to NO2 and N2O gases have been investigated, and the mechanism study shows that the adsorption energy, bond length of the gas molecule on the VP surface, and the decomposition of N2O led to the differential responses. This work is one of the pioneer studies of VP gas sensors and presents a new sensing method for the discriminative analysis of NO2 and N2O for greenhouse gas emission monitoring and air quality control.

Fast, specific, and ultrasensitive antibiotic residue detection by monolayer WS2-based field-effect transistor sensor.

Antibiotic residues cause increasing concern in environmental ecology and public health, which needs efficient analysis strategy for monitoring and control. In this study, a fast, specific, and ultrasensitive sensor based on field-effect transistor (FET) has been proposed for the detection of ampicillin (AMP). The sensor involves monolayer tungsten disulfide (WS2) nanosheet as the sensing channel, single-stranded DNA (ssDNA) as the sensing probe, and gold nanoparticle (Au NP) as the linker. The WS2/Au/ssDNA FET sensor responds rapidly to AMP in a wide linear detection range (10-12-10-6 M) and has low limit of detection (0.556 pM), which meets the permissible standards of AMP in water and food. The sensing mechanism study suggests that the excellent sensor response results from the increased number of negative charges in the Debye length and the consequent accumulation of holes in WS2 channel after the addition of AMP. Moreover, satisfactory sensing performance was confirmed in real water samples, indicating the potential application of the proposed method in practical AMP detection. The reported FET sensing strategy provides new insights in antibiotic analysis for risk assessment and control.

Single-Atom Pt-Functionalized Ti3C2Tx Field-Effect Transistor for Volatile Organic Compound Gas Detection.

MXenes have shown exceptional electrochemical properties and demonstrate great promise in chemiresistive gas analysis applications. However, their sensing applications still face low sensitivity and specificity, slow response, and poor stability among the many challenges. Herein, a novel synthetic approach is reported to produce single-atom Pt (Pt SA)-implanted Ti3C2Tx MXene nanosheets as the sensing channel in field-effect transistor (FET) gas sensors. This is a pioneer study of single-atom catalysts loaded on MXene nanosheets for gas detection, which demonstrates that Pt SA can greatly enhance the sensing performance of pristine Ti3C2Tx. The Pt SA-Ti3C2Tx sensor exhibits high sensitivity and specificity toward ppb level (a low detection limit of 14 ppb) triethylamine (TEA) with good multicycle sensing performance. Moreover, the mechanism study and density functional theory (DFT) simulation show that the chemical sensitization effect and TEA adsorption enhancement from highly catalytic and uniformly distributed Pt SA lead to the enhanced sensing performances. This work presents a new prospect of single-atom catalysts for gas analysis applications, which will promote the development of cutting-edge sensing techniques for gas detection for public health and environment.

H2S sensing under various humidity conditions with Ag nanoparticle functionalized Ti3C2Tx MXene field-effect transistors.

Despite the critical need to monitor H2S, a hazardous gas, in environmental and medical settings, there are currently no reliable methods for rapid and sufficiently discriminative H2S detection in real-world humid environments. Herein, targeted hybridizing of Ti3C2Tx MXene with Ag nanoparticles on a field-effect transistor (FET) platform has led to a step change in MXene sensing performance down to ppb levels, and enabled the very high selectivity and fast response/recovery time under room temperature for H2S detection in humid conditions. For the first time, we present a novel relative humidity (RH) self-calibration strategy for the accurate detection of H2S. This strategy can eliminate the influence of humidity and enables the accurate quantitative detection of gas in the total RH range. We further elucidate that the superior H2S sensing performance is attributed to the electron and chemical sensitization effects. This study opens new avenues for the development of high-performance MXene-based sensors and offers a viable approach for addressing real-world humidity effect for gas sensors generally.

Ti3C2Tx MXene sensor for rapid Hg2+ analysis in high salinity environment.

Mercury is one of the leading chemicals of concern and receives much attention in environmental safety. It is of great necessity to develop advanced Hg2+ analysis method for rapid detection and monitoring. Field-effect transistor (FET) sensor, an emerging electronic sensor, has received great attention in environmental analysis since it has unique advantages in achieving rapid analysis of chemicals. Herein, an FET sensor is constructed with Ti3C2Tx MXene as the channel material to detect Hg2+ in water. The sensor displays rapid and selective response to Hg2+. Moreover, the sensor achieves satisfactory performance in Hg2+ detection in high salinity environment (1 M NaCl), which benefits its applications in real water analysis. Based on the investigation of sensing mechanism, the strong response of Ti3C2Tx MXene FET sensor to Hg2+ is due to the adsorption and reduction of Hg2+ to Hg+ on the Ti3C2Tx surface. This reported label-free Ti3C2Tx MXene platform can detect Hg2+ in high salinity environment with high specificity, which has significant application potential for on-site monitoring and risk assessment of Hg2+ in aqueous systems.

Label-Free, Fast Response, and Simply Operated Silver Ion Detection with a Ti3C2Tx MXene Field-Effect Transistor.

Silver (Ag) is a widely used heavy metal, and its oxidation state (Ag+) causes serious harm to organisms after bioaccumulation and biomagnification, posing urgent demand for the rapid, efficient, and simply operated Ag+ detection techniques. In this work, a fast, portable, and label-free Ag+ detection sensor based on a Ti3C2Tx MXene field-effect transistor (FET) is reported. The Ti3C2Tx MXene works as the sensing element in the FET sensor, which shows excellent sensing performance, i.e., fast response (few seconds) and good sensitivity and selectivity to Ag+ without any detection label or probe. Utilizing the visual photograph, transmission electron microscopy image, and Ag elemental mapping analysis, the sensing mechanism of the label-free Ti3C2Tx MXene FET sensor is demonstrated to be the in situ reduction of Ag+ and the formation of Ag nanoparticles (AgNPs). Moreover, Ag+ detection in real samples shows that the proposed FET devices have satisfactory sensing capability for Ag+ in tap water and river water. This study puts forward a novel FET strategy for Ag+ detection in aqueous systems, which is of essential and inspiring meaning for motivating the potential applications of MXene-based sensor devices in analytical applications and the realization of on-site environmental monitoring.

Rapid synthesis of multifunctional ß-cyclodextrin nanospheres as alkali-responsive nanocarriers and selective antibiotic adsorbents.

Novel hypercross-linked ß-cyclodextrin nanospheres are rapidly synthesized with 4-amino-6-hydroxy-2-mercaptopyrimidine as a cross-linker within 5 min at a low temperature of 60 °C in the open water phase, thereby radically simplifying and accelerating the conventional time-consuming and environmentally harsh synthesis of cyclodextrin-containing polymers. The nanospheres demonstrate excellent and controllable performance as alkali-responsive nanocarriers and selective adsorbents for antibiotics.

Highly Enhanced Gas Sensing Performance Using a 1T/2H Heterophase MoS2 Field-Effect Transistor at Room Temperature.

Monolayer MoS2 (ML-MoS2) with various polymorphic phases attracts growing interests for device applications in recent years. Herein, a field-effect transistor (FET) gas sensor is developed on the basis of monolayer MoS2 with a heterophase of a 1T metallic phase and a 2H semiconducting phase. Lithium-exfoliated MoS2 nanosheets own a monolayer structure with rich active sites for gas adsorption. With thermal annealing from 50 to 300 °C, the initial lithium-exfoliated 1T-phase MoS2 gradually transforms into the 2H phase, during which the 1T and 2H heterophases can be modulated. The 1T/2H heterophase MoS2 shows p-type semiconducting properties and prominent adsorption capability for NO2 molecules. The highest response is observed for 100 °C annealed MoS2 of a 40% 1T phase and a 60% 2H phase, which shows a sensitivity up to 25% toward 2 ppm NO2 at room temperature in a very short time (10 s) and a lower limit of detection down to 25 ppb. This study demonstrates that the gas detection capability of ML-MoS2 could be boosted with the heterophase construction, which brings new insights into transition-metal dichalcogenide gas sensors.

High Anti-Interference Ti3C2Tx MXene Field-Effect-Transistor-Based Alkali Indicator.

MXenes, a group of emerging two-dimensional (2D) transition metal carbides or nitrides, have attracted wide interest due to their unique structures and properties. Their stability and applicability in different media especially in an alkaline environment are directly associated with their potential applications and are not yet explored. Herein, a field-effect transistor (FET) is fabricated with single/double-layer Ti3C2Tx MXene. The Ti3C2Tx FET indicator shows a fast (∼1 s), sensitive, and selective response to alkali. Moreover, the device can work even in a high-salinity (2 M NaCl) environment, suggesting its high anti-interference ability for alkali in a high-ionic-strength environment. Using an in situ morphological image evolution study, it is demonstrated that the response signal results from alkali-induced denaturation of Ti3C2Tx nanosheets. The Ti3C2Tx-based alkali FET indicator and systematic evaluation on alkali-induced structure evolution of Ti3C2Tx provide essential insights into MXene-based FETs and future applications of MXene in alkaline environments.

Ultraselective antibiotic sensing with complementary strand DNA assisted aptamer/MoS2 field-effect transistors.

Although aptamer has been demonstrated as an important probe for antibiotic determination, the selective sensing of different antibiotics is still a challenge due to their structure similarities and wide folding degrees of aptamer. Herein, a field-effect transistor using MoS2 nanosheet as the channel and an aptamer DNA (APT) with its configuration shaped by a complementary strand DNA (CS) is employed for kanamycin (KAN) determination. This probe structure contributes to an enhanced selectivity and reliability with reduced device-to-device variations. This MoS2/APT/CS sensor shows time-dependent performance in antibiotic sensing. Prolonged detection time (20 s-300 s) leads to an enhanced sensitivity (1.85-4.43 M-1) and a lower limit of detection (1.06-0.66 nM), while a shorter detection time leads to a broader linear working range. A new sensing mechanism relying on charge release from probe is proposed, which is based on the "replacement reaction" between KAN and APT-CS. This sensor exhibits an extremely high selectivity (selectivity coefficient of 12.8) to kanamycin over other antibiotics including streptomycin, tobramycin, amoxicillin, ciprofloxacin and chloramphenicol. This work demonstrates the merits of probe engineering in label-free antibiotic detection with FET sensor, which presents significant promises in sensitive and selective chemical and biological sensing.

Metal-Organic Framework-Based Sensors for Environmental Contaminant Sensing.

Increasing demand for timely and accurate environmental pollution monitoring and control requires new sensing techniques with outstanding performance, i.e., high sensitivity, high selectivity, and reliability. Metal-organic frameworks (MOFs), also known as porous coordination polymers, are a fascinating class of highly ordered crystalline coordination polymers formed by the coordination of metal ions/clusters and organic bridging linkers/ligands. Owing to their unique structures and properties, i.e., high surface area, tailorable pore size, high density of active sites, and high catalytic activity, various MOF-based sensing platforms have been reported for environmental contaminant detection including anions, heavy metal ions, organic compounds, and gases. In this review, recent progress in MOF-based environmental sensors is introduced with a focus on optical, electrochemical, and field-effect transistor sensors. The sensors have shown unique and promising performance in water and gas contaminant sensing. Moreover, by incorporation with other functional materials, MOF-based composites can greatly improve the sensor performance. The current limitations and future directions of MOF-based sensors are also discussed.