Improved Cyclic Performance of Si Anodes for Lithium-Ion Batteries by Forming Intermetallic Interphases between Si Nanoparticles and Metal Microparticles

Silicon, an anode material with the highest capacity for lithium-ion batteries, needs to improve its cyclic performance prior to practical applications. Here, we report on a novel design of Si/metal composite anode in which Si nanoparticles are welded onto surfaces of metal particles by forming intermetallic interphases through a rapid heat treatment. Unlike pure Si materials that gradually lose electrical contact with conductors and binders upon repeated charging and discharging cycles, Si in the new Si/metal composite can maintain the electrical contact with the current collector through the intermetallic interphases, which are inactive and do not lose physical contact with the conductors and binders, resulting in significantly improved cyclic performance. Within 100 cycles, only 23.8% of the capacity of the pure Si anode is left while our Si/Ni anode obtained at 900 °C maintains 73.7% of its capacity. Therefore, the concept of employing intermetallic interphases between Si nanoparticles and metal particles provides a new avenue to improve the cyclic performance of Si-based anodes

Ultrasensitive Chemical Sensing through Facile Tuning Defects and Functional Groups in Reduced Graphene Oxide

Herein, we report on a facile, low-cost, and efficient method to tune the structure and properties of chemically reduced graphene oxide (rGO) by applying a transient voltage across the rGO for ultrasensitive gas sensors. A large number of defects, including pits, are formed in the rGO upon the voltage activation. More interestingly, the number of epoxide and ether functional groups in the rGO increased after the voltage activation. The voltage-activated rGO was highly sensitive to NO₂ with a sensitivity 500% higher than that of the original rGO. The lower detection limit can reach an unprecedented ultralow concentration of 50 ppb for NO₂ sensing. Density functional theory (DFT) calculations revealed that the high sensitivity to NO₂ is attributed to the efficient charge transfer from ether groups to NO₂, which is the dominant sensing mechanism. This study points to a promising method to tune the properties of graphene-based materials through the creation of additional defects and functional groups for high-performance gas sensors

Ultrasensitive Mercury Ion Detection Using DNA-Functionalized Molybdenum Disulfide Nanosheet/Gold Nanoparticle Hybrid Field-Effect Transistor Device

Mercury, one of the most harmful pollutants in water, has a significant negative impact on human health. The molybdenum disulfide (MoS₂) nanosheet, due to its unique electronic properties, is a promising candidate for high-performance sensing materials. Here, we report a DNA-functionalized MoS₂ nanosheet/gold nanoparticle hybrid field-effect transistor (FET) sensor for the ultrasensitive detection of Hg²⁺ in an aqueous environment. Specific DNA was used in the hybrid structure as the capture probe for the label-free detection. By monitoring the electrical characteristics of the FET device, the performance of the sensor was investigated. Our sensor shows a rapid response (1–2 s) to Hg²⁺ and an ultralow detection limit of 0.1 nM, which is much lower than the maximum contaminant level (MCL) for Hg²⁺ in drinking water (9.9 nM) recommended by the U.S. Environmental Protection Agency (EPA). In addition, the sensor shows a high selectivity to Hg²⁺ compared with other interfering metal ions, e.g., As⁵⁺, Cd²⁺, Pb²⁺, and so forth. This rapid and ultrasensitive method for Hg²⁺ detection can either be potentially developed into stand-alone hand-held sensors or be integrated into existing water equipment for continuously monitoring the water quality

Pulse-Driven Capacitive Lead Ion Detection with Reduced Graphene Oxide Field-Effect Transistor Integrated with an Analyzing Device for Rapid Water Quality Monitoring

Rapid and real-time detection of heavy metals in water with a portable microsystem is a growing demand in the field of environmental monitoring, food safety, and future cyber-physical infrastructure. Here, we report a novel ultrasensitive pulse-driven capacitance-based lead ion sensor using self-assembled graphene oxide (GO) monolayer deposition strategy to recognize the heavy metal ions in water. The overall field-effect transistor (FET) structure consists of a thermally reduced graphene oxide (rGO) channel with a thin layer of Al₂O₃ passivation as a top gate combined with sputtered gold nanoparticles that link with the glutathione (GSH) probe to attract Pb²⁺ ions in water. Using a preprogrammed microcontroller, chemo-capacitance based detection of lead ions has been demonstrated with this FET sensor. With a rapid response (∼1–2 s) and negligible signal drift, a limit of detection (LOD) < 1 ppb and excellent selectivity (with a sensitivity to lead ions 1 order of magnitude higher than that of interfering ions) can be achieved for Pb²⁺ measurements. The overall assay time (∼10 s) for background water stabilization followed by lead ion testing and calculation is much shorter than common FET resistance/current measurements (∼minutes) and other conventional methods, such as optical and inductively coupled plasma methods (∼hours). An approximate linear operational range (5–20 ppb) around 15 ppb (the maximum contaminant limit by US Environmental Protection Agency (EPA) for lead in drinking water) makes it especially suitable for drinking water quality monitoring. The validity of the pulse method is confirmed by quantifying Pb²⁺ in various real water samples such as tap, lake, and river water with an accuracy ∼75%. This capacitance measurement strategy is promising and can be readily extended to various FET-based sensor devices for other targets

Fast and Selective Room-Temperature Ammonia Sensors Using Silver Nanocrystal-Functionalized Carbon Nanotubes

We report a selective, room-temperature NH₃ gas-sensing platform with enhanced sensitivity, superfast response and recovery, and good stability, using Ag nanocrystal-functionalized multiwalled carbon nanotubes (Ag NC–MWCNTs). Ag NCs were synthesized by a simple mini-arc plasma method and directly assembled on MWCNTs using an electrostatic force-directed assembly process. The nanotubes were assembled onto gold electrodes with both ends in Ohmic contact. The addition of Ag NCs on MWCNTs resulted in dramatically improved sensitivity toward NH₃. Upon exposure to 1% NH₃ at room temperature, Ag NC–MWCNTs showed enhanced sensitivity (∼9%), very fast response (∼7 s), and full recovery within several minutes in air. Through density functional theory calculations, we found that the fully oxidized Ag surface plays a critical role in the sensor response. Ammonia molecules are adsorbed at Ag hollow sites on the AgO surface with H pointing toward Ag. A net charge transfer from NH₃ to the Ag NC–MWCNTs hybrid leads to the conductance change in the hybrid

Rapid, Sensitive, Label-Free Electrical Detection of SARS-CoV‑2 in Nasal Swab Samples

Rapid diagnosis of coronavirus disease 2019 (COVID-19) is key for the long-term control of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) amid renewed threats of mutated SARS-CoV-2 around the world. Here, we report on an electrical label-free detection of SARS-CoV-2 in nasopharyngeal swab samples directly collected from outpatients or in saliva-relevant conditions by using a remote floating-gate field-effect transistor (RFGFET) with a 2-dimensional reduced graphene oxide (rGO) sensing membrane. RFGFET sensors demonstrate rapid detection (<5 min), a 90.6% accuracy from 8 nasal swab samples measured by 4 different devices for each sample, and a coefficient of variation (CV) < 6%. Also, RFGFET sensors display a limit of detection (LOD) of pseudo-SARS-CoV-2 that is 10 000-fold lower than enzyme-linked immunosorbent assays, with a comparable LOD to that of reverse transcription-polymerase chain reaction (RT-PCR) for patient samples. To achieve this, comprehensive systematic studies were performed regarding interactions between SARS-CoV-2 and spike proteins, neutralizing antibodies, and angiotensin-converting enzyme 2, as either a biomarker (detection target) or a sensing probe (receptor) functionalized on the rGO sensing membrane. Taken together, this work may have an immense effect on positioning FET bioelectronics for rapid SARS-CoV-2 diagnostics

Evidence of Nanocrystalline Semiconducting Graphene Monoxide during Thermal Reduction of Graphene Oxide in Vacuum

As silicon-based electronics are reaching the nanosize limits of the semiconductor roadmap, carbon-based nanoelectronics has become a rapidly growing field, with great interest in tuning the properties of carbon-based materials. Chemical functionalization is a proposed route, but syntheses of graphene oxide (G-O) produce disordered, nonstoichiometric materials with poor electronic properties. We report synthesis of an ordered, stoichiometric, solid-state carbon oxide that has never been observed in nature and coexists with graphene. Formation of this material, graphene monoxide (GMO), is achieved by annealing multilayered G-O. Our results indicate that the resulting thermally reduced G-O (TRG-O) consists of a two-dimensional nanocrystalline phase segregation: unoxidized graphitic regions are separated from highly oxidized regions of GMO. GMO has a quasi-hexagonal unit cell, an unusually high 1:1 O:C ratio, and a calculated direct band gap of ∼0.9 eV

Evidence of Nanocrystalline Semiconducting Graphene Monoxide during Thermal Reduction of Graphene Oxide in Vacuum

As silicon-based electronics are reaching the nanosize limits of the semiconductor roadmap, carbon-based nanoelectronics has become a rapidly growing field, with great interest in tuning the properties of carbon-based materials. Chemical functionalization is a proposed route, but syntheses of graphene oxide (G-O) produce disordered, nonstoichiometric materials with poor electronic properties. We report synthesis of an ordered, stoichiometric, solid-state carbon oxide that has never been observed in nature and coexists with graphene. Formation of this material, graphene monoxide (GMO), is achieved by annealing multilayered G-O. Our results indicate that the resulting thermally reduced G-O (TRG-O) consists of a two-dimensional nanocrystalline phase segregation: unoxidized graphitic regions are separated from highly oxidized regions of GMO. GMO has a quasi-hexagonal unit cell, an unusually high 1:1 O:C ratio, and a calculated direct band gap of ∼0.9 eV