In this work, we combine first principles calculations with non-equilibrium Green's function (NEGF) methods to investigate the adsorption of common heavy metals (As, Cd and Hg) onto 2D h-BN. Our results indicate that h-BN monolayers are particularly promising for the sensitive detection of arsenic (As). Using DFT-NEGF we compute structure, energies, band, density of states, charge redistribution, desorption times and transport characteristics. As adsorption produces pronounced As-N orbital hybridization, introduces near-Fermi states, reduces bandgap by 54% compared to the pristine h-BN monolayer and induces a net magnetic moment of 3.0 mu B, opening additional conduction channels and yielding an exceptional electrical sensitivity((1.95 & times; 104% at 0.9 V)) and a rapid room-temperature recovery time. By contrast, Cd and Hg interact predominantly via van der Waals and polarization effects, introduce states well above the Fermi level, produce negligible charge transfer and no spin polarization, and therefore cause only minor conductance changes. These results identify pristine h-BN as an environmentally benign, high selective platform for real-time heavy metal detection.

Metal oxide semiconductor sensors based on zinc oxide (ZnO) and its composites are found to be very sensitive in detecting acetic acid vapor. However, its operating temperatures usually exceed 200 °C. In this work, an environmentally friendly and controllable electrochemical approach for constructing poly(4,4',4″-Tris(carbazol-9-yl)-triphenylamine) (PTCTA) and ZnO composite films was successfully obtained for acetic acid sensing at room temperature. The conjugated microporous polymer (CMP) films of PTCTA were synthesized via an electropolymerization (EP) method using 4,4',4″-Tris(carbazol-9-yl)-triphenylamine (TCTA) molecule as a precursor. Subsequently, ZnO was deposited in situ to fabricate homogeneous PTCTA/ZnO composite films. The resulting PTCTA/ZnO composite films achieved a response value of 2.42 for 200 ppm acetic acid vapor at room temperature, which was significantly outperforming standalone PTCTA or ZnO films. This enhanced sensing capability was attributed to the porous structure, the synergistic effects of the p-n heterojunction at the PTCTA/ZnO interface and the oxygen adsorption/desorption occurring on the ZnO surface. What's more, PTCTA/ZnO composite films demonstrated structural stability and flexibility. The results suggested that the developed novel PTCTA/ZnO composite films showed great potential for acetic acid determination.

Non-Kirchhoff states of thermal radiation, which benefit from their nontrivial nonreciprocal emissivity properties, are crucial for addressing pressing challenges such as global climate change, energy crisis, and overheating of electronic devices. However, significant challenges remain in the quest to develop a design paradigm characterized by nonreciprocal switching to facilitate transformative breakthroughs in non-Kirchhoff radiative devices. Here, we develop a temperature-activated switchable nonreciprocal thermal emitter comprising a silicon cylindrical grating array on InAs/VO2 films, which enables switchable nonreciprocal thermal radiation for TE modes at lambda = 9.481 mu m and theta = +/- 10 degrees, resulting in a remarkable nonreciprocity of 0.45, a high Q-factor of approximate to 403 for the emissivity, and a switch ratio of 146. Leveraging magneto-optical quasi-bound states in the continuum coupling and VO2's phase transition, the structure achieves robust control: (i) a nonreciprocal "on" state with enhanced light-matter interactions in VO2's insulating phase, and (ii) a nonreciprocal "off" state with negligible effects in its metallic phase for both TE and TM modes, making it a polarization-selective emitter with switchable nonreciprocal thermal radiation. This work bridges the gap in switchable nonreciprocal thermal radiation research and provides insights into the design of practical nonreciprocal thermal structures, with applications in thermal camouflage, energy conversion, and thermal management.

Microfluidic switches are important operating units in microfluidics that enable controlled fluid flow on the chip, providing more functionality of platform. Most fiber based photofluidic devices mainly modulate temperature gradient and microflow by varying optical power. However, only power regulation limits the diversity of the optical field, which makes it difficult to achieve microfluidic control at different localized regions. Here, optical field of a tilted fiber Bragg grating (TFBG) can be theoretically modulated by the incident light wavelength and direction based on the finite element method. A photothermal vortices based microfluidic switch is built by TFBG with multiple linear heat sources. In the simulation, when the incident light is coupled in the forward or reverse direction of TFBG, the reflected position of the optical field is positively moved along the grating region as the wavelength increases. In the experiment, the opening of the microfluidic at different positions and directions can be clearly observed when the wavelength-matched laser is incident at the TFBG in the forward or reverse direction. It is believed that the microfluidic switch provides ideas for more flexible operation and functional integration for photothermal microfluidic devices in the future.

Due to the serious impact of hydrogen sulfide (H2S) on the environment and human health, a series of sensors have been increasingly used in industrial production and daily life. In this work, we introduce a novel, to the best of our knowledge, detection method for trace H2S in the liquid and gaseous phases based on the dual-quenching mechanism (DQE) of silver ion-doped nitrogen-sulfur co-doped carbon dots (N, S-CDs@Ag+). Ag+ could significantly enhance the fluorescence intensity and detection sensitivity. In the linear detection range of 10–120 nM H2S solution, the N, S-CDs@Ag+ sensor has a limit of detection (LoD) of 0.83 nM and a response time of 1 min. An enhanced fluorescent sensing film is prepared by assembling N, S-CDs@Ag+ on a silica microsphere (SM) microstructured substrate (N, S-CDs@Ag+/SM@PVA) using the layer-by-layer method. In the linear detection range of 1–50 ppm, the film sensor has the advantages of low detection limit (0.41 ppm), fast response time (5 min), stable performance, electromagnetic interference resistance, ease of integration, and in-field detection. It is expected to develop into a compact portable on-site H2S trace sensor.

Nonreciprocal thermal radiation allows the violation of Kirchhoff's law, as the spectral directional emissivity and absorptivity at the same angle can be different. Prior research has elucidated that certain optical resonance modes facilitate amplification of nonreciprocity at specific angles or wavelengths. However, achieving nonreciprocal thermal radiation with both wide-angle coverage and narrowband characteristics poses a fundamental yet challenging problem. In this work, we demonstrate a nonreciprocal thermal emitter that achieves both wideangle and narrowband through a periodic structure composed of magneto-optical materials. With an external magnetic field (B = 3 T or 1 T), the pronounced nonreciprocity arising from the magneto-optical localized resonance mode at 6.52 mu m or 7.18 mu m facilitates a distinct difference between the emissivity and absorptivity across a wide angular range from near 0 degrees-89 degrees. The robustness of the wide-angle and narrowband nonreciprocal thermal radiation is demonstrated with +/- 5 % fluctuations in structural parameters. The performance of the nonreciprocity with azimuthal angle phi ranging from 0 degrees to 360 degrees is also investigated. This work holds promising potential for applications in thermal management, directional thermal camouflage, high-efficiency thermophotovoltaic systems, and more.

High-quality conjugated microporous polymer (CMP) films with orientation and controlled structure are extremely desired for applications. Here, we report the effective construction of CMP 3D composite films (pZn/PTPCz) with a controlled porosity structure and preferred orientation using the template-assisted electropolymerization (EP) approach for the first time. The structure of pZn/PTPCz composite thin films and nitrophenol sensing performance were thoroughly studied. When compared to the control CMP film made on flat indium tin oxide (ITO) substrates, the as-prepared pZn/PTPCz composite films showed significantly enhanced fluorescent intensity and much better sensing performance for the model explosive. This was attributed to the metal-enhanced fluorescence (MEF) of porous nanostructured zinc (pZn) and the additional macroporosity of the pZn/PTPCz composite films. This work provides a feasible approach for creating oriented 3D CMP-based thin films for advanced applications. This work provides the effective construction of CMP 3D composite films (pZn/PTPCz) with a controlled porosity structure and preferred orientation using the template-assisted electropolymerization (EP) approach for the first time. When compared to the control CMP film made on flat substrates, the as-prepared pZn/PTPCz composite films showed significantly enhanced fluorescent intensity and much better sensing performance for the model explosive. image

Quantum dots (QDs) exhibit excellent optical and chemical properties, making them advantageous for fluorescence sensing. However, gas sensor using QDs is often hampered by challenges such as gas diffusion and low concentration. This work describes the development of a nitrogen dioxide (NO2) fluorescence gas sensor that utilizes a QDs@Aerogels/SM composite nanofilm containing CdTe QDs modified by reduced glutathione (GSH), silica microspheres (SMs), and silica aerogel. The SM and porous aerogels create a uniform porous structure that enhances the distribution of QDs. Compared to the pure QDs film, the QDs@Aerogels/SM composite film exhibits enhanced fluorescence intensity. The porous structure promotes the adsorption of NO2, which improves the detection sensitivity. The QDs@Aerogels/SM composite film was applied in a portable gas sensor. The sensor demonstrates a good linear response to NO2 gas in the range of 0-10 ppm, with an ultra-low detection limit of 0.096 ppm and high selectivity. The uniform distribution of aerogel and SM enhances the stability of the composite nanofilm, and the fluorescence of the films remains virtually unchanged over a period of 60 days which ensures its optimal performance over extended periods of use. The fluorescent NO2 sensor demonstrated selective and sensitive quenching upon exposure to NO2, making it ideal for environmental monitoring and further applications. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

This study explores the potential of MoS2 monolayers as heavy metal sensors for As, Cd, Hg, and Pb using density functional theory (DFT) and Non-Equilibrium Green’s Function (NEGF) simulations. Our findings reveal that As and Pb adsorption significantly alters the surface structure and electronic properties of MoS2, introducing impurity levels and reducing the band gap. Conversely, Cd and Hg exhibit weaker interactions with the MoS2 surface. The MoS2 monolayer sensors demonstrate exceptional sensitivity for all four target heavy metals, with values reaching 126,452.28% for As, 1862.67% for Cd, 427.71% for Hg, and 83,438.90% for Pb. Additionally, the sensors demonstrate selectivity for As and Pb through distinct response peaks at specific bias voltages. As and Pb adsorption also induces magnetism in the MoS2 system, potentially enabling magnetic sensing applications. The MoS2 monolayer’s moderate adsorption energy facilitates rapid sensor recovery at room temperature for As, Hg, and Cd. Notably, Pb recovery time can be significantly reduced at elevated temperatures, highlighting the reusability of the sensor. These results underscore the potential of MoS2 monolayers as highly sensitive, selective, and regenerable sensors for real-time heavy metal detection.

This study explores the potential of β-SnSe monolayers as a promising material for ozone (O3) sensing using density functional theory (DFT) combined with the non-equilibrium Green’s function (NEGF) method. The adsorption characteristics of O3 molecules on the β-SnSe monolayer surface were thoroughly investigated, including adsorption energy, band structure, density of states (DOSs), differential charge density, and Bader charge analysis. Post-adsorption, hybridization energy levels were introduced into the system, leading to a reduced band gap and increased electrical conductivity. A robust charge exchange between O3 and the β-SnSe monolayer was observed, indicative of chemisorption. Recovery time calculations also revealed that the β-SnSe monolayer could be reused after O3 adsorption. The sensitivity of the β-SnSe monolayer to O3 was quantitatively evaluated through current-voltage characteristic simulations, revealing an extraordinary sensitivity of 1817.57% at a bias voltage of 1.2 V. This sensitivity surpasses that of other two-dimensional materials such as graphene oxide. This comprehensive investigation demonstrates the exceptional potential of β-SnSe monolayers as a highly sensitive, recoverable, and environmentally friendly O3 sensing material.

Optofluidic techniques have evolved as a prospering strategy for microparticle manipulation via fluid. Unfortunately, there is still a lack of manipulation with simple preparation, easy operation, and multifunctional integration. In this Letter, we present an optofluidic device based on a graphite oxide (GO)-coated dual-fiber structure for multifunctional particle manipulation. By changing the optical power and the relative distance of the fibers, the system can excite thermal fluidic vortices with three inter-coupled states, namely uncoupled, partially coupled and completely coupled states, and therefore can realize capture, sorting, and transportation of the target particles. We conduct a numerical analysis of the whole system, and the results are consistent with the experimental phenomena. This versatile device can be utilized to manipulate target particles in complex microscopic material populations with the advantages of flexible operation, user-friendly control, and low cost.

In recent years, gold nanomaterials have become a hot topic in photothermal tumor therapy due to their unique surface plasmon resonance characteristics. The effectiveness of photothermal therapy is highly dependent on the shape and size of gold nanoparticles. In this work, we investigate the photothermal therapeutic effects of four different sizes of gold nanorods (GNRs). The results show that the uptake of short GNRs with aspect ratios 3.3–3.5 by cells is higher than that of GNRs with aspect ratios 4–5.5. Using a laser with single pulse energy as low as 28 pJ laser for 20 s can induce the death of liver cancer cells co-cultured with short GNRs. Long GNRs required twice the energy to achieve the same therapeutic effect. The dual-temperature model is used to simulate the photothermal response of intracellular clusters irradiated by a laser. It is found that small GNRs are easier to compact because of their morphological characteristics, and the electromagnetic coupling between GNRs is better, which increases the internal field enhancement, resulting in higher local temperature. Compared with a single GNR, GNR clusters are less dependent on polarization and wavelength, which is more conducive to the flexible selection of excitation laser sources.

Heavy metal pollution has a negative impact on both human health and the environment. The monitoring of heavy metal is therefore very important from a practical standpoint. In this study, the adsorption energy, charge transfer, band, densities of states, and sensitivity of SnSe monolayers toward heavy metals (As, Cd, Cr, Hg, Ni, Pb) were investigated using density functional theory combined with the non-equilibrium Green's function approach. The calculations show that SnSe monolayers have excellent sensitivities exceeding the limit of quantitation (LOQ) towards As, Cd, Hg, and Pb, which are as high as 384467%, 1462%, 1791%, and 26160%, respectively. Moreover, analyzing response peaks at various bias voltages can identify the composition of heavy metals from diverse sources, providing valuable insights for selective heavy metal monitoring. SnSe monolayers exhibit wide bias voltage windows that enhance sensor sensitivity by reaching the detection threshold, while also simplifying sensor encapsulation, resulting in higher reliability. The SnSe monolayer exhibits rapid recovery times for As, Hg, and Cd at room temperature, while for Pb, heating to 498 K is required for rapid recovery. These findings show that SnSe monolayers have a strong potential for constructing extremely sensitive and selective heavy metal sensors that are also reusable, implying that SnSe monolayers might serve as a possible online sensor for environmental monitoring.

Monitoring heavy metals helps prevent heavy metal contamination from affecting human health. However, existing monitoring technologies encounter challenges in real-time detection. Using density functional theory and non-equilibrium Green's function method, sensing capacities of SnS monolayer towards heavy metals are analyzed by adsorption energy, charge transfer, energy band structure, the density of states, differential charge density, recovery time, and transport performance. SnS monolayers exhibit high selectivity and good sensitivity of 13527% and 368860% for detecting As and Pb at the coverage of 1, respectively. With recovery times of 2.99 s for As and 76.44 s for Pb at 598 K, SnS monolayers can detect As or Pb at ambient temperature and be reused at high temperatures. SnS monolayers can selectively detect As and Pb through their response peaks at different bias voltages. SnS monolayers can detect Cd with a sensitivity of 442% in the concentration as low as coverage 1, when desorb at a recovery time of 31.2 & mu;s at 298 K, showing strong potential for ambient temperature sensors for Cd. SnS monolayers require Hg in high concentration, as high as coverage of more than 7, to reach the detection limit. The highest sensitivity of SnS monolayers towards Hg is 326% at the condition of a 0.6-V bias voltage and 8 coverage. Overall, our research provides fresh insight into low-cost, environmentally friendly materials for online heavy metal detection.

Real-time monitoring of volatile organic compounds (VOCs) is crucial for both industrial production and daily life. However, the non-reactive nature of VOCs and their low concentrations pose a significant challenge for developing sensors. In this study, we investigated the adsorption behaviors of typical VOCs (C2H4, C2H6, and C6H6), on pristine and Pt-decorated SnS monolayers using density functional theory (DFT) calculations. Pristine SnS monolayers have limited charge transfer and long adsorption distances to VOC molecules, resulting in VOC insensitivity. The introduction of Pt atoms promotes charge transfer, creates new energy levels, and increases the overlap of the density of states, thereby enhancing electron excitation and improving gas sensitivity. Pt-decorated SnS monolayers exhibited high sensitivities of 241,921.7%, 35.7%, and 74.3% towards C2H4, C2H6, and C6H6, respectively. These values are 142,306.9, 23.8, and 82.6 times higher than those of pristine SnS monolayers, respectively. Moreover, the moderate adsorption energies of adsorbing C2H6 and C6H6 molecules ensure that Pt-decorated SnS monolayers possess good reversibility with a short recovery time at 298 K. When heated to 498 K, C2H4 molecules desorbs from the surface of Pt-decorated SnS monolayer in 162.33 s. Our results indicate that Pt-decorated SnS monolayers could be superior candidates for sensing VOCs with high selectivity, sensitivity, and reversibility.

The efficient and homogeneous mixing of fluids is crucial for microfluidic applications, such as chemical reactions, biological analyses, and material synthesis. This study designs a novel micromixer for efficient and controllable mixing based on photothermal vortices, which are generated from an array of linear heat sources as excited by a laser. The mixing performance is theoretically investigated using a multiphysics-coupled system based on the finite element method. We reveal the interactions between vortices and the mixing mechanism of fluids. The vortices provide a stable strength and adjustment ability to disturb fluid interfaces and enhance the mixing efficiency. Additionally, the effects of the vertical distance between two waveguides, optical power, and inlet mean velocity on the mixing performance are explored. As a result, the calculated mixing efficiency is 99.89%, which could be regarded as an important reference of the micromixer with an excellent mixing performance. The purpose of this study is to provide a new method for rapid, efficient, and controllable mixing for a myriad of chemical research and biotechnological applications.

Surface-enhanced Raman scattering (SERS) spectroscopy has attracted tremendous interest as a highly sensitive label-free tool to detect pollutants in aqueous environments. However, the high cost and poor reusability of conventional SERS substrates restrict their further applications in rapid and reproducible pollutant detection. Here, we report a reliable optical manipulation method to achieve rapid photothermal self-assembly of Au nanoparticles (AuNPs) in water within 30 s by a tapered optical fiber, which is utilized for highly sensitive SERS substrate preparation. The results show that the SERS substrate achieves low detection limits of 10-9 mol/L with an enhancement factor (EF) of 106 for chemical pollutants solutions, including thiram, pyrene, and rhodamine 6G. The SERS enhancement effect based on assembled AuNPs was more than 20 times that based on a gold colloid solution. As a result, the smart reversible assembly of AuNPs exhibits switchable plasmonic coupling for tuning SERS activity, which is promising for the application of SERS-based sensors and environmental pollutant detection.

Currently, the frontier of nanomaterials has been an extraordinary way for biological and chemical analysis. Using quantum dots (QDs) has served as a promising strategy for copper ion sensing. Various microreactors have been utilized to enhance the sensitivity and stability and shorten the detection time. By integrating a photothermal waveguide into a microfluidic platform, we have developed a photothermal microreactor for enhanced microbubbles, vortex, and microdroplets can be simultaneously generated due to the enhanced photothermal effect of graphene oxide and the evanescent field of microfiber. Due to the cooperation of gathering QDs by vortex fields, enlarging surface area on account of droplets, and accelerating molecular motion based on increasing temperature, this system can achieve highly enhanced detection of copper ions in a small sample volume of 2 mu L within 5 min, where the detection limit is 3 orders of magnitudes lower than that of the original method. Such a photothermal microreactor is pollution-free and cost-effective with high efficiency and hypotoxicity, being highly potential as a powerful microsensing strategy for environmental monitoring as well as chemical analysis.

As a highly functional platform, lab-on-fiber (LOF) has exhibited amazing potential to be used in ultrasensitive surface-enhanced Raman spectroscopy (SERS) detection. However, the low detection efficiency and high cost of most SERS-based LOF platform have severely limited their further applications in environmental monitoring, biomedicine, etc. Here, we report a reusable SERS-based LOF platform through a Au-coated optical fiber integrated into a patterned microfluidic chip. With the assistance of laser-induced thermophoresis, we successfully obtained rich "hot spots" on the Au-coated optical fiber by reversible accumulation of gold nanoparticles within 5 min. Experimental results indicate that it has a low detection limitation of 10(-10) mol/L (M) for environmental pollutant molecules. Fortunately, with the dynamic and reversible accumulation of gold nanoparticles controlled by laser on/off, the platform shows excellent reversibility and stability under multiple detection-cleaning cycles, which are better than those of the LOF platform based on chemical modification and photochemical deposition. The thermophoresis-based LOF platform with the advantages of easy operation, miniaturization, and high reusability provides a cost-effective approach for SERS detection.

Fluorescent sensors are resistant to electromagnetic interference and are electrically insulated, allowing for highly accurate measurements. Quantum dots (QDs) serve as outstanding sensing materials owing to the unique optical properties such as tunable photoluminescence (PL), excellent visible light activity, and high chemical and physical stability. In this paper, we develop an optical humidity sensor based on a QDs nanocomposite film. The film is made of polyvinyl alcohol (PVA), SiO2 microsphere (SM), and QDs through the layer-by-layer self-assembly method. The mechanism of humidity detection is moisture-induced quenching of the QDs fluorescence intensity. The results reveal that our sensor shows a good linear response to relative humidity in the range of 5% to 97%, a fast response-recovery time of 25 s and 20 s, and good repeatability for more than 50 cycles as well as high stability for over 180 days. Possessing the remarkable property, optical humidity sensors are envisaged for great potential applications in environmental monitoring.