Ammonia Sensor Research Articles

Near-room-temperature operating ammonia sensors fabricated using hydrothermally in situ synthesized WS2/rGO nanocomposites

Near-room-temperature operating ammonia sensors fabricated using hydrothermally in situ synthesized WS2/rGO nanocomposites

Study on Ammonia Content and Distribution in the Microenvironment Based on Covalent Organic Framework Nanochannels.

A crack-free micrometer-sized compact structure of 1,3,5-tris(4-aminophenyl)benzene-terephthaldehyde-covalent organic frameworks (TAPB-PDA-COFs) was constructed in situ at the tip of a theta micropipette (TMP). The COF-covered theta micropipette (CTP) then created a stable liquid-gas interface inside COF nanochannels, which was utilized to electrochemically analyze the content and distribution of ammonia gas in the microenvironments. The TMP-based electrochemical ammonia sensor (TEAS) shows a high sensing response, with current increasing linearly from 0 to 50,000 ppm ammonia, owing to the absorption of ammonia gas in the solvent meniscus that connects both barrels of the TEAS. The TEAS also exhibits a short response and recovery time of 5 ± 2 s and 6 ± 2 s, respectively. This response of the ammonia sensor is remarkably stable and repeatable, with a relative standard deviation of 6% for 500 ppm ammonia gas dispensing with humidity control. Due to its fast, reproducible, and stable response to ammonia gas, the TEAS was also utilized as a scanning electrochemical microscopy (SECM) probe for imaging the distribution of ammonia gas in a microspace. This study unlocks new possibilities for using a TMP in designing microscale probes for gas sensing and imaging.

Enhancement of Ammonia Sensors Using In2O3 Sensing Electrode by Adjusting Particle Size and NiCo2O4 Reference Electrode

A mixed potential ammonia sensor using In2O3 sensing electrode was prepared, and its sensing performance was enhanced by adjusting particle size with calcination heating rate as well as the utilization of NiCo2O4 reference electrode. It was found that the sensor with a calcination heating rate of 2 °C min−1 had the best performance, with a sensitivity of −61.27 mV decade−1 at 525 °C, and the TEM results showed that the average particle size was 70.36 nm. Furthermore, the sensor exhibited good stability against oxygen concentration fluctuation. The results also indicated that the mixed potential has a linear relationship with the logarithm of NH3 concentration, suggesting that the ammonia sensors in this study conform to the mixed potential theory. To address the issue that most ammonia sensors are susceptible to NO2 interference, NiCo2O4 was used as reference electrode to replace the Pt reference electrode, which could greatly offset the response of NO2 and improve the sensors selectivity. In summary, the developed In2O3/YSZ/NiCo2O4 sensor exhibited a great potential for NH3 monitoring in SCR systems.

Response Enhancement of Pt Nanoparticles Decorated AlGaN/GaN HEMTs Treated by Photo-Electrochemical Method for Ammonia Gas Sensing at Room Temperature

In this work, we have designed an ammonia sensor based on Pt nanoparticles (NPs) decorated AlGaN/GaN high electron mobility transistors (HEMTs) operating at 300 K. The sensor was optimized by photo-electrochemical (PEC) method to achieve better ammonia gas sensing performance. And the threshold voltage of the HEMT based device was significantly positively shifted from −4.14 V to 0.32 V and the gate voltage corresponding to the maximum transconductance peak shifted from −3.60 V to 1.00 V via the PEC method. Simultaneously, PEC treatment can increase the surface-area-to-volume (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> /V) ratio of the sensing window to enhance the ammonia gas sensing ability. The “spill-over” effect of Pt NPs provided more active sites on the surface of the sensing area. Pt NPs loaded AlGaN/GaN HEMT based sensor exhibited a relatively short response and recovery times of 29 s and 238 s, respectively, and the sensitivity increased from 0.34 % to 8.69 % towards 100 ppm ammonia when drain voltage was kept at 1.00 V at 300 K. The low limit of detection (LOD) of 20 ppm was obtained in this paper. The results showed that the studied device treated by the PEC method is indeed promising for ammonia detection in the future.

Fast Response and Low Detection Limit of Ammonia Sensor Based on WO3 Nanoparticles-Decorated BiFeO3 Nanoplates

In this paper, an ammonia sensor based on BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> composites is presented. BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoplates and WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoparticles were prepared by a simple hydrothermal method. The composites were observed by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The gas-sensitive properties of the composites and the single material were systematically compared. The experimental results show that the BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> composites sensor has an excellent response towards ammonia with good long-term stability, short response/recovery time and low detection limit. The gas-sensitive mechanism is further explained that the possible reason for the enhanced gas-sensitive performance is the formation of n-n heterojunctions between BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoplates and WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanoparticles. The BiFeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /WO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> composites were shown to be a potential room temperature ammonia sensing material.

Effect of Ethyl Cellulose on Ammonia Sensing Abilities of Gas Sensors Fabricated Using MoS2 Functional Ink for Printed Electronics Application

Two-dimensional transition metal dichalcogenides have emerged as an excellent alternative to metal oxide and polymer-based conventional gas sensors. Liquid synthesis/processing of these materials has opened up doors for developing printed gas sensors. However, the formulation of ink and tuning its rheology require some additives. Ethyl cellulose (EC) has been consistently utilized for this purpose. In this letter, we have qualitatively assessed the role of EC addition on the performance of gas sensors based on the MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanosheets. In the process, we first optimized the ultrasonication time to achieve an optimal gas sensing performance. Furthermore, we optimized centrifugation time since it is an important parameter governing the printability of the ink. We further optimized the addition of EC in the solution to formulate printable ink. Ammonia sensors based on MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> solutions with and without EC were developed, and their performance has been compared at the assay of absolute response, baseline drift, response time, and recovery time. It is clearly evident that the addition of EC not only affects the device baseline current levels but also deteriorates the absolute response and minimum detection limit.

Selective Recognition of Ammonium over Potassium Ion with Acyclic Receptor Molecules Bearing 3,4,5-Trialkylpyrazolyl Groups

Among the 1,3,5-trisubstituted 2,4,6-triethylbenzenes bearing pyrazolyl groups, the compounds with 3,5-dimethylpyrazolyl moieties were found to be effective receptors for ammonium ions (NH4 +). The current study investigated the extent to which the incorporation of an additional alkyl group in the 4-position of the pyrazole ring affects the binding properties of the new compounds. 1H NMR spectroscopic titrations and investigations using isothermal titration calorimetry revealed that this small structural variation leads to a significant increase in the binding strength towards NH4 + and also improves the binding preference for NH4 + over K+. In addition to the studies in solution, crystalline complexes of the new triethyl- and trimethylbenzene derivatives, bearing 3,4,5-trialkylpyrazolyl groups, with NH4 +PF6 − were obtained and analyzed in detail. It is noteworthy that two of the crystal structures discussed in this work are characterized by the presence of two types of ammonium complexes. Studies focusing on the development of new artificial ammonium receptors are motivated, among other things, by the need for more selective ammonium sensors than those based on the natural ionophore nonactin.

Pyramid-shaped MMn2O4/rGO (M = Ni, Co) nanocomposites and their application in ammonia sensors

Pyramid-shaped MMn2O4/rGO (M = Ni, Co) nanocomposites and their application in ammonia sensors

Development of Solid-State Chemiresistive Devices for Simultaneous Detection of Nitrate, Nitrite and Ammonium Ions in Aqueous Solutions

The presence of various ions is an important factor in evaluating water quality. Nitrate, nitrite and ammonium in water can cause health issues and pose environmental concerns1,2. Some sources of the nitrogen species are from natural water and some of them arise from industrial and agricultural activities. Currently commercially available sensors for measuring nitrogen compounds in water are based on colorimetric techniques and potentiometric methods incorporating ion selective electrodes. Progress still needs to be made towards fabricating devices with less instrumentation costs, less complexity, less maintenance and without need for any reagents to facilitate measurement of species1. Chemiresistive sensors are solid-state devices which can be simply fabricated from two contacts and a conductive sensing material affixed on a suitable substrate. They operate by detecting modulations in resistance of the conducting film due to surface charge transfer as a result of interactions with the analyte(s)3.Here, we demonstrate chemiresistive devices capable of quantifying aqueous nitrate, nitrite and ammonium ions selectively. Due to challenges in the aqueous phase such as ionic strength effect, probability of side reactions, non-specific bonding on the surface, low interaction energy between analyte and surface, chemiresistive technology has not been developed extensively in water quality sensors4,5. In this study, we have overcome the issues in water by coating the chemiresistive devices with selective membranes. If the fabricated sensors are used as an array, the total nitrogen concentration in water can be measured online which is a significant advance since nitrate, nitrite and ammonium may interconvert and a single nitrate, nitrite or ammonium sensor by itself cannot give the total amount of nitrogen in a sample. For device fabrication, p-doped carbon nanotubes were selected as a sensitive conductive layer which were modified with selective membranes to improve the sensing performance. Nitrite sensors worked over a dynamic range of 67 ppb to 67 ppm with a 27.6% response at 67 ppm. Nitrate showed 13.2% response from 2.2 ppm to 220 ppm. Ammonium devices operated over a dynamic range of 10 ppb to 100 ppm with a 23.6% response at 100 ppm. The proposed response mechanism involves both an electrostatic gating effect and surface charge transfer. Compared with paper-based colorimetric sensors, the proposed devices perform better with a lower detection limit and the ability to perform continuous online measurements. Moreover, the chemiresistive responses of the devices were compared with their potentiometric responses and found to be equally sensitive but more selective. Unlike ion-selective electrodes, the resulting devices do not require the use of reference electrodes and are therefore potentially more robust for use in continuous water analyzers and in resource-poor settings. The chemiresistive devices showed low interferences and good reversibility. They were also tested in river water samples and showed satisfactory results. The fabricated devices are an advanced proof of concept and have the potential to replace the current technology. Nuñez, L., Cetó, X., Pividori, M. I., Zanoni, M. V. B. & del Valle, M. Development and application of an electronic tongue for detection and monitoring of nitrate, nitrite and ammonium levels in waters. Microchem. J. 110, 273–279 (2013).Li, D., Xu, X., Li, Z., Wang, T. & Wang, C. Detection methods of ammonia nitrogen in water: A review. TrAC - Trends Anal. Chem. 127, 115890 (2020).Choi, S. J. & Kim, I. D. Recent Developments in 2D Nanomaterials for Chemiresistive-Type Gas Sensors. Electronic Materials Letters vol. 14 (The Korean Institute of Metals and Materials, 2018).Kruse, P. Review on water quality sensors. J. Phys. D. Appl. Phys. 51, (2018).Dalmieda, J., Zubiarrain-Laserna, A., Saha, D., Selvaganapathy, P. R. & Kruse, P. Impact of Surface Adsorption on Metal-Ligand Binding of Phenanthrolines. J. Phys. Chem. C 125, 21112–21123 (2021). Figure 1

TiO2 Hollow Nanofiber/Polyaniline Nanocomposites for Ammonia Detection at Room Temperature

AbstractAmmonia (NH3) detection has gained considerable attention in agricultural and environmental monitoring, chemical and pharmaceutical processing, and disease diagnosis, which requires the development of sensors with high sensitivity. Herein, we propose a novel gas sensor based on nanocomposites of TiO2 hollow nanofibers and polyaniline (PANI) for the sensitive detection of ammonia at room temperature. TiO2 nanostructures in anatase phase were prepared by the combination of coaxial electrospinning and calcination treatment. The resulting material was mixed with PANI and deposited onto gold interdigitated electrodes (IDEs). The hybrid platforms exhibited superior sensing performance compared to the platform based on their individual phases, which is ascribed to a synergistic effect from p‐n heterojunction formation. Specifically, the platforms based on TiO2/PANI nanocomposite showed a fast response towards NH3 (e. g., 55 s at 10 ppm) at room temperature (25 °C). Additionally, the platform demonstrated the ability to detect NH3 at low concentrations (10–30 ppm) and a detection mechanism was proposed to explain the results. Overall, these results show the promise of electrospun TiO2 hollow nanofibers/PANI composites for the development of high‐performance room temperature ammonia sensors.

Interplay of electrode geometry and bias on charge transport in organic heterojunction gas sensors

Modulation of charge transport in an organic heterojunction sensor is a promising strategy to enhance its gas sensing properties. Herein, a heterostructure consisting of a bilayer assembly of perfluorinated copper phthalocyanine and lutetium bis-phthalocyanine is investigated for ammonia sensor development in two different electrode geometries and in a wide range of applied bias. The microstructure of the heterostructure retains the bulk electronic and structural properties of the individual components and shows granular distribution of phthalocyanine crystallites on the surface. The charge transport of the heterojunction devices depends on the electrode geometry and the applied bias. Notably, interfacial charge transport gets faster, while bulk charge transport remains constant with increasing bias in both devices. But, the small gap between the electrodes fastens the bulk and the interfacial charge transport by 75 and 5 times, respectively, compared to the big gap electrodes. The implication of faster charge transport in the small gap electrodes-based sensor is demonstrated on its ammonia sensing properties, exhibiting higher response and shorter response time. Moreover, the response of the sensor exponentially increases with increasing bias. The high sensitivity and stability of the sensor at different relative humidity make it a suitable NH3 sensor for real environment applications.

Preparation of CeVO4 with VO2 as precursor performing high selectivity and sensitivity to ammonia

In this study, nano rod-like pure CeVO 4 and composite CeVO 4 are prepared from VO 2 as a precursor, adjusting the doping ratio of Ce. XPS results show that the V atoms on the surface of CeVO 4 are in the form of the V 5+ and V 3+ . V 3+ acts as the hanging key on the CeVO 4 surface and is used as an active site, conducive to the subsequent adsorption of ammonia and redox reactions. Thus, the free electrons absorbed by O 2 - return to the surface of CeVO 4 and improve its ammonia adsorption sensitivity. The prepared CeVO 4 ammonia sensor shows a high response (77,825%) and a faster recovery time (~2 s) at room temperature. To explore the effect of water molecules on the ammonia sensitivity of the sensor. Sensors are placed in salt solutions with different humidity. Results reveal a small resistance change in samples at low humidity, indicating that the ammonia gas could be monitored in real-time under low humidity conditions. • The phase and morphology of CeVO 4 are adjusted by Ce doping with VO 2 as a precursor. • V 3+ on surface of CeVO 4 as an active site raise the ammonia sensitivity of sensor. • The CeVO 4 sensor shows high and fast response to NH 3 with realtime test function.

“Electro-dissolution” of gold nanoclusters for constructing ammonia sensor

• The sensor overcomes the common obstacles in ammonia detection, the high energy barrier of ammonia electrocatalysis and the toxicity of N -ads. • Further improved the electro-dissolution mechanism for ammonia detection by theoretical analysis and expanded the application to more substances. • The economical and facile constructed sensor has excellent reproducibility under high-intensity work both in theory and practice. Overcoming the electrocatalytic energy barrier mediated by Gerischer-Mauerer's mechanism has always been a major challenge in ammonia detection. The previous report [1] that ammonia can electro-dissolve Au gives us inspiration to establish a more efficient and reusable electrochemical transmission technique for ammonia detection and, above all, remove the ammonia electrocatalytic barrier. In this work, the latent electro-dissolution activity of ammonia towards Au was employed to construct the sensing interface. The sensor applied the potentiostatic electrodeposition method to grow Au crystals on the surface of carbon cloth, offering a simple and low-cost alternative for practical production. Additionally, the electro-dissolution sensing method effectively addresses the limitation of high energy barrier and toxic products ( N -ads) in catalytic oxidation of ammonia. Cyclic Voltammetry and Tafel curve demonstrate the electrochemical properties of Au/CC and help to predict the relationship between the ammonia concentration and current through theoretical analysis, which were further confirmed by an i-t curve. We proved that the sensor has excellent reproducibility under high-intensity work in theory and it exhibits high stability over 7 weeks in practice. The economical and facile constructing electrode method and the outstanding performance in long-term reuse greatly reduce the cost. Generally, the sensor is suitable for continuous ammonia monitoring in wastewater and quantitative analysis of products by chemical companies.

Amperometric ammonia sensors for low detection limit with BaZr(1-x)YxO3-δ proton electrolytes

• BaZr 1-x Y x O 3-δ proton conductors were used as electrolyte in solid-state NH 3 sensors. • Electrolysis was proposed to detect ammonia by measuring the proton migration in BZY electrolytes. • The lowest detection limit of the amperometric NH 3 sensor can be 500 ppb. Ammonia (NH 3 ) sensor is a critical part in the selective catalytic reduction (SCR) system for the reduction of oxynitride emission. Here, novel amperometric NH 3 sensors are proposed based on BaZr (1-x) Y x O 3-δ (BZY, x = 0.1, 0.2, 0.3, 0.4) proton electrolytes. The influence of yttrium content on the structure, morphology and conductivity of BZY electrolytes is investigated systematically. Benefiting from the best conductivity of BaZr 0.8 Y 0.2 O 3-δ (BZY20) among these electrolytes, the sensor with the BZY20 electrolyte exhibits a low detection limit of 0.5 ppm at a relative low working temperature of 350℃. Furthermore, the sensor shows the highest sensitivity, good selectivity and repeatability to NH 3 . This work opens the way for the promising application of solid-state NH 3 sensor for low detection limit at low working temperatures.

Fabrication and Characterization of P3HT/MoS₂ Thin-Film Based Ammonia Sensor Operated at Room Temperature

The composites of polymers and two-dimensional (2D) materials show promising applications in the area of gas sensing. In this work, we report an efficient ammonia gas (NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) sensor based on poly(3-hexylthiophene)/ molybdenum disulfide (P3HT/MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) nanocomposite. The sensing device has been fabricated in bottom-gate top contact organic field-effect transistor (OFET) assembly using P3HT/MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as active channel material. The changes in the electrical response of OFET has been measured and analyzed for various ammonia gas concentration at room temperature. The sensing device in the form of an OFET structure is preferred due to multi-parameter characteristics to explore gas sensing applications. The active sensing layer has been fabricated via a self-assembled, cost-effective floating film transfer (FTM) technique. An optimized uniform sensing film of thickness 25±3 nm is used to analyze the change in the electrical characteristic of the device in terms of I/O characteristics, mobility, threshold voltage, trapped charge density, etc., for various ammonia concentrations. The OFET with nanofiber morphology of mobility 0.147 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V-s shows the threshold voltage of −3.78 V (in the air) and changes to −10.71 V after 100 ppm ammonia gas exposure. The device has shown a limit of detection (LOD) of 904 ppb and a sensing response of 63.45% at 100 ppm ammonia concentration. The extraction of multi-parameter sensing characteristics of the device has been conducted in a closed chamber with an ambient environment. The fabricated sensor is therefore having potential applications in high-performance ammonia sensing applications.

A new ternary Eu(III) β‐diketonate complex with diimine ligand and its application as fluorescent probe for highly sensitive and selective ammonia sensor

The rapid and accurate detection of ammonia is very important for manufacture and environmental monitoring, which needs to be developed urgently. Herein, a thin film‐based fluorescence sensor is fabricated by using a ternary europium (III) complex probe for ammonia. The new complex Eu(TPM)3(2‐PBO) (1) was designed and synthesized by utilizing a trifluoromethyl substituted β‐diketone ligand TPM and a diimine ligand 2‐PBO (TPM = 1,1,1‐trifluoro‐5,5‐dimethyl‐2,4‐hexanedione, 2‐PBO = 2‐(2′‐pyridyl)‐benzoxazole). This complex probe was synthetically characterized by elemental analysis, crystallographic and spectroscopic analysis, and photoluminescence (PL) study. The crystallographic analysis revealed complex 1 as a neutral complex structure with the Eu(III) center in a distorted square antiprism EuO6N2 coordination polyhedron. Based on this complex probe, a thin film fluorescence sensor with highly sensitive and selective response to ammonia was developed by polymethyl methacrylate (PMMA): complex composite and cellulose paper support. When the paper‐based sensor was exposed to ammonia, its PL emission showed a sensing behavior of rapid quenching. Surprisingly, this new method can achieve excellent limit of detection as low as 2.740 × 10−6 ppm.

Core-shell Au@SiO2 nanocrystals doped PANI for highly sensitive, reproducible and flexible ammonia sensor at room temperature

Herein, we report a facile and straightforward synthetic strategy for preparing flexible NH3 sensors with high performance and application prospects. Interestingly, core–shell Au@SiO2 nanocrystals (NCs) doped polyaniline (PANI) were innovatively employed as the sensitive material and the NH3 sensors were constructed via a simple droplet-evaporation self-assembly process on the polyimide substrates. Experimental results show that the well-designed NH3 sensor with ∼ 20 wt% of Au@SiO2 NCs doping PANI exhibited high sensitivity, flexibility and combined reproducibility at room temperature: the device’s detection limit of NH3 reached a 10 ppb level; the device’s concentration deviation induced by large-angle and cycled bending could be kept within 0.6 ppm, and the maximum response variation was less than 2.7% through 30 days of monitoring; Additionally, the designed NH3 sensor does have insusceptibility to the ambient relative humidity (from 48% to 66%). Indeed the sensing mechanism of our NH3 sensor was discussed from the Au@SiO2 NCs doped PANI structure, the crucial role of abundant hydroxyl (–OH) functional groups, and the catalytic activity of Au NPs. Overall, this study demonstrates an alternative and effective pathway to fabricate high-performance and applicable NH3 sensors, which may be conducive to further application for environmental NH3 detection and human kidney disease diagnosis.

Highly sensitive and selective room temperature ammonia sensor based on polyaniline thin film: in situ dip-coating polymerization

Highly sensitive and selective room temperature ammonia sensor based on polyaniline thin film: in situ dip-coating polymerization

Optical ammonia sensor based on Yb3+, Er3+, Tm3+ co-doped NaYF4 up-conversion material/phenol red composites

In this paper, optical ammonia sensor based on Yb3+, Er3+, Tm3+ co-doped NaYF4 up-conversion material/phenol red composites was proposed. Phenol red and Yb3+, Er3+, Tm3+ co-doped NaYF4 were mixed thoroughly and transferred into PE conical shell to form ammonia sensitive unit. The epoxy resin was coated onto two end sides of PE conical shell to fix ammonia sensitive composite. The absorption intensity of up-conversion luminescence located at 663 nm will be affect by the concentration of ammonia attribute to the reaction between ammonia and phenol red. The detected intensity near 663 nm decreases exponentially with the increasing ammonia concentration. The water absorption of epoxy resin benefit for the detection of ammonia. The signal wavelength will not be affected by the background visible light due to the 980 nm wavelength of excitation is far from the signal wavelength. The response time and recover time of the sensor also were measured and discussed.

Polyhedral silver clusters as single molecule ammonia sensor based on charge transfer-induced plasmon enhancement

The unique plasmon resonance characteristics of nanostructures based on metal clusters have always been the focus of various plasmon devices and different applications. In this work, the plasmon resonance phenomena of polyhedral silver clusters under the adsorption of NH3, N2, H2, and CH4 molecules are studied by using time-dependent density functional theory. Under the adsorption of NH3, the tunneling current of silver clusters changes significantly due to the charge transfer from NH3 to silver clusters. However, the effects of N2, H2, and CH4 adsorption on the tunneling current of silver clusters are negligible. Our results indicate that these silver clusters exhibit excellent selectivities and sensitivities for NH3 detection. These findings confirm that the silver cluster is a promising NH3 sensor and provide a new method for designing high-performance sensors in the future.