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Flower-like In(OH) 3 was synthesized by a facile homogeneous precipitation method and subsequently calcined at 300 °C to prepare nanosheets assembled 3D flower-like mesoporous In 2 O 3 , which was then modified with Au nanoparticles via sol-immobilization method to produce 3D hierarchical mesoporous Au/In 2 O 3 for ethanol detection. The as-prepared Au/In 2 O 3 were carefully characterized by XRD, SEM, HRTEM and XPS techniques. The flower-like structure was assembled by many ultrathin coarse mesoporous In 2 O 3 nanosheets, and Au nanoparticles with an average size of 3.3 nm were evenly dispersed on In 2 O 3 nanosheets. The 3D flower-like mesoporous 1%Au/In 2 O 3 has a high specific surface area of about 130 m2 g−1 and shows the best sensitivity to ethanol among the flower-like mesoporous Au/In 2 O 3 materials. It can sensitively detect ethanol gas at a relatively low temperature of 160 °C with a response of 115–50 ppm ethanol, increased by nearly 11 times compared to In 2 O 3 at 210 °C. The 3D flower-like mesoporous 1%Au/In 2 O 3 also has good selectivity to ethanol with response about 9.4, 26.1, 20.9 and 29.5 times higher than that to acetone, methanol, toluene and xylene, and it displays excellent linear relationship between the response and the ethanol concentration. The markedly improved sensitivity and selectivity of the 3D flower-like mesoporous 1%Au/In 2 O 3 results from both the electronic sensitization and chemical sensitization effects of Au nanoparticles. In short, the 3D flower-like mesoporous 1%Au/In 2 O 3 possesses excellent sensitivity, selectivity, repeatability, linear relationship and long-term stability at 160 °C. Therefore, the obtained 3D flower-like mesoporous 1%Au/In 2 O 3 has great potential for ethanol gas detection. [Display omitted] • 3D flower-like mesoporous In 2 O 3 was synthesized via facile precipitation and calcination process. • 3D flower-like mesoporous Au/In 2 O 3 was prepared by sol-immobilization method. • 3D flower-like mesoporous Au/In 2 O 3 showed excellent ethanol sensing performance. [ABSTRACT FROM AUTHOR]

Non-metallic surface-enhanced Raman scattering (SERS) demonstrates an attractive potential in clinical immunoassay thanks to the brilliant biocompatibility and chemical enhancement of semiconductor substrates. Herein, SERS-based quantitative assay of SARS-CoV-2 in saliva was carried out by constructing SiC@RP nanotowers (NTs) and Si nanoparticles. Ascribed to the efficient light absorption and molecular enrichment capacity of the hierarchical tower morphology as well as the synergistic chemical enhancement in the semiconductor heterojunction, the SiC@RP NTs achieved a minimum limit of detection as 7.6 × 10-11 g/mL for SARS-CoV-2. Concurrently, the correction of the detection signal by the intrinsic Raman signal of Si nanoparticles drastically improved the stability and reliability of the detection, facilitating a relative standard deviation (RSD) data within ± 9.53%. Ultimately, the real-time SERS monitoring of saliva samples displayed an ultra-high response rate of no less than 83.2%. Such a non-metallic SERS immunoassay with high sensitivity and attractive reliability is expected to play a key role in future clinical monitoring application. • Sensitivity was enhanced by utilizing the synergistic chemical enhancement of SiC@RP compound semiconductor. • Light-limiting effect and molecular enrichment was improved by the unique morphology of SiC nanotowers. • The intrinsic Raman signal of silicon probes was used as an internal standard signal. • High throughput detection of SARS-CoV-2 in saliva with a LOD of 7.6 × 10-11 g/mL was realized. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) are solution-synthesized semiconductor nanocrystals with size typically below 10 nm. Their large surface-to-volume ratio and abundant active surface sites, combined with the grain size effect and solution-processability make CQDs promising building blocks for low-cost and high-performance gas sensors. Here we employed the ligand exchange strategy to develop low-power and highly sensitive H 2 S gas sensors based on PbS CQDs. Following the layer-by-layer spin-coating of PbS CQDs capped with long-chain oleic acid ligands from synthesis, a surface treatment using different inorganic salts was conducted for ligand exchange in air ambient at room temperature. Upon exposure to 50 ppm of H 2 S at 135 °C, the resistance of all those sensors decreased shown as the response and the Pb(NO 3 ) 2 treatment yielded highest response (4218 at 135 °C) with shortest response/recovery time. We tentatively proposed a H 2 S-induced and temperature-promoted p-to-n transition of PbS CQDs as the sensing mechanism and the role of Pb(NO 3 ) 2 treatment was attributed to an n-type remote doping effect realized by the ligand exchange, which was further supported by the energy dispersive spectrometry (EDS) and ultraviolet photoelectron spectroscopy (UPS) analysis. [ABSTRACT FROM AUTHOR]

Abstract: Porous tin oxide films were prepared via an electrophoretic deposition process and their sensing response toward nitrogen gas (4.1–100ppm) at 25–120°C were investigated. The TEM and SEM images indicated a porous microstructure of the SnO2 film composed of nanocrystals. It is found that the sensing response increased monotonically with increasing operating temperature and gas concentration. Above 80°C, repeatable response and recovery characteristics toward NO2 gas injection and release cycles could be obtained. The response and recovery time at different temperatures were also studied. Typically, the SnO2 sensor had a response of 61 toward 13.7ppm of NO2 with good selectivity against NH3 and SO2 gases when operated at 105°C. The response time (T90) and recovery time (T10) were 83s and 45s, respectively. Discussion based on surface chemistry theory suggests that at 105°C, NO2 may interact with SnO2 both by trapping the free electrons directly and indirectly through the surface adsorbed oxygen ions, increasing the potential barrier across grain boundaries of SnO2 and hence making its resistance to increase. In summary, the simplicity and versatility of the electrophoretic deposition make it very attractive and promising in preparation of high-quality oxide gas sensors. [Copyright &y& Elsevier]

• In-situ synthesis of Au/Fe 3 O 4 hybrid was achieved by a green and scalable method. • Au/Fe 3 O 4 hybrid showed superior electrochemical sensing properties for H 2 O 2. • Au/Fe 3 O 4 has low detection limit, high sensitivity and wide linear detection range. • The high performance was ascribed to the positive synergistic effects Au and Fe 3 O 4. The easy, green, and energy-saving fabrication of high-performance electrocatalysts toward detecting trace amounts of hydrogen peroxide (H 2 O 2) in different media remains challenging for a sustainable future. Herein, we establish a one-pot fabrication of Au nanoparticles and Fe 3 O 4 hybrids (Au/Fe 3 O 4) through a sustainable and scalable protocol involving the redox reduction between chloroauric acid and ferrous sulfate at room temperature. The method does not require any additional reducing agent, organic solvent or energy input. Despite the protocol's simplicity, the achieved magnetic Au/Fe 3 O 4 exhibits excellent H 2 O 2 detection properties, i.e., a low detection limit of 0.108 μM (S/N = 3), a wide linear detection range of 0.001–1 mM, a high sensitivity of 266 μA mM−1 cm−2, and high selectivity in PBS solution. This electrocatalyst can be used to detect H 2 O 2 in milk and juice samples below the residue limit required by the US Food and Drug Administration (<14.7 μM). The Au/Fe 3 O 4 hybrid can also be used to detect H 2 O 2 in basic solution with improved electrocatalytic performance. This simple method can further be extended to prepare other metals (Pd, Pt, and Ag)/Fe 3 O 4 for electrocatalytic enzyme-free H 2 O 2 sensing with high efficiency. [ABSTRACT FROM AUTHOR]

The formulation of substrates with reliable quantitative detection and robust molecular anchoring is crucial for surface-enhanced Raman scattering (SERS) technique. In this context, an appealing hydrophilic-hydrophobic polymer strip with Raman internal standard (IS) was generated by in-situ growing hydrophilic non-metallic black phosphorus/metal-organic frameworks (BP/ZIF-67) onto special regions of hydrophobic polydimethylsiloxane (PDMS) matrix, which dramatically promoted the concentration of target molecules. Furthermore, a specific detection of coronavirus disease 2019 (SARS-CoV-2) N-protein with a limit of 6.4 × 10−6 mg/mL was facilitated, benefiting from the selective capture rendered by the mesoporous surface of ZIF-67 and the ultra-high enhancement effect arose from BP/ZIF-67 hybrid structure-triggered charge transfer resonance process. Moreover, the extent of quantification in the SERS assay was significantly remedied due to the IS strategy. Especially, the slight local surface plasmon resonance (LSPR) capability of BP could readily provoke additional electromagnetic field to complement its powerful chemical enhancement, which was significantly superior to other non-metallic substrates. Such an upgraded platform may deliver another prospering technology for dependable virus monitoring. [Display omitted] • SERS-active polymer strip with BP/ZIF-67 for straightforward virus detection. • Comprehensive explanation of chemical-electromagnetic synergistic enrichment mechanism. • Quantitative detection of SARS-CoV-2 with LOD of 6.4 × 10−6 mg/mL was achieved. [ABSTRACT FROM AUTHOR]

Chemiresistive gas sensors have emerged as a promising generation of detection systems for identifying trace biomarker molecules in exhaled breath, potentially replacing conventional devices for early-stage disease diagnosis. However, their potential is currently limited by the absence of sensing materials that exhibit both humidity resistance and ultrasensitivity. In this study, we investigate the potential of WO 3 nanoparticles (NPs) supported by Nb 2 CTx MXene (WO 3 /Nb 2 CTx) as a highly efficient material for acetone sensing. Our results demonstrate that the synergistic interplay between WO 3 NPs and Nb 2 CTx MXene support generates an intriguing interface with chemical/electronic coupling, thereby further enhancing the gas sensing performance. The WO 3 /Nb 2 CTx sensor exhibits exceptional sensing performance for acetone, with ultrasensitivity (Ra/Rg = 2.4 at 50 ppb) and an ultrafast response time (8 s), surpassing that of WO 3 alone, while maintaining excellent stability. Moreover, the sensor exhibits outstanding response intensity, rapid response time (9 s), superior selectivity, and remarkable reversibility at a relative humidity of approximately 90 %. Additionally, we evaluate the gas-sensing properties of the sensor towards simulated exhaled breath of diabetic patients. In conclusion, our study presents a novel approach that integrates NPs and MXenes, which holds promise for the development of gas sensors with resistance to humidity interference. • WO 3 /Nb 2 CTx heterojunction is designed for acetone detection. • WO 3 /Nb 2 CTx sensor demonstrates ultrasensitive acetone detection at ∼90 % RH. • The Nb 2 CTx facilitates the generation of oxygen vacancies and enhances charge transfer. [ABSTRACT FROM AUTHOR]

• QCM-based humidity sensors were fabricated through one-step colloidal synthesis strategy. • Ligand exchange removing the organic long chains on SnO 2 surface which expose more active sites. • DFT was introduced to investigate adsorption energy of H 2 O on SnO 2 (110) and (101) planes. • High humidity sensitivity was achieved with fast response and recovery speed. In this paper, a quartz crystal microbalance (QCM)-based humidity sensor has been fabricated by colloidal tin oxide (SnO 2) nanowires. The SnO 2 nanowires were synthesized via a colloidal process that employing SnCl 4 ethanol solutions mixed with oleic acid (OA) and oleylamine (OLA). The spin-coating method was chosen to deposit the sensitive film at room temperature without high-temperature sintering. Furthermore, the Cu(NO 3) 2 methanol solution was used to remove the organic long chains coated on the surface of the colloidal SnO 2 nanowires and expose more adsorption sites. The characterizations of the material were studied by means of FTIR, XRD, and FE-SEM. The saturated salt solution method was used to investigate the humidity sensing performance (response, recovery, repeatability, etc.) of the QCM sensor in the range of 11%–97%. The results showed that the sample with 12 h synthesis has the best humidity response. This may be attributed to the larger specific surface area which makes the material provide more adsorption sites for water molecules, and more (110) planes formed which could absorb more water molecules proved by the Density Functional Theory (DFT) calculation. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) are promising materials candidates for next-generation semiconductor gas sensors, due to their high surface activity and solution-processability. Despite the improved sensitivity demonstrated by PbS CQDs, their long-term stability remains a challenge for practical applications. In this paper, we propose a stabilization strategy for PbS CQD gas sensors by using atomic-ligand engineering. The oleic acid ligands surrounding PbS CQDs are replaced by halide ligands (Cl–, Br– and I–, respectively) via a phase-transfer ligand exchange method. The sensitivity and long-term stability of the PbS CQD gas sensor towards nitrogen dioxide (NO 2) at room temperature are impressively improved. The excellent humidity stability of the iodine ligand exchanged PbS CQD gas sensor is also demonstrated. The mechanism is investigated by real-time electrical measurement, combined with operando diffuse reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis. The results indicate that the large atomic radius and high binding energy of iodide ligands enhance surface passivation and provide favorable conditions for NO 2 adsorption and charge transfer. This study highlights the importance of surface ligand engineering in the development of practical CQD gas sensors. • Atomic-ligand engineering is proposed to stabilize PbS CQD for NO 2 detection. • Iodine ligands improve detection limit to 0.78 ppb with stability in 0–90% RH range. • Iodide ligands enhance passivation and facilitate NO 2 adsorption & charge transfer. [ABSTRACT FROM AUTHOR]

Highlights • Small-size and high-crystallinity PbS CQDs were synthesized via a simple cation exchange method. • The PbS CQDs were successfully integrated into the SAW delay lines by spin-coating at room temperature. • The CQD-coated SAW sensor exhibited high sensor response to low-concentration of NO 2 gas at room temperature. Abstract Surface acoustic wave (SAW) sensors have great advantages in real-time and in-situ gas detection due to their wireless and passive characteristics. Using nanostructured sensing materials to enhance the SAW sensor's responses has become a research focus in recent years. In this paper, solution-processed PbS colloidal quantum dots (CQDs) were integrated into quartz SAW devices for enhancing the performance of NO 2 detection operated at room temperature. The PbS CQDs were directly spin-coated onto ST-cut quartz SAW delay lines, followed by a ligand exchange treatment using Pb(NO 3) 2. Upon exposure to 10 ppm of NO 2 gas, the sensor coated with untreated PbS CQDs showed response and recovery times of 487 s and 302 s, and a negative frequency shift of −2.2 kHz, mainly due to the mass loading effect caused by the absorption of NO 2 gas on the surface of the dense CQD film. Whereas the Pb(NO 3) 2 -treated sensor showed fast response and recovery times of 45 s and 58 s, and a large positive frequency shift of 9.8 kHz, which might be attributed to the trapping of NO 2 molecules in the porous structure and thus making the film stiffer. Moreover, the Pb(NO 3) 2 -treated sensor showed good stability and selectivity at room temperature. [ABSTRACT FROM AUTHOR]

Highlights • Excellent crystallinity and solution processability of In 2 O 3 QDs enable low temperature sensor fabrication and operation. • High response of 90@5 ppm H 2 S was achieved at near room temperature with fast response/recovery kinetics. • CuO formation through ligand exchange and annealing treatment helps achieve sensitive and selective response toward H 2 S. • O2− and O− were the main chemisorbed oxygen species on In 2 O 3 surfaces at near room temperature with the ratio of 1:1. Abstract Indium oxide (In 2 O 3) nanomaterials have been investigated extensively as promising candidates for gas sensor applications. Here, we fabricate near room temperature operable H 2 S-sensitive gas sensors based on In 2 O 3 colloidal quantum dots (CQDs). Room-temperature film deposition of In 2 O 3 CQDs followed by surface ligand exchange treatment through Cu inorganic salts was employed to construct the sensor devices. Combined with a moderate annealing treatment, the long-chain ligands surrounding the quantum dot surfaces were completely removed to enhance gas adsorption and carrier transport, simultaneously resulting in the formation of CuO that may act as a catalytic promoter or form p-n heterojunction for selective H 2 S detection. The sensors exhibited high response up to 90 toward 5 ppm of H 2 S with response/recovery time of 72 s/200 s respectively, suggestive of a performance improvement compared to the In 2 O 3 -based H 2 S sensors reported in existing literature. The power law analysis indicated that the main oxygen species adsorbed on the surfaces were O 2 − and O− with the proportion of approximate 1:1 at near room temperature. The gas-sensing mechanism was attributed to the decisive role of surface states in determining the electrical conduction of quantum dot gas sensors. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) are considered as one of the ideal materials candidates for next-generation electronics and optoelectronics. Their large surface-to-volume ratio with exchangeable surface ligands offers a versatile freedom for the regulation of the semiconductor gas sensors. Here we demonstrated an atomic-ligand exchange strategy to construct highly sensitive and selective SnO 2 quantum dot gas sensors. Both the cations and anions of the atomic ligands were engineered to enhance the gas adsorption and carrier transport via a film-level atomic ligand exchange treatment, among which the CuCl 2 -treated SnO 2 CQD gas sensors exhibiting highest response of 1755 toward 50 ppm H 2 S with a fast response and recovery time (48 s/35 s) at 70 °C. The Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and UV–vis absorption spectra suggest that the long-chain organic ligands capping on the SnO 2 CQDs were successfully exchanged by the atomic ligands and the quantum confinement of the CQDs were well conserved, which is favorable to preserve the catalytic activities of QD materials in real gas-sensing devices. Simultaneously, the copper (II) introduced on the surface of SnO 2 CQD films can also act as a catalytic promoter by forming p-CuO/n-SnO 2 heterojunctions, thereby enhancing the H 2 S-sensing performance at relatively low temperatures. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs) are promising building blocks for low-cost and high-performance gas sensors due to their excellent solution processability and extremely small size. Among chalcogenide CQDs, PbSe has a large exciton Bohr radius and exhibits strong confinement energies, facilitating the fast charge-carrier transport. However, CQDs-based devices are susceptible to degrade due to the poor stability of CQDs. Here, in order to obtain air-stable PbSe CQDs for gas sensing application, we synthesized PbSe CQDs using a cation exchange method with in situ chloride and cadmium passivation. The sharp absorption peak in UV–vis absorption spectra confirmed strong quantum confinement in the PbSe CQDs and their average diameter was estimated to be 2.87 ± 0.23 nm. To construct gas sensors, PbSe CQDs were spin-coated onto ceramic substrates and then Pb(NO 3 ) 2 treatment was carried out to remove the long-chain ligands surrounding PbSe CQDs. At 25 °C, the sensor was highly sensitive and selective to NO 2 with a response of 22.3 at 50 ppm and a fast response time of 7 s. Moreover, the sensor response showed a 85.2% stability as the time increased up to 20 days, suggesting the potential applications of PbSe CQDs for NO 2 monitoring at room temperature. [ABSTRACT FROM AUTHOR]

SnO 2 quantum wire/reduced graphene oxide nanocomposites (SnO 2 QW/rGO) were synthesized by a facile one-step hydrothermal method with rGO and SnCl 4 . 5H 2 O as the precursors. The SnO 2 QW/rGO nanocomposites well-dispersed in ethanol were spin-coated onto ceramics substrates to construct chemiresistive gas sensors. The H 2 S-sensing isotherm curves were obtained based on the real-time response curves of the SnO 2 QW/rGO gas sensors when operated at different temperatures ranging from 30 °C to 70 °C, from which the adsorbing/sensing performance of the specific materials were extracted and the kinetic parameters (such as response rate constant k and activation energy E a ) of the sensing-materials were quantitatively modeled. The H 2 S-sensing mechanism was found to follow Langmuir isotherm and pseudo-first-order model. Compared to pure SnO 2 QW sensors, the SnO 2 QW/rGO gas sensors exhibited higher sensitivity and faster response rate toward H 2 S, which was attributed to its lower activation energy. The SnO 2 QW/rGO gas sensors can even detect H 2 S at room temperature, highly attractive for the detection of H 2 S detection with lower power consumption. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots (CQDs), due to the excellent solution processability, low cost and ease of integration, are emerging as promising candidates for gas sensors. Here, colloidal zinc oxide quantum dots were synthesized through a simple colloidal method with oleic acid (OA) as the surface-capping ligand. The well dispersed ZnO CQDs were spin-coated onto ceramic substrates to construct chemiresistive gas sensors. The film-level ligand exchange treatment was applied to remove the long-chain surface-capping which thereby facilitated efficient gas adsorption and carrier transport. The optimal sensor exhibited the best performance with a response of 113.5 upon 50 ppm of H 2 S exposure at room temperature, with a fast response time being 16s. The obtained results suggested that ZnO CQDs are promising materials candidate for high-performance gas sensors. [ABSTRACT FROM AUTHOR]

Tungsten oxide (WO 3 ) has been intensely investigated as an important gas-sensing materials. Here the sensitive and selective H 2 S gas sensors based on WO 3 quantum dots that were synthesized via a colloidal process using WCl 6 ethanol solutions mixed with oleic acid and oleylamine were demonstrated. The solution processability of the colloidal WO 3 quantum dots enabled a room-temperature sensor fabrication without high-temperature sintering. The optimal sensor response toward 50 ppm of H 2 S is 57 with the response time of 47 s, and the response was fully recoverable upon H 2 S release at 80 °C. The sensing mechanism was discussed by using first-principles calculation based on density functional theory (DFT). Their highly sensitive and fast response at lower operating temperature, combined with the benefit of ease fabrication, make the colloidal tungsten oxide quantum dots highly attractive for the construction of low cost gas sensor with reduced power consumption. [ABSTRACT FROM AUTHOR]

Human health and environmental safety are imperceptibly disturbed by illegally used plasticizers. A fluorescence sensor array based on B-doped graphene quantum dots was designed to detect six plasticizers. Specifically, the dexterous design is the first to disperse B-doped graphene quantum dots in two solvents of different polarities (N,N-Dimethylformamide and Cyclohexane), select three characteristic fluorescence peaks of B-doped graphene quantum dots in the above two solvents, and construct a 3 × 2 array, with a total of 6 array points. The basis of the detection is that the plasticizers affect the dispersion of B-doped graphene quantum dots in different solutions, which are accompanied by the change of its fluorescence signals. Or the plasticizers affect the electron transfer process of B-doped graphene quantum dots in different solvents, resulting in fluorescence quenching. Fluorescence information output by the sensor array showed a good linear relationship with the concentrations of the six plasticizers. The quantitative detection capability can be specified as: the detection range is 100 ng/mL-195 mg/mL, and the detection limit is 1.05–11.58 ng/mL. The fluorescence sensor array also showed good analytical performance in real samples, with recoveries ranging from 95% to 106%. This method has satisfactory specificity, reproducibility, stability and practicality, making it potential for application. • B-GQDs fluorescence sensor array for detecting plasticizers. • B-GQDs have diverse fluorescence properties in different polar solvents. • The plasticizer affects the polarity of the solvent as the detection principle. • The highly sensitive and ultra-rapid detection of six plasticizers was completed. [ABSTRACT FROM AUTHOR]

Human health and environmental safety are imperceptibly disturbed by illegally used plasticizers. A fluorescence sensor array based on B-doped graphene quantum dots was designed to detect six plasticizers. Specifically, the dexterous design is the first to disperse B-doped graphene quantum dots in two solvents of different polarities (N,N-Dimethylformamide and Cyclohexane), select three characteristic fluorescence peaks of B-doped graphene quantum dots in the above two solvents, and construct a 3 × 2 array, with a total of 6 array points. The basis of the detection is that the plasticizers affect the dispersion of B-doped graphene quantum dots in different solutions, which are accompanied by the change of its fluorescence signals. Or the plasticizers affect the electron transfer process of B-doped graphene quantum dots in different solvents, resulting in fluorescence quenching. Fluorescence information output by the sensor array showed a good linear relationship with the concentrations of the six plasticizers. The quantitative detection capability can be specified as: the detection range is 100 ng/mL-195 mg/mL, and the detection limit is 1.05–11.58 ng/mL. The fluorescence sensor array also showed good analytical performance in real samples, with recoveries ranging from 95% to 106%. This method has satisfactory specificity, reproducibility, stability and practicality, making it potential for application. • B-GQDs fluorescence sensor array for detecting plasticizers. • B-GQDs have diverse fluorescence properties in different polar solvents. • The plasticizer affects the polarity of the solvent as the detection principle. • The highly sensitive and ultra-rapid detection of six plasticizers was completed. [ABSTRACT FROM AUTHOR]

This study proposed a high sensitivity optical fiber relative humidity sensor (OFHS). Besides, a fullerene derivative, C 60 -THAM, was synthesized and firstly reported as a molecule receptor in the OFHS. Compared with the widely researched carbon-based materials in OFHS, the C 60 -THAM film has abundant amino dangling bonds, hence emerges naturally as excellent receptors for water molecules. Besides, a cascaded Fabry-Perot interferometer (FPI) was fabricated in the core of single-mode fiber (SMF) without surface damage by femtosecond laser. In the OFHS, the relative humidity (RH) was measured by the Vernier effect. The working principle of the OFHS was analyzed through calculation and simulation. In the experiment, C 60 -THAM was coated on the plant fiber end. The sensitivity of the sensor is about 0.42 nm/RH as the relative humidity change from 30 % to 65 % while the optical-matter reaction length is only about 150 nm. Moreover, the sensor exhibited a stable performance as the RH was decreasing from 65 % to 30 %. The OFHS in this work is fast response and the response time for the rising and decay process was about 2.2 s and 3.2 s respectively. • A fullerene derivative, C 60 -THAM, was synthesized and its application in the fiber humidity sensor was researched. • The humidity sensor is fast response and the rising and decay time is about 2.2 s and 3.2 s respectively. • The sensitivity is 0.42 nm/RH while the optical-matter reaction length is 150 nm. [ABSTRACT FROM AUTHOR]

The discovery of odorant receptors inspiring researchers to refine the artificial olfactory system with the better design of receptor function and transducer function. Colloidal quantum dots (CQDs) offer an abundance of available surface area for chemical and electronic interactions, making them ideal receptors for gas molecules. In this paper, we propose optical fiber antenna (OFA) that mimic the structure and function of biological antenna by using CQDs as the artificial receptors for gas molecules. The charge transfer between the gas molecules and quantum dots is designed to modulate the interaction between the quantum dot solids and light through the variation of refractive index (RI) of quantum receptors. Specifically, lead sulfide (PbS) CQDs serving as NO 2 receptors were deposited on the optical structure for comparison. The solution-processability of CQDs enable their uniform and conformal coating on the fiber. The OFA exhibited a sensitivity of 35 pm ppm−1 for NO 2 sensing at room temperature with the detection limit estimated to be 1 ppb. The proof of OFA concept may pave the way to artificial olfactory networking and will benefit for the development of high precise, large scale, real time distributed gas monitoring application beyond human olfaction. • Optical fiber antenna that mimics the structure and function of biological antenna for gas molecules detection was proposed. • The charge transfer will modulate the interaction between the QD solids and light through the variation of RI of receptors. • OFA exhibited a sensitivity of 35 pm ppm-1 for NO 2 sensing with the detection limit estimated to be 1 ppb. [ABSTRACT FROM AUTHOR]

Colloidal quantum dot (CQD) is emerging as new substitution gas sensing materials due to the excellent accessibility of gas molecules to CQD surfaces realized via surface ligand removal. Here we demonstrated highly sensitive and selective H 2 S gas sensors based on PbS CQD solids. The sensor resistance decreases upon H 2 S gas exposure and the response is defined as the ratio of the sensor resistance in clean air to that in H 2 S gas. As the operating temperature increased within the range 50–135 °C, the sensor response increased while the response and the recovery time decreased. The sensor was fully recoverable toward 50 ppm of H 2 S at 108 °C and the highest response was 2389 at 135 °C with the response and recovery time being 54 s and 237 s, respectively. The dependence of sensor response on the H 2 S gas concentration in the range of 10–50 ppm is linear, suggesting a theoretical detection limit of 17 ppb toward H 2 S at 135 °C. Meanwhile, the sensor showed superb response selectivity toward H 2 S against SO 2 , NO 2 and NH 3 . We propose that the PbS CQDs film where the surface states determine the conduction type via remote doping may undergo a p-to-n transition due to H 2 S exposure at elevated temperatures. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) sensors have great advantages in real-time and in-situ gas detection due to the inherent advantages of passive and wireless operation. This inevitably requires the sensor to improve gas sensing performances at room temperature. The facet engineering of metal oxide (MOS) provided an effective way to obtain MOS gas-sensitive materials with superior performance by the facet-dependent properties. Here, we developed a novel strategy to prepare SnO 2 quantum wires with different (110) facets ratio by adjusting the synthesis time. The as-prepared SnO 2 quantum wires were integrated into SAW devices to optimize the performance of the gas sensor. When the synthesis time was 8 h, the response of the SAW gas sensor was enhanced with the frequency change of 17 kHz, the response and recovery times of 45 s and 96 s, respectively. Our experimental results revealed that the effect of mass loading was the responsible underlying mechanism for the superior NO 2 gas sensing performances. In addition, the adsorption and charge transfer properties between the SnO 2 surface and NO 2 molecules were further discussed by QCM and resistance measurement, respectively. The calculation of density functional theory (DFT) also proves the adsorption energy of NO 2 on the SnO 2 (110) facet is larger than the (101) facet and (211) facet, indicating that the (110) facet is more beneficial to the adsorption of NO 2 molecules. This indicated that the facet engineering of MOS by facet-dependent properties to enhance gas sensitivity may open new opportunities for the design of SAW sensor. [Display omitted] • The SnO 2 with different (110) facets ratio were prepared by adjusting the synthesis time. • The SnO 2 with more exposed (110) facets exhibited high sensor response and low detection limit. • Chemiresistor sensor and QCM sensor were used to understand the SAW sensing mechanism for the NO 2. [ABSTRACT FROM AUTHOR]

Aqueous organic amines are threatening to organisms and ecosystem balance. Although many techniques have been used for detection, the simultaneous identification of both its type and concentration is still challenging due to its structural similarity and low environmental concentration. Sensor array is a powerful sensing technology to identify analytes via unique fingerprint patterns. However, the information from general sensor array based on the weak interaction limited its discernibility ability to similar substances. Here, we propose to design molecules with various sensing units based on strong interactions and hence rich spectral change, then construct a tri-probe sensor array for efficient fluorescent differentiation of aqueous organic amine. Different fluorescence responses to different concentrations and types of organic amines were produced by this array. Varied interaction between the probes and the amines was proved by NMR spectra analysis. The combination of probes can produce rich and complementary fluorescence changes. These unique fluorescence response patterns can be well identified and processed using hierarchical analysis (HCA) and linear discriminant analysis (LDA), enabling the 99.35% accurate differentiation of 5 concentration orders (1 μM ~ 10 mM) of 6 kinds of amines. Blind detections for samples of diethylamine, diisopropylamine in tap water and propylamine, hexylamine, trimethylamine, triethylamine in other five domestic wastewater all can be classified and distinguished successfully. The influence of temperature, pH and mental ions are also considered. This sensing method, with the feature of facile preparation, fast response, and excellent discrimination accuracy, can provide a potential option for fast quality test of water. The colorimetric sensor array based on molecular design and algorithm (HCA and LDA) can detect amine components in water environments with the accuracy of 99.35%, whose concentration covers the concentration of 1 μM to 10 mM. The detection and differentiation of amines helps pinpoint types of pollutant, which is of great significance to the rap-id primary screening of the concentration of organic amines in environmental water and the preliminary location of the source of drug production. [Display omitted] • A fluorescent sensor array based on RGB changes which can classify types and concentration of amines is provided. • By molecular design, a maximum output with minimum probes to detect multiple amines are realized. • Through HCA and LDA, this fluorescent sensor array can identify amines (1 μM to 10 mM) in water with the accuracy of 99.35%. [ABSTRACT FROM AUTHOR]

Abstract: A surface acoustic wave (SAW) H2S gas sensor with high sensitivity and good recovery characteristics was presented. SnO2 films with an average grain size of 25nm were deposited as the sensitive film at the surface of the SAW devices using an aqueous sol–gel technique. The sensitivity toward H2S gas was increased by optimizing parameters including film thickness and operating temperature. The maximal response (center frequency change) toward 68.5ppm of H2S was 112.232kHz when the sensor was operated at 120°C with SnO2 film thickness of 275nm. The frequency response of the SAW sensor showed good selectivity and a linear relation to H2S gas with different concentrations. We demonstrated that the dominant sensing mechanism of this SAW sensor is the acoustoelectric effect arising from the electrical conductivity change of the SnO2 film. Further analysis of the optimum parameters and the good recovery characteristics were conducted based on the acoustoelectric effect. [Copyright &y& Elsevier]

Abstract: Pure and Cu-doped SnO2 thin films are prepared by aerosol-assisted chemical vapor deposition for H2S detection. Three doping routes are used to prepare thin films with different structures. The response and recovery characteristics are analyzed. The thin film is able to completely recover between testing cycles at room temperature and has the response and recovery times of 60 and 90sec, respectively. The selectivity test illustrates that the film is only sensitive to H2S and acts no response to CO and CH4 at all. The relationships between response and gas concentration as well as operating temperature are also discussed. [Copyright &y& Elsevier]

Abstract: SnO2 thin films are prepared by sol–gel spin-coating technique and different cooling rates are employed in annealing process. The influences of cooling rate and re-annealing on gas sensing characteristics of thin films are investigated, concluding slow cooling rate benefits gas sensing characteristics. The variation of oxygen vacancies density is found to be responsible for the conclusions. Thus, a model of oxygen vacancy distribution is proposed based on the formation and dynamics of vacancies. The diffusion equation is established on the basis of diffusion and exclusion of vacancies in cooling process and the steady state solution reveals a gradient distribution of oxygen vacancies, which exhibits a trend that vacancies accumulate near the surface. Combining the solution of distribution equation and Schottky model, the quantitative expressions of film resistance (R/R 0) and response (S) are formulated. The validity and limitation of the model are also discussed. [Copyright &y& Elsevier]

Abstract: SnO2 thin films on alumina and silicon substrates are prepared by sol–gel technique using dip-coating method. The films are sensitive to H2S gas and the one on alumina exhibits response of 81 at low concentration of 3.4ppm. The sensor response and film conductance are measured in the atmosphere with different reducing gas concentration and furthermore the relationship between film conductance variation and gas concentration is summarized as a linear curve in a logarithmic coordinate with the slope of 1/2, coinciding with the power law. Based on this relationship, the modification of the gas diffusion theory is performed by substituting the former linear assumption with a new one. The modified expression is validated by correlations of experimental sensor response versus film thickness and gas concentration. The probable application of the modified expression on explaining response of thin films to various reducing and oxidizing gases is proposed. [Copyright &y& Elsevier]

[Display omitted] • SnO2 colloidal nanowires was synthesized by solvothermal without high-temperature sintering. • Pd-SnO2 colloidal nanowires exhibited high response, fast response/recovery H2 sensing at 150 ℃. • Sensing mechanism was investigated by theoretical calculation and adsorption kinetics study. Sensitive H 2 gas sensors are highly desirable for the prediction and early-warning of H 2 leakage. Low-dimensional nanostructures of metal oxide semiconductor emerge as promising materials candidates, but it remains a challenge to preserve the nanostructures in the real sensors. In this work, we demonstrated highly sensitive H 2 gas sensors based on porous network of SnO 2 nanowires that exhibited ultrasmall diameter ∼ 2 nm. Colloidal SnO 2 nanowires synthesized via a solvothermal process were drop-coated onto the commercial alumina substrates, followed by in-situ annealing treatment at 350 °C to remove the surface ligands. The sensors exhibited sensitive response with linear dependence on the H 2 gas concentration ranging from 2 ppm to 100 ppm when operated at 250 °C. Typically, the sensor had a response of 13 toward 40 ppm of H 2 , with the response and recovery time being 15 s and 31 s, respectively. To further improve the sensor performance, Palladium doped SnO 2 nanowires were thoroughly investigated. It's shown that, the operating temperature of the sensor decreased from 250 °C to 150 °C after Pd doping, and the response and recovery time decreased to 6 s/3 s. The superb sensitivity was attributed to the enhanced gas reception, electron transport as well as utility factor owing to the network nanostructure of ultrathin SnO 2 nanowires and catalytic activity of Pd, according to theoretical calculation and adsorption kinetics studies. Combined with the excellent solution processability, the colloidal SnO 2 nanowires are potentially attractive for next-generation gas sensors with lower power consumption and integration with silicon-based substrates. [ABSTRACT FROM AUTHOR]

• A size-selective ZIF-8 used for coating on the external surface of the biomimetic PCN-222. • This sensor can make catechol detection solvent-durability, long-term stability and reliable. • The yolk/shell PCN-222@ZIF-8 based sensor showed high sensitivity for catechol but not for dopamine or L-DOPA. • This work opens a new avenue for construction of MOF@MOF biomimetic sensors. Metal-organic frameworks (MOFs) have potential as heterogeneous biomimetic catalysts due to their high surface area, tunable porosity, and diversity of metals and functional groups. However, the activity and substrate specificity of pure monomeric MOFs still must be improved. Here, a size-selective MOF coating on the external surface of a biomimetic MOF is used to overcome these limitations of pure monomeric MOFs. The synthesis process of the biomimetic material involved first the coating of porous coordination network (PCN-222) cores with polyvinylpyrrolidone (PVP) as a structure-directing agent and then the modification of zeolitic imidazolate frameworks (ZIF-8). The yolk/shell PCN-222@ZIF-8-based sensor showed high selectivity for catechol but not for dopamine or L-DOPA. The PCN-222@ZIF-8 hybrid material-based sensor displayed 10 times more sensitivity than the PCN-222-based sensor, with low limit of detection (LOD) at 33 nmol L−1. Thus, ZIF-8 is a shell which allows the diffusion of specific substrate to the active sites of the PCN-222 and enriches the substrate. Furthermore, the PCN-222@ZIF-8 exhibits solvent adaptability, which overcomes the drawback of the natural HRP enzyme. This work opens a new avenue for construction of MOF@MOF biomimetic sensors and other applications. [ABSTRACT FROM AUTHOR]

• Employment of GaN honeycomb nanonetwork for the FET type H 2 gas sensor. • Demonstration of a H 2 sensor with small LOD ∼34 ppb and fast response ∼3 s. • Employment of Pt nanonetwork as the catalyst for H 2 gas dissociation. • First discovery of electron tunneling effect during H 2 gas detection. Material architecture design plays a crucial role in developing gas sensors. GaN has been proposed as a promising material for H 2 gas sensor. However, it is subject to long response time and large low limit of detection (LOD). via spherical metal pattern technology, honeycomb can be created in GaN nanostructure but has yet to be explored. Herein, the GaN honeycomb nanonetwork was utilized to fabricate a field effect transistor (FET) type hydrogen (H 2) gas nanosensor and its H 2 gas sensing performances were systematically investigated. Through the combination of the novel honeycomb nanonetwork with the field effect modulation, we demonstrate high performance H 2 gas sensor with wide detection concentration range, fast response, and small LOD. It is worth noting that the response time for H 2 gas is very fast, as short as ≤3 s. Most importantly, the LOD for this FET type sensor is as small as ∼ 34 ppb. Density functional theory (DFT) calculation was utilized to study the H 2 gas sensing mechanism. Significant reduction of Schottky barrier and improvement of the tunneling probability of the Pt-GaN metal-semiconductor interface were observed. Finally, a model is proposed to explain the H 2 gas sensing mechanism. [ABSTRACT FROM AUTHOR]

• For the first time used Cu(OH) 2 nanowires and graphene oxide as the sensing film of humidity sensor. • The prepared humidity sensor showed short response time (1.9 s) and recovery time (7.6 s). • The potential application of the prepared humidity sensor in respiration monitoring was demonstrated. Respiration is an essential physiological process of human body and acts as a vital sign for personal health. Humidity sensing is a promising way to monitor respiration based on the humidity change when people breathing. Here we demonstrate Cu(OH) 2 nanowires and graphene oxide (GO) based quartz crystal microbalance (QCM) humidity sensor for real-time respiration monitoring. The Cu(OH) 2 nanowires/GO composites humidity-sensitive film was fabricated by the method of in-situ growth and drop-casting. The morphology and structure of the Cu(OH) 2 nanowires/GO composites were characterized by energy dispersive spectrometer (EDS), Raman, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopic (TEM), high resolution TEM (HRTEM), and energy dispersive X-ray spectroscopy (EDXS). The nanocomposites with large surface area and abundant oxygen-rich functional groups lead to good humidity sensing performance. When changing relative humidity (RH) between 0 and 80%, our device exhibits high sensitivity (52.1 Hz/%RH), fast response and recovery (within 1.9 s and 7.6 s, respectively) and high linearity (R2 = 0.9968). Different breathing patterns can be distinguished, including normal breathing, apnea, speaking, nose and mouth respiration, and humidity variations before and after water intake, showing potential applications in analyzing human health-status. [ABSTRACT FROM AUTHOR]

• A fluorimetric test strips-based strategy was developed using Au-Ag nanospheres and metal–organic frameworks of ZIF-8. • Au-Ag nanospheres were fabricated with strong fluorescence by harvesting Au-Ag nanoclusters using a desolvation route. • A vacuum-aided drying route was applied with super-hydrophobic patterns for uniform coating of nano-probes on strips. • Test strips were shelled with ZIF-8 showing further improved fluorescence, environmental robustness, and storage stability. • The fluorimetric test strips can probe Cys in hela cells with high sensitivity and selectivity. A fluorimetric test strips-based strategy has been initially developed for probing trace cysteine (Cys) in hela cells using gold-silver (Au-Ag) nanospheres and metal-organic frameworks of ZIF-8. Bimetallic Au-Ag nanoclusters were first synthesized by the protein-templated biominerization and then harvested by a desolvation route to form Au-Ag nanospheres showing strong fluorescence that could be specifically quenched by Cys. The as-prepared nanospheres were coated onto test strips to be further shelled with ZIF-8 by using a vacuum-aided fast drying route with super-hydrophobic patterns. It was discovered that the so fabricated test strips could not only achieve uniform coatings of fluorescent nano-probes, but also the ZIF-8 shell-enabled improvement of fluorescence, environmental and storage stabilities. In addition to the evaluation of Cys in serum samples, the developed fluorimetric test strips can facilitate the direct detection of Cys in hela cells with the linear concentrations ranging from 0.0032 to 32.0 μM, thus promising for the point-of-care monitoring of low-level Cys for the clinical early diagnosis of some diseases like cancers. Besides, such a proposed protocol forthe fabrication of stable and uniform test strips using MOFs coatings and super-hydrophobic patterns may be tailored for designing various solid-state testing platforms for the extensive analysis applications. [ABSTRACT FROM AUTHOR]