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Herein, we report a rapid and sensitive colorimetric detection of Hg2+ by designing a specific DNA probe with phosphorothioate RNA modification (PS-probe) for Hg2+ recognition and utilizing DNA-modified gold nanoparticles (DNA-AuNPs) as the transducer. The distance between two DNA-AuNPs is controlled by a linker DNA, providing the linker DNA-regulated aggregation or dispersion status of AuNPs in solution. Exonuclease III (Exo III) can trigger the recycled digestion of linker DNA strands, inhibiting the reformation of aggregated nanoparticles and hence leading to a color shift from purple to red. However, the Hg2+-induced cleavage of the PS-probe can efficiently prevent the digestion of linker DNA strands by Exo III and hence reassemble the modified AuNPs to form aggregates in purple color. Thus, a positive correlation between the linker DNA strands left and the addition of Hg2+ provides a quantitative basis for Hg2+ sensing. A linear range of A520/A700 versus Hg2+ concentration is achieved in the range 2–100 nM associated with a detection limit as low as 1.30 ± 0.04 nM. Moreover, the biosensor exhibits excellent selectivity for Hg2+. The strong selectivity behavior was confirmed by recoveries ranging from 96 to 114% in real water samples. [ABSTRACT FROM AUTHOR]

Development of room-temperature gas sensors with excellent sensing performances for detection of dimethyl methylphosphonate (DMMP, a simulant of organophosphate) has aroused considerable attention. However, the weak adsorption ability of sensing materials toward DMMP molecules causes poor sensing performances. In this work, a multisite strategy for enhancing sensitivity was proposed by introduction of both N-doped carbon nanoparticles (N-CNPs) and copper ions onto the surface of rGO (designated as GNC). Impressively, optimal GNC-3 exhibits the response value of 10.2% toward 100 ppm DMMP, which is 5.3 times higher than that of pristine rGO. This mechanism for multisite-assisted enhanced DMMP sensing performances was investigated by combined characterizations of Fourier-transform infrared spectra, UV-Vis spectra, photoluminescence spectra and Mott-Schottky curves. Besides the construction of multisite, improvement of hydrogen bonding interactions between DMMP molecules and N-CNPs in hybrids assisted by copper ions, and decrease of conduction band potential by formation of ternary hybrids also contribute to enhance the sensitivity of DMMP sensors. These findings not only provided new insights into designing high-performance room-temperature gas sensors, but also promoted the fundamental research on sensing mechanism for room-temperature gas sensors. • A multisite strategy for enhancing sensitivity was proposed by constructing three kinds of DMMP adsorption active sites. • GNC hybrids demonstrate 5.3-fold improvement in response to 100 ppm DMMP compared to pristine rGO hybrids. • This mechanism for multisite-assisted enhanced DMMP sensing performances was confirmed by the spectroscopy. [ABSTRACT FROM AUTHOR]

Cyanobacterial harmful algal blooms in freshwater systems can produce cyanotoxins, such as microcystins (MCs) and nodularins (NODs), presenting serious threats to human health and ecosystems. Required routine monitoring of cyanotoxins in water samples, as posed by U.S. EPA drinking water contaminant candidate list 5 (CCL5), demands for cost-effective, reliable and sensitive MCs/NODs detection methods. We report the development of a colorimetric paper-based immunochip assisted by nanozyme catalysis with a smartphone readout system for rapid detection of cyanotoxins in water. We show that the introduction of biorthogonal click reaction enables in situ facile self-assembly of multi-layers of peroxidase-like nanozyme onto the anti-MCs/NODs monoclonal antibody. We can detect 13 variants of MCs/NODs even in the sub-microgram per liter range with detection limit of below 0.7 μg/L and satisfactory recovery percentages between 88 and 120% in different water matrices. Our technology shows a good correlation with the well-developed ELISA technology, demonstrating its great potential applications in resource-limited or less-developed regions for on-site and large-scale screening of cyanotoxins in water environment. [Display omitted] • A paper-based biochip with high sensitivity and throughput for cyanotoxins. • A layer-by-layer bioorthogonal click reaction for nanozyme amplification. • Limit of detection below 0.7 μg/L towards 13 variants of cyanotoxins. • Satisfactory recoveries in various water environments. • An entire detection cycle time of less than 60 min. [ABSTRACT FROM AUTHOR]

Optimally increasing the catalytic activity of Co3O4‐based materials is crucial for promoting their practical applications for acetone detection; however, this still remains challenging. Herein, a strategy is proposed in this work to increase the catalytic activity of Co3O4 toward the oxidation of acetone through the synergistic effect of boron doping and chemical reduction, which can substantially improve the sensing performance for acetone detection. The characterization results confirm that the present strategy facilitates the formation of more oxygen vacancies and increases the content of Co2+ ions serving as active sites. As expected, the optimal sensor yields a higher response. To extend the practical application to the auxiliary diagnosis of diabetes through exhaled breath, the optimal sensors distinguished between acetone concentrations in the breath of healthy individuals and in the simulated breath of patients with diabetes. Detailed gas‐sensing measurements reveal that the enhanced acetone sensing performance is attributed to the increased catalytic activity of materials for oxidation of acetone by the Mars–van Krevelen, Langmuir–Hinshelwood, and Eley–Rideal mechanisms. This study provides new insights into the fabrication of high‐performance metal oxide‐based gas sensors by improving the catalytic activity of sensing materials. [ABSTRACT FROM AUTHOR]

A novel U-shaped fiber-optic evanescent-wave fluorescent immunosensor was designed that exploits light-sheet excitation of skew rays in a passive fiber for sensitive microcystin-LR (MC-LR) detection in real-time. In particular, a light sheet comprising a thin plane of light can be concentrated into exciting the optimum ray group, resulting in enhanced interaction between light and fluorophores. Meanwhile, skew rays excited by transmitting light into an optical fiber with an angle offset allow a much higher number of total-internal-reflections with increased interaction length along the fiber interface, which strengthens the light-matter interactions. Under the optimal angle offset, the proposed evanescent wave fluorescent immunosensor is the first demonstration of integrating light-sheet skew rays and a U-shaped fiber-optic probe for enhanced sensitivity. The results show that fluorescence sensitivity of the U-shaped fiber-optic probe with light-sheet skew rays excitation is 16 times higher than that of collimated skew rays excitation. Combined with this newly designed light-sheet skew rays enhanced U-shaped fiber-optic fluorescent immunosensor, a sensitive and real-time MC-LR detection method was established based on the indirect competitive immunoassay principle. Real environmental water samples spiked with MC-LR were determined by the immunosensor with recovery rates between 85% and 112%. The present system could be an alternative tool for the on-site environmental monitoring, in-field food safety assurance and clinical diagnostics. It also advances the fiber-optic sensors field in terms of experimental design. 1. The first to apply light-sheet excitation of skew rays in optical fiber based evanescent wave fluorescent immunosensor for immunoassay towards MC-LR in water samples. 2. Fluorescence sensitivity of the U-shaped fiber-optic probe with light-sheet skew rays excitation is 16 times higher than that of collimated skew rays excitation. 3. An indirect competitive immunoassay is adopted for sensitive real-time microcystin-LR (MC-LR) detection. 4. Application of this system was confirmed with high recoveries in real environmental water samples. 5. Optical fiber surface can be reused for about 100 times. [ABSTRACT FROM AUTHOR]

• A dual-functional smartphone-based sensor was developed. • Facile light path was integrated into an attachment aligned to a smartphone camera. • In colorimetric mode, various analytes were detected sensitively with wide linear ranges. • In chemiluminescent mode, the reliability of this sensor was proved by H 2 O 2 detection. • A fluoride concentration map in Suzhou, China, was generated by this sensor. Reliable field techniques for sensing and mapping environmental contamination has the potential to revolutionize environmental monitoring, among which smartphone-based sensors (SPSs) are playing an increasing role owing to the low cost and the widespread ownership of smartphone. How to integrate more functions on SPSs has been a hot field of research. In this study, a dual-functional SPS for colorimetric and chemiluminescence detection were developed through simple and efficient light path design within an integrated 3D-printed attachment, and the smartphone application design makes it possible for simpler analysis, storage and transmission of data. In colorimetric detection, due to the use of white LED and diffraction grating, this sensor could determinate samples in various color, and five contaminants, including fluoride, ammonia nitrogen, orthophosphate, turbidity, and chlorine, were detected with good reliability. The chemiluminescence determination of H 2 O 2 indicated broader potential application fields. As a successful case study, this SPS was used to map the fluoride concentration of surface water in Suzhou (China) with good sensitivity (0.06 mg/L limit of detection, 0.1∼2 mg/L linear range). In summary, the dual-functional and on-site sensing capabilities of this SPS show prospects in the field of environmental monitoring, even in medical diagnosis, food safety and so on. [ABSTRACT FROM AUTHOR]

• Facile and ultrasensitive detection of Hg2+ was achieved with an LOD of 0.2 nM. • Cofactor replacement from Mg2+ to Co2+ removed barrier of unmodified AuNPs aptasensor. • An aptasensor was constructed by Exo-III assisted target recycling amplification. Facile and ultrasensitive detection of Hg2+ in water environment remains challenging. Exonuclease III (Exo-III)-assisted target recycling is one of the most popular amplification strategies. Although the magnesium (II) ions are widely acting as cofactors of Exo-III, we recognized that Mg2+ cofactors would strongly disturb the charge distribution on citrate-stablized gold nanoparticles (in the general sense, unmodified AuNPs) surface, thus generate false positive colorimetric signals. To address this issue, we first put forward the view that the cobalt (II) ions can function as the Exo-III cofactor and successfully construct a novel label-free colorimetric aptasensor for facile and ultrasensitive detection of Hg2+ using Hg2+-triggered Exo-III-assisted signal amplification and unmodified AuNPs as indicators. A hairpin-looped DNA probe was rationally designed with thymine-rich recognition termini and specifically recognized trace Hg2+ by a stable T–Hg2+–T structure. A blue-to-red color change of AuNPs with the addition of Hg2+ provided the quantitative detection of Hg2+ with a limit of detection of 0.2 nM and a linear working range from 0.5 nM to 5.0 nM. The whole testing time for one assay was approximately 40 min. Real water samples, even containing Hg2+ at 1 nM, could be determined by the aptasensor with recovery rates from 97% to 103%. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO)-based materials are deemed as promising candidates for fabrication of room-temperature gas sensors, while a tougher challenge is to develop an effective strategy for improving gas responses. Here, a noble metal decoration strategy is developed to enhance NO2 responses of α-Fe2O3/SnO2–rGO hybrids. Noble metal decorated α-Fe2O3/SnO2–rGO hybrids were prepared by depositing noble metals onto α-Fe2O3/SnO2–rGO hybrids through reduction of noble metal ions by NaBH4. Most importantly, Pt modified α-Fe2O3/SnO2–rGO hybrids (designated as Pt-FSR) exhibit the highest response value of 21.3 toward 5 ppm NO2, which is much higher than that of α-Fe2O3/SnO2–rGO (8.8). Combined characterization studies indicate that the enhanced NO2 response of Pt-FSR is attributed to the narrow band gap of Pt-FSR, small particle size and excellent catalytic activity of Pt. The NO2 sensing mechanism is also investigated by FT-IR spectroscopy. The findings proposed in this work not only broaden the study of room-temperature gas sensors, but also provide suggestions for discovering the gas sensing mechanism. [ABSTRACT FROM AUTHOR]

To meet the severe water pollution status, multi-target biosensor becomes one of research focus. We herein report a novel duplex functional fluorescent biosensor for the label-free and separate detection of Pb 2+ and Hg 2+ with high sensitivity and selectivity. A K + -induced fluorescent G-quadruplex probe was assembled by a guanine-rich sequence (AGRO100) and N-methyl mesoporphyrin IX(NMM). It changed into a more stably non-fluorescent G-quadruplex structure and a hairpin-like structure upon binding Pb 2+ and Hg 2+ ions, respectively. As a result, the fluorescence decreased with relation to the addition of targets, allowing the separate detection of Pb 2+ and Hg 2+ ions at concentrations as low as 5 nM and 18.6 nM. The linear correlation existed between the fluorescence intensity and the concentration of Pb 2+ and Hg 2+ over the range of 10–200 nM (R 2  = 0.98) and 20–1000 nM (R 2  = 0.99), respectively. All real lake samples, even containing Pb 2+ or Hg 2+ at 50 nM, could be determined by the duplex functional fluorescent probe with recovery rates 96% and 104%, respectively. Considering that this sensor is label-free, simple, time-saving, cost-effective and easy-to-handle, it is possible to pave its way for Pb 2+ and Hg 2+ detection in various application fields. [ABSTRACT FROM AUTHOR]

Toluene is widely used as a solvent and reactant in a wide range of industrial fields; however, gaseous toluene is toxic to humans, causing severe acute respiratory effects. In this case, Co3O4-based chemiresistive gas sensors are promising candidates for monitoring toluene. However, it is challenging to prepare Co3O4-based sensing materials with good toluene sensing performances on a large-scale. In this study, oxygen vacancy-rich Co3O4 materials were successfully synthesized via the reduction of commercial Co3O4 using NaBH4 as the reducing agent (designated as Co3O4-R), and the oxygen vacancy concentrations in Co3O4-R materials were effectively modulated by regulating the NaBH4 concentration. With an increase in oxygen vacancies, the optimal Co3O4-R-5 samples displayed better sensing performances toward 100 ppm toluene at 190 °C than that of the pristine commercial Co3O4, including an enhanced response value of 3.18 (vs. 1.22 for commercial Co3O4) and fast response time of 48 s and recovery time of 38 s. The combination of band structure analysis and chemisorption analysis indicated that the enhanced toluene sensing performances of Co3O4-R is attributed to the synergistic effect of reducing the band gap and activating the surface oxygen species. This work demonstrates the first utilization of commercial Co3O4 for toluene sensing applications, providing a universal and high-throughput preparation method to prepare gas sensing materials using commercial metal oxides. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Pd-SR-V O is fabricated by Pd nanoparticles and oxygen vacancy to modulate SnO 2 modified RGO. • Impressively, the response value of Pd-SR-V O for 1 ppm NO 2 at room temperature reaches to 9.8. • Notably, the response even could reach to 3.0 in 100 ppb NO 2 at room temperature. • The improvement of sensitivity is attributed to the synergy of Pd NPs and oxygen vacancies. Reduced graphene oxides (RGO)-based materials exhibit high carrier mobility and selective recognition ability to NO 2 , making them constitute promising platform for room-temperature NO 2 detection. However, the low sensitivity becomes the main bottleneck for their further development. Here, we demonstrate that synergy of Pd nanoparticles (NPs) and oxygen vacancies can modulate the surface active sites over SnO 2 NPs modified RGO hybrids (labeled as SR), leading to improving the sensitivity of room-temperature NO 2 sensors. Experimentally, a wet-chemical method was used to introduce oxygen vacancies onto SR, leading to forming SR with rich oxygen vacancies (labeled as SR-Vo), which were subsequently deposited with Pd NPs, resulting in preparing Pd NPs loaded SR-Vo hybrids (labeled as Pd-SR-Vo). Impressively, the response value to 1 ppm NO 2 of Pd-SR-Vo hybrids reaches to 9.8, which is much higher than that of R-Vo hybrids (5.6) and SR hybrids (3.3). The improvement of sensitivity toward NO 2 for Pd-SR-Vo hybrids is attributed to the synergy effect of Pd NPs and oxygen vacancies, including shortening the band gap of Pd-SR-Vo hybrids with raising conduction band level, widening the width of electron depletion layer between SnO 2 -Vo and RGO, introducing Schottky contact between Pd and SnO 2 -Vo, improving efficiency for gas sensing reaction. This work not only provides an efficient approach to fabricate high-performance NO 2 sensors, but also opens a new avenue for sensing materials design and modification. [ABSTRACT FROM AUTHOR]

The hydrogen bonding interactions are potentially employed to fabricate high-performance room-temperature gas sensors for detection of organophosphorus. Nevertheless, the low response toward target gases of conventional sensing materials hinders their further applications. Herein, an isolated Cu-N 5 sites engineering strategy is reported to improve sensing performances for polypyrrole-reduced graphene oxide hybrids (PPy-rGO)-based room-temperature dimethyl methyl phosphate (DMMP) sensors. The isolated Cu-N 5 sites were simply constructed by adsorption of Cu2+ ions with PPy-rGO hybrids owing to strong metal-support interactions. X-ray absorption fine structure analysis indicates that Cux+ ions with mean chemical valence of + 1.07 nearly atomically distributed on support with coordination structure of Cu-N 5. Benefiting from the structure regulation by Cux+ ions, as-constructed DMMP sensor demonstrated 4.5-fold improvement in response to 100 ppm DMMP and 2.5-fold improvement in limit of detection, compared to PPy-rGO hybrids. The density functional theory, spectroscopic characterizations and quartz crystal microbalance tests prove that the construction of Cu-N 5 sites not only heightens hydrogen bonding interactions between N H bonds and DMMP molecules induced by newly formed coordination interactions between Cux+ ions and N H bonds, but also serves as new active sites for adsorption of DMMP molecules. This work offers a new avenue for developing high-performance room-temperature gas sensors by heightening hydrogen bonding interactions. • Isolated Cu-N 5 sites-assisted heightening hydrogen bonds strategy is proposed to construct room-temperature DMMP sensors. • Cux+-PPy-rGO hybrids demonstrate 4.5-fold improvement in response to 100 ppm DMMP compared to PPy-rGO hybrids. • The limit of detection of the Cux+-PPy-rGO based sensor is 2 ppm. [ABSTRACT FROM AUTHOR]

The development of metal oxides-based gas sensors for DMMP detection simultaneously possessing low operating temperature, low limit of detection and high sensitivity remains formidable challenges. In this work, a facile and efficient colloidal assembly approach is proposed to prepare Au modified SnO 2 hybrids (Au-SnO 2) with perfect metal-semiconductor interface and successfully used in DMMP detection application. After optimization, the best DMMP sensors based on Au-SnO 2 hybrids display outstanding sensing performances, including high response (1.88 to 680 ppb DMMP), low operating temperature (200 °C), extremely low limit of detection (34 ppb), as well as short response/recovery time (25 s/72 s). The sensing mechanism analysis reveals that the excellent sensing performances are mainly attributed to the synergy of chemical oxidation of DMMP catalyzed by Au-SnO 2 hybrids and physical adsorption of DMMP by hydrogen-bonding interactions. The present work not only provides an insight into the DMMP sensing mechanism, but also offers a promising general approach for development of high-performance gas sensors. [Display omitted] • A facile and efficient colloidal assembly approach waa proposed to synthesize Au modified SnO 2 hybrids. • The Au-SnO 2 -based sensor exhibits high response of 1.88 towards 680 ppb DMMP. • The limit of detection of the Au-SnO 2 -based sensor was 34 ppb. • An integrated chemical oxidation and hydrogen-bonding DMMP sensing mechanism model was first proposed. [ABSTRACT FROM AUTHOR]

The α-MoO 3 -based materials have been intensively investigated as chemiresistive-type gas sensors due to their excellent sensing performances for gas sensing applications. However, there still remains formidable challenges for developing a simple and scalable approach to synthesize α-MoO 3 with controllable structures. Herein, we demonstrated a glucose-assisted combustion synthesis strategy for the synthesis of α-MoO 3 materials with controllable structures. They were obtained by heat treatment of the gels containing ammonium heptamolybdate tetrahydrate and glucose. Owing to the coordination interactions between glucose and heptamolybdate, α-MoO 3 -2 sample obtained by adding 1.8 g of glucose featured the highest oxygen vacancy concentration with an O/Mo atomic ratio of 2.61. The gas sensing measurements indicated that α-MoO 3 -2 had excellent sensing performances for detecting ethanol. Such ethanol sensor displayed the lowest detection concentration of 5 ppm ethanol, high response of 3.86 toward 20 ppm ethanol, and wide detection range of 5–100 ppm. This study sheds light on preparation of metal oxides with controllable structures on a scalable way for various applications. • A glucose-assisted combustion synthesis method have been developed to preparation of MoO3 samples. • The MoO3 sample thus obtained possesses high oxygen vacancy concentration and surface chemical-adsorbed oxygen species. • The MoO3 sample exhibits excellent sensing performances for ethanol sensing. [ABSTRACT FROM AUTHOR]