Actual Detection Limit Research Articles

Metal-organic frameworks-derived hollow Co3O4 nanotubes for efficient detection of toluene vapor

Low chemical reactivity of toluene remains a limiting factor for its efficient detection. Catalytic oxides (eg. Co3O4)-based sensors always exhibit reliable selectivity towards toluene vapor owing to the specific catalytic oxidation activity. However, the sensor response (especially the actual detection limit) still requires for further improving in a harsh ambience. In this paper, a metal-organic framework (MOF)-derived hollow Co3O4 nanotubes has been demonstrated using a sacrificial template (MoO3 nanorods) method. Benefiting from the efficient surface and internal spaces for gas diffusion and gas-solid interaction, this hollow nanotubular Co3O4-based gas sensor declares a low actual detection limit (∼1 ppm), favorable selectivity, and reliable stability towards toluene gas at 200 °C. Moreover, the sensor responses slightly reduce as the increased ambient humidity under a wide range (25–95 %), indicating a suitable feature of anti-humidity response. This work sheds the rationally designing catalytic oxides for detecting low reactive gas molecules (eg. toluene).

Rapid and Ultrasensitive Approach for the Simultaneous Detection of Multilocus Mutations to Distinguish Rifampicin-Resistant Mycobacterium tuberculosis.

The untested empirical medications exacerbated the development of multidrug-resistant Mycobacterium tuberculosis (MDR-TB). Here, we develop a rapid and specific method based on loop-mediated isothermal amplification and duplex-specific nuclease for distinguishing rifampicin-resistant M. tuberculosis. Three probes were designed for the codons 516, 526, and 531 on the RNA polymerase β-subunit (rpoB) gene. These three sites accounted for more than 90% of the total mutations of the ropB gene in the rifampicin-resistant strain. The approach can perform simultaneous and sensitive detection of three mutant sites with the actual detection limit as 10 aM of DNA and 62.5 cfu·mL-1 of bacteria in 67 min under isothermal conditions. Moreover, the positive mode of the approach for MDR-TB can not only deal with the randomness and diversity of mutations but also provide an easier way for medical staff to read the results. Therefore, it is a particularly valuable method to handle major and urgent MDR-TB diagnostics.

Porosity engineering of ZnO nanorods for efficient sensing of n-butanol vapor

• ● A surface mesopores-abundant ZnO nanorod was successfully prepared. • ● This ZnO-based sensor showed a high response (R a /R g =193.7) towards 100 ppm n-butanol. • ● The actual detection limit was achieved as low as 0.1 ppm. • ● An ultrahigh selectivity towards n-butanol was also observed. Porosity engineering is proved as a valid strategy for promoting the gas-sensing response. In this paper, a surface mesopores-rich ZnO nanorod has been successfully demonstrated via a simple solvothermal and followed calcination approach. The microstructure, crystal phase, and surface porosity are further determined by various techniques. Owing to the abundant porosity for favorable gas-permeability and gas-solid interactions, the as-fabricated ZnO sensor displays an apparent response for detecting n-butanol vapor in terms of high response (R a /R g =193.7 – 100 ppm), low detection limit (∼0.1 ppm), as well as remarkable selectivity. Especially, these sensing results towards n-butanol are obviously better than those of reported common ZnO nanorods. This work suggests a reliable method for designing efficient gas sensor by porosity-creating method onto the metal oxide surfaces.

Conductometric H2 sensors at room temperature based on palladium nanoparticles on ceria

The rapid detection of hydrogen (H2) at 25 ℃ was of important. Here, A strategy was used to construct a hydroxyl-oxygen vacancy model by functionalizing palladium nanoparticles (Pd NPs) on cubic, rod and spherical CeO2, through a simple reduction process to obtain the Ce4+/Ce3+ transited and the generated of Pd. The results have shown that the 5.0 wt% Pd NPs /CeO2-C sensor exhibited sensitive H2 sensing performance (response value Ra/Rg of 1322 for 1% H2), and fast sensing speed (response time of only 3 s for 1% H2 and 2 s for 3% H2) in the air at 25 °C, the actual detection limit of the instrument is only 50 ppm. Probably due to the reduction of ascorbic acid, the chemisorbed oxygen and Ce3+ were raised by a factor of 2.95 and 1.62. The synergistic effect of the hydroxyl-oxygen vacancy model and Pd presents a new idea for the detection of hydrogen at 25 ℃.

On the latent limit of detection of thermogravimetric analysis

Thermogravimetric analysis (TGA) is one of the most popular thermoanalytical methods. In this study, theoretical analysis is performed regarding the detection and quantitation limit of % real mass loss of TGA. It is proven that in a TGA measurement, independently of the readability of the sensor and the initial mass sample, there is a hidden error and a prohibitive lowest detection limit (ultimate latent limit of detection, LLoDultimate) imposed by sample’s buoyancy. The actual limit of detection is a function of temperature and is influenced by LLoDultimate. For this actual limit the term “latent limit of detection” (LLoD) is introduced in order to distinguish it from the detection limit defined in theory of Instrumental Analysis. Wherever possible, experimental support is also provided. Besides some general consequences of LLoDultimate recognition e.g. improving detectability, underestimation of mass loss, specific consequences and applications of LLoDultimate for studying thermochemical transition, are discussed.

Graphitic carbon-doped SnO2 nanosheets-wrapped tubes for chemiresitive ppb-level nitric oxide sensors operated near room temperature

The development of low-temperature metal oxide-based sensors with high sensing response towards harmful ppb-level gases remains challenging. Based on the idea of biological structure imitation, we choose wooden hydrangea petals as biotemplate and carbon source to controllably replicate graphitic carbon-doped SnO2 material (GC/SnO2-6) by simply calcining the salt solution-soaked precursor at 600 °C. Its morphology is tube bundle wrapped by corrugated sheets that formed by cross-linkage of nanoparticles. The internal surface of tube wall is decorated with nanoaggregates. The fabricated GC/SnO2-6 sensor exhibits response value of 256.3 towards 1 ppm NO at 50 ℃, which is 9.9 times higher than that (S = 26.0) of pure SnO2-7 material obtained by calcining at 700 ℃ in air. Meanwhile, this sensor also has short recovery time (42 s), low actual detection limit (50 ppb), satisfactory moisture resistance and long-term stability. Such excellent comprehensive gas-sensing performance is attributed to the homogeneous mesopore and large specific surface area of its biomorphic structure, as well as the synergism of graphitic carbon doping and abundant oxygen vacancies. In addition, the enhanced sensing mechanism is also explored in detail.

Fabrication of a humidity-resistant formaldehyde gas sensor through layering a molecular sieve on 3D ordered macroporous SnO2 decorated with Au nanoparticles

The development of highly-sensitive and moisture resistant semiconductor metal oxide (SMO) gas sensors for practical application remains a challenge. Here, a three-dimensional ordered macroporous (3DOM) SnO2 decorated with Au nanoparticles (NPs) was obtained via a facile self-assembly template method and the Au content was optimized. The resulting 3DOM Au/SnO2 gas sensor displayed remarkable performance, with its response and lower actual detection limit to formaldehyde 10.2 times higher and 500 times lower, respectively, compared to the undecorated 3DOM SnO2 sensor at 110 °C. Meanwhile, the fast response-recovery process and the repeatability, stability, and selectivity of the sensor indicate that it can meet the requirements for practical application. Density functional theory (DFT) calculations revealed that the Au/SnO2 NPs have strong adsorption energies and electrical conductivity, allowing for selective formaldehyde detection. Further, the 3MCM-48 layer protects the 3DOM Au/SnO2 layer from moisture, allowing at least 80 % of the initial response value to formaldehyde to be maintained even at> 90 % relative humidity. Hence, the proposed strategy represents, for the first time, a universal and effective way to achieve high response and moisture-resistant formaldehyde sensors and demonstrates the potential of SMO gas sensors for indoor air monitoring.

Screening of Single-Stranded DNA Aptamer Specific for Florfenicol and Application in Detection of Food Safety.

In this work, the single-stranded DNA (ssDNA) aptamers specific to florfenicol (FF) and having a high binding affinity were prepared using the magnetic bead-based systematic evolution of ligands by the exponential enrichment technique (MB-SELEX). After 10 rounds of the MB-SELEX screening, aptamers that can simultaneously recognize FF and its metabolite florfenicol amine (FFA) were obtained. The aptamer with the lowest dissociation constant (Kd) was truncated and optimized based on a secondary structure analysis. The optimal aptamer selected was Apt-14t, with a length of 43 nt, and its dissociation constant was 4.66 ± 0.75 nM, which was about 7 times higher than that of the full-length sequence. The potential binding sites and interactions with FF were demonstrated by molecular docking simulations. In addition, a colorimetric strategy for nanogold aptamers was constructed. The linear detection range of this method was 0.00128–500 ng/mL and the actual detection limit was 0.00128 ng/mL. Using this strategy to detect florfenicol in actual milk and eggs samples, the spiked recoveries were 88.9–123.1% and 84.0–112.2%, respectively, and the relative standard deviation was less than 5.6%, showing high accuracy.

Ultrasensitive Formaldehyde Sensor Based on SnO2 with Rich Adsorbed Oxygen Derived from a Metal Organic Framework.

SnO2 has been a commonly researched gas-sensing material due to its low cost, good performance, and good stability. However, gas sensors based on pure SnO2 usually show a low response or high working temperature. In this work, laminar SnO2 was obtained by using a Sn-based metal organic framework(Sn-MOF)@SnO2 as a precursor. Sn-MOF@SnO2 is prepared at low temperatures using water and dimethylformamide as a solvent, which is simple, low cost, and easily reproducible. After sintering, Sn-MOF@SnO2 is derived to SnO2 with rich adsorbed oxygen, large specific surface area, and unique nanoparticle piled pores, thus showing excellent gas-sensing properties. The prepared SnO2 has an ultrahigh response value of 10,000 to 10 ppm formaldehyde at an optimal working temperature of 120 °C, a fast response/recovery time of 33 s/142 s, and an actual detection limit of lower than 10 ppb as well as high selectivity and high stability. Density functional theory calculations show that the exposed (110) plane of oxygen-rich vacancies in laminar SnO2 can effectively increase the coadsorption capacity of O2 and formaldehyde molecules, thereby improving the formaldehyde gas-sensing performance of the material. The present original approach paves the way to design advanced materials with excellent gas-sensing properties as well as broad application prospects in formaldehyde monitoring.

Biotemplate-derived mesoporous Cr2O3 tube bundles for highly sensitive and selective detection of trace acetone at low temperature

The development of Cr2O3-based acetone sensor is challenging due to no report on its high sensing ability. To this end, we simply dipped poplar branches into chromic chloride solution to obtain immersed precursors, which were then calcined in air to controllably synthesize two biomorphic Cr2O3 tube bundles. Amongst, the hierarchical tube structure (Cr2O3-500) calcined at 500 °C is replicated from small-size nanoparticles, so that it has uniform mesopore distribution and large specific surface area. Such microstructural features not only favor the rapid accessibility of gas molecules to sensing layer, but also provide an effective platform of more active sites for facilitating surface adsorption and chemical reaction. Especially, under the synergism of few non-stoichiometric CrO3-x species, Cr2O3-based sensor achieves highly sensitive and selective detection to trace acetone gas for the first time. At 133 °C, Cr2O3-500 exhibits high response value (S = 110.1) to 100 ppm acetone gas and low actual detection limit (10 ppb, S = 1.3). Simultaneously, it also has rapid response-recovery characteristics, good stability and moisture resistance. In addition, the sensing mechanism is discussed in details.

Biotemplate-directed synthesis of Cr2O3 mesoporous monotubes for enhanced sensing to trace H2S gas

Herein, Cr2O3 nanomaterials with high sensing towards trace H2S at low energy consumption were controllably synthesized by simple chromium nitrate solution immersion and air calcination using waste willow catkins as bio-template. Amongst, Cr-400 hierarchical structure obtained from the calcination of 400 °C exhibits monotube morphology assembled by well-crystalline nanoparticles, and it has uniform mesoporous distribution and large specific surface area. This structure features help to the fast accessibility of gas molecules and provide an effective platform for surface adsorption and chemical reaction, which dramatically enhances the detection ability of Cr2O3-based sensor to trace H2S gas for the first time. At low operating temperature of 133 °C, Cr-400 sensor exhibits high response value (S = 24.4) to 50 ppm H2S gas and low actual detection limit (100 ppb). Simultaneously, it also has good comprehensive gas-sensing performance involving reversible response-recovery, high selectivity, satisfactory stability and moisture resistance. In addition, we also discussed the enhanced gas-sensing mechanism in details.

Sensitive and single-shot OH and temperature measurements by femtosecond cavity-enhanced absorption spectroscopy.

In many low-temperature plasmas (LTPs), the OH radical and temperature represent key properties of plasma reactivity. However, OH and temperature measurements in weakly ionized LTPs are challenging, due to the low concentration and short lifetime of OH and the abrupt temperature rise caused by fast gas heating. To address such issues, this Letter combined cavity-enhanced absorption spectroscopy (CEAS) with femtosecond (fs) pulses to enable sensitive single-shot broadband measurements of OH and temperature with a time resolution of ∼180 ns in LTPs. Such a combination leveraged several benefits. With the appropriately designed cavity, an absorption gain of ∼66 was achieved, enhancing the actual OH detection limit by ∼55× to the 1011 cm-3 level (sub-ppm in this work) compared with single-pass absorption. Single-shot measurements were enabled while maintaining a time resolution of ∼180 ns, sufficiently short for detecting OH with a lifetime of ∼100 μs. With the broadband fs laser, ∼34,000 cavity modes were matched with ∼95 modes matched on each CCD pixel bandwidth, such that fs-CEAS became immune to the laser-cavity coupling noise and highly robust across the entire spectral range. Also, the broadband fs laser allowed simultaneous sensing of many absorption features to enable simultaneous multi-parameter measurements with enhanced accuracies.

Selection and Characterization of DNA Aptamers for Constructing Aptamer-AuNPs Colorimetric Method for Detection of AFM1.

Aflatoxin M1 (AFM1), one of the most toxic mycotoxins, is a feed and food contaminant of global concern. To isolate the ssDNA aptamer of AFM1, synthesized magnetic graphene oxide nanomaterials, 12 rounds of subtractive systematic evolution of ligands by exponential enrichment (SELEX) selection were carried out. As a result, 24 candidate aptamers were selected, and their sequence similarity exceeded 97%. Their binding affinity and specificity were further examined by fluorescence and biofilm interferometry (BLI) methods. One aptamer (Apt-5) against AFM1 with a high affinity and specificity was isolated and demonstrated to be the optimal aptamer, whose dissociation constant reached the nanomolar level, Kd = 8.12 ± 1.51 nM. Additionally, molecular docking studies were used to predict the possible binding sites and mechanisms of the two. Based on Apt-5, an unlabeled aptamer-AuNPs colorimetric method was established to detect AFM1 in milk with a linear range of 0.078–10 ng/mL, and the actual detection limit was 0.078 ng/mL. These results demonstrated that this detection technique could be useful for the quantitative determination of AFM1 in milk and dairy products.

Non-nucleic acid extraction and ultra-sensitive detection of African swine fever virus via CRISPR/Cas12a.

Early diagnosis of the African swine fever virus (ASFV) is the main preventive measure for ASFV. Here, we developed a fluorescent biosensor and lateral flow assay (LFA) strip based on direct PCR combined with CRISPR/Cas12a system for ASF. Direct PCR can simultaneously split samples and efficiently amplify without sacrificing sensitivity, which eliminated the steps of nucleic acid extraction. Furthermore, by the CRISPR/Cas12a, the biosensor addressed false positives caused by non-specific amplification and had high sensitivity with the actual limit of detection (LOD) of 7.6×10-4 ng·μL-1 (4 copies·μL-1). In addition, the strategy was built on the lateral flow assay (LFA) strip to achieve visual and portable detection for point-of-care testing. Moreover, the biosensor by a fluorometer and LFA strip showed a high accuracy to rival qPCR in actual sample detection. Therefore, the biosensor is an ultra-sensitive and specific tool that can replace traditional methods. KEY POINTS: • No nucleic acid extraction, direct PCR-simplified steps, and reduced time and cost • CRISPR/Cas12a solved the false positives caused by nonspecific amplification • The combination of the LFA strip and biosensor is more convenient for POC detection.

Intrinsic specificity of plain ammonium citrate carbon dots for Helicobacter pylori: Interfacial mechanism, diagnostic translation and general revelation.

The exploitation of carbon dots (CDs) is now flourishing; however, more effort is needed to overcome their lack of intrinsic specificity. Herein, instead of synthesizing novel CDs, we reinvestigated three reported CDs and discovered that plain ammonium citrate CDs (AC-CDs) exhibited surprising specificity for Helicobacter pylori. Notably, we showed that the interfacial mechanism behind this specificity was due to the affinity between the high abundant urea/ammonium transporters on H. pylori outer membrane and the surface-coordinated ammonium ions on AC-CDs. Further, we justified that ammonium sulfate-citric acid CDs also possessed H. pylori-specificity owing to their NH4+ doping. Thereby, we suggested that the incorporation of a molecule that could be actively transported by abundant membrane receptors into the precursors of CDs might serve as a basis for developing a plain CD with intrinsic specificity for H. pylori. Moreover, AC-CDs exhibited specificity towards live, dead, and multidrug-resistant H. pylori strains. Based on the specificity, we developed a microfluidics-assisted in vitro sensing approach for H. pylori, achieving a simplified, rapid and ultrasensitive detection with two procedures, shortened time within 45.0 ​min and a low actual limit of detection of 10.0 ​CFU ​mL−1. This work sheds light on the design of more H. pylori-specific or even bacteria-specific CDs and their realistic translation into clinical practice.

A dual-function luminescent probe for copper(II) ions and pH detection based on ruthenium(II) complex

A new ruthenium complex-based luminescent probe Ru-impa for Cu2+ and pH detection has been synthesized and characterized. Ru-impa could rapidly and selectively detect Cu2+ in aqueous solutions and the working pH ranges from weakly acidic to alkaline. The detection limit calculated using the S/N and S/B ratio was 24.7 nM and 3.4 μM, respectively. The test strips for practical detecting application were also prepared and the actual detection limit in drinking water was found to be 3 μM, which is lower than the WHO-guided drinking water limit (30 µM) and the upper limit of human serum free copper content (1.7–3.9 μM). Luminescence imaging study showed that Ru-impa could monitor Cu2+ level fluctuation in the cells. In addition, Ru-impa also shows a sensitive on-off luminescence response when pH > 10, indicating that it can also be used as a pH sensor under extremely alkaline conditions.

Micro-newton strain force and temperature synchronous fiber sensor with a high Q-factor based on the quartz microbubble integrated in the capillary-taper structure.

A micro-newton strain force and temperature synchronous fiber sensor with a high Q-factor is proposed. The sensor is based on a commercial quartz microbubble (QMB, the diameter is less than 80 µm) that is attached to the end surface of the suspending taper integrated in the hollow core fiber. The multi-beam interference and long-active-length make the sensor show both high sensitivity (0.150 nm/mN) and Q-factor (1470 based on the 3dB-bandwidth). The actual detection limit of the strain force reaches about 50 µN. The UV-cured polymer between the QMB and taper improves the temperature sensitivity. The strain force and temperature can be demodulated synchronously by using band-pass filtering and sensing matrix. The sensor can have actual application in micro-newton strain force detection as its low cost and flexible structure.

Improved triple-module fluorescent biosensor for the rapid and ultrasensitive detection of Campylobacter jejuni in livestock and dairy

Campylobacter jejuni (C. jejuni) is a major pathogen responsible for the food-borne illness, campylobacteriosis. To comply with regulatory requirements, its total concentration in food and animal feces must be extremely low. As a result, monitoring this bacterium requires an immediate and cost-effective approach that meets the requirements of the food and livestock industries. The current study reports the development of an improved biosensor comprising three modules viz. a novel transducing module (1), a bi-functional binding/actuating module (2), and an enrichment module (3), synthesized using commercially available components. Module 3, composed of magnetic beads functionalized with a C. jejuni-specific aptamer, utilizes magnetic separation to isolate and enrich C. jejuni from samples. The resulting module 3–C. jejuni complexes can bind module 2 copolymer to form ternary complexes. When these ternary complexes are separated and reacted with module 1, composed of a ferric ion/fluorescein sodium (Fe3+/FLNa) pair, they chelate Fe3+ ions, resulting in the recovery of FLNa after magnetic separation via fluorescence. The as-synthesized biosensor demonstrated a high sensitivity range of 10–107 CFU/mL, and a detection limit of 3 CFU/mL. Additionally, microfluidics was used to eliminate interferences resulting from the module 3-enriched products, while detecting C. jejuni in real-world samples. Herein, the biosensor demonstrated an actual limit of detection (LOD) of 101 CFU/mL within ≈60 min. Thus, the biosensor and the assisting treatments offer a rapid and ultrasensitive platform for detecting C. jejuni in livestock and dairy industries, outperforming conventional approaches.

Spiny gold nanoparticles colloids as substrate for sensing of methyl parathion based on surfaced-enhanced Raman scattering

Herein, two kinds of spiny gold nanoparticles (S-AuNPs1, S-AuNPs2) and a triangular AuNPs (T-AuNPs) colloids were synthesized and utilized as surface-enhanced Raman scattering (SERS) substrates for the methyl parathion (MP) detection. High enhancement factors at 104 level were obtained for three substrates, which is resulted from the high density of “hot spot”. Favorable quantitative analysis capability of three AuNPs toward MP was acquired in the concentration range of micromoles to millimoles per liter, with actual detection limits at several micromoles per liter. Reproducibility and feasibility of the sensors were also verified. All these results suggest the promising potential of application for AuNPs with small curvature radius of nanostructures in trace detection.

Qualitative analysis of gas detection limit of Fourier infrared spectroscopy

The minimum amount that can be detected and quantitatively analyzed by Fourier infrared spectrometer depends on the signal-to-noise ratio of the measured gas spectrum. In order to use Fourier transform infrared absorption spectroscopy to measure CO<sub>2</sub>, CO, CH<sub>4</sub>, N<sub>2</sub>O and other greenhouse gases, the signal-to-noise ratio and instrument detection limit of the mixed gas are studied. We propose a method to calculate the gas detection limit of the instrument through the HITRAN simulation spectrum. In addition, we build an experimental platform to verify the accuracy of the detection limit approximation based on the HITRAN simulation spectrum calculation, which serves as the actual measurement detection limit of the instrument, and we also analyze the reasons why there appears the error between the existing experimental platform and optimization scheme and their deficiencies as well.