Actual Detection Limit Research Articles

Ultrasensitive on-site colorimetric detection of Campylobacter in oyster with a portable biosensing platform based on hydroxamate/Fe3+–violurate chromogenic reaction and smartphone

The contamination of Campylobacter in shellfish poses a health risk for its pathogenicity associated with campylobacteriosis. However, an efficient method to detect this risk is unavailable. Herein, we introduce a portable colorimetric biosensing platform that comprises three modules: an enrichment module 1, a binding and transduction module 2, and a smartphone-based module 3. Module 1 is an aptamer-modified 96-well plate for the specific capture of Campylobacter in a simple and high-throughput manner. Module 2 features a bifunctional biopolymer of L-glutamic acid γ-hydroxamate–alginate–Fe3+ coordinating fusarinine C, which can bind the captured Campylobacter cells and transduce them into amplified color signals upon reaction with Fe3+–violurate complexes. Module 1 achieves a capture efficiency of 97.24 %, and the subsequent addition of module 2 renders colorimetric indication of Campylobacter ranging from 101 to 106 CFU/mL, achieving an actual limit of detection of 8 CFU/mL validated by Campylobacter single-cells. Moreover, the generated colors can be recognized and converted into cell densities by module 3 with ultrasensitivity. Notably, this biosensor–smartphone platform accomplishe reliable high-throughput colorimetric detection of Campylobacter in real samples with an accuracy of 80 %. This work showcases a proof of principle for efficient on-site detection of Campylobacter contamination regarding shellfish farming.

Porphyrin complex-based reversible fluorescent film sensor for differentiating and detecting sarin mimics vapor

This study presents a TAPP-based fluorescent sensor for diethylchlorophosphate (DCP), a surrogate for sarin, addressing the critical challenge of detecting nerve agents. The sensor can form a reversible weak bond interaction with the PO group in sarin by using the reversible weak bond complexation mechanism in the porphyrin cavity, which is the key to realize the reversible function of the sensor. In this study, we constructed a fluorescence probe that combines the advantages of physical process and chemical reaction process sensing, which not only ensures selectivity, but also realizes continuous and reversible real-time detection of DCP. The sensor demonstrates excellent photochemical stability and sensitivity, with an actual detection limit of 10 ppt and a theoretical detection limit of 1 ppt. In addition, it can differentiate challenging interferents like HCl through response kinetics, offering a practical, cost-effective, and environmentally sustainable solution for nerve agent detection in high-risk environments.

Label-Free and DNAzyme-Mediated Biosensor with a High Signal-to-Noise Ratio for a Lumpy Skin Disease Virus Assay.

Lumpy skin disease virus (LSDV) is a severe and highly contagious form of cowpox. As LSDV continues to mutate and there is no vaccine and treatment in nonendemic countries, early detection of LSDV becomes an important basis for epidemic prevention and control, especially for detection of conserved sequences. A new label-free and sensitive fluorescence method was developed based on a light-up RNA aptamer for detecting LSDV. The method integrated recombinase polymerase amplification (RPA), CRISPR/Cas12a, 10-23 DNAzyme, and Baby Spinach RNA aptamer for triple cascade signal amplification. Based on highly sensitive and specific RPA and CRISPR/Cas12a, DNAzyme achieved a third signal amplification. Additionally, the Baby Spinach RNA aptamer had stronger fluorescence signals and higher quantum yields. The label-free method had ultrahigh sensitivity with the actual detection limit as 1.29 copies·μL-1. The method was 100-fold more sensitive compared to RPA with Cas12a. Moreover, it had no cross-reactivity with viruses belonging to the Capripoxvirus, such as sheep pox virus and goat pox virus with genetic homology as 97%. Furthermore, the method displayed 100% accuracy in 50 actual samples. Therefore, the method based on RPA, Cas12a, and 10-23 DNAzyme had advantages in LSDV detection and provided a new solution for LSD prevention and control.

Research on the minimum detection limit for measuring high-purity gases by gas chromatography

Abstract At present, the application fields of high-purity gases (purity reached 99.999% and above) include the semiconductor manufacturing industry, chemical analysis, fuel cells, aerospace, medicine, etc., and the quality and purity requirements of high-purity gases are also getting higher and higher. As the only detector that can detect ppb-level trace impurities, the pulsed discharge helium ionization detector (PDHID) is the most used detector in the field of high-purity gases. The minimum detection limit of existing PDHID-related analysis methods is usually calculated theoretically. In order to verify the actual minimum detection limit of PDHID, a multi-group gas distribution system was used in this paper to dilute the permanent gas components in the high-purity gas, and the gas chromatograph with pulsed discharge helium ionization detector (GC-PDHID) was used to detect the obtained different concentrations of standard gases. The experimental results showed that PDHID possessed high sensitivity, good linearity, and a wide linear range. The actual minimum detection limit for the permanent gas components in the high-purity gas could reach the ng/g (ppb) level, which could realize the detection of ultra-low concentration samples, and further verify the actual minimum detection limit of PDHID. This experiment provides a reference basis for the analysis of trace gases in the gas industry, especially in industries such as high-purity and ultra-high-purity gases and gas for the electronics industry, and is of great significance in actual production work.

Nature-inspired fungal fusarinine C-powered dual-mode fluorometric/colorimetric biosensing of fecal Helicobacter pylori with high-reliability

Conventional diagnostic approaches for Helicobacter pylori lack sufficient sensitivity, accuracy, and flexibility, especially for low-density H. pylori infection. To overcome this limitation, we developed a highly reliable fluorometric/colorimetric dual-mode biosensing technique to detect minute quantities of H. pylori in human stool samples. Inspired by natural porphyrins, we discovered that the water-soluble fungal siderophore fusarinine C (FsC) emitted intense green fluorescence owing to intramolecular through-bond and intermolecular through-space conjugation, and turned reddish upon coordination with Fe3+. With FsC as an intrinsic fluorometric/colorimetric probe, a dual-mode biosensor was developed. It included an enrichment module of truncated H. pylori-specific-aptamer-modified superparamagnetic nanoparticles to capture H. pylori from samples, and a transduction module of alginate conjugated with FsC[Fe3+] and an optimized amount of FsC without Fe3+ to amplify the captured H. pylori to fluorescent and/or color signals. Remarkably, significantly increased sensitivity was achieved for this biosensor, with an actual limit of detection of 5 CFU/mL and single-cell-level detection resolution, as validated using laser-tweezer-sorted single H. pylori cells. Moreover, highly reliable dual-mode detection of low-density H. pylori (between 5 and 10 CFU/mL) was demonstrated. Using the colorimetric mode, a smartphone-biosensor platform for sensitive point-of-care testing of fecal H. pylori within 20 min was demonstrated, outperforming the clinical fecal antigen test strips; meanwhile, the fluorometric mode of the biosensor, owing to its greater sensitivity, can verify the colorimetric detection of minute H. pylori. This study first showcased a FsC-powered dual-mode biosensor for ultra-sensitive and accurate point-of-care detection of H. pylori with high reliability.

On the defect detection limits of flash thermography in reflection mode: A comprehensive parametric 3D FE study

Optical flash thermography is a promising non-destructive testing technique which offers a fast, full-field and non-contact inspection. This study provides a comprehensive study into the influence of different factors on the physical defect detection limits of hidden defects with flash thermography, which is a missing key piece in the present literature.Therefore, a large-scale parametric 3D finite element study is performed in order to explore the actual defect detection limits for a substantial range of inspection conditions:i.Defect parameters: type, size and depth.ii.Material parameters: anisotropic diffusivity and stacking sequence.iii.Excitation parameters: heating non-uniformity, excitation energy and temporal excitation profile.iv.Acquisition parameters: sampling frequency and measurement noise.The finite element model is carefully designed using the commercial Abaqus software in order to ensure both accuracy and computational efficiency, and its reliability in quantifying defect detectability is experimentally validated. Decisive defect detection thresholds are substantiated, through which the detection limits in several (fiber reinforced) materials are concisely visualized and critically compared for the raw thermographic sequence and well-known processing techniques for flash thermography.

Mesopore engineering of Co3O4 nanoplates for enhanced detection of toluene vapor

It remains a significant challenge for efficient detection of toluene vapor because of the low chemical reactivity. In this paper, the Co3O4 nanoplates with various mesopore widths (5.1, 12.6, and 19.8 nm) onto their surfaces have been successfully achieved using a simple hydrothermal and followed annealing route. Moreover, the sensor based on this Co3O4 nanoplate with mesopore width of 5.1 nm presents an obvious toluene-sensing response (including actual detection limit of 1 ppm, and excellent selectivity) at a low working temperature (140 °C). The improved toluene-sensing can be tracked from suitable mesopore size and specific catalytic activity of the Co3O4 nanoplates, which are advantageous for gas adsorption and diffusion, as well as facilitating the rapid oxidation of toluene gas. This work announces a reliable strategy to detect low reactive gas by constructing rational mesopores-width over the catalytic oxide.

Completely Free from PAM Limitations: Asymmetric RPA with CRISPR/Cas12a for Nucleic Acid Assays.

Experimentally, Cas12a can recognize multiple protospacer adjacent motif (PAM) sequences and is not restricted to the "TTTN". However, the application of the CRISPR/Cas12a system is still limited by the PAM for double-stranded DNA (dsDNA). Here, we developed asymmetric RPA (Asy-RPA) to completely break the limitations of PAM. Asy-RPA not only achieved efficient amplification but also converted dsDNA to single-stranded DNA (ssDNA) without complicated steps. The ssDNA products activated the trans-cleavage activity of Cas12a, outputting signals. The application of Asy-RPA completely freed Cas12a from the PAM, which can be more widely used in nucleic acid detection, such as lumpy skin disease virus, with an actual detection limit as low as 1.21 × 101 copies·μL-1. More importantly, Cas12a was intolerant to mutations on ssDNA. This provided technical support for the detection and identification of wild-type Mycobacterium tuberculosis (WT-TB) and rifampin-resistant mutant-type M. tuberculosis (MT-TB). The detection limit was as low as 1 fM for 1% mixed samples. The detection and availability of different treatment options for treatment-resistant and WT-TB were significant for the elimination of TB. In summary, the platform consisting of Asy-RPA and CRISPR/Cas12a was suitable for the detection of various viruses and bacteria and was a boon for the detection of dsDNA without recognizable PAM.

Mof-derived hierarchical Co3O4 assembled by porous nanocages towards toluene-sensing ability

Assembly of building blocks into porous hierarchical architecture can contribute the gas diffusion and gas–solid reaction. In this work, a novel hierarchical microstructure constructed with metal–organic framework (MOF)-derived Co3O4 porous nanocages was succeeded in synthesizing through a PVP-mediated wet-chemical and followed annealing route. This as-prepared Co3O4 sample integrate the structural merits of porous hierarchical surface, high specific surface area (69.6 m2/g), and rich contents of Co3+ and oxygen species (chemisorbed oxygen and oxygen vacancy). As a result, this as-prepared Co3O4 sensor possessed a clear response to toluene at the low working temperature (175 °C) in terms of the approving selectivity, high response value (Rg/Ra = 23 – 100 ppm), and real actual detection limit of 0.1 ppm. This paper provides a reliable way to design hierarchical structure over catalytic oxide (eg. Co3O4) for probing low reactive gas (eg. toluene).

Field-friendly and ultra-fast detection platform without nucleic acid extraction for virus detection

The polymeric chain reaction (PCR) has come under fire for being time-consuming, requiring expensive equipments, and requiring the extraction and purification of nucleic acids. Here, an ultra-fast and sensitive detection platform without nucleic acid extraction solved the above problems. Firstly, the RoomTemp Sample Lysis Kit released the nucleic acid in 3 min and removed the inhibition to facilitate the amplification reaction. What's more, ultra-fast PCR (UF-PCR) can complete 40 cycles in just 15 min and 50 s. To improve the sensitivity and provide more convenient reading modes, CRISPR/Cas12a was mediated to detect Lumpy skin disease virus (LSDV). The platform output fluorescence and Lateral flow dipstick (LFD) signals. The actual detection limit was 2 × 101 copies·μL−1. The portable platform realized visualization, excellent sensitivity and quick speed. In summary, the field-friendly testing platform had great potential in practical testing.

MOF-derived Mo-doped stacked Co3O4 nanosheets for chemiresistive toluene vapor sensing

Toluene is one typical indoor pollutant, which is harmful to our health and safety. However, it remains a hinder for high-performance detecting it due to the low chemical reactivity. In this paper, the Mo-doped stacked Co3O4 nanosheets derived from metal-organic frameworks (MOF) are successfully prepared using a facile wet-chemical route and subsequent annealing treatment. The incorporation of Mo6+ into Co3O4 lattice promotes the contents of Co3+ and specific surface area. Consequently, the as-fabricated gas sensor using 0.5 at% Mo-doped Co3O4 announces a remarkable response (Rg/Ra = 42.90–100 ppm), actual detection limit (∼ 0.1 ppm), and apparent selectivity towards toluene gas at a low temperature (∼ 150 °C). Furthermore, an in-situ DRIFTS result proves the possible intermediates (such as benzene alcohol, benzaldehyde, and benzoic acid) in this toluene-sensing reaction. The enhancement in toluene-sensing response is also clarified in detail from the aspects of structural merits and Mo-doped effect in this stacked Co3O4 nanosheets. The research results further verify a viable solution for detecting low reactive gas using high valence cation-doped catalytic oxides.

Abundant active sites triggered by Co-doped SnS2 for ppb-level NO2 detection

Nitrogen dioxide (NO2) has serious negative effects on human health and atmospheric environment, thus necessitating the development of NO2 sensor for trace NO2 detection. The performance of gas sensor is closely related to active sites of sensing materials. Doping is an available strategy to modulate the number of active sites. Herein, Co-doped SnS2 nanomaterials were prepared by a facile one-step solvothermal method for NO2 sensing. The introduction of Co2+ inhibits the growth of SnS2 grain size and introduces S vacancy, which provides more active sites for NO2 adsorption. As a result, the sensor based on 10 wt% Co-doped SnS2 exhibits a response value of 169 % (S=(Rg-Ra)/Ra× 100 %) for 1 ppm NO2, high selectivity against other gases, appreciable moisture resistance, and low actual limit of detection (the response of 89.7 % to 1 ppb NO2) at 190 ℃. The remarkable sensing properties are mainly attributed to the abundant active sites and strong adsorption ability.

Pd nanoparticles decorated SnO2 ultrathin nanosheets for highly sensitive H2 sensor: Experimental and theoretical studies

This study is attempted to improve the hydrogen sensing performance of SnO2 based sensors by simultaneously employing two strategies of morphology control and noble metal loading. Therefore, SnO2 ultrathin nanosheets with thickness not exceeding 3.5 nm were successfully synthesized by a hydrothermal method and then different content of Pd nanoparticles were uniformly loaded onto SnO2 surface by in situ reduction with ascorbic acid. The gas sensing properties demonstrated that the introduction of Pd not only altered the selectivity of the SnO2 sensor from ethanol to hydrogen, but also significantly improved the gas sensitivity and reduced the working temperature. And the optimal 1.0%Pd/SnO2 sensor owned the highest sensitivity (75), fastest response-recovery property (21 s/13 s) to 20 ppm of hydrogen at 220 °C, and the actual detection limit is as low as 0.1 ppm. Furthermore, 1.0%Pd/SnO2 sensor exhibited excellent repeatability, reproducibility and acceptable anti-interference of humidity. The DFT studies suggest that the physisorption of the hydrogen molecules on the surface of SnO2, but chemisorption on the surface of Pd/SnO2. The improved H2 sensing performance of Pd/SnO2 sensor attributes its ultrathin thickness of SnO2 and catalytic dissociation of Pd to O2 and H2.

Kinetics-Driven Dual Hydrogen Spillover Effects for Ultrasensitive Hydrogen Sensing.

Palladium (Pd)-modified metal oxide semiconductors (MOSs) gas sensors often exhibit unexpected hydrogen (H2 ) sensing activity through a spillover effect. However, sluggish kinetics over a limited Pd-MOS surface seriously restrict the sensing process. Here, a hollow Pd-NiO/SnO2 buffered nanocavity is engineered to kinetically drive the H2 spillover over dual yolk-shell surface for the ultrasensitive H2 sensing. This unique nanocavity is found and can induce more H2 absorption and markedly improve kinetical H2 ab/desorption rates. Meanwhile, the limited buffer-room allows the H2 molecules to adequately spillover in the inside-layer surface and thus realize dual H2 spillover effect. Ex situ XPS, in situ Raman, and density functional theory (DFT) analysis further confirm that the Pd species can effectively combine H2 to form Pd-H bonds and then dissociate the hydrogen species to NiO/SnO2 surface. The final Pd-NiO/SnO2 sensors exhibit an ultrasensitive response (0.1-1000ppm H2 ) and low actual detection limit (100 ppb) at the operating temperature of 230 °C, which surpass that of most reported H2 sensors.

Ultrafine Pt-doped SnO2 mesopore nanofibers-based gas sensor for enhanced acetone sensing

There is still an urgent need to develop a highly sensitive semiconductor oxide sensor capable of detecting trace disease biomarkers within the exhaled breath. Here, we propose an electrospinning technique and annealing process to obtain platinum (Pt) nanoparticles doped ultrafine SnO2 mesopore nanofiber. As a result of the strong synergistic effect between Pt and ultrafine SnO2 mesopore nanofiber structure, the change of oxygen adsorption caused a significant increase in resistance variation. The ultrafine nanofiber structure and one-dimensional interconnection of SnO2 are beneficial to the high gas accessibility and fast recovery. The results indicated that the Pt/SnO2 sensor have a high response value (31.2 for 2 ppm acetone), rapid response-recovery times, an actual detection limit (100 ppb), and satisfactory acetone selectivity. The above results demonstrate that Pt-doped ultrafine SnO2 nanofibers are potentially helpful as non-invasive real-time diabetic diagnosis materials.

Multiple accurate and sensitive arrays for Capripoxvirus (CaPV) differentiation

Capripoxvirus (CaPV) contains three viruses that have caused massive losses in the livestock and dairy industries. Accurate CaPV differentiation has far-reaching implications for effectively controlling outbreaks. However, it has a great challenge to distinguishing three viruses due to high homology of 97%. Here, we established a sensitive CRISPR/Cas12a array based on Multiple-recombinase polymerase amplification (M-RPA) for CaPV differentiation, which provided a more comprehensive and accurate differentiation mode targeting VARV B22R and RPO30 genes. By sensitive CRISPR/Cas12a and M-RPA, the actual detection limits of three viruses were as low as 50, 40 and 60 copies, respectively. Moreover, Lateral flow dipstick (LFD) array based on CRISPR/Cas12a achieved portable and intuitive detection, making it suitable for point-of-care testing. Therefore, CRISPR/Cas12a array and LFD array paved the way for CaPV differentiation in practice. Additionally, we constructed a real-time quantitative PCR (qPCR) array to fill the qPCR technical gap in differentiation and to facilitate the quarantine departments.

Low-temperature and dual-sensing NO2/dimethylamine sensor based on single-crystal WO3 nanoparticles-supported sheets synthesized by simple pyrolysis of spoiled WCl6 powder

Herein, nanoparticle-supported WO3 sheets were simply prepared by direct pyrolysis of spoiled WCl6 powder. The influence of calcination temperature on their composition and morphology transformation was explored through the characterizations of powder X-ray diffractometer, X-ray photoelectron spectrometer, scanning and transmission electron microscope. Amongst, the W-600 sheet-like structure obtained by calcination at 873 K is cross-linked by homogeneous nanoparticles, and has meso/macro-pore distribution, single-crystal nature and relatively small band gap. These favorable factors promote rapid gas diffusion, increase the electron migration rate, as well as expose more active sites for surface chemical reaction. Especially, under the synergism of surface unsaturated W6+ Lewis acid, the fabricated W-600 sensor achieves dual-sensing to dimethylamine (DMA) and NO2 for the first time. It exhibits a good response (S = 35.3) to 100 ppm DMA at 298 K, and also presents a high response (S = 125) to 1 ppm NO2 at 323 K. The actual detection limit can be as low as 1 ppm (DMA) and 10 ppb (NO2). Meanwhile, this sensor still has reversible response-recovery characteristics, satisfactory stability and moisture resistance. Furthermore, the dual-functional sensing mechanism was also explored in detail.

Integrated label-free erbium-doped fiber laser biosensing system for detection of single cell Staphylococcus aureus

A critical challenge to realize ultra-high sensitivity with optical fiber interferometers for label free biosensing is to achieve high quality factors (Q-factor) in liquid. In this work a high Q-factor of 105, which significantly improves the detection resolution is described based on a structure of single mode -core-only -single mode fiber (SCS) with its multimode (or Mach-Zehnder) interference effect as a filter that is integrated into an erbium-doped fiber laser (EDFL) system for excitation. In the case study, the section of core-only fiber is functionalized with porcine immunoglobulin G (IgG) antibodies, which could selectively bind to bacterial pathogen of Staphylococcus aureus (S. aureus). The developed microfiber-based biosensing platform called SCS-based EDFL biosensors can effectively detect concentrations of S. aureus from 10 to 105 CFU/mL, with a responsivity of 0.426 nm wavelength shift in the measured spectrum for S. aureus concentration of 10 CFU/mL. The limit of detection (LoD) is estimated as 7.3 CFU/mL based on the measurement of S. aureus with minimum concentration of 10 CFU/mL. In addition, when a lower concentration of 1 CFU/mL is applied to the biosensor, a wavelength shift of 0.12 nm is observed in 10% of samples (1/10), indicating actual LoD of 1 CFU/mL for the proposed biosensor. Attributed to its good sensitivity, stability, reproducibility and specificity, the proposed EDFL based biosensing platform has great potentials for diagnostics.

Development of a portable bioaerosol capture device for influenza virus detection

Many bacteria and viruses are spreading in the air in the living environment, and high concentrations of viruses entering the human body will cause harm. This research is committed to developing a virus collector, which is used to collect influenza and coronavirus in the air. In our system, the intake fan can beget negative pressure into the water circulation channel and bring the virus into it, and then the sensor chip will obtain the electrical signal. In this study, we successfully used methylene blue to simulate viruses in the air. The result of this experiment showed that the distance between the air virus collector and the atomizer was 30 cm in height, 60 cm & 90 cm in length. The capture efficiency was respectively 1.1% and 0.8%. Also, we use lateral flow immunochromatographic assay to detect the collected samples of Influenza H1N1 Hemagglutinin Protein, and the actual limit of detection is 16.97 ng/ml. In addition, the experiments also proved that the water circulation device in this study could accumulate the methylene blue samples onto the sensor. In the future, it can be used with the sensor chip as a virus detection platform which can collect and monitor viruses simultaneously. By using this device, people can be warned and take the necessary precautions to reduce the chance of the transmission of viruses.

Practical Strategy for Arsenic(III) Electroanalysis without Modifier in Natural Water: Triggered by Iron Group Ions in Solution

Significant progress has been made in nanomaterial-modified electrodes for highly efficient electroanalysis of arsenic(III) (As(III)). However, the modifiers prepared using some physical methods may easily fall off, and active sites are not uniform, causing the potential instability of the modified electrode. This work first reports a promising practical strategy without any modifiers via utilizing only soluble Fe3+ as a trigger to detect trace-level As(III) in natural water. This method reaches an actual detection limit of 1 ppb on bare glassy carbon electrodes and a sensitivity of 0.296 μA ppb-1 with excellent stability. Kinetic simulations and experimental evidence confirm the codeposition mechanism that Fe3+ is preferentially deposited as Fe0, which are active sites to adsorb As(III) and H+ on the electrode surface. This facilitates the formation of AsH3, which could further react with Fe2+ to produce more As0 and Fe0. Meanwhile, the produced Fe0 can also accelerate the efficient enrichment of As0. Remarkably, the proposed sensing mechanism is a general rule for the electroanalysis of As(III) that is triggered by iron group ions (Fe2+, Fe3+, Co2+, and Ni2+). The interference analysis of coexisting ions (Cu2+, Zn2+, Al3+, Hg2+, Cd2+, Pb2+, SO42-, NO3-, Cl-, and F-) indicates that only Cu2+, Pb2+, and F- showed inhibitory effects on As(III) due to the competition of active sites. Surprisingly, adding iron power effectively eliminates the interference of Cu2+ in natural water, achieving a higher sensitivity for 1-15 ppb As(III) (0.487 μA ppb-1). This study provides effective solutions to overcome the potential instability of modified electrodes and offers a practical sensing platform for analyzing other heavy-metal anions.