Minimum Detection Limit Research Articles

MXene-Enhanced Bi2S3/CdIn2S4 Heterojunction Photosensitive Gate for DEHP Detection in a Signal-On OPECT Aptamer Biosensor.

Organic electrochemical transistors with signal amplification and good stability are expected to play a more important role in the detection of environmental pollutants. However, the bias voltage at the gate may have an effect on the activity of vulnerable biomolecules. In this work, a novel organic photoelectrochemical transistor (OPECT) aptamer biosensor was developed for di(2-ethylhexyl) phthalate (DEHP) detection by combining photoelectrochemical analysis with an organic electrochemical transistor, where MXene/Bi2S3/CdIn2S4 was employed as a photoactive material, target-dependent DNA hybridization chain reaction was used as a signal amplification unit, and Ru(NH3)63+ was selected as a signal enhancement molecule. The poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-based OPECT biosensor modulated by the MXene/Bi2S3/CdIn2S4 photosensitive material achieved a high current gain of nearly a thousand times at zero bias voltage. The developed signal-on OPECT sensing platform realized sensitive and specific detection of DEHP, with a detection range of 1-200 pM and a minimum detection limit of 0.24 pM under optimized experimental conditions, and its application to real water samples was also evaluated with satisfactory results. Hence, the construction of this OPECT biosensing platform not only provides a promising tool for the detection of DEHP but also reveals the great potential of the OPECT application for the detection of other environmental toxins.

Core-shell structured lignin-stabilized silver nanoprisms for colorimetric detection of sulfur ions

Widespread occurrence of sulfides in domestic and industrial wastewater contributes to environmental pollution and poses risks to human health. Therefore, the development of highly selective, sensitive, and rapid sulfur ion (S2−) detection probes in aquatic ecosystems is of paramount importance. In this study, lignin-stabilized silver nanoprisms (EHL@AgNPRs) were prepared using the seed growth and self-assembly methods. Based on this, a novel, high-performance, and environmentally friendly S2− colorimetric detection method was proposed. Lignin is believed to coat the surface of AgNPRs through cation-π and electrostatic interactions, acting as an excellent dispersant and stabilizer to prevent aggregation and shape deformation. This allows AgNPRs to maintain localized surface plasmon resonance (LSPR) characteristics and superior colorimetric sensing sensitivity towards S2− even after 30 d. The EHL@AgNPRs exhibited remarkable selectivity towards S2− with a minimum detection limit of 41.3 nM. The conjugation of lignin with AgNPRs offers a highly promising approach for the rapid detection of S2− in natural aquatic environments and for the valorization of lignin.

Evanescent wave quartz-enhanced photoacoustic spectroscopy employing a side-polished fiber for methane sensing

We present an all-fiber-based laser gas analyzer (LGA) employing quartz-enhanced photoacoustic spectroscopy (QEPAS) and a side-polished fiber (SPF). The LGA comprises a custom quartz tuning fork (QTF) with 0.8 mm prong spacing, two acoustic micro-resonators (mR) located on either side of the prong spacing, and a single-mode fiber containing a 17 mm polished section passing through both mRs and QTF. The SPF polished face is positioned to enable the evanescent wave (EW) to create a photoacoustic wave and excite the fundamental flexural mode of the QTF. Sensor performance was demonstrated using methane in nitrogen gas mixtures, with CH4 mixing ratios ranging from 75 ppmv to 1% (by volume), measured with an accumulation time of 300 ms, and a minimum detection limit of 34 ppmv subsequently determined. The EW-QEPAS sensor is ideal for miniaturization, as it does not contain any free-space optics and is suitable for gas sensing in harsh environments and where mobility is required.

Carbon monoxide impurities in hydrogen detected with resonant photoacoustic cell using a mid-IR laser source

We report on a photoacoustic sensor system based on a differential photoacoustic cell to detect the concentration of CO impurities in hydrogen. A DFB-QCL laser with a central wavelength of 4.61 µm was employed as an exciting source with an optical power of 21 mW. Different concentrations of CO gas mixed with pure hydrogen were injected into the photoacoustic cell to test the linear response of the photoacoustic signal to the CO concentration. The stability of the long-term operation was verified by Allan-Werle deviation analysis. The minimum detection limit (MDL, SNR=1) results 8 ppb at 1 s and reaches a sub-ppb level at 100 s of integration time. Dynamic response of the system is linear and has been tested up to the concentration of 6 ppm. Saturation conditions are expected to be reached for CO concentration larger than 100 ppm.

Novel electrochemical/fluorescence dual-mode biosensor based on covalent organic framework for tetracycline detection

Excessive antibiotic residues increased the environmental damage and safety of animal products, leading to serious health threats. In this study, a dual-mode probe was developed and applied as an electrochemical/fluorescence sensor for tetracycline (TET) detection. The probe, comprising a fluorescent covalent organic framework, electroactive methylene blue, gold nanoparticles (AuNPs) and single-stranded DNA, was synthesized by self-assembly. A glassy carbon electrode was functionalized with molybdenum disulfide nanosheets, AuNPs, and aptamers. The probe exhibited fluorescent signals in solution and electrochemical signals after being specifically connected to the electrode via hybridization. In the presence of TET, the probe is be competitively expelled from the modified electrode, resulting in an increase in the fluorescent signal and a decrease in the electrochemical signal. The developed electrochemical/fluorescence dual-mode sensor enabled sensitive TET detection in the concentration range of 10 nM–10 mM, with minimum detection limits of 0.03 nM (electrochemical) and 0.05 nM (fluorescence). With its high selectivity, superior reproducibility, and excellent stability, the proposed dual-mode sensor demonstrates high reliability, and excellent application prospects for TET detection in milk and river water samples.

Development of a Rapid Epstein-Barr Virus Detection System Based on Recombinase Polymerase Amplification and a Lateral Flow Assay.

The quality of cellular products used in biological research can directly impact the ability to obtain accurate results. Epstein-Barr virus (EBV) is a latent virus that spreads extensively worldwide, and cell lines used in experiments may carry EBV and pose an infection risk. The presence of EBV in a single cell line can contaminate other cell lines used in the same laboratory, affecting experimental results. We developed three EBV detection systems: (1) a polymerase chain reaction (PCR)-based detection system, (2) a recombinase polymerase amplification (RPA)-based detection system, and (3) a combined RPA-lateral flow assay (LFA) detection system. The minimum EBV detection limits were 1 × 103 copy numbers for the RPA-based and RPA-LFA systems and 1 × 104 copy numbers for the PCR-based system. Both the PCR and RPA detection systems were applied to 192 cell lines, and the results were consistent with those obtained by the EBV assay methods specified in the pharmaceutical industry standards of the People's Republic of China. A total of 10 EBV-positive cell lines were identified. The combined RPA-LFA system is simple to operate, allowing for rapid result visualization. This system can be implemented in laboratories and cell banks as part of a daily quality control strategy to ensure cell quality and experimental safety and may represent a potential new technique for the rapid detection of EBV in clinical samples.

Development of a high-throughput DNA isolation method for livestock and poultry meat based on mesoporous metal-organic framework-coated solid-phase microextraction device

A rapid, portable, simple, low-cost, and high-throughput DNA isolation method was developed for the quantitative identification of meat adulteration based on mesoporous UiO-66 coated solid phase microextraction (SPME) devices. The high-throughput DNA extraction system consists of 96 UiO-66 SPME devices and a polyformaldehyde plate, which can extract DNA from 96 livestock and poultry meat samples simultaneously. At the same time, several parameters of the high throughput DNA isolation method were optimized, including lysis buffer volume, elution buffer volume, lysis time and elution time, etc. Compared with the single DNA isolation device, the 96-SPME high-throughput extraction system maintains the original good universality, reproducibility, chemical stability, and reusability. On this basis, it obtained higher DNA concentration (80 ± 34 ng μL−1), satisfactory DNA purity (A260/A280=2.4) and shorter extraction time (less than 7.2 s per sample), which are much more convenient and efficient than the conventional kit method and the single SPME DNA isolation method. In addition, the conventional multiplex polymerase chain reaction and real-time polymerase chain reaction techniques were used for the qualitative and quantitative detection of meat adulteration. The DNA obtained from this extraction method is highly reproducible and sensitive for the identification of duck ingredients in beef, with a detection range of 1–100 % and a minimum detection limit of 1 % (w/w).

Hydrothermally synthesized MXene Ti3C2/Zn2SnO4 based nanocomposite for H2S sensing at room temperature

Hydrogen sulfide (H2S) gas sensors with high response and minimum limit of detection at room temperature are of great importance to ensure the safety of humans and the environment. A series of samples such as MXene Ti3C2, Ti3AlC2, WS2, MoSe2/Zn2SnO4 and spherical Zn2SnO4 nanoparticles were synthesized via hydrothermal method in this paper. Different characterizations were performed on these samples to check crystal structures, morphologies, chemical states, etc. And gas sensing properties were also performed and analyzed deeply. A series of sensor sheets were fabricated via the spin coating method based on synthesized samples for gas sensing properties. MXene Ti3C2/Zn2SnO4-5 based gas sensor detected the highest response (110) towards 8 ppm H2S with excellent selectivity, the minimum limit of detection (0.01 ppm), mediate long-term stability and good reproducibility compared with other fabricated sensors at room temperature. Also, the sensor response was increased with the increase of H2S concentration. Experimental results showed that the highest response of Ti3C2/Zn2SnO4-5 based gas sensor was accredited to heterojunction, higher BET surface area, and increased oxygen species. The simple way synthesized nanocomposite and fabricated sensors throw a novel idea for tracing H2S at the lowest concentration to prevent different diseases.

Quantum cascade laser absorption sensor for in-situ, real-time and sensitive measurement of high-temperature SO2 and SO3

We report a mid-infrared quantum cascade laser absorption sensor capable of measuring SO2 and SO3 simultaneously and sensitively at elevated temperatures. In the sensor development, the intense transitions of SO2 and SO3 in the mid-infrared region of 1129 cm−1 and 1398 cm−1 were exploited by two quantum cascade lasers. A high-temperature multipass cell was adopted to increase the absorption path length to 10 m. The quantitative concentrations of SOx were directly obtained from the calibration-free wavelength modulation spectroscopic method, which was validated at varied temperature and pressure conditions. From Allan deviation analysis, we achieved a minimum detection limit of 8 parts per billion (ppb) for SO2 and 3 ppb for SO3, with an average time of 100 s. Lastly, we successfully demonstrated the real-time and sensitive measurement of SO2 and SO3 during the oxidation reaction of SO2 by O3 at 460 K. Our laser sensor shows great potential for in-situ and real-time monitoring of SOx from combustion emissions.

Heterostructures of hollow Co3O4 nanocages wrapped in NiO cilia for conductometric NO2 sensing at room temperature

Metal organic frameworks (MOFs) have drawn the spotlight in the field of gas sensing due to their miraculous geometrical and electronic structures, as well as simple and controllable self-assembly processes. Here, NiO@Co3O4 heterostructures to be synthesized using heating reflux method by vertically wrapping ultra-thin NiO cilia on the surface of hollow ZIF-67 nanocages and applying this as a template for thermal annealing. The unique hollow structure and rich mesoporous structure provide space for gas diffusion and carrier migration. The prepared NiO@Co3O4-350 sensor achieves a high response of 47.4 and exceedingly short response/recovery time (1.3 and 9.6 s) at room temperature, with a minimum detection limit of only 10 ppb and good selectivity, repeatability and long-term stability for NO2 gas. This work highlights the significance of morphology and structure for improving gas sensing performance, which sheds a thought-provoking light on the design and preparation of composite oxide sensors.

Triple-range adjustable plane-concave multipass gas cell for high-precision trace gas detection based on TDLAS

A triple-range adjustable plane-concave multipass gas cell (PC-MPGC) was developed for high-precision trace gas detection based on tunable diode laser absorption spectroscopy. Effective optical path lengths (EOPLs) of 64.5, 42.5, and 20.5 m could be easily achieved by adjusting the incident beam angle. The trace gas sensor system employed a 1.653 µm distributed feedback diode laser to target a strong methane (CH4) absorption line, and direct absorption spectroscopy (DAS) was used to evaluate the performance of the system with a 64.5 m EOPL. A Savitzky–Golay filtering algorithm was employed to denoise the measured signal, and a third harmonic signal was used for laser frequency locking. A signal-to-noise ratio (SNR) of 191 was achieved, which corresponds to a detection sensitivity of 0.78 ppmv. The system response time was obtained through measurement of CH4 at concentration of 0 ppmv and 20 ppmv at 298 K and 1 atm, and it was found to be 11 s. Kalman filtering was applied to improve the detection sensitivity of the gas sensor. The stability of the system was analyzed using Allan deviation, and a minimum detectable limit of 21 ppbv was obtained for an integration time of 580 s. In situ continuous monitoring of atmospheric CH4 characteristics was performed for 72-h. The development of a new type of PC-MPGC paves the way for the detection of multicomponent gases at different absorption path lengths.

Real-time detection of Seneca Valley virus by one-tube RPA-CRISPR/Cas12a assay.

Senecavirus A (SVA) is a highly contagious virus that causes vesicular disease in pigs. At present, laboratory detection methods, such as virus isolation and polymerase chain reaction (PCR), required precision instruments and qualified personnel, making them unsuitable for point-of-care tests (POCT). Fortunately, the emergence of CRISPR/Cas system has provided new opportunities for fast and efficient pathogen detection. This study successfully developed a precise and sensitive detection platform for diagnosing SVA by combining the CRISPR system with recombinase polymerase amplification (RPA). The minimum detection limit of the assay was 10 copies of the SVA genome. Meanwhile, the assay demonstrated high specificity. To validate the effectiveness of this system, we tested 85 swine clinical samples and found that the fluorescence method had a 100% coincidence rate compared to RT-qPCR. Overall, the RPA-CRISPR/Cas12a assay established in our study is a highly effective method for detecting SVA and holds great potential for practical applications in the resource-limited settings.

High sensitivity miniaturized multi-pass absorption enhanced differential Helmholtz photoacoustic gas sensor

A high sensitivity photoacoustic (PA) gas sensor based on multi-pass absorption differential Helmholtz cell with a chamber volume of only 37 mL was proposed. The reported cell has an absorption path length of 2.5 m, which can effectively enhance the optical excitation. The differential Helmholtz structure can heighten the photoacoustic signal and effectively suppress ambient noise. To optimize the differential Helmholtz resonant PA cell, the PA field distribution of the cell was calculated by thermoviscous acoustic theory using the finite element method. The detection performance of the sensor was evaluated using a distributed feedback laser operating at a center wavelength of 1650.44 nm and targeting CH4 gas. Compared with a single pass, the PA signals were enhanced by 11 times in multiple pass mode. The differential mode suppressed 30 % of background noise. The calculated normalized noise equivalent absorption (NNEA) coefficient was 3.45 × 10-10 cm-1WHz1/2. The experimental results showed that the minimum detection limit (MDL) of CH4 was 6.6 ppb with an averaging time of 100 s.

Cavity-enhanced photoacoustic dual-comb spectroscopy

Photoacoustic dual-comb spectroscopy (DCS), converting spectral information in the optical frequency domain to the audio frequency domain via multi-heterodyne beating, enables background-free spectral measurements with high resolution and broad bandwidth. However, the detection sensitivity remains limited due to the low power of individual comb lines and the lack of broadband acoustic resonators. Here, we develop cavity-enhanced photoacoustic DCS, which overcomes these limitations by using a high-finesse optical cavity for the power amplification of dual-frequency combs and a broadband acoustic resonator with a flat-top frequency response. We demonstrate high-resolution spectroscopic measurements of trace amounts of C2H2, NH3 and CO in the entire telecommunications C-band. The method shows a minimum detection limit of 0.6 ppb C2H2 at the measurement time of 100 s, corresponding to the noise equivalent absorption coefficient of 7 × 10−10 cm−1. The proposed cavity-enhanced photoacoustic DCS may open new avenues for ultrasensitive, high-resolution, and multi-species gas detection with widespread applications.

Construction of a molecularly imprinted fluorescent sensor based on an amphiphilic block copolymer-metal-organic framework for the detection of oxytetracycline in milk.

A metal-organic framework (MOF) is a good carrier for molecular imprinting due to its high surface area and strong adsorption capacity, but its poor dispersibility in aqueous solution is one of the significant drawbacks, which can severely impede its effectiveness. Amphiphilic block copolymers are good hydrophilic materials and have the potential to overcome the shortcomings of MOFs. In order to improve the hydrophilicity of molecularly imprinted fluorescent materials, we have applied a combination of molecularly imprinted technology and amphiphilic block copolymers on MOFs for the first time. Amphiphilic PAVE copolymer is selected as the molecular imprinted functional monomer to improve the hydrophilicity of UiO-66-NH2. The synthesized PAVE-MOF-MIP has adequate water dispersion ability and fluorescence activity. When encountering oxytetracycline, PAVE-MOF-MIP will produce fluorescence quenching, it is used to construct a fluorescence detection platform for oxytetracycline detection. Compared with traditional MIP@MOF, PAVE-MOF-MIP has better water dispersion ability and detection accuracy. Under optimal conditions, the linear range of oxytetracycline detection is 10-100 μmol L-1, and the minimum limit of detection (LOD) is 86 nmol L-1. This paper proposes a novel approach to use amphiphilic block copolymers as molecularly imprinted monomers on MOFs, providing an innovative idea that has not been previously explored.

Low-cost and highly sensitive colorimetric and visual detection of amikacin in milk using melamine functionalized gold nanoparticles.

This study developed a rapid, low-cost and highly sensitive analytical method using melamine functionalized gold nanoparticles (MA-Au NPs) as a colorimetric sensor to detect amikacin in milk. The MA-Au NPs were synthesized using a self-assembly process and analyzed using absorption spectroscopy, transmission electron microscopy (TEM), and Fourier transform infrared (FT-IR) spectroscopy. The MA-Au NPs exhibited a distinct surface plasmon resonance (SPR) absorption peak at 520 nm and demonstrated excellent spherical dispersion. The reaction parameters were optimized, with a Au NP concentration of 2.0 × 10-7 mol L-1, MA concentration of 1.0 × 10-6 mol L-1, pH of 4.0, and reaction time of 15 minutes. In the optimization experiment, the effects of unmodified Au NPs and MA-Au NPs as colorimetric sensors for amikacin determination were compared. As a specific amount of amikacin was added to the Au NP solution, the reaction solution showed a visible change from wine red to purple and then to blue gray; a red-shift in the absorption spectrum of the solutions was observed, which could also be analyzed using the A640/A520 value, and the color changes were recorded using smartphones for visual detection through RGB (red-green-blue) data image analysis, which made the detection easy and fast. As a result, two approaches were devised using visible absorption spectra and smartphones. A linear correlation was established between the A640/A520 value and the concentration of amikacin in the range of 4.0 to 16.0 × 10-8 mol L-1. The minimal limit of detection (LOD) for absorption spectrum analysis was 3.75 × 10-9 mol L-1, whereas for smartphone analysis, it was 6.0 × 10-8 mol L-1. The recoveries ranged from 103.09% to 104.51%, while the relative standard deviations (RSDs) ranged from 3.76% to 4.25%. The proposed method was used to detect actual milk samples. The results showed that the method is simple, selective, and practical.

A simple low-cost flexible plasmonic patch based on spiky gold nanostars for ultra-sensitive SERS sensing.

Recently, transparent and flexible surface-enhanced Raman scattering (SERS) substrates have received great interest for direct point-of-care detection of analytes on irregular nonplanar surfaces. In this study, we proposed a simple cost-effective strategy to develop a flexible SERS patch utilizing multibranched sharp spiked gold nanostars (GNS) decorated on a commercially available adhesive Scotch Tape for achieving ultra-high SERS sensitivity. The experimental SERS measurements were correlated with theoretical finite element modeling (FEM), which indicates that the GNS having a 2.5 nm branch tip diameter (GNS-4) exhibits the strongest SERS enhancement. Using rhodamine 6G (R6G) as a model analyte, the SERS performance of the flexible SERS patch exhibited a minimum detection limit of R6G as low as 1 pM. The enhancement factor of the SERS patch with GNS-4 was calculated as 6.2 × 108, which indicates that our flexible SERS substrate has the potential to achieve ultra-high sensitivity. The reproducibility was tested with 30 different spots showing a relative standard deviation (RSD) of SERS intensity of about 5.4%, indicating good reproducibility of the SERS platform. To illustrate the usefulness of the flexible SERS sensor patch, we investigated the detection of a carcinogenic compound crystal violet (CV) on fish scales, which is often used as an effective antifungal agent in the aquaculture industry. The results realized the trace detection of CV with the minimum detection limit as low as 1 pM. We believe that our transparent, and flexible SERS patch based on GNS-4 has potential as a versatile, low-cost platform for real-world SERS sensing applications on nonplanar surfaces.

Highly sensitive detection of oxygen based on light-induced thermoelastic spectroscopy with a high power diode laser

Oxygen (O2) is a fundamental element in the atmosphere. It is important to detect it in various fields. In this paper, a sensitive O2 sensor based on light-induced thermoelastic spectroscopy (LITES) with a high power diode laser is reported. A distributed feedback (DFB) diode laser emitting at 760 nm with output power of 16.8 mW was employed as the light source. The O2 absorption line at 13144.54 cm-1 was selected for the investigation. Wavelength modulation spectroscopy (WMS) technique and second harmonic signal demodulation (2f) were adopted to improve the sensing performance. For the concentration dynamic range from 20% to 80%, a linear relationship between the amplitude of 2f signal and O2 concentration was demonstrated. Allan deviation analysis was conducted to evaluate the long-term stability of the sensor system and the minimum detection limit (MDL) was measured to be 583 ppm at the optimum integration time of 100 s. Further improvement of this O2-LITES sensor system was also discussed.

Near infrared ammonia sensing system based on on‐axis cavity‐enhanced absorption spectroscopy using board‐level mode‐locked circuit

AbstractWe proposed a near‐infrared gas sensing system based on mode‐locked cavity‐enhanced absorption spectroscopy. A distributed feedback fiber laser (DFB‐FL) with a central wavelength of 1550 nm was employed as the light source, coupling with a Fabry–Perot (F‐P) cavity with an effective optical path length of 42.7 m served as the gas cell. By utilizing a homemade mode‐locked electric circuit and Pound–Drever–Hall (PDH) technique, the mode‐locking between the DFB‐FL and F‐P cavity was achieved with long‐term fluctuation of 3.2%. System performance was verified using ammonia as the analyte gas with a target line at 1550.17 nm. Allan variance analysis revealed that the minimum detection limit was 15.8 ppm with an averaging time of 216 s, corresponding to an absorption coefficient of 2.3 × 10−7 cm−1.

Impact of Transport Mechanism on Binding Kinematics and Sensitivity of FET Biosensors

In this work, the impact of bioanalyte concentration and the dominant transport mechanism of biomolecules on the binding kinematics of the target biomolecules at the sensing surface have been investigated in detail. A comprehensive analysis of the fundamental parameters such as equilibrium response time and equilibrium density of the binding molecules at the sensing surface considering different concentrations of the analytes and their transport mechanisms has been performed. The impact of these realistic artifacts on the current sensitivity of emerging junctionless field effect transistors (JLFETs) and tunnel field effect transistors (TFETs)-based ion-sensitive field effect transistor (ISFET) has been investigated. Moreover, depending on the bioanalyte concentration, design guidelines for the dimensions of the sensing surface have been provided for a minimum limit of detection (LOD). The impact of charge screening and nonspecific binding on current sensitivity has also been discussed in depth. We believe that the guidelines presented in this work will enable the community to conceptualize, understand, and design novel label-free biosensors more rationally considering the practical scenario.