Minimum Detection Limit Research Articles

Trace gas detection system based on multi-reflection differential Helmholtz cell and VMD-airPLS algorithm

In this paper, a photoacoustic spectroscopy sensor based on multi-reflection differential Helmholtz cell and Variational Mode Decomposition-adaptive iteratively reweighted penalized least squares (VMD-airPLS) algorithm is proposed to improve the signal-to-noise ratio (SNR) and reduce the response time of the system. The Helmholtz photoacoustic cell, fabricated from brass, allows multiple reflections of the laser light within its resonant cavity, effectively increasing the gas absorption path by a factor of ∼ 6. The VMD-airPLS algorithm suppresses incoherent noise and slowly varying baseline noise over time. To validate the performance of the system, methane is measured using a laser with a wavelength of 1653.7 nm. Experimental results demonstrate a significant enhancement in the sensitivity of system, up to approximately 2.2 times, and an improvement in the SNR by up to approximately 4.2 times compared to single-pass system. The minimum detection limit for methane is ∼ 96.79 ppb.

Development and evaluation of three multienzyme isothermal rapid amplification assays for fowl adenovirus serotype 4

Fowl adenovirus serotype 4 (FAdV-4) is the main causative agent of hydropericardium hepatitis syndrome (HHS), which has resulted in huge economic losses to the poultry industry in recent years. Hence, a rapid and simple visual detection method is needed for identification of FAdV-4. In this study, three multienzyme isothermal rapid amplification (MIRA) assays, basic MIRA, MIRA-qPCR and MIRA-LFD were developed for detection of FAdV-4. The amplification primers and reaction conditions were optimized, and the specificity and sensitivity of the assays were evaluated. The MIRA assays were specific for FAdV-4 with no cross-reaction with novel goose astrovirus, H9 subtype avian influenza virus, duck enteritis virus, Muscovy duck reovirus, or duck circovirus. The basic MIRA assay required only one primer pair and the reaction can be completed within 30 min at 36 °C. The MIRA-qPCR and MIRA-LFD assays were completed in 20 min with a minimum detection limit of 1 × 101 copies/μL and 1 × 102 copies/μL, respectively. The results of the MIRA-LFD assay can be observed directly with the naked eye, omitting the need for specialized instruments. The positive rate of three proposed MIRA assays were consistent with that of the conventional PCR assay. The MIRA assays are simple, rapid, and effective diagnostic tools for field detection of FAdV-4.

Bio-inspired one-pot synthesis of luminescent silver nanoparticles and its significant utility as a fluorescence nano sensor for analysis of two adjunctive COVID-19 drugs.

This study reveals one-step green synthesis of plant inspired silver nanoparticles (Ag-NPs). The synthesis procedure relies on the bio-reduction of Ag+ to Ag0 using orange waste (orange peel) extract as cheap, readily available, sustainable, biocompatible feedstocks as a reducing and stabilizing agent. The prepared Ag-NPs passed through a full characterization procedure for better confirmation and elucidation of optical and structural properties. The fluorescence of the prepared Ag-NPs has a quantum yield of 17.15% enabling its potential use in chemical sensing of drugs. Ag-NPs are conceived to be used as a fluorescent nano sensor for sensitive, ecofriendly, rapid spectrofluorimetric determination of two recent direct oral anticoagulants, namely, rivaroxaban (RIV) and edoxaban tosylate monohydrate (EDT); COVID-19 adjunctive drugs in their raw materials and pharmaceutical tablets. The fluorescence of the prepared Ag-NPs at 333nm was found to be substantially quenched in existence of increasing concentrations of each drug. The quenching mechanisms were studied and explained. The validation of the method revealed linear correlation over the ranges of 0.5-10µg/ml with an excellent regression correlation (r=0.9999) for both drugs with minimum detection limits of 0.14 and 0.16µg/ml for rivaroxaban and edoxaban tosylate monohydrate, correspondingly. Three different metrics were employed for verifying the greenness profile of the presented study. The findings of the greenness assessment were congruent and compatible with the green synthesis procedure, ecofriendly analysis, and the exclusion of using organic solvents and noxious materials opening an avenue for green synthesis of nanoparticles instead of chemical and physical methods.

Systematic characterization of new EBT4 radiochromic films in clinical x-ray beams

Objective. We aim to characterize kinetics of radiation-induced optical density in newly released EBT4 radiochromic films exposed to clinical x-rays. Several film models and batches were evaluated for the film sensitivity, optical signal increasing with time, relative film noise, and minimum detectable limits (MDL).Approach. Radiochromic film pieces from a single batch of EBT3 and three batches of EBT4 were exposed to doses of 77.38 cGy, 386.92 cGy, and 773.84 cGy using a 6 MV x-ray beam. The films were scanned with a flatbed scanner at specific time intervals up to 120 h. The time-series net optical density of red, green and blue colors was corrected for response of the scanner with time and studied to establish the saturation characteristics of film polymerization process. Dose-response from 3.86 cGy to 1935 cGy was also determined for each color. MDL of the films was quantitatively defined as the dose that would double the net optical density of red color above the standard deviation of the residual signal at zero dose. The relative noise characteristics of EBT3 versus EBT4 were studied as a function of time, dose and scanner resolution.Main Results. For doses ≥ 100 cGy, analysis revealed a stability of optical density beyond 48 h post-exposure for EBT3 and EBT4 films. EBT3 films attained 80%-90% of their net optical density at 48 h within minutes of irradiation, compared to 72%-88% for EBT4 films. The rate of growth was slowest for blue color, fastest for red, while green was in between the two. The MDL for EBT4 averaged 15 cGy for three batches, whereas EBT3 films reliably detected doses as low as 8.5 cGy.Significance. Several batches of the new EBT4 film showed slightly lower response compared to its predecessor over 3.86 cGy to 1935 Gy range. For all practical purposes, the post-irradiation growth of polymers ceases between 48 to 60 h for both EBT films. Overall, the EBT4 film exhibited noise characteristics similar to EBT3, except for lower doses where the noise was observed to be higher than its predecessor.

Tapered coreless optical fiber-based refractive index sensor for acetone concentration detection

A fast-response optical fiber sensor is designed and fabricated to detect different concentrations of volatile acetone. The proposed sensor structure was fabricated by splicing a segment of tapered coreless fiber (CLF) amid two single-mode fibers (SMF). Herein, tuned tapered diameters and lengths of CLF’s cladding were immersed in various concentrations of the acetone solutions to sense the effective refractive index (RI) variations. Accordingly, the sensor’s performance with tuned diameters at different lengths of the CLF was optimized to realize the suitable size of amplified evanescent fields. The sensor responded remarkably towards acetone concentrations, with a superior sensitivity of 336.102 nm/RIU, 0.163 nm/%, and 27.531 × 10−5 nm/ppm at 5 cm length and 60 µm taper diameter of CLF. The examined sensor possesses a fast response time with a minimum detection limit of 0.244 RIU, 5.025%vol, and 2.9 ppm. Though the rapid evaporation (volatility) of the acetone compound exempted it from air pollutants, many industrial and human body processes produce acetone which needs to be detected. The examined sensor may have the potential to detect in a non-invasive approach with high accuracy and rapid diabetes in humans, lung cancer, etc.

Detection of HBV pgRNA by catalytic hairpin assembly combined with two Kinds of immunochromatographic strips

Serum HBV pregenomic RNA (pgRNA), as an important marker of HBV replication activity, has significant potential in virological monitoring and efficacy evaluation. In this study, two highly sensitive HBV pgRNA detection platforms were developed based on catalytic hairpin assembly technology, combined with flow lateral immunochromatography and colloidal gold immunochromatography. The signal amplification achieved by CHA technology avoids the dependence of RT-qPCR on thermal cycling equipment. The experimental results showed that the minimum detection limit of CHA-LFIA was 1 pM, and the minimum detection limit of CHA-GICA was 10 pM. Both CHA-LFIA and CHA-GICA had good specificity and could effectively distinguish between target RNA and non-target sequences. The results of CHA-LFIA and CHA-GICA were highly consistent with those of RT-qPCR, and had the potential for clinical application. This study provides a simple, rapid and innovative solution for the detection of HBV pgRNA, which does not rely on expensive equipment, and can be used for the early diagnosis and treatment monitoring of HBV infection.

An Economic and Reliable PCR Approach to Distinguish the Primary Pathogens Armillaria mellea and A. ostoyae From Other European Armillaria Species

ABSTRACTArmillaria is a soil‐borne genus of basidiomycetes whose species can cause stem and root rot in woody plants. The effects of plant‐pathogenic Armillaria species are well known in forests, but are underestimated in urban areas, where cases causing damage to trees and shrubs in green spaces have been steadily increasing in Switzerland since the 1980s. In this study, we present a simple, rapid, and cost‐effective protocol for high‐throughput diagnostics of the two primary pathogens A. mellea and A. ostoyae based on partial PCR amplification of the RPB2 gene. The specificity and sensitivity of the presented duplex PCR‐I and single‐plex PCR‐II were evaluated using different methods: (i) testing both PCRs on tree pathogenic or soil‐borne fungi of genera other than Armillaria, (ii) using dilution series of Armillaria‐DNA to determine a minimum detection limit, and (iii) sequencing the selected RPB2 region to verify the primer sequences and positions. The utility of PCR‐I and PCR‐II as a high‐throughput method was successfully tested on 65 DNA samples of Armillaria from Switzerland. Finally, an uninvolved person compared both classical methods, pairing test and sequencing, with PCR‐I and PCR‐II in a blind test. This study provides a reliable and alternative protocol for the rapid diagnosis of A. mellea and A. ostoyae causing root rot of woody plants.

Dual metal-organic-frameworks mediated resonance energy transfer for ultrasensitive electrochemiluminescence immunosensing.

Anelectrochemiluminescence (ECL) biosensor for carcinoembryonic antigen (CEA) based on electrochemiluminescence resonance energy transfer (ECL-RET) was designed. Tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)32+) was used as an energy donor for ECL-RET, and an Au nanoparticle-modified MOF framework (AuCoFe MOF) was used as an energy receptor for ECL-RET. The ECL emission spectra of Ru(bpy)32+ were in the range 550 to 680nm, and a zinc oxalate MOF encapsulating Ru(bpy)32+ (Ru@ Zn oxalate MOF) was prepared. The UV-vis absorption spectrum of AuCoFe MOF ranges from 280 to 700nm and overlaps with emission spectra of Ru@Zn oxalate MOF, which is critical for RET. The AuCoFe MOF-Ab2 bioconjugate, target CEA antigen, and the Ru@Zn oxalate MOF-Ab1 bioconjugate together form a sandwich structure, resulting in quenching of the ECL signal of Ru@Zn oxalate MOF by AuCoFe MOF. Under the optimized experimental conditions, the ECL-RET sensor exhibited excellent analytical performance in CEA detection with a linear range of 1.0 × 10-13 to 1.0 × 10-8mgmL-1; the minimum limit of detection is 1.4 × 10-14mgmL-1 (S/N = 3); and its recoveries of spiked samples ranging from 99.1 to 100.7%. The developed sensor has excellent stability, reproducibility, and specificity and is suitable for the detection of CEA in human serum and has the potential to provide sensitive detection of other biomarkers of diseases.

Sensitivity improvement of a deuterium-deuterium neutron generator based in vivo neutron activation analysis (IVNAA) system.

Our lab has been developing a deuterium-deuterium (DD) neutron generator-based neutron activation analysis (NAA) system to quantify metals and elements in the human body in vivo. The system has been used to quantify metals such as manganese, aluminum, sodium in bones of a living human. The technology provides a useful way to assess metal exposure and to estimate elemental deposition, storage and biokinetics. It has great potential to be applied in the occupational and environmental health fields to study the association of metal exposure and various health outcomes, as well as in the nutrition field to study the intake of essential elements and human health. However, the relatively low sensitivity of the system has greatly limited its applications. Neutron moderation plays an important role in designing an IVNAA facility, as it affects thermal neutron flux in irradiation cave and radiation exposure to the human subject. This study aims to develop a novel thermal neutron enhancement method to improve the sensitivity of the in vivo neutron activation analysis (IVNAA) system for elemental measurement but still maintain radiation dose. Utilizing a compact DD neutron source, we propose a new and practical moderator design that combines high density polyethylene with heavy water to enhance thermal neutrons by reducing thermal neutron absorption. All material dimensions are calculated by PHITS, a general-purpose Monte Carlo simulation program. The improvement of the new design predicted by the Monte Carlo simulation for the quantification of one of the elements, manganese was verified by experimental irradiation of manganese-doped bone equivalent phantoms. For the same radiation dose, a 67.9% thermal neutron flux enhancement is reached. With only 4.2% increase of radiation dose, the simulated thermal neutron flux and activation can be further increased by 84.2%. A 100% thermal neutron enhancement ratio is also achievable with a 20% dose increase. The experimental results clearly show higher manganese activation gamma ray counts for each specific phantom, with a significantly reduced minimum detection limit. Additionally, the photon dose was suppressed. The thermal neutron enhancement method can increase the number of useful neutrons significantly but maintain the radiation dose. This greatly decreased the detection limit of the system for elemental quantification at an acceptable dose, which will broadly expand the application of the technology in research and clinical use. The method can also be applied to other neutron medical applications, including neutron imaging and radiotherapy.

A novel phosphate detection sensor: From FTIR to EC-QCL

Excessive discharges of industrial and domestic sewage containing high concentrations of phosphorus are causing damage to the environment, so the detection of these pollutants in bodies of water is extremely critical. External cavity quantum cascade laser (EC-QCL) spectroscopy is a novel measurement technology that surpasses conventional infrared spectroscopy techniques. In this research, we propose a transmission detection system with a long optical path based on an EC-QCL for the detection of phosphate concentration in water bodies. Linear regression models were established based on this detection system, with all determination coefficients higher than 0.98 and a minimum detection limit smaller than 5.1 ppm. Additionally, the high-power spectral density of the EC-QCL permits the construction of a model using the raw radiation intensity data, as opposed to the conventional technique which depends on a reference background. The results show that the overall performance of the model based on the raw radiation intensity is similar to that of the model based on absorbance data. The EC-QCL detection system proposed in this study can ensure accuracy in the detection of pollutants, and the advantage of miniaturization provides a novel idea for the following development of portable phosphate in-situ sewage detection sensors.

Microstructured Self-Healing Flexible Tactile Sensors Inspired by Bamboo Leaves.

Wearable electronic devices with multifunctions such as flexible, integrated, and self-powered play a crucial role in the fields of health monitoring, motion monitoring, and human-computer interaction. However, their core basic components, flexible pressure sensors, face challenges including poor long-term stability and insufficient real-time sensing accuracy. In order to solve the challenges of long-term, stable, and accurate sensing of the sensor, this paper prepares polydimethylsiloxane (SHPDMS) with intrinsic self-healing property and designs a high-sensitivity self-healing capacitive flexible pressure sensor with dual microstructures (grating microstructured electrodes and microporous dielectric layer) as the substrate based on SHPDMS. Specifically speaking, the self-healing of the sensor under mild conditions was realized by introducing reversible imine bonds with low bonding energy into the polydimethylsiloxane (PDMS) flexible substrate, which solved the problem of the material's long-term service durability. A grating-like microstructure was introduced into the flexible electrode by using a spotted bamboo taro leaf as a template, and a dual microstructure sensor was constructed by combining it with a microporous dielectric layer doped with single-walled carbon nanotubes. This way reduces the elastic modulus of the dielectric layer, improves the dielectric constant of the sensor under loading, and thus significantly improves the sensor's sensitivity and extends the measurement accuracy in a low-stress range. The prepared self-healing flexible sensor achieves a sensitivity of 3.6 kPa-1, a minimum detection limit of 5 Pa, a response recovery time of less than 80 ms, and stability over 5000 cycles, which exceeds most previously reported silicone rubber-based capacitive flexible sensors.

A novel tapered quartz tuning fork-based laser spectroscopy sensing

A novel tapered quartz tuning fork (QTF) was designed to enhance its stress magnitude and charge distribution in QTF-based laser spectroscopy, which had a low resonant frequency of 7.83 kHz and a wide fork gap for long energy accumulation time and easy optical alignment. Compared to the reported rectangular QTF, this tapered QTF transfers the maximum stress position from the root to the middle to improve its sensing performance. Furthermore, the unique design eliminates the 90° right angles typically found in standard QTFs, which often lead to undesired “webs” and “facets” during the etching process. This design minimizes performance degradation by reducing the presence of residual unexpected materials. QTF-based laser spectroscopy of quartz-enhanced photoacoustic spectroscopy (QEPAS) and light-induced thermoelastic spectroscopy (LITES) were adopted to verify its performance. Compared with the widely used standard QTF, the total surface charge of the tapered QTF was improved 5.08 times and 5.69 times in QEPAS and LITES simulations, respectively. Experiments revealed that this tapered QTF-based QEPAS sensor had a 3.02 times improvement in signal-to-noise-ratio (SNR) compared to the standard QTF-based system. Adding an acoustic micro-resonator to this tapered QTF-based QEPAS sensor improved the signal level by 97.20 times. The minimum detection limit (MDL) for acetylene (C2H2) detection was determined to be 16.45 ppbv. In the LITES technique, compared to the standard QTF, this tapered QTF-based sensor had a 3.60 times improvement in SNR. The MDL for C2H2 detection was determined to be 146.39 ppbv.

A highly sensitive electrochemical aptasensor for detecting broad-spectrum estrogen molecules in clinical samples

The lack of sensitive and accurate monitoring methods for in vivo estrogen levels presents challenges for better prevention of estrogen-induced diseases. We have developed a label-free electrochemical aptasensor that demonstrates high sensitivity and selectivity for the broad-spectrum detection of estrogen molecules. This biosensor uses gold nanoparticles for electrochemical signal amplification and aptamers for broad-spectrum target recognition, enabling precise detection of trace amounts of estrogen in serum samples. The aptasensor demonstrates high sensitivity in estrogen detection, with a linear detection range of 0.01–1 nM and a minimum detection limit of 3 pM. It also exhibits excellent selectivity and interference resistance, with a detection error of less than 19 %, even in the presence of high concentrations of other biological substances. Additionally, molecular dynamics simulations were performed to provide insights into the molecular mechanism of aptamer broad-spectrum recognition and construction principles underlying the sensor. We anticipate that this aptasensor will serve as a robust, convenient, and cost-effective detection method, offering a valuable solution for the prevention of estrogen-induced diseases.

Circular DNA enhanced amplification-free CRISPR/Cas12a assays for end-user friendly ultra-sensitive Porphyromonas gingivalis diagnosis

Periodontitis not only leads to tooth loss but is also associated with various systemic symptoms. Porphyromonas gingivalis (Pg) is the microorganism most closely linked to periodontitis. A rapid and accurate Pg detection method holds significant potential health benefits for patients. While several nucleic acid amplification-based diagnostic methods have been developed, there is a current lack of rapid diagnostic tools for Pg, particularly at chair-side level. Here, two detection methods for the Pg 16S gene based on the CRISPR/Cas12a system have been developed. To achieve ultra-high sensitivity in the developed CRISPR/Cas12a assays without pre-amplification, we designed a circular DNA molecule (termed as Cir-amplifier) which amplifies the signal output of the Cas12a reactions in a cascade response manner. The Cir-amplifier enhanced Fluorescence-Cas12a reaction achieved a minimum detectable limit of 0.39 CFU of Pg within 80-minute under room-temperature. In addition, the Cir-amplifier enhanced Lateral Flow Detection (LFD)-Cas12a reaction has demonstrated the ability to detect a minimum of 3.9 CFU of Pg in 90 min, with results observable by the naked eye. The potential of the two methods for Pg detection in clinical samples has been demonstrated, showing 100 % sensitivity compared to the traditional real-time PCR method. In summary, we have established two efficient detection methods for Pg that eliminate the need for pre-amplification, hence no amplicon contaminations, making them promising candidates for chair-side Pg diagnosis. Furthermore, the Cir-amplifier has been demonstrated to be adaptable to CRISPR/Cas systems producing various signal formats. The Cir-amplifier is expected to become a universal CRISPR/Cas enhancer.

A sandwich-type electrochemical sensor based on RGO-CeO2-Au nanoparticles and double aptamers for ultrasensitive detection of glypican-3.

Asandwich-type electrochemical aptasensor for ultrasensitive detection ofglypican-3 (GPC3)was constructed using GPC3 aptamer (GPC3Apt) labelled reduced graphene oxide-cerium oxide-gold nanoparticles (RGO-CeO2-Au NPs) as the signal probe and the same GPC3Apt as the capture probe. The electrochemical redox properties of CeO2 (Ce3+/Ce4+) in the RGO-CeO2-Au NPs indicate the electrochemical signals. When the target GPC3 was present, an "aptamer-protein-aptamer" sandwich structure was formed on the sensing interface due to the specific binding between the protein and aptamers, resulting in an increased electrochemical redox signal detected by differential pulse voltammetry (DPV) technique. Under optimal conditions, the established aptasensor exhibited a logarithmic linear relationship between the current response and GPC3 concentration in the range 0.001-100.0ng/mL, with a minimum detection limit of 0.74pg/mL. Using the spike-recovery tests for measurement of the human serum samples, the recovery was from 99.26 to 114.01%, and the RSD range was 3.04 to 5.34%. Furthermore, the sandwich-type electrochemical aptasensor exhibited excellent performance characteristics such as good stability, high specificity, and high sensitivity, demonstrating effective detection of GPC3 in human serum samples and can be used as a clinical detection tool for GPC3.

Development and application of a quadruplex real-time PCR method for Torque teno sus virus 1, Porcine circovirus type 2, pseudorabies virus, and porcine parvovirus.

In clinical diagnosis of porcine diseases, co-infection with multiple viruses often leads to similar clinical symptoms. Postweaning multisystemic wasting syndrome (PMWS) can be caused by infections with TTSuV or PCV2, while PCV2, PRV, and PPV can cause respiratory and reproductive disorders in pigs. The overlapping clinical and pathological features of these infections necessitate the development of a rapid and specific method for differentiating and detecting these four DNA viruses. In this study, four pairs of primers and TaqMan probes were designed targeting the conserved sequence of TTSuV, the Rep gene of PCV2, the gE gene of PRV, and the VP2 gene of PPV. After optimizing reaction conditions, including annealing temperature, primer concentration, and probe concentration, a quadruplex real-time PCR method was developed. This method can specifically detect TTSuV1, PCV2, PRV, and PPV simultaneously, with no cross-reactivity with ASFV, CSFV, PRRSV, PEDV, PSV, and TGEV. The minimum detection limit for each virus was 10 copies/μl, and the inter-assay and intra-assay coefficients of variation ranged from 0.33% to 1.43%. Subsequently, 150 clinical samples were tested to evaluate the practical applicability of this method. The positive rates for TTSuV1, PCV2, PRV, and PPV were 8.6% (13/150), 10.67% (16/150), 14% (21/150), and 11.33% (17/150), respectively. The results indicate that the established quadruplex real-time PCR method can assist in the accurate and rapid diagnosis of TTSuV1, PCV2, PRV, and PPV in clinical settings, providing robust support for the prevention and control of these infections.

Development of a chemiluminescent immunoassay based on magnetic solid phase for quantification of homocysteine in human serum

BackgroundHomocysteine (HCY) is a sulfur-containing amino acid that is an independent or important risk factor for the occurrence of many chronic diseases and is one of the most important indicators for determining health risks. However, existing HCY detection methods do not meet the requirements of clinical diagnosis. Therefore, there is an urgent need to establish new detection methods to meet the needs of clinical detection.ResultsIn this study, we used the principle of competitive method to establish a new method for the determination of HCY in human serum using a chemiluminescent enzyme immunoassay in conjunction with a chemiluminescent assay instrument that uses magnetic microparticles as the solid phase of the immunoreaction. The established method achieved satisfactory results in terms of minimum detection limit, specificity, accuracy, and clinical application. The limit of detection was 0.03 ng/mL. The intra-assay coefficient of variation (CV) was 1.94–5.05%, the inter-assay CV was 2.29–6.88%, and the recovery rate was 88.60–93.27%. Cross-reactivity with L-cysteine ranged from 0.0100 to 0.0200 μmol/L, and cross-reactivity with glutathione ranged from 0.0100 to 0.200 μmol/L, all of which were less than the limit of detection (LoD) of this method. The linear factor R of this method was greater than 0.99.ConclusionsIn summary, the developed method showed a good correlation with the product from Abbott. A total of 996 clinical patients with cardiovascular diseases were evaluated using the method developed in this study.

Resonant Cell-Based 1f Photoacoustic Gas Analyzer Immune to Light Power Fluctuation and Frequency Mismatch.

To overcome the light power fluctuation and frequency mismatch in photoacoustic spectroscopy (PAS), we proposed a self-corrected 1f-only resonant cell-based PAS (1f-RCPAS) gas analyzer. Based on the theoretical analysis of the 1f signal, a signal processing algorithm considering laser power-current nonlinearity is proposed. The 1f-only algorithm is well-tailored for the resonant systems, requiring no time-division multiplexing. The algorithm is further improved to extend the dynamic range. The T-type resonant cell incorporating a graphene sticker is utilized for effectively amplifying the acoustic signals from both the gas and solid to achieve normalization. No optical path alignment is needed. For the low resonance frequency, a digital orthogonal-vector lock-in amplifier is used, further simplifying the system setup. The gas analyzer is used to measure methane (CH4) with the near-infrared absorption peak at 1651 nm. The experiments demonstrated immunity to fiber coupling loss, laser power drift over time, and frequency mismatch caused by property differences between air and standard gases. The R2 value in the concentration calibration reaches 0.99995, and the minimum detection limit given by the Allan variance reaches 3.5 ppb at an average time of 105 s.

Optimization of complexing membranes for platinum analysis in water at part per trillion levels by X-ray fluorescence

BackgroundPlatinum is a critical metal, especially in medicine and catalysis. Its concentration in aquatic ecosystems may gradually affect aquatic animals due to its ability to bioaccumulate. Additionally, the recycling of platinum has become crucial, so new extraction methods are needed. In recent years, there has been increasing interest in environmental studies based on X-Ray Fluorescence, due to the requirements of green chemistry. Complexing membranes have been used for platinum analysis in combination with X-ray Fluorescence, although with a relatively high detection limit. ResultsSeveral optimizations were introduced to achieve a significantly improved detection limit and repeatability. Self-supported membranes were used for the first time and proved to be highly effective in binding platinum from aqueous solutions. An extensive search was conducted to identify an appropriate chemical element to serve as an internal standard; osmium met many of the necessary criteria and was successfully used as an internal standard, leading to a remarkable improvement in the method's precision. The effect of various elements present in natural waters was examined, and no interferences were observed. The method gave equally reliable results in all types of water, including seawater. Through substantial optimization procedures, a minimum detection limit up of 37 ng L−1 was achieved with a 1000 s irradiation time. The potential aging of the membrane was investigated, showing that the membrane does not deteriorate for at least one month when stored at refrigeration temperature. SignificanceThe newly introduced self-supported complexing membranes improved the platinum detection limit by more than 100-fold, enabling, for the first time, platinum analysis at low ng L−1 concentration levels using X-ray Fluorescence. This method can be used to various types of natural waters, including seawater with near-complete recovery from the aquatic matrix. This research may also contribute to improving the minimum detection limits of the method for other trace elements besides platinum.

β-Cyclodextrin-Modified Laser-Induced Graphene Electrode for Detection of N6-Methyladenosine in RNA.

Laser-induced graphene (LIG) possesses characteristics of easy handling, miniaturization, and unique electrical properties. We modified the surface of LIG by electropolymerizing β-cyclodextrin (β-CD), which was used to immobilize antibodies on the electrode surface for highly sensitive detection of targets. N6-methyladenosine (m6A) is the most prevalent reversible modification in mammalian messenger RNA and noncoding RNA, influencing the development of various cancers. Here, β-CD was electropolymerized to immobilize the anti-m6A antibody, which subsequently recognized the target m6A. This was integrated into the catalytic hydrogen peroxide-hydroquinone (H2O2-HQ) redox system using phos-tag-biotin to generate electrochemical signals from streptavidin-modified horseradish peroxidase (SA-HRP). Under optimal conditions, the biosensor exhibited a linear range from 0.1 to 100 nM with a minimum detection limit of 96 pM. The method was successfully applied to the recovery analysis of m6A from HeLa cells through spiking experiments and aims to inspire strategies for point-of-care testing (POCT).