Detecting and quantifying Veillonella by real-time quantitative PCR and droplet digital PCR

Veillonella spp. are Gram-negative opportunistic pathogens present in the respiratory, digestive, and reproductive tracts of mammals. An abnormal increase in Veillonella relative abundance in the body is closely associated with periodontitis, inflammatory bowel disease, urinary tract infections, and many other diseases. We designed a pair of primers and a probe based on the 16S rRNA gene sequences of Veillonella and conducted real-time quantitative PCR (qPCR) and droplet digital PCR (ddPCR) to quantify the abundance of Veillonella in fecal samples. These two methods were tested for specificity and sensitivity using simulated clinical samples. The sensitivity of qPCR was 100 copies/μL, allowing for the accurate detection of a wide range of Veillonella concentrations from 103 to 108 CFU/mL. The sensitivity of ddPCR was 11.3 copies/μL, only allowing for the accurate detection of Veillonella concentrations from 101 to 104 CFU/mL because of the limited number of droplets generated by ddPCR. ddPCR is therefore more suitable for the detection of low-abundance Veillonella samples. To characterize the validity of the assay system, clinical samples from children with inflammatory bowel disease were collected and analyzed, and the results were verified using isolation methods. We conclude that molecular assays targeting the 16S rRNA gene provides an important tool for the rapid diagnosis of chronic and infectious diseases caused by Veillonella and also supports the isolation and identification of Veillonella for research purposes. KEY POINTS: • With suitable primer sets, the qPCR has a wider detection range than ddPCR. • ddPCR is suitable for the detection of low-abundance samples. • Methods successfully guided the isolation of Veillonella in clinical sample.

Covalent organic framework with donor-acceptor structure for rapid and sensitive photothermal sensing detection

Given the serious harm caused by dietary intake of diethylstilbestrol (DES), it is urgent to explore rapid and sensitive DES sensing methods. In this work, a photothermal DES immunochromatography sensor based on covalent organic framework (COF) was constructed. The performance of COF in the field of photothermal sensing was systematically investigated for the first time. A donor-acceptor type of COF with a photothermal conversion rate of 51.17 % was synthesized. The logarithm of the DES concentrations-temperature change value standard curve was plotted. The intensity of the photothermal sensing signal was inversely proportional to the sample concentration. The detection limit of the proposed photothermal method (0.24 μg·L-1) was 10 times higher than that of visual detection (3 μg·L-1). This work not only constructed a novel detection method for DES sensing, but also provided a feasible demonstration for the application of COF in photothermal sensing and expanded the application of their photothermal properties.

A powerful method for In Situ and rapid detection of trace nanoplastics in water-Mie scattering

The pervasive presence of nanoplastics (NPs) in environmental media has raised significant concerns regarding their implications for environmental safety and human health. However, owing to their tiny size and low level in the environment, there is still a lack of effective methods for measuring the amount of NPs. Leveraging the principles of Mie scattering, a novel approach for rapid in situ quantitative detection of small NPs in low concentrations in water has been developed. A limit of detection of 4.2 μg/L for in situ quantitative detection of polystyrene microspheres as small as 25 nm was achieved, and satisfactory recoveries and relative standard deviations were obtained. The results of three self-ground NPs showed that the method can quantitatively detect the concentration of NPs in a mixture of different particle sizes. The satisfactory recoveries (82.4% to 110.3%) of the self-ground NPs verified the good anti-interference ability of the method. The total concentrations of the NPs in the five brands of commercial bottled water were 0.07 to 0.39 μg/L, which were directly detected by the method. The proposed method presents a potential approach for conducting in situ and real-time environmental risk assessments of NPs on human and ecosystem health in actual water environments.

Amplification-free quantitative detection of genomic DNA using lateral flow strips for milk authentication

With the globalization and complexity of the food supply chain, the market is becoming increasingly competitive and food fraudulent activities are intensifying. The current state of food detection faced two primary challenges. Firstly, existing testing methods were predominantly laboratory-based, requiring complex procedures and precision instruments. Secondly, there was a lack of accurate and efficient quantitative detection methods. Taking cow's milk as an example, this study introduced a novel method for nucleic acid quantification in dairy products, based on lateral flow strips (LFS). The core idea of this method is to design single-stranded DNA (ssDNA) probes to hybridize with mitochondrial genes, which are abundant, stable, and species-specific in dairy products, as detection targets. Drawing inspiration from the principles of nucleic acid amplification, this research innovatively established a new DNA hybridization method, named LAMP-Like Hybridization (HybLAMP-Like). Leveraging the denaturation and DNA polymerization functions of the bst enzyme, efficient binding of the probe and template strand was achieved. This method eliminated the need for nucleic acid amplification, simplifying the procedure and mitigating aerosol contamination, thereby ensuring the accuracy of the detection results. The method exhibited exceptional sensitivity, capable of detecting extremely low to 12.5 ng in visual inspection and 3.125 ng when using a reader. In terms of practicality, it could achieve visual detection of cow's milk content as low as 1% in adulterated dairy products. When combined with a portable LFS reader, it also enabled precise quantitative analysis of milk adulteration.

Highly sensitive detection of multiple antiviral drugs using graphitized hydroxylated multi-walled carbon nanotubes/ionic liquids-based electrochemical sensors

Global outbreaks and the spread of viral diseases in the recent years have led to a rapid increase in the usage of antiviral drugs (ATVs), the residues and metabolites of which are discharged into the natural environment, posing a serious threat to human health. There is an urgent need to develop sensitive and rapid detection tools for multiple ATVs. In this study, we developed a highly sensitive electrochemical sensor comprising a glassy carbon electrode (GCE) modified with graphitized hydroxylated multi-walled carbon nanotubes (G-MWCNT-OH) and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6, IL) for the detection of six ATVs including famciclovir (FCV), remdesivir (REM), favipiravir (FAV), hydroxychloroquine sulfate (HCQ), cepharanthine (CEP) and molnupiravir (MOL). The morphology and structure of the G-MWCNT-OH/IL nanocomposites were characterized comprehensively, and the electroactive surface area and electron conductivity of G-MWCNT-OH/IL/GCE were determined using cyclic voltammetry and electrochemical impedance spectroscopy. The thermodynamic stability and non-covalent interactions between the G-MWCNT-OH and IL were evaluated through quantum chemical simulation calculations, and the mechanism of ATV detection using the G-MWCNT-OH/IL/GCE was thoroughly examined. The detection conditions were optimized to improve the sensitivity and stability of electrochemical sensors. Under the optimal experimental conditions, the G-MWCNT-OH/IL/GCE exhibited excellent electrocatalytic performance and detected the ATVs over a wide concentration range (0.01-120 μM). The limit of detections (LODs) were 42.3 nM, 55.4 nM, 21.9 nM, 15.6 nM, 10.6 nM, and 3.2 nM for FCV, REM, FAV, HCQ, CEP, and MOL, respectively. G-MWCNT-OH/IL/GCE was also highly stable and selective to the ATVs in the presence of multiple interfering analytes. This sensor exhibited great potential for enabling the quantitative detection of multiple ATVs in actual water environment.

Ratiometric SERS quantification of SO2 vapor based on Au@Ag-Au with Raman reporter as internal standard

Practical gas sensing application requires sensors to quantify target analytes with high sensitivity and reproducibility. However, conventional surface enhanced Raman scattering (SERS) sensor lacks reproducibility and quantification arising from variations of "hot spot" distribution and measurement conditions. Here, a ratio-dependent SERS sensor was developed for quantitative label-free gas sensing. Au@Ag-Au nanoparticles (NPs) were filtered onto anodic aluminum oxide (AAO) forming Au@Ag-Au@AAO SERS substrate. 4-MBA was encapsulated in the gap of Au@Ag-Au and served as the internal standard (IS) to calibrate SERS signal fluctuation for improved quantification ability. Combined with headspace sampling method, SO2 residue in traditional Chinese medicine (TCM) can be extracted and captured on the immediate vicinity of Au@Ag-Au surface. The intensity ratio I613 cm-1/I1078 cm-1 showed excellent linearity within the range of 0.5 mg/kg-500 mg/kg, demonstrating superior quantification performance for SO2 detection. Signals for concentration as low as 0.05 mg/kg of SO2 could be effectively collected, much lower than the strictest limit 10 mg/kg in Chinese Pharmacopoeia. Combined with a handheld Raman spectrometer, handy and quantitative TCM quality evaluation in aspect of SO2 residue was realized. This ratiometric SERS sensor functioned well in rapid on-site SO2 quantification, exhibiting excellent sensitivity and simple operability.

Quantitative prediction of AFB1 in various types of edible oil based on absorption, scattering and fluorescence signals at dual wavelengths

This study aims to address the challenge of matrix interference of various types of edible oils on intrinsic fluorescence of aflatoxin B1 (AFB1) by developing a novel solution. Considering the fluorescence internal filtering effect, the absorption (μa) and reduced scattering (μ's) coefficients at dual wavelengths (excitation: 375 nm, emission: 450 nm) were obtained by using integrating sphere technique, and were used to improve the quantitative prediction results for AFB1 contents in six different kinds of edible oils. A research process of "Monte Carlo (MC) simulation - phantom verification - actual sample validation" was conducted. The MC simulation was used to determine interference rule and correction parameters for fluorescence, the results indicated that the escaped fluorescence flux nonlinearly decreased with the μa, μ's at emission wavelength (μa,em, μ's,em) and μa at excitation wavelength (μa,ex), however increased with the μ's at excitation wavelength (μ's,ex). And the required optical parameters to eliminate the interference of matrix on fluorescence intensity are: effective attenuation coefficients at excitation and emission wavelengths (μeff,ex, μeff,em) and μ's,ex. Phantom verification was conducted to explore the feasibility of fluorescence correction based on the identified parameters by MC simulation, and determine the optimal machine learning method. The modelling results showed that least squares support vector regression (LSSVR) model could reach the best performance. Three kinds of edible oil (peanut, rapeseed, corn), each with two brands were used to prepare oil samples with different AFB1 contamination. The LSSVR model for AFB1 based on μeff,ex, μeff,em, μ's,ex and fluorescence intensity at 450 nm was calibrated, both correlation coefficients for calibration (Rc) and the validation (Rv) sets could reach 1.000, root mean square errors for calibration (RMSEC) and the validation (RMSEV) sets were as low as 0.038 and 0.099 respectively. This study proposed a novel method which is based solely on the absorption, scattering, and fluorescence characteristics at excitation and emission wavelengths to achieve accurate prediction of AFB1 content in different types of vegetable oils.

Ratiometric fluorescent biosensor for detection and real-time imaging of nitric oxide in mitochondria of living cells

Nitric oxide (NO), a ubiquitous gaseous messenger, plays critical roles in various pathological and physiological progresses. The abnormal levels of NO in organisms are closely related to a large number of maladies. Mitochondria are the main area that produce NO in mammalian cells. Thus, detecting and real-time imaging of NO in mitochondria is of great significance for exploring the biological functions of NO. Herein, a ratiometric fluorescent biosensor (Mito-GNP-pNO520) is developed for sensitive and selective detection and real-time imaging of NO in mitochondria of living cells. The detection is achieved through the fluorescence off-on response of Mito-GNP-pNO520 toward NO. This biosensor shows excellent characteristics, such as high sensitivity toward NO with a low detection limit of 0.25 nM, exclusive selectivity to NO without interference from other substances, good biological stability and low cytotoxicity. More importantly, the biosensor is specifically located in mitochondria, enabling the detection and real-time imaging of endogenous and exogenous NO in mitochondria of living cells. Therefore, our biosensor offers a new approach for dynamic detecting and real-time imaging of NO in subcellular organelles, providing an opportunity to explore new biological effects of NO.

Real-time visualization the pH fluctuations of living cells with a ratiometric near-infrared fluorescent probe

In situ real-time quantitative monitoring pH fluctuation in complex living systems is vitally significant. In the current work, a ratiometric near-infrared (NIR) probe (MCyOH) was developed to confront this challenge. MCyOH exhibited good sensitivity, photostability, reversibility, and an ideal pKa (pKa = 6.65). Ratiometric character of MCyOH is beneficial to accuracy detect the pH fluctuations in living cells under different stimulation. The observations showed that intracellular pH was decreased when HepG2 cells under oxidative stress or starvation conditions. In particular, HepG2 cells was acidulated after addition of ethanol, however, the acidification phenomenon was attenuated or disappeared when HepG2 cells preincubated with disulfiram or fomepizole. Finally, MCyOH was successfully applied to observe the increasement of intracellular pH when HepG2 cells treated with fomepizole individually. Overall, MCyOH would be a practical candidate to explore pH-associated physiological and pathological varieties.

Concentration analysis of metal-labeled nanoplastics in different water samples using electrochemistry

Despite the threats posed by nanoplastics to the environment and human health, little was known about the occurrence, formation, migration, and environmental impacts of nanoplastics due to the lack of quantitative and sensitive detection techniques. In this work, an electrochemical strategy for the detection of nanoplastics based on Ag labeling was proposed. Positively charged silver ions were attached to negatively charged polystyrene nanoplastics (PSNPs), and then the silver ions on the surface of PSNPs were reduced to Ag by sodium borohydride. Subsequently, the concentration of PSNPs was determined by identifying the signal of Ag by differential pulse voltammetry. The method showed different sensitivity for PSNPs of different sizes (100, 367, 500 nm). For tap water samples, the reason for the change in Ag electrochemical signal was discussed. The sensitivity of the method to PSNPs in tap water was investigated. The feasibility of the method for environmental water samples was verified using spiked lake water and spiked seawater, and satisfactory recoveries (93-112 %) were obtained for PSNPs of different sizes and concentrations. This study provided a sensitive, low-cost, and simple method without complex instrumentation, which was important for the determination of PSNPs in environmental water samples.

Honeycomb-like AgNPs@TiO2 array SERS sensor for the quantification of micro/nanoplastics in the environmental water samples

There has been a growing concern over the micro/nanoplastics pollution and treatment. The fast qualitative and quantitative analysis of these small plastic particles is the crucial issues. Herein, a novel honeycomb-like AgNPs@TiO2 array-based surface-enhanced Raman scattering (SERS) sensor was developed for efficient identification and analysis of the micro/nanoplastics in the environmental water samples. The plasmonic AgNPs were uniformly anchored within the periodic TiO2 nanocage arrays to form a AgNPs@TiO2 array. The dual enhancement mechanisms in the AgNPs@TiO2 hybrid structure endow the SERS sensor high sensitivity to detect trace amount of micro/nanoplastics down to 50 μg/mL with a hand-held Raman spectrometer. Further, this SERS sensor successfully discerns two-component mixtures of the micro/nanoplastics due to the fingerprint feature. In addition, the superior reproducibility (RSD of 9.69%) of the SERS sensor assures the quantitative detection reliability, realizing quantitative analysis of Polystyrene (PS) microplastics in tap water, lake water, soil water and seawater with detection limits of 100 μg/mL, 100 μg/mL, 100 μg/mL, 100 μg/mL and 250 μg/mL, respectively. The recovery rates of PS microspheres in four water environments ranged from 97.6% to 109.7%, with the RSD ranging from 0.49% to 10.23%. This honeycomb AgNPs@TiO2 array sensor provides a promising application prospect in the detection of micro/nanoplastics contaminants from the environmental water.

A NIR ratiometric fluorescent probe for the rapid detection of hydrogen sulfide in living cells and zebrafish

Hydrogen sulfide (H2S) acts as a gas transporter and cell protector and plays a role in a number of disorders and signaling processes. Given that the half-life of H2S in biological systems is between seconds and minutes, the development of rapid and accurate technologies for reliable monitoring H2S levels and dynamics in organisms is critical. However, it is still difficult to design innovative near-infrared fluorescent probes that can quickly and accurately detect H2S. Here, we constructed a novel NIR ratiometric fluorescent probe based on the "aldehyde group auxiliary strategy", Cy-H2S, for the quantitative detection and precise imaging of H2S in living cells and zebrafish. Cy-H2S responded quickly (150 s) and was highly sensitive (0.179 μM) to H2S donor. Cy-H2S was further successfully employed to track endogenous H2S fluctuation in HCT116 cells and zebrafish and evaluated the release efficiency of the H2S prodrug in a NIR ratiometric imaging way. Cy-H2S has the potential to be used as a reliable indication of H2S levels in living cells and zebrafish, as well as an innovative and practical instrument for furthering the physiological research of H2S, which will encourage the creation of advanced NIR ratiometric probes for a variety of biological applications.

Real-time detection of plasma ferritin by electrochemical biosensor developed for biomedical analysis

Rapid quantification of plasma ferritin levels holds utmost importance for the effective management of different chronic illnesses. We report the development of a novel biosensor for quantitative and selective detection of ferritin from a drop of blood plasma. Developed electrochemical biosensing platform contains a semiconductor nano-structured decorated screen-printed electrode (SND-SPE). The hydrothermally synthesized ZnO-Mn3O4 nanocomposite which has been coated on the electrode surfaces, imparts the specificity in ferritin diagnostics. Cyclic voltametric (CV) measurements with blood plasma shows a prominent reduction peak of ∼ - 0.76 V for specific ferritin reduction. The amperometric sensor shows a known concentration of 0.3 µg/dl ferritin-containing plasma generates 15 µA of current for single-time use. The efficacy of the device is evaluated by detecting ferritin in human plasma samples. The limit of detection and response time of the developed sensor are 0.04 µg/dl and 0.1 s respectively. The layer of ZnO-Mn3O4 nanocomposite has played as an excellent catalyst during the specific reduction of Fe3+ ion and the merits of the device in terms of high robustness, ultrafast detection, highly stable, low-cost, and a biodegradable sensor, make it attractive for the deployment in point-of-care settings.

Engineered DNA molecular machine for ultrasensitive detection of environmental lead pollution

Dynamic monitoring of environmental Pb2+ is of utmost importance for food safety and personal well-being. Herein, we report a novel, rapid, and practical fluorescence detection platform for Pb2+. The platform comprises two essential components: an engineered DNAzyme probe (EDP) and a responsive functionalized probe (RFP). The EDP demonstrates specific recognition of Pb2+ and the subsequent release of free DNA fragments. The released DNA fragments are then captured using the RFP to form DNA complexes, which undergo multiple cascade amplification reactions involving polymerases and nickases, resulting in the generation of a large number of fluorescence signals. These signals can detect Pb2+ at concentrations as low as 0.114 nmol/L, with a dynamic range spanning from 0.1 nmol/L to 50 nmol/L. Moreover, the platform exhibits excellent sensitivity and selectivity for Pb2+ detection. To further validate its effectiveness, we successfully quantitatively detected lead contamination in water from Chaohu Lake, and the results aligned closely with those obtained using inductively coupled plasma-mass spectrometry (ICP-MS). Moreover, this platform is suitable for detecting Pb2+ in seawater, soil, and fish samples. These findings confirm the suitability of the current detection platform for the dynamic assessment of Pb contamination in ecological environments, thereby contributing to environmental and food safety.

Green in situ immobilisation of gold nanoparticles on bacterial nanocellulose membranes using Tannic acid and its detection of Fe3

Oxidative stress is one of the factors that promote melanogenesis. Trivalent iron ions play a key role in regulating the iron-catalysed oxidative stress response. A novel SERS flexible membrane sensor based on tannic acid with good sensitivity and uniformity was prepared by green in situ reduction of gold nanoparticles on bacterial cellulose membrane（BCM）with a simple and highly selective method to detect Fe3+. Under alkaline conditions, Fe3+ is adsorbed on the BCM-TA@Au NPs flexible membrane by tannic acid (TA) through chelation, thus enabling the detection of Fe3+. Furthermore, this simple detection system has a wide linear detection range and high sensitivity to effortlessly evaluate Fe3+ at concentrations up to 10-7 M. More importantly, the proposed SERS flexible substrate performed well in determining Fe3+ concentrations in B16 melanocytes, providing new insights into the factors affecting the melanin synthesis pathway and providing a potential biomarker for melanoma treatment.

Thin layer chromatography coupled with surface enhanced Raman scattering for rapid separation and on-site detection of multi-components

The separation and detection of multi-component mixtures has always been a challenging task. Traditional detection methods often suffer from complex operation, high cost, and low sensitivity. Surface enhanced Raman scattering (SERS) technique is a high sensitivity, powerful and rapid detection tool, which can realize the specific detection of single substance components, but it must solve the problem that multi-component mixtures cannot be accurately determined. Thin layer chromatography (TLC) technology, as a high-throughput separation technology, uses chromatographic plate as the stationary phase, and could select different developing phases for separation experiments. The advantages of TLC technology in short distance and rapid separation are widely used in protein, dye and biomedical fields. However, TLC technology has limitations in detection ability and difficulty in obtaining ideal signal intensity. The combination of TLC technology and SERS technology made the operation procedure simple and the sample size small, which can achieve rapid on-site separation and quantitative detection of mixtures. Due to the rapid development of TLC-SERS technology, it has been widely used in the investigation of various complex systems. This paper reviews the application of TLC-SERS technology in food science, environmental pollution and biomedicine.

Combining multisite functionalized magnetic nanomaterials with interference-free SERS nanotags for multi-target sepsis biomarker detection

Surface-enhanced Raman scattering (SERS) is an ultra-sensitive vibration spectroscopy technology, with the advantages of multi-index and non-destructive quantitative detection, has attracted much attention in the joint detection of biomarkers. A novel SERS biosensor with multisite capture and interference-free quantification was designed for the joint detection of the sepsis biomarker interleukin-6 (IL-6) and procalcitonin (PCT). This biosensor had two interference-free core-shell SERS probes with highly efficient electromagnetic enhancement and a multisite functionalized magnetic nanomaterial with high adsorption capacity. They formed sandwich structure with the targets through boronic affinity and immunoreaction, and the multi-target quantitative analysis of biomarkers in serum was performed using a portable Raman spectrometer in the Raman-silent region. The SERS biosensor was exhibited highly sensitive with detection limits of 0.584 and 2.99 pg/mL for IL-6 and PCT, respectively. In addition, it exhibited excellent selectivity and specificity even with the interference of other proteins. As this SERS method showed excellent performance in the detection of sepsis, it has great potential for multi-index detection in clinical diagnosis of major diseases.

Structures of water on the surface of anatase TiO2 studied by diffuse reflectance near-infrared spectroscopy

Investigating the structures of water on metal oxides is helpful for understanding the mechanism of the adsorptions in the presence of water. In this work, the structures of adsorbed water molecules on anatase TiO₂ (101) were studied by diffuse reflectance near-infrared spectroscopy (DR-NIRS). With resolution enhanced spectrum by continuous wavelet transform (CWT), the spectral features of adsorbed water at different sites were found. In the spectrum of dried TiO₂ powder, there is only the spectral feature of the water adsorbed at 5-coordinated titanium atoms (Ti_5c). With the increase of the adsorbed water, the spectral feature of the water at 2-coordinated oxygen atoms (O_2c) emerges first, and then that of the water interacting with the adsorbed water can be observed. When adenosine triphosphate (ATP) was adsorbed on TiO₂, the intensity of the peaks related to the adsorbed water decreases, indicating that the adsorbed water is replaced by ATP due to the strong affinity to Ti_5c. Therefore, there is a clear correlation between the peak intensity of the adsorbed water and the adsorbed quantity of ATP. Water can be a NIR spectroscopic probe to detect the quantity of the adsorbed ATP. A partial least squares (PLS) model was established to predict the content of adsorbed ATP by the spectral peaks of water. The recoveries of validation samples are in the range of 92.00-114.96% with the relative standard deviations (RSDs) in a range of 2.13-5.82%.

Quantitative detection of surface defect using laser-generated Rayleigh wave with broadband local wavenumber estimation

Laser ultrasonic technology has been widely used in surface defect detection attribute to its non-contact, non-destructive and high spatial resolution characteristics. This paper proposes a surface defect quantitative detection method using laser-generated Rayleigh wave with broadband local wavenumber estimation. In this method, considering the broadband characteristics of laser-generated Rayleigh wave, the broadband local wavenumber estimation is presented to achieve the defect imaging accurately, and then the defect geometric parameters are estimated based on image segmentation. A surface defect detection experiment using the laser ultrasonic detection system is conducted to verify the effectiveness of the proposed method. The experimental results show that the proposed method has superior imaging effect for vertical and inclined defects than the standing wave energy method or reflected wave energy method. Besides, the geometric parameters such as length, width, and inclination angle of a surface defect can be accurately identified by the proposed method, the errors of vertical defects are 1.6% in length and 4.0% in width respectively, as well as the maximum and minimum error of inclined defects are 5.0% and 1.28% in inclination angle respectively. The research results provide a potential application for the fast and non-destructive surface defect detection of metal structures.

Nb2C MXene self-assembled Au nanoparticles simultaneously based on electromagnetic enhancement and charge transfer for surface enhanced Raman scattering

Recent years, two-dimensional transition metal carbonitrides (MXene) have attracted much attention in the field of surface-enhanced Raman scattering (SERS). However, the relatively low enhancement of MXene is a major challenge. Herein, Nb₂C-Au NPs nanocomposites were prepared by electrostatic self-assembly method, which have a synergistically conjugated SERS effect. The EM hot spots of Nb₂C-Au NPs are significantly enlarged and expanded, while the surface Fermi level is decreased. This synergistic effect could improve the SERS performance of the system. Consequently, for the dye molecules CV and MeB, the detection limits reach 10^-10 M and 10^-9 M, respectively, while for biomolecule adenine, the detection limit is as low as 5 × 10^-8 M. The results also show the good concentration-dependent linearity, uniformity, reproducibility and stability of SERS substrate. Nb₂C-Au NPs could be a fast, sensitive and stable SERS platform for label-free and non-destructive detection. This work may expand the application of MXene based materials in the field of SERS.

Sensitive amplified luminescent proximity homogeneous assay for the quantitative detection of CA242

We here developed a sensitive and stable amplified luminescent proximity homogeneous assay (AlphaLISA) method for fast quantification of CA242 in human serum. Donor and acceptor beads modified with carboxyl groups could be coupled with CA242 antibodies after activation in the AlphaLISA method. CA242 was rapidly detected by the double antibody sandwich immunoassay. The method yielded good linearity (>0.996) and detection range (0.16-400 U/mL). The intra-assay precisions of CA242-AlphaLISA were between 3.43% and 6.81% (< 10%), and the inter-assay precisions were between 4.06% and 9.56% (< 15%). The relative recoveries ranged from 89.61% to 107.29%. Detection time for the CA242-AlphaLISA method was only 20 min. Moreover, results of CA242-AlphaLISA and time-resolved fluorescence immunoassay had satisfactory correlation and consistency (ρ = 0.9852). The method was successfully applied to the analysis of human serum samples. Meanwhile, serum CA242 has a good detection value in the identification and diagnosis of pancreatic cancer and the monitoring of disease degree. Furthermore, the proposed AlphaLISA method is expected to be an alternative to traditional detection methods, laying a good foundation for the further development of kits to detect other biomarkers in future studies.

Converting commonly-used paper into nano-engineered fluorescent biomass-based platform for rapid ClO- quantitative detection in living cells and water sources

Hypochlorous acid (HClO) and derivative ionic form (ClO^-) are significant components of reactive oxygen species, and thus various diseases are correlatively related to the concentration of ClO^-. Recently, paper-based indicators have been confirmed to be efficient strategy for sensing hazardous and noxious substances. However, most of these materials can only achieve qualitative detection of the substrates. Herein, an extremely simple manufacturing strategy was proposed to convert commonly-used paper into nano-engineered fluorescent biomass-based platform (CMJL-FP) integrated with on-demand self-assembled colorimetric and ratiometric fluorescence sensor (CMJL) for rapid ClO^- quantitative detection in organisms or water sources using smartphones. The CMJL exhibited a highly selective and sensitive ratiometric response to ClO^- at a low detection limit (LOD = 92.6 nM). The associating interactions between the fluorescence nano-particles and micro-nano fibers of CMJL-FP ensure good-stability during ClO^- detection. It has been experimentally demonstrated that CMJL-FP allows one to realize the rapid quantitative detection of ClO^- ions in living cells and large-scale water sources by using color recognition software as part of a simple smartphone. Therefore, integrating the proposed fluorescent paper with smartphones provides an effective, sustainable, cheap and conceptual strategy for quantitative detection of hazardous and noxious substances in organisms and environments.

Quantitative detection of dopamine in human serum with surface-enhanced Raman scattering (SERS) of constrained vibrational mode

Dopamine (DA) is a crucial neurotransmitter involved in the hormonal, nervous, and vascular systems being considered as an index to diagnose neurodegenerative diseases, including Parkinson's and Alzheimer's disease. Herein, we demonstrate the quantitative sensing of DA using the peak shift in surface-enhanced Raman scattering (SERS) of 4-mercaptophenylboronic acid (4-MPBA), resulting from the concentration of DA. To enable the signal enhancement of Raman scattering, Ag nanostructure was built with one-step gas-flow sputtering. 4-MPBA was then introduced using vapor-based deposition, acting as a reporter molecule for bonding with DA. The gradual peak-shift from 1075.6 cm^-1 to 1084.7 cm^-1 was observed with the increasing concentration of DA from 1 pM to 100nM. The numerical simulation revealed that DA bonding induced a constrained vibrational mode corresponding to 1084.7 cm^-1 instead of a C-S-coupled C-ring in-plane bending mode of 4-MPBA corresponding to 1075.6 cm^-1. Proposed SERS sensors depicted reliable DA detection in human serum and good selectivity against other analytes, including glucose, creatinine, and uric acid.

The synthesis of gold nanoclusters with high stability and their application in fluorometric detection for Hg2+ and cell imaging

Sensing Hg²⁺ is significant to protecting human health and environmental ecosystems, for its toxicity and genotoxicity. Here, highly stable fluorescent folic acid (FA)-protected Au nanoclusters (FA-AuNCs) were synthesized by optimizing the reactive parameters with high quantum yield of 34.7%. Main components of Au₄L were confirmed by MALDI-TOF, and the electron-rich residues of FA shell enabled FA-AuNCs excellent photostability. FA-AuNCs exhibited sensitive response behavior to Hg²⁺ with a minimum detectability of 1.3 nM, and presented extreme effect to the detection of Hg²⁺ in real water. Notably, the cellular imaging and in-situ detection of Hg²⁺ in cells can be achieved visually. The high selectivity was attributed to the chemical bond formed between Au⁺ (4f¹⁴5d¹⁰) and Hg²⁺ (4f¹⁴5d¹⁰). And the internal filter effect and static quenching effect were proved triggering the quenching of FA-AuNCs. The ultra-stable FA-AuNCs provide a potential promising opportunity for the in-situ tracing Hg²⁺ from environmental and biological samples.

Single-cell HER2 quantification via instant signal amplification in microdroplets

Accurate and ultrasensitive evaluation of human epidermal growth factor receptor 2 (HER2) protein is key to early diagnosis and subtype differentiation of breast cancer. Single-cell analyses to reduce ineffective targeted therapies due to breast cancer heterogeneity and improve patient survival remain challenging. Herein, we reported a novel droplet microfluidic combined with an instant cation exchange signal amplification strategy for quantitative analysis of HER2 protein expression on single cells. In the 160 μm droplets produced by a tapered capillary bundle, abundant Immuno-CdS labeled on HER2-positive cells were replaced by Ag ⁺ to obtain Cd²⁺ that stimulated Rhod-5N fluorescence. This uniformly distributed and instantaneous fluorescence amplification strategy in droplets improves sensitivity and reduces signal fluctuation. Using HER2 modified PS microsphere to simulate single cells, we obtained a linear fitting of HER2-modified concentration and fluorescence intensity in microdroplets with the limit detection of 11.372 pg mL^-1. Moreover, the relative standard deviation (RSD) was 4.2-fold lower than the traditional immunofluorescence technique (2.89% vs 12.21%). The HER2 protein on SK-BR-3 cells encapsulated in droplets was subsequently quantified, ranging from 9862.954 pg mL^-1 and 205.26 pg mL^-1, equivalent to 9.795 × 10⁶ and 2.038 × 10⁵ protein molecules. This detection system provides a universal platform for single-cell sensitive quantitative analysis and contributes to the evaluation of HER2-positive tumors.

Development of a double-antibody sandwich ELISA for rapidly quantitative detection of residual non-structural proteins in inactivated foot-and-mouth disease virus vaccines

Foot-and-mouth disease (FMD) is a highly contagious and economically devastating disease of cloven-hoofed animals. Vaccination and surveillance against non-structure protein (NSP) are the most efficacious and cost-effective strategy to control this disease. Therefore, vaccine purity control is vital for successful prevention. Currently, vaccine purity is tested by an in-vivo test that recommended in the World Organization for Animal Health (WOAH), but it is time consuming and costly. Herein, we develop a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) for quantitative detection of residual NSPs in inactivated FMD virus (FMDV) vaccines. In this assay, the monoclonal antibody 3A24 was selected as capture antibody and biotinylated 3B4B1 (Biotin-3B4B1) as detection antibody. A standard curve was developed using the NSP 3AB concentration versus OD value with the linear range of concentration of 2.5-160 ng/mL. The lowest limit of detection was 2.5 ng/mL. In addition, we determined 2.5 ng/mL of NSP as an acceptable threshold value of FMD vaccine purity using a dose-response experiment in cattle. The DAS-ELISA combined with the threshold value of FMD vaccine purity could provide a quick and simple tool for evaluation the antigenic purity of FMD vaccine during the manufacturing process.

Lotus leaf mastoid inspired Ag micro/nanoarrays on PDMS film as flexible SERS sensor for in-situ analysis of pesticide residues on nonplanar surfaces

Conventional surface-enhanced Raman scattering (SERS) molecular detection are based on hard and brittle substrate, which are not suitable for in-situ detection of analytes adsorbed on nonplanar surfaces. Here, we report a simple biomimetic synthesis method to fabricate lotus leaf mastoid structured AgNPs micro/nanoarrays as reliable SERS substrate. By ideal replicating mastoid structure of lotus leaf into a flexible and transparent PDMS film, followed by depositing plasmonic AgNPs, a powerful chemical sensor with high sensitivity and multiplex detecting capability is demonstrated. The employ of periodic mastoid structure array endows the sensor with high signal repeatability (RSD ∼ 8.6 %), solving the general repeatability problem of SERS substrates. In addition, the detailed designed flexible and transparent PDMS substrate is capable of identifying trace analytes on curved surfaces with excellent durability. In the proof-of-concept experiment, a limit of detection (LOD) of (10^-5 M to 10^-7 M) was achieved on a portable Raman device for three common pesticides residues (thiram, fonofos and triadophos) on dendrobium leaves and stem according to the molecular fingerprint, indicating its excellent in-situ detection capability. Further, the multiplex detection ability of the Ag/PDMS film is also demonstrated by analyzing the mixture of four typical analytes. Benefiting from its high signal uniformity, this flexible Ag/PDMS substrate also showed good quantitative detection capabilities.

Noninvasive direct bilirubin detection by spectral analysis of color images using a Mini-LED light source

Urine test paper is a standard, noninvasive detection method for direct bilirubin, but this method can only achieve qualitative analysis and cannot achieve quantitative analysis. This study used Mini-LEDs as the light source, and direct bilirubin was oxidized to biliverdin by an enzymatic method with ferric chloride (FeCl₃) for labeling. Images were captured with a smartphone and evaluated for red (R), green (G), and blue (B) colors to analyze the linear relationship between the spectral change of the test paper image and the direct bilirubin concentration. This method achieved noninvasive detection of bilirubin. The experimental results demonstrated that Mini-LEDs can be used as the light source to analyze the grayscale value of the image RGB. For the direct bilirubin concentration range of 0.1-2 mg/dL, the green channel had the highest coefficient of determination coefficient (R²) of 0.9313 and a limit of detection of 0.56 mg/dL. With this method, direct bilirubin concentrations higher than 1.86 mg/dL can be quantitatively analyzed with the advantage of rapid and noninvasive detection.

Core-shell SERS nanotags-based western blot

Western blot (WB) is the most commonly used scheme for protein identification in life science, but it still faces great challenges in the accurate quantitative detection of low-abundance proteins. Here, we proposed a novel surface-enhanced Raman scattering-based Western blot (SERS-WB) to solve this challenge. SERS nanotags were used as quantitative labels of proteins, which were composed of gold-silver core-shell nanoparticles, and Nile blue A (NBA) molecules were anchored on the interface of the core and shell. The results show that the SERS-WB possessed excellent sensitivity with detection limit of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) protein of 0.15 pg, as well as wide linear dynamic range (LDR) of 382 fg to 382 ng. In addition, the target protein on nitrocellulose (NC) membrane could be directly identified by colorimetric signal due to the aggregation effect of nanoparticles, which greatly simplifies the procedure. This as-proposed strategy will bring new thoughts to technological innovation of WB.

Highly efficient carbon dots for quantitatively visualizing pH fluctuations in cells, zebrafish, mice and tumors

In vivo pH is closely related to complicated physiological and pathological processes. Quantitatively probing pH and visualizing pH variation via fluorescence (FL) imaging technique in living cells and organisms is crucial but difficult to accomplish. Herein, green fluorescent carbon dots (CDs) were synthesized, and their distinct advantages of extraordinarily high fluorescence quantum yield (FQY, 71.4%), unique photostability, high selectivity, sterling biocompatibility, appropriate pKa for biosensing, enable CDs to serve as pH-activatable probes for real time quantitative detection of continuous pH fluctuation in living cells, zebrafish, mice and tumors. We believe CDs are presently among the best-of-breed pH probes for comprehensive biomedical applications.

Development of a reverse-transcription droplet digital PCR method for quantitative detection of Cucumber green mottle mosaic virus

Cucumber green mottle mosaic virus (CGMMV) is a re-emerging threat to the production of greenhouse cucumber and other Cucurbitaceae crops worldwide. This seed-borne virus can easily spread from a contaminated seed to seedlings and adjacent plants by mechanical contact between the foliage of diseased and healthy plants, causing extensive yield losses. An accurate method for detecting and quantifying this virus is urgently needed to ensure the safety of the global seed trade. Here, we report the development of a reverse-transcription droplet digital polymerase chain reaction (RT-ddPCR)-based method for specific and high-sensitive detection of CGMMV. By testing three primer-probe sets and optimizing reaction conditions, we showed that the newly developed RT-ddPCR method is highly specific and sensitive, with a detection limit of 1 fg/μL (0.39 copy/μL). The sensitivity of the RT-ddPCR method was compared with that of real-time fluorescence quantitative RT-PCR (RT-qPCR) using a series of plasmid dilutions and total RNAs extracted from infected cucumber seeds, and the detection limit of RT-ddPCR was 10 times higher than RT-qPCR with plasmid dilutions and 100 times higher than RT-qPCR for detecting CGMMV from infected cucumber seeds. The RT-ddPCR method was further assessed for detecting CGMMV from a total of 323 samples of Cucurbitaceae seeds, seedlings, and fruits as compared with the RT-qPCR method. We found that the infection rate of CGMMV on symptomatic fruits was as high as 100%, whereas infection rates were lower for seeds and lowest for seedlings. Notably, the results of two methods in detecting CGMMV from different cucurbit tissues showed the high consistency with Kappa value from 0.84 to 1.0, demonstrating that the newly developed RT-ddPCR method is highly reliable and practically useful for large-scale CGMMV detection and quantification.

The sensitive detection and mechanism of Fe-3,5-dimethyl pyrazole fluorescent sensor to diethylenetriamine pentamethylene phosphonic acid: Experimental study and quantum chemical calculation

Diethylenetriamine pentamethylene phosphonic acid (DTPMP) is one of the most commonly used amino organic phosphonates. The existing methods for DTPMP detection are complicated, time-consuming, and cannot detect trace DTPMP in the natural environment. In the present work, the Fe-based 3,5-dimethyl pyrazole fluorescent sensor (Fe-DP) was constructed. The addition of Fe³⁺ to DP solution can greatly decrease the fluorescent intensity of DP, while the addition of different concentrations of DTPMP will restore the fluorescence intensity of DP to different degrees, to achieve quantitative detection of DTPMP, and the detection limit (LOD) of DTPMP was lower as 0.105 μΜ. The Fe-DP fluorescent sensor exhibited excellent anti-interference ability and good stability. Moreover, the fluorescence quenching mechanism of DP by Fe³⁺ was revealed by UV absorption spectrum and Multiwfn wavefunction analysis based on density function theory (DFT). The results revealed that the excitation of DP belonged to local excitation, in which the electrons were donated primarily by the N atom with double bond and redistributed within the pyrazole ring.The fluorescence quenching of adding Fe³⁺ was not caused by resonance energy transfer or charge transfer, which did not belong to dynamic quenching, but due to the ground state complex formed by the coordination of Fe³⁺ and the double bond N atom on the DP pyrazole ring.

Facilely self-assembled and dual-molecule calibration aptasensor based on SERS for ultra-sensitive detection of tetrodotoxin in pufferfish

Tetrodotoxin (TTX) is one of the most lethal neurotoxins, so the reliable quantitative analysis of TTX is crucial for food and environmental safety monitoring. Herein, a novel dual-molecule calibration aptasensor was developed for detection of TTX based on Surface-enhanced Raman scattering (SERS). The adaptive surface has high affinity recognition sites for the target of interest, which ensures the high specificity and stability of the aptasensor. In addition, the uniquely labeled signal molecules located in the Raman silent region (1800-2400 cm^-1) can avoid the interference of other exogenous biological signal molecules. Meanwhile, in quantitative analysis, the SERS signal generated by the reporter is calibrate in real time using the second-order peak of silicon molecule (Si). The detection linear range of the aptasensor was 0.0319 ng/mL-319.27 ng/mL, with a limit of detection (LOD) of 0.024 ng/mL and the excellent uniformity (RSD = 8.8%) for TTX detection. As a promising and versatile detection candidate, the ultra-sensitive quantitative detection aptasensor of TTX had important practical significance, which can offer more favorable persuasion for TTX analysis in real seafood samples.

Cleavable molecular beacon-based loop-mediated isothermal amplification assay for the detection of adulterated chicken in meat

A simple, sensitive, specific and fast method based on the loop-mediated isothermal amplification (LAMP) technique and cleavable molecular beacon (CMB) was developed for chicken authentication detection. LAMP and CMB were used for DNA amplification and amplicon analysis, respectively. Targeting the mitochondrial cytochrome b gene of chickens, five primers and one CMB probe were designed, and their specificity was validated against nine other animal species. The structure of CMB and concentrations of dNTPs, MgSO₄, betaine, RNase H2, primers and CMB were optimized. The CMB-LAMP assay was completed within 17 min, and its limit of detection for chicken DNA was 1.5 pg μL^-1. Chicken adulteration as low as 0.5% was detected in beef, and no cross-reactivity was observed. Finally, this assay was successfully applied to 20 commercial meat products. When combined with our developed DNA extraction method (the extraction time was 1 min: lysis for 10 s, washing for 20 s and elution for 30 s), the entire process (from DNA extraction to results analysis) was able to be completed within 20 min, which is at least 10 min shorter than other LAMP-based methods. Our method showed great potential for the on-site detection of chicken adulteration in meat.

Sensitive and handy detection of pesticide residue on fruit surface based on single microsphere surface-enhanced Raman spectroscopy technique

HYPOTHESIS

Surface-enhanced Raman spectroscopy (SERS) has become an emerging and reliable tool for detecting pesticide residues due to its high sensitivity, fast testing speed and easy sample handling. SERS active substrates are the key to achieve efficient and sensitive detection. However, for the most widely used noble metal nanoparticles, there are problems of high noble metal nanoparticle usage and random aggregation. The micron-scale Raman spot is focused on multiple randomly aggregated nanoparticles during the test, resulting in poor reproducibility. Therefore, the development of micron-scale cost-effective SERS substrates with good reproducibility and simple detecting method is of great significance in practical detection.

EXPERIMENTS

Through deposition of silver nanoparticles (Ag-NPs) by chemical reduction on the surface of monodisperse sulfonated polystyrene (SPS) microspheres, micron-sized PS@Ag-NPs core-shell microspheres were prepared with excellent SERS activity. After that, two simple protocols (Method I and Method II) were explored for the determination of thiram on apple epidermis.

FINDINGS

Based on our developed strategy of the single microsphere SERS technique, we successfully fabricated uniform PS@Ag-NPs substrate with high SERS activity and excellent detection sensitivity. The single microsphere SERS technique possesses the capability of anti-dilutability and the utilization of ultra-low PS@Ag-NPs microsphere dosage, realizing qualitative and quantitative detection of thiram on apple with detection limits far below the standard stipulated by China and the European Union.

Rapid and sensitive detection of zearalenone in corn using SERS-based lateral flow immunosensor

Zearalenone (ZEN) is a universal mycotoxin contaminant in corn and its products. A surface-enhanced Raman scattering (SERS) based test strip was proposed for the detection of ZEN, which had the advantages of simplicity, rapidity, and high sensitivity. Core-shell Au@AgNPs with embedded reporter molecules (4-MBA) were synthesized as SERS nanoprobe, which exhibited excellent SERS signals and high stability. The detection range of ZEN for corn samples was 10-1000 μg/kg with the limit of detection (LOD) of 3.6 μg/kg, which is far below the recommended tolerable level (60 μg/kg). More importantly, the SERS method was verified by HPLC in the application on corn samples contaminated with ZEN, and the coincidence rates were in the range of 86.06%-111.23%, suggesting a high accuracy of the SERS assay. Therefore, the SERS-based test strip with an analysis time of less than 15 min is a promising tool for accurate and rapid detection of ZEN-field contamination.

A dual-positive charges strategy for sensitive and quantitative detection of mitochondrial SO2 in cancer cells and tumor tissue

Mitochondrial sulfur dioxide (SO₂) correlates with various activities of the development and progression of cancer. However, the specific biological function of mitochondrial SO₂ in cancerous cells remains amphibolous. Therefore, it is of great significance and urgency to develop a rapid and accurate method to monitor the dynamic fluctuations of mitochondrial SO₂ in cancer cells and tumor tissue. Herein, in this work, we introduce a "dual-positive charges" strategy for simultaneously enhancing the sensitivity and mitochondrial targeting ability of SO₂ detection in cancer cells for the first time. For proof of concept, the dual positive charged probe DCP was rationally designed and synthesized based on chromenoquinoline fluorophore. Correspondingly, we also synthesized single positive charged SO₂ probe MCP as controls. As expected, the detection limit of dual positive charged DCP for SO₂ detection was 0.06 μM, which was 7-fold lower than that of the single positive charged probe MCP. Besides, DCP showed a higher mitochondrial co-localization coefficient in cancer cells and it could distinguish cancer cells (HeLa) and normal cells (L929) in co-incubated system. In a word, the evidence suggested that the implementation of dual-positive charges strategy greatly improved the sensitivity to SO₂ response and the specificity of mitochondrial targeting in cancer cells. Finally, DCP was successfully applied to monitor SO₂ fluctuation in cancer cells, tumor tissue and living zebrafish. Thus, this work provides a powerful tool to investigate the role of mitochondrial SO₂ in cancer and other related diseases.

A monoclonal antibody for identifying capsaicin congeners in illegal cooking oil and its applications

In this work, we studied the preparation of a high-affinity antibody and its immunochromatographic applications to simultaneously identify capsaicin(LJJ), dihydrocapsaicin(HLJ), nordihydrocapsaicin, homodihydrocapsaicin, and other congeners in illegal cooking oil. We used dihydrocapsaicin hapten-conjugated carrier protein BSA as the immunogen according to the formaldehyde method, and conjugated capsaicin and OVA as the coated detection antigen according to the formaldehyde method. We subsequently screened and cloned a hybridoma cell line 2B3 with the highest affinity, which could stably secrete monoclonal antibodies against compounds in the capsaicin family. We then established a capsaicin indirect ELISA standard curve, which was fitted using the linear regression equation R = 0.9987, curve y = -2.3x + 0.2, and IC₅₀ = 0.2 ng/mL. The cross-reaction rate for capsaicin was 100%, 116% for dihydrocapsaicin, 88% for homodihydrocapsaicin, and 94% for nordihydrocapsaicin. In the second application, we established a simple and accurate sample pretreatment method and a quantum dot-labeled test strip to quickly and quantitatively detect capsaicin family compounds in illegal cooking oil in 8 min. The average recovery rates for each spiked concentration were between 75% and 107.8%, and the coefficient of variation values for each spiked concentration were less than 15%. The high-affinity antibody we identified could simultaneously identify capsaicin, dihydrocapsaicin, nordihydrocapsaicin, homodihydrocapsaicin, and other congeners in illegal cooking oil, and the antibody could be quickly and accurately applied for the qualitative and quantitative detection of capsaicin family residues in illegal cooking oil.

A novel qPCR-based method to quantify seven phyla of common algae in freshwater and its application in water sources

The light microscope is widely used to count algae, however, there are some disadvantages associated with this method, such as time consuming and laborious. In this study, a qPCR-based method was established for quantifying seven phyla of common algae in freshwater, including Cyanophyta, Chlorophyta, Euglenophyta, Bacillariophyta, Dinophyta, Cryptophyta, and Chrysophyta. The accuracy of qPCR in estimating algal cells was confirmed by comparing it with the microscopic counting. The qPCR was used to detect the cell concentration of seven phyla of algae in Longhu Reservoir, showing that green algal blooms occurred during the monitoring period. The intensity of algal blooms was further evaluated according to the classification standard, which suggested that the grade of this bloom was mild. An early warning system was proposed to early warn the occurrence of algal blooms in two water sources, Longhu Reservoir and Dongzhang Reservoir. The qPCR method developed in this study could be a useful tool in the monitoring of algae. The early warning system reported here will have important implications for the effective warning of algal blooms.

Rapid qualitative and quantitative detection of Salmonella typhimurium using a single-step dual photometric/fluorometric assay

A dual-signal photometric/fluorometric assay was established for rapid, qualitative, and quantitative detection of Salmonella typhimurium (S. typhimurium). This method was composed of two parts: (1) a single-step photometric (SSC) assay containing gold nanoparticles (AuNPs), poly-diallyldimethylammonium chloride (PDDA), and S. typhimurium-specific aptamer, and (2) a fluorescence (FL) assay containing carboxyl-modified CdSe/ZnS quantum dots (QDs-_COOH). Users just need to drop samples contaminated with S. typhimurium into SSC assay; the apparent color change from red to blue can be observed in a short time (20 min). A smartphone app was developed to read the semiquantitative result. By subsequently adding one drop of FL assay into the reaction mixture, the generated fluorescence intensity reflected the concentration of S. typhimurium. The naked eye limit of detection (LOD) and fluorescent LOD were 10³ cfu/mL and 10 cfu/mL, respectively. This method exhibited good selectivity. The reliability and practicability were verified by testing contaminated food, drinking water, and pets' urine.

Optimization of a real time PCR methodology for HCV RNA quantification in saliva samples

Saliva may be an alternative biological specimen to expand HCV detection. This study aims to evaluate an in-house quantitative RT-PCR for HCV RNA quantification in saliva. A total of 80 individuals (56 anti-HCV/HCV RNA + and 24 negative controls) donated serum and saliva, that were tested using an in-house quantitative PCR for HCV RNA. The median viral load was 4.77 log10 copies/mL (1.04-7.0 log10 copies/mL) in serum and 2.31 log10 copies/mL (1.0-3.84 log10 copies/mL) in saliva. A sensitivity and specificity of 80 % was observed for HCV detection in saliva, which demonstrates the usefulness of in-house real-time PCR to quantify HCV RNA in saliva samples, which might increase the access of molecular diagnosis of HCV in laboratories that lack complex infrastructures for molecular testing and in individuals with poor venous access.

A Simple and Rapid Light-Initiated Chemiluminescence Assay for Quantitation of Artemisia-Specific Immunoglobulin E

BACKGROUND

Light-initiated chemiluminescence assay (LICA) is a homogeneous assay that has been successfully used for the quantitation of food allergen-specific immunoglobulin E (sIgE), but not inhaled allergen-sIgE. Simultaneously, current assays used to detect allergen-sIgE are serum consuming and/or time consuming. Hence, we established a method for the quantitation of Artemisia-sIgE based on LICA and verified its performance according to the clinical guideline documents, laying a foundation for the quantitation of inhaled and food allergen-sIgE in parallel on LICA.

METHODS

The assay was established after optimizing the first incubation time and the dilutions of Artemisia-coated chemibeads, biotinylated goat anti-human IgE, and serum. In order to quantitate Artemisia-sIgE, the calibration curve was established with a high positive serum of known concentration. The assay performance was confirmed per the clinical guideline documents. In addition, the correlation between the results of LICA and capture enzyme-linked immunosorbent assay was evaluated.

RESULTS

The developed LICA's coefficients of variation of repeatability and intermediate precision were 3.20%, 2.14%, and 3.85% and 4.30%, 4.00%, and 4.40%, respectively. The limit of detection was 0.10 kUA/L, and the limit of quantitation was 0.11 kUA/L. The range of linearity was from 0.27 kUA/L to 97.53 kUA/L (r = 0.9968). The correlation coefficient (r) for the correlation analysis between results of LICA and capture ELISA was 0.9087. This assay was successfully applied in 64 human serum samples, showing good sensitivity (82.20%) and specificity (100%).

CONCLUSION

An Artemisia-sIgE quantitation assay based on LICA was successfully established. Its performance satisfied the clinical requirements and could be widely used in clinical laboratories.

Development of an indirect competitive enzyme linked immunosorbent assay for the quantitative detection of Mycoplasma hyopneumoniae during the vaccine production process

Inactivated Mycoplasma hyopneumoniae vaccine is used extensively to control M. hyopneumoniae infection worldwide. Quantification techniques are essential in the process of standardizing and validating vaccines. In this study, we developed and optimized an indirect competitive enzyme linked immunosorbent assay (ic-ELISA) for the rapid quantification of M. hyopneumoniae antigen during vaccine production. Briefly, whole M. hyopneumoniae antigen was coated onto microtiter plates, and a polyclonal antibody against M. hyopneumoniae recombinant elongation factor thermo unstable (EF-Tu) protein was prepared and added with the samples to be tested. The methods were optimized and showed significant reproducibility, with coefficients of variation of 4.01% and 6.14% for the intra-and inter-assays, respectively. Quantification of M. hyopneumoniae cultures at different growth stages using the ic-ELISA test showed a similar curve to that of the traditional color changing units (CCU) assay, with a delay in the time when the amount reached the peak and started to fall. In the inactivated vaccine production process, the cultures could be harvested later than that for the live vaccine, at about 12 h after the end of the logarithmic growth phase. Different batches of cultures were measured for their relative potency value compared with the in-house reference vaccine, which was used to determine whether the cultures met the antigen amount requirements for vaccine preparation. The curves of the CCU titer and ic-ELISA titer in the logarithmic phase correlated strongly and a linear regression equation was established to calculate the CCU values rapidly using the ic-ELISA results. In conclusion, an ic-ELISA method was established to rapidly assess the amount of antigen in an M. hyopneumoniae culture during the vaccine production process.

A General Approach to Design Dual Ratiometric Fluorescent and Photoacoustic Probes for Quantitatively Visualizing Tumor Hypoxia Levels In Vivo

Herein, we describe an energy balance strategy between fluorescence and photoacoustic effects by sulfur substitution to transform existing hemicyanine dyes (Cy) into optimized NIRF/PA dual ratiometric scaffolds. Based on this optimized scaffold, we reported the first dual-ratio response of nitroreductase probe AS-Cy-NO₂ , which allows quantitative visualization of tumor hypoxia in vivo. AS-Cy-NO₂ , composed of a new NIRF/PA scaffold thioxanthene-hemicyanine (AS-Cy-1) and a 4-nitrobenzene moiety, showed a 10-fold ratiometric NIRF enhancement (I₇₇₃ /I₇₃₃ ) and 2.4-fold ratiometric PA enhancement (PA₇₃₀ /PA₆₇₀ ) upon activation by a biomarker (nitroreductase, NTR) associated with tumor hypoxia. Moreover, the dual ratiometric NIRF/PA imaging accurately quantified the hypoxia extent with high sensitivity and high imaging depth in xenograft breast cancer models. More importantly, the 3D maximal intensity projection (MIP) PA images of the probe can precisely differentiate the highly heterogeneous oxygen distribution in solid tumor. Thus, this study provides a promising NIRF/PA scaffold that may be generalized for the dual ratiometric imaging of other disease-relevant biomarkers.

coli O157:H7 by coupling immunomagnetic separation and quantum dot-based paper strip

Simple and visual quantitative detection of foodborne pathogens can effectively reduce the outbreaks of foodborne diseases. Herein, we developed a simple and sensitive quantum dot (QD)-based paper device for visual and quantitative detection of Escherichia coli (E. coli) O157:H7 based on immunomagnetic separation and nanoparticle dissolution-triggered signal amplification. In this study, E. coli O157:H7 was magnetically separated and labeled with silver nanoparticles (AgNPs), and the AgNP labels can be converted into millions of Ag ions, which subsequently quench the fluorescence of QDs in the paper strip, which along with the readout can be visualized and quantified by the change in length of fluorescent quenched band. Owing to the high capture efficiency and effective signal amplification, as low as 500 cfu mL^-1 of E. coli O157:H7 could be easily detected by naked eyes. Furthermore, this novel platform was successfully applied to detect E. coli O157:H7 in spiked milk samples with good accuracy, indicating its potential in the detection of foodborne pathogens in real samples.

Lateral flow immunoassay based on gold magnetic nanoparticles for the protein quantitative detection: Prostate-specific antigen

Point-of-care testing (POCT) demands for rapidly obtaining test results by means of portable analytical instruments and auxiliary reagents at the sampling site. It's important for tumor marker to be recognized and detected in early clinical diagnosis. Many studies focused on producing small portable devices that would allow fast, accurate, and on-site detection. This study aimed to report a magnetic quantitative lateral flow immunoassay (LFIA) system based on poly (acrylic acid) (PAA)-modified gold magnetic nanoparticles (PGMNs) for detecting prostate-specific antigen (PSA) qualitatively and quantitatively. The result was easily achievable with a portable magnetic reader within 15 min. Under optimal conditions, as low as 0.17 ng/mL PSA could be detected. The method was validated using a well-established Solin electrochemiluminescence immunoassay and showed high consistency in detecting 84 serum samples (R² = 0.98). The quantitative LFIA based on PGMNs established in this study was proven to be rapid, accurate, sensitive, and inexpensive. As a POCT, it can be potentially developed for the quantitative diagnosis of other disease-related protein biomarkers.

Development of non-enzymatic and photothermal immuno-sensing assay for detecting the enrofloxacin in animal derived food by utilizing black phosphorus-platinum two-dimensional nanomaterials

The two-dimensional black phosphorus nanosheets (BPNSs) provide strong support for the construction of nanozymes with high catalytic performance due to the sheet structure and high electronic activity. A peroxidase-like BP-Pt nanocomposites was successfully synthesized using the instability of BPNS, a non-enzymatic immunosensing assay (NISA) was established with BP-Pt as immunosensing probe. Take the antibiotic enrofloxacin (ENR) as the target, NISA realized the highly sensitive ENR detection with detection limit (IC15) of 0.005 μg/L. In addition, based on the good photothermal performance of oxTMB at 808 nm, a photothermal immunosensing assay (PT-NISA) was established, and ENR detection results was similar to NISA were obtained. In the analysis of the samples, the same detection results as the commercially available enzyme-linked immunoassay kit were obtained. These NISA and PT-NISA provide a more rapid and promising strategy for detecting food contaminants, and was expected to be used to detect other highly sensitive biological macromolecules.

A time-resolved fluorescence lateral flow immunoassay for rapid and quantitative serodiagnosis of Brucella infection in humans

Brucellosis is a worldwide infectious zoonotic disease, posing severe threats to human health and social-economic development. By comparing with time-consuming, low sensitive and non-quantitative conventional serological methods, herein, protein G (prG) coupled with europium nanospheres (EuNPs) (detection probe) and highly purified Brucella lipopolysaccharide (LPS) (capture antigen) were used to develop a novel time-resolved fluorescence lateral flow immunoassay (TF-LFIA) for detecting anti-Brucella IgG antibody in human plasmas. The entire testing took 15 min. With a satisfactory purity, the purified LPS weakly cross-reacted with Y. enterocolitica O9 diagnostic antibody; however, none reacted with sera from patients with other Gram-negative bacterial infections. Following coefficient of determination (R² = 0.9961), 0.3 IU/mL was reported as the limit of detection (LOD), much lower than those of Serological Agglutination Test (SAT), Rose-Bengal Plate Agglutination Test (RBPT) and colloidal gold LFIA (CG-LFIA). Intra-day and inter-day precisions (CV, coefficient variation) of TF-LFIA varied less than 8% or 12 %, while intra-day and inter-day accuracies were 94-106 % or 93-107 %, respectively. The correlation coefficient (R²) of TF-LFIA measurement to the different concentrations of spiked Brucella antibody was 0.9967, suggesting TF-LFIA had high reliability and reproducibility. TF-LFIA was demonstrated for 100 % specificity, 98.57 % sensitivity and 99.63 % accuracy in detection of Brucella antibody from clinical samples, respectively, significantly higher compared to SAT and RBPT. In conclusion, the established TF-LFIA is a simple, rapid and quantitative immunoassay for early diagnosis or epidemiological surveillance of Brucella infection in humans.

Advances in fluorescent probes for detection and imaging of amyloid-β peptides in Alzheimer's disease

Amyloid plaques generated from the accumulation of amyloid-β peptides (Aβ) fibrils in the brain is one of the main hallmarks of Alzheimer's disease (AD), a most common neurodegenerative disorder. Aβ aggregation can produce neurotoxic oligomers and fibrils, which has been widely accepted as the causative factor in AD pathogenesis. Accordingly, both soluble oligomers and insoluble fibrils have been considered as diagnostic biomarkers for AD. Among the existing analytical methods, fluorometry using fluorescent probes has exhibited promising potential in quantitative detection and imaging of both soluble and insoluble Aβ species, providing a valuable approach for the diagnosis and drug development of AD. In this review, the most recent advances in the fluorescent probes for soluble or insoluble Aβ aggregates are discussed in terms of design strategy, probing mechanism, and potential applications. In the end, future research directions of fluorescent probes for Aβ species are also proposed.

Preparation of Yellow Fluorescent N,O-CDs and its Application in Detection of ClO. J Fluoresc 2021;31:659-666. [PMID: 33534115 DOI: 10.1007/s10895-021-02686-4]

Accurate and efficient detection of ClO^- was extremely important due to the harm of ROS in the environment and organism. In this paper, yellow fluorescent N,O-CDs were successfully prepared by the solvothermal method. The microscopic size of the N,O-CDs was approximately spherical with an average particle size of 4.8 ± 0.8 nm. The fluorescence quantum yield in ethanol solution was calculated as 10.5 % using fluorescein as the standard reference. The as-fabricated N,O-CDs had high sensitivity and low detection limit (7.5 µM) for quantitatively detecting ClO^- with a linear range from 0.07 mM to 0.16 mM. The probe not only shows good selectivity and anti-interference to metal ions, anions and amino acids but also has excellent light stability and thermal stability. Also, a wide selection range for pH was demonstrated.