Colloidal gold nanoparticle probe-based immunochromatographic assay for the rapid detection of chromium ions in water and serum samples

A fluorescent chemosensor for selective detection of chromium (III) ions in environmentally and biologically relevant samples

A simple single step one pot multicomponent reaction was performed to synthesize N-(tert-butyl)-2-(furan-2-yl)imidazo[1,2-a]pyridine-3-amine (TBFIPA). The synthesized TBFIPA was subjected to library of cations to study its ability for selective and sensitive detection of specific metal ions. Selective detection of chromium ions by TBFIPA were found from the significant hypsochromic shift (335 nm → 285 nm) in the UV-Visible spectra. The fluorescent TBFIPA displays complete quenching of fluorescence under UV lamp (365 nm) only in the presence of chromium without the interference of common metal ions. Binding constant (ka) obtained from Benesi-Hildebrand plot is 0.21 × 105 M-1, limit of detection (LOD) and limit of quantification (LOQ) of TBFIPA toward Cr3+ ions are 4.70 × 10-7 M and 1.56 × 10-7 M, respectively. The mechanism proposed during complex formation were supported by stoichiometric Job continuous variation plot, 1H NMR titration and ESI-MS spectroscopic data. All the experimental confirmation for complex formation were corroborated with theoretical DFT studies optimized using RB3LYP/6-31G(d) basis set. The selectivity and sensitivity of TBFIPA toward Cr3+ ions are found suitable to design a user-friendly silica based portable test kit. Alongside, TBFIPA was successfully utilized for imaging onion epidermal cells. Furthermore, the results obtained for biological, environmental, and industrial samples provided solid evidence to estimate chromium ions using TBFIPA in these real samples.

Development of lectin-based lateral flow assay for fucosylated alpha-fetoprotein

Fucosylated alpha-fetoprotein (AFP-L3) is a more specific and sensitive biomarker for early diagnosis of hepatocellular carcinoma (HCC) than only the alpha-fetoprotein (AFP) level. Rapid and simple detection of AFP-L3 level greatly facilitates the early detection as well as the treatment of HCC, resulting in the reduction of mortality. Here, we developed a rapid and sensitive lateral flow assay (LFA) using lectin Lens culinaris agglutinin (LCA), which has a specific affinity to AFP-L3 fraction of AFP, as a biorecognition element for determination of the fucosylation of AFP. The assay is based on a sandwich format performed on a lateral flow test strip. LCA was immobilized on the membrane as a test line (T). Quantitative detection of AFP-L3 was achieved by measuring the green color intensity of captured gold nanoparticle conjugates on the T and control line (C) utilizing an in-house test strip reader. The calculated absorbance obtained by the green color intensity signals proportionally increased with AFP concentrations. The developed lectin-based LFA provided a detection limit of 0.8 ng/mL for AFP with a linear range between 1.5 and 160.0 ng/mL within an assay time of 10 min. Recoveries between 74.5% and 113.2% with relative standard deviations of 5.2%-8.7% for measuring spiked human serum were also achieved. The results reveal that the proposed assay offers a rapid, sensitive, and specific method, which is useful for development in point-of-care testing for early detection and treatment of HCC.

Colloidal gold and fluorescent immunochromatographic test strips for canine parvovirus detection

Canine parvovirus (CPV) is an acute and highly infectious virus causing disease in puppies and, thus, affecting the global dog industry. The current CPV detection methods are limited by their sensitivity and specificity. Hence, the current study sought to develop a rapid, sensitive, simple, and accurate immunochromatographic (ICS) test to detect and control the spread and prevalence of CPV infection. More specifically, 6A8, a monoclonal antibody (mAb) with high specificity and sensitivity, was obtained by preliminary screening. The 6A8 antibody was labelled with colloidal gold particles. Subsequently, 6A8 and goat anti-mouse antibodies were coated onto a nitrocellulose membrane (NC) as the test and control lines, respectively. Furthermore, 6A8 and rabbit IgG antibodies were labelled with fluorescent microspheres and evenly sprayed onto a glass fibre membrane. Both strips could be prepared in 15 min with no noticeable cross-reactivity with other common canine intestinal pathogens. The strips were simultaneously used to detect CPV in 60 clinical samples using real-time quantitative PCR, hemagglutination, and hemagglutination inhibition assays. The colloidal gold (fluorescent) ICS test strip was stable for 6 (7) and 4 (5) months at 4 °C and room temperature (18-25 °C). Both test strips were easy to prepare and rapidly detected CPV with high sensitivity and specificity. Moreover, the results were easily interpretable. This study establishes a simple method for two CPV diseases, colloidal gold and fluorescent immunochromatographic (ICS) test strips. KEY POINTS: • CPV test strips do not exhibit cross-reactivity with other canine intestinal pathogens. • The strips are stable for months at 4 °C and at room temperature (18-25 °C). • These strips are a promising approach for the timely diagnosis and treatment of CPV.

Molecular-electromechanical system for unamplified detection of trace analytes in biofluids

Biological research and diagnostic applications normally require analysis of trace analytes in biofluids. Although considerable advancements have been made in developing precise molecular assays, the trade-off between sensitivity and ability to resist non-specific adsorption remains a challenge. Here, we describe the implementation of a testing platform based on a molecular-electromechanical system (MolEMS) immobilized on graphene field-effect transistors. A MolEMS is a self-assembled DNA nanostructure, containing a stiff tetrahedral base and a flexible single-stranded DNA cantilever. Electromechanical actuation of the cantilever modulates sensing events close to the transistor channel, improving signal-transduction efficiency, while the stiff base prevents non-specific adsorption of background molecules present in biofluids. A MolEMS realizes unamplified detection of proteins, ions, small molecules and nucleic acids within minutes and has a limit of detection of several copies in 100 μl of testing solution, offering an assay methodology with wide-ranging applications. In this protocol, we provide step-by-step procedures for MolEMS design and assemblage, sensor manufacture and operation of a MolEMS in several applications. We also describe adaptations to construct a portable detection platform. It takes ~18 h to construct the device and ~4 min to finish the testing from sample addition to result.

Quantitative detection of malachite green in sediment by a time-resolved immunofluorescence method combined with a portable 3D printing equipment platform

Rapid detection technology of aquaculture fishery drug residues is needed to supplement large-scale instrument methods. To do this, the time-resolved fluorescence immunoassay (TRFIA) method and portable three-dimensional (3D) printing equipment platform were used, in combination with smartphones, to detect malachite green (MG) in pond sediments. The TRFIA was coupled to MG monoclonal antibodies (mAb) through lanthanide metal microspheres europium (Eu³⁺). The labeled antibody produced competitive immunity in the immune reaction system, and the specific fluorescence intensity in the product was determined by a portable 3D printing equipment platform to achieve quantitative analysis. To test this method, leucomalachite green (LMG) was converted to MG by oxidation of dicyanoquinone (DDQ), and a qualitative analysis was achieved. Methodological evaluation results were satisfactory, recoveries were 83 %-104 %, the limit of detection (LOD) was 0.3 ng/g, the limit of quantitation (LOQ) was 0.7 ng/g, and the coefficient of variation was 1.3 %-7.3 %. The linear equation y = -0.1496x + 0.5585 was in the range of 0-10 ng/g. The linear regression correlation coefficient was 99.2 %. The TRFIA was confirmed and positive samples were measured. Results were consistent with the standard method, which demonstrated that the TRFIA was feasible and that the detection results were reliable. Compared with the national standard method, the TRFIA saves time, is more convenient, and has high sensitivity. It provides an efficient technical method for the rapid screening of MG in the sediments of aquaculture environments.

Lateral Flow Immunoassay Reader Technologies for Quantitative Point-of-Care Testing

Due to the recent pandemic caused by coronavirus disease 2019 (COVID-19), the lateral flow immunoassay used for its rapid antigen test is more popular than ever before. However, the history of the lateral flow immunoassay is about 60 years old, and its original purpose of use, such as a COVID-19 rapid antigen test or a pregnancy test, was the qualitative detection of a target analyte. Recently, the demand for quantitative analysis of lateral flow immunoassays is increasing in various fields. Lateral flow immunoassays for quantitative detection using various materials and sensor technologies are being introduced, and readers for analyzing them are being developed. Quantitative analysis readers are highly anticipated for their future development in line with technological advancements such as optical, magnetic field, photothermal, and electrochemical sensors and trends such as weight reduction, miniaturization, and cost reduction of systems. In addition, the sensing, processing, and communication functions of portable personal devices such as smartphones can be used as tools for the quantitative analysis of lateral flow immunoassays. As a result, lateral flow immunoassays can efficiently achieve the goal of rapid diagnosis by point-of-care testing. Readers used for the quantification of lateral flow immunoassays were classified according to the adopted sensor technology, and the research trends in each were reviewed in this paper. The development of a quantitative analysis system was often carried out in the assay aspect, so not only the readers but also the assay development cases were reviewed if necessary. In addition, systems for quantitative analysis of COVID-19, which have recently been gaining importance, were introduced as a separate section.

Nanobiosensors for detection of opioids: A review of latest advancements

Opioids are generally used as analgesics in pain treatment. Like many drugs, they have side effects when overdosing and causeaddiction problems.Illegal drug use and misuse are becoming a major concern for authorities worldwide; thus, it is critical to have precise procedures for detecting them in confiscated samples, biological fluids, and wastewaters. Routine blood and urine tests are insufficient for highly selective determinations and can cause cross-reactivities. For this purpose, nanomaterial-based biosensors are great tools to determine opioid intakes, continuously monitoring the drugs with high sensitivity and selectivity even at very low sample volumes.Nanobiosensors generally comprise a signal transducer nanostructure in which a biological recognition molecule is immobilized onto its surface. Lately, nanobiosensors have been extensively utilized for the molecular detection of opioids. The usage of novel nanomaterials in biosensing has impressed biosensing studies. Nanomaterials with a large surface area have been used to develop nanobiosensors with shorter reaction times and higher sensitivity than conventional biosensors. Colorimetric and fluorescence sensing methods are two kinds of optical sensor systems based on nanomaterials. Noble metal nanoparticles (NPs), such as silver and gold, are the most frequently applied nanomaterials in colorimetric techniques, owing to their unique optical feature of surface plasmon resonance. Despite the progress of an extensive spectrum of nanobiosensors over the last two decades, the future purpose of low-cost, high-throughput, multiplexed clinical diagnostic lab-on-a-chip instruments has yet to be fulfilled. In this review, a concise overview of opioids (such as tramadol and buprenorphine, oxycodone and fentanyl, methadone and morphine) is provided as well as information on their classification, mechanism of action, routine tests, and new opioid sensing technologies based on various NPs. In order to highlight the trend of nanostructure development in biosensor applications for opioids, recent literature examples with the nanomaterial type, target molecules, and limits of detection are discussed.

Hapten designs based on aldicarb for the development of a colloidal gold immunochromatographic quantitative test strip

The common carbamate insecticide aldicarb is considered one of the most acutely toxic pesticides. Herein, rational design was used to synthesize two haptens with spacers of different carbon chain lengths. The haptens were then used to immunize mice. The antibodies obtained were evaluated systematically, and a colloidal gold immunochromatographic strip was developed based on an anti-aldicarb monoclonal antibody. The 50% inhibition concentration and linear range of anti-aldicarb monoclonal antibody immunized with Hapten 1 were 0.432 ng/mL and 0.106–1.757 ng/mL, respectively. The cross-reactivities for analogs of aldicarb were all <1%. The limit of detection of the colloidal gold immunochromatographic strip was 30 μg/kg, and the average recoveries of aldicarb ranged from 80.4 to 110.5% in spiked samples. In the analysis of spiked samples, the test strip could accurately identify positive samples detected by the instrumental method in the GB 23200.112-2018 standard but produced some false positives for negative samples. This assay provides a rapid and accurate preliminary screening method for the determination of aldicarb in agricultural products and environments.

Indirect Competitive ELISA for the Determination of Total Chromium Content in Food, Feed and Environmental Samples

Background: This study aimed to prepare monoclonal antibodies (mAbs) with high immunoreactivity, sensitivity, and specificity for the chelate (Cr(III)-EDTA) of trivalent chromium ion (Cr(III)) and ethylenediamine tetraacetic acid (EDTA). Further, the study established an indirect competitive enzyme-linked immunosorbent assay (icELISA) for detecting the total chromium content in food, feed, and environmental samples. Methods: Hapten Cr(III)-iEDTA was synthesized by chelating Cr(III) with isothiocyanatebenzyl-EDTA (iEDTA). Immunogen Cr(III)-iEDTA-BSA formed by chelating Cr(III)-iEDTA with bovine serum albumin (BSA), and coating antigen Cr(III)-iEDTA-OVA formed by chelating Cr(III)-iEDTA with ovalbumin (OVA) were prepared using the isothiocyanate method and identified by ultraviolet spectra (UV) and inductively coupled plasma optical emission spectrometry (ICP-OES). Balb/c mice were immunized with the Cr(III)-iEDTA-BSA, and the anti Cr(III)-EDTA mAb cell lines were screened by cell fusion. The Cr(III)-EDTA mAbs were prepared by induced ascites in vivo, and their immunological characteristics were assessed. Results: The immunogen Cr(III)-iEDTA-BSA was successfully synthesized, and the molecular binding ratio of Cr(III) to BSA was 15.48:1. Three hybridoma cell lines 2A3, 2A11, and 3D9 were screened, among which 2A3 was the best cell line. The 2A3 secreted antibody was stable after six passages, the affinity constant (Ka) was 2.69 × 109 L/mol, its 50% inhibition concentration (IC50) of Cr(III)-EDTA was 8.64 μg/L, and it had no cross-reactivity (CR%) with other heavy metal ion chelates except for a slight CR with Fe(III)-EDTA (1.12%). An icELISA detection method for Cr(III)-EDTA was established, with a limit of detection (LOD) of 1.0 μg/L and a working range of 1.13 to 66.30 μg/L. The average spiked recovery intra-assay rates were 90% to 109.5%, while the average recovery inter-assay rates were 90.4% to 97.2%. The intra-and inter-assay coefficient of variations (CVs) were 11.5% to 12.6% and 11.1% to 12.7%, respectively. The preliminary application of the icELISA and the comparison with ICP-OES showed that the coincidence rate of the two methods was 100%, and the correlation coefficient was 0.987. Conclusions: The study successfully established an icELISA method that meets the requirements for detecting the Cr(III)-EDTA chelate content in food, feed, and environmental samples, based on Cr(III)-EDTA mAb, and carried out its preliminary practical application.

Development and application of a colloidal-gold dual immunochromatography strip for detecting African swine fever virus antibodies

African swine fever (ASF) is an acute and highly contagious infectious disease caused by the African swine fever virus (ASFV). Currently, there is no vaccine against ASF worldwide, and no effective treatment measures are available. For this reason, developing a simple, rapid, specific, and sensitive serological detection method for ASFV antibodies is crucial for the prevention and control of ASF. In this study, a 1:1 mixture of gold-labeled p30 and p72 probes was used as the gold-labeled antigen. The p30 and p72 proteins and their monoclonal antibodies were coated on a nitrocellulose membrane (NC) as a test (T) line and control (C) line, respectively. A colloidal-gold dual immunochromatography strip (ICS) for ASFV p30 and p72 protein antibodies was established. The results showed that the colloidal-gold dual ICS could specifically detect ASFV antibodies within 5-10 min. There was no cross-reaction after testing healthy pig serum; porcine reproductive and respiratory syndrome virus (PRRSV), foot-and-mouth disease type A virus (FMDV-A), foot-and-mouth disease type O virus (FMDV-O), porcine circovirus type 2 (PCV-2), and classical swine fever virus (CSFV) positive sera. A positive result was obtained only for the positive control P1. The sensitivity of the test strips was 1:256, which was equivalent to that of commercially ELISA kits. Their coincidence rate with the two commercial ASFV ELISA antibodies detection kits was higher than 98%. The test strips were stably stored at 18-25 °C and 4 °C for 4 and 6 months, respectively. The colloidal-gold dual ICS prepared in this study had high sensitivity and specificity and were characterized by rapid detection, simple operation, and easy interpretation of results. Therefore, they are of great significance to diagnose, prevent, and control African swine fever. KEY POINTS: • We establish an antibody detection that is quick and can monitor an ASF infection. • We observe changes in two protein antibodies to dynamically monitor ASF infection. • We use diversified detection on a single test strip to detect both antibodies.

Modification of a nitrocellulose membrane with nanofibers for sensitivity enhancement in lateral flow test strips

Lateral-flow analysis (LFA) is a convenient, low-cost, and rapid detection method, which has been widely used for screening of diseases. However, sensitivity enhancement in LFA is still a focus in this field and remains challenging. Herein, we propose an electrospinning coating method to modify the conventional nitrocellulose (NC) membrane and optimize the liquid flow rate for enhancing the sensitivity of the NC based LFA strips in the detection of human chorionic gonadotropin (HCG) and luteinizing hormone (LH). It can be seen that coating the NC membrane with nitrocellulose fibers could obtain a NC based strip with HCG and LH detection limits of 0.22 and 0.36 mIU mL-1 respectively, and a quantitative linear range of 0.5-500 mIU mL-1. The results show that electrospinning is effective in modifying conventional NC membranes for LFA applications.

AuNP Coupled Rapid Flow-Through Dot-Blot Immuno-Assay for Enhanced Detection of SARS-CoV-2 Specific Nucleocapsid and Receptor Binding Domain IgG

BACKGROUND

Serological tests detecting severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) are widely used in seroprevalence studies and evaluating the efficacy of the vaccination program. Some of the widely used serological testing techniques are enzyme-linked immune-sorbent assay (ELISA), chemiluminescence immunoassay (CLIA), and lateral flow immunoassay (LFIA). However, these tests are plagued with low sensitivity or specificity, time-consuming, labor-intensive, and expensive. We developed a serological test implementing flow-through dot-blot assay (FT-DBA) for SARS-CoV-2 specific IgG detection, which provides enhanced sensitivity and specificity while being quick to perform and easy to use.

METHODS

SARS-CoV-2 antigens were immobilized on nitrocellulose membrane to capture human IgG, which was then detected with anti-human IgG conjugated gold nanoparticle (hIgG-AuNP). A total of 181 samples were analyzed in-house. Within which 35 were further evaluated in US FDA-approved CLIA Elecsys SARS-CoV-2 assay. The positive panel consisted of RT-qPCR positive samples from patients with both <14 days and >14 days from the onset of clinical symptoms. The negative panel contained samples collected from the pre-pandemic era dengue patients and healthy donors during the pandemic. Moreover, the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of FT-DBA were evaluated against RT-qPCR positive sera. However, the overall efficacies were assessed with sera that seroconverted against either nucleocapsid (NCP) or receptor-binding domain (RBD).

RESULTS

In-house ELISA selected a total of 81 true seropositive and 100 seronegative samples. The sensitivity of samples with <14 days using FT-DBA was 94.7%, increasing to 100% for samples >14 days. The overall detection sensitivity and specificity were 98.8% and 98%, respectively, whereas the overall PPV and NPV were 99.6% and 99%. Moreover, comparative analysis between in-house ELISA assays and FT-DBA revealed clinical agreement of Cohen's Kappa value of 0.944. The FT-DBA showed sensitivity and specificity of 100% when compared with commercial CLIA kits.

CONCLUSION

The assay can confirm past SARS-CoV-2 infection with high accuracy within 2 minutes compared to commercial CLIA or in-house ELISA. It can help track SARS-CoV-2 disease progression, population screening, and vaccination response. The ease of use of the assay without requiring any instruments while being semi-quantitative provides the avenue of its implementation in remote areas around the globe, where conventional serodiagnosis is not feasible.

Lateral flow immunogold assay as a rapid detection tool for screening of congenital hypothyroidism

Congenital hypothyroidism (CH) is one of the most common preventable causes of mental retardation. The majority of infants are diagnosed after detection through newborn screening programs using thyroid-stimulating hormone (TSH) test. A rapid immunochromatographic lateral flow assay based on monoclonal antibodies (MAbs) colloidal gold nanoparticles was developed in a sandwich format for the detection of TSH. Two MAbs binding distinct TSH epitopes are used; one is conjugated to the detection reagent while the other is immobilized at the test line on the membrane. The colloidal gold was prepared by the reduction of gold salt coupled with MAbs and this optimal concentration was determined by spectrophotometry method. The sensitivity of our developed lateral flow immunoassay was determined using 5, 10, 15, 25 and 50 μUI/mL of TSH. The color intensity of the test line was directly proportional to the TSH concentration and the visual limit of detection was 10 μUI/mL. Twenty samples of umbilical cord serum were analyzed by the developed strips and the intensity of the signal was in agreement with the results obtained by the conventional radioimmunoassay method. The results suggest that this rapid test can be used in initial screening for congenital hypothyroidism especially in rural areas.

An aptamer-exonuclease III (Exo III)-assisted amplification-based lateral flow assay for sensitive detection of Escherichia coli O157:H7 in milk

Escherichia coli O157:H7 (E. coli O157:H7), one of the most widespread foodborne pathogens, can cause a series of diseases and even lead to death. In this study, a highly sensitive method was developed by combining aptamer-exonuclease III (Exo III)-assisted amplification with lateral flow assay (LFA) based on gold nanoparticles (AuNP). The compound of single-stranded (ss) DNA-anti-E. coli O157:H7 aptamer (ssDNA-aptamer) was formed by hybridization between designed target ssDNA and aptamer. When E. coli O157:H7 was present, target bacteria were bound with the aptamer, and the free target ssDNA was hybridized with the probes of the designed hairpin (HP) structure. Exo III digests the 3' double-stranded blunt end of the complex and releases the enzyme product. Because the remaining sequence of the HP of the designed enzyme product was the same as the target ssDNA sequence, the target ssDNA could be amplified. Finally, the enhanced target ssDNA was combined with AuNP-LFA to achieve visual detection of E. coli O157:H7. The quantitative ability of this platform for E. coli O157:H7 was 7.6 × 10¹ cfu/mL in pure culture, and the detection limit in milk was 8.35 × 10² cfu/mL. This LFA was highly specific to E. coli O157:H7, and the time for detection of E. coli O157:H7 in milk was 4 h. Hence, this system has important application prospects in the detection of pathogenic bacteria in dairy products.

Combination of phenylboronic acid and oligocytosine for selective and specific detection of lead(ii) by lateral flow test strip

Detection of lead (II) in water sources is of high importance for protection from this toxic contaminant. This paper presents the development and approbation of a lateral flow test strip of lead (II) with the use of phenylboronic acid as chelating agent and oligocytosine chain as receptor for the formed complexes. To locate the bound lead (II) on the test strip, phenylboronic acid was conjugated with carrier protein (bovine serum albumin) and applied as a binding line. In turn, the oligocytosine was conjugated with gold nanoparticle to provide coloration of the finally formed complexes (bovine serum albumin - phenylboronic acid - lead (II) - oligocytosine - gold nanoparticle). This combination of two binding molecules provides the «sandwich » assay with direct dependence of label binding from the analyte content. The technique is characterized by high sensitivity (0.05 ng mL^-1) and the absence of cross-reactions with other metal ions which are often satellite in natural waters. The developed lateral flow tests were successfully applied for lead (II) detection in water. Time of the assay was 5 min. The reached parameters confirm efficiency of the proposed technique for rapid and non-laborious testing under nonlaboratory conditions.

Magnetic Resistance Sensory System for the Quantitative Measurement of Morphine

Point-of-care testing (POCT) is characterized by fast detection, simple use, and cost efficiency. As the focus of healthcare shifts to precision medicine, population health, and chronic disease management, the potential impact of POCT has increased significantly in the past decade. Immunochromatographic test strips (ICTSs) are currently the most promising POCT diagnostic format due to the advantages of fast detection, simple operation and cost-effective. The lateral flow immune analyzer (LFIA) system that uses magnetic resistance (MR) sensors as readers and magnetic nanoparticle labeling materials has attracted wide attention due to its high sensitivity and specificity. This paper designs a quantitative lateral flow immunoassay instrument for MR sensors using InSb single crystals as magnetoresistive elements. MR sensors detect samples of ICTSs labeled with superparamagnetic nanoparticles (SMNPs). The collected weak magnetic signal is processed by the designed amplifying circuit and software algorithm. As a result, the MR system can quantitatively detect the concentration of morphine (MOP), and has good repeatability. Compared with other optical detection instruments, the system has good specificity because there is very low background noise in the detection sample. The size of the whole system is [Formula: see text], and it has the characteristics of compactness and fast detection.

Sensitive and rapid detection of Cr3+ in live cells by a red turn-on fluorescent probe

A new probe RB-CR for the detection of Cr³⁺ was constructed based on the conjugation between rhodamine B and phenylthiourea. The Cr³⁺ could trigger opening of the rhodamine spirolactam of RB-CR upon complexation selectively, sensitively and rapidly, resulting in a pronounced enhancement of absorption and fluorescence signal. Further fluorescence imaging study has suggested that RB-CR could be applied as a probe for Cr³⁺ surveillance in living HepG2 cells with low cytotoxicity, which provide us the feasibility of exploring the Cr³⁺ recognition process by the turn-on fluorescence response.

Simultaneous and accurate visual identification of chicken, duck and pork components with the molecular amplification integrated lateral flow strip

We propose a visual strategy for simultaneous detection of multiple adulterated components in beef by integration of multiple polymerase chain reaction (mPCR) with the lateral flow strip (LFS). The primer sets for adulterated components are uniquely designed with different nucleic acid tags (NAT), enabling the amplicons with specific wobbled sequences at two opposite ends. The wobbled sequences will precisely hybridize with the pre-immobilized capture probes on T lines (T1, T2 and T3) and C line, contributing to the coloration of LFS. Taking advantages of extraordinary amplification efficiency of PCR and simplicity of LFS, common adulterated components including chicken, duck and pork can be easily detected with LOD as low as 0.01% (wt%), which is comparable to that of quantitative real-time polymerase chain reaction (qPCR) but with more simplified operations and reduced costs. The method can be extended to identification of other components by replacing the functional primer set. This method can be a useful candidate for meat quality control at the resource-limited setups.

On-spot quantitative analysis of dicamba in field waters using a lateral flow immunochromatographic strip with smartphone imaging

Dicamba herbicide is increasingly used in the world, in particular' with the widespread cultivation of genetically modified dicamba-resistant crops. However, the drift problem in the field has caused phytotoxicity against naive, sensitive crops, raising legal concerns. Thus, it is particularly timely to develop a method that can be used for on-the-spot rapid detection of dicamba in the field. In this paper, a lateral flow immunochromatographic strip (LFIC) was developed. The quantitative detection can be conducted by an app on a smartphone, named "Color Snap." The tool reported here provides results in 10 min and can detect dicamba in water with a LOD (detection limit) value of 0.1 mg/L. The developed LFIC shows excellent stability and sensitivity appropriate for field analysis. Our sensor is portable and excellent tool for on-site detection with smartphone imaging for better accuracy and precision of the results. Graphical abstract.

Polydopamine nanospheres as high-affinity signal tag towards lateral flow immunoassay for sensitive furazolidone detection

Currently, the low sensitivity and poor binding stability of detection probe prepared via electrostatic adsorption have become the dilemmas of colloidal gold-based lateral flow immunoassays (Au-LFIAs). In this connection, polydopamine nanospheres (PDA NPs) with an eminent covalent connectivity property were introduced as a promising substitute to improve the stability of probe and sensitivity of LFIA. Whereafter, the PDA NPs-based LFIA was applied for the monitoring of furazolidone (FZD) in food samples because of the potential carcinogenic/mutagenic effects to human of its metabolite (3-amino-2-oxazolidinone, AOZ). Compared with electrostatic adsorption, the binding stability of PDA NPs-based probes was superior. And, as expected, the PDA NPs-based LFIA biosensor exhibited higher sensitivity than that of the Au-LFIA with a detection limit of 3.5 ng mL^-1 for AOZ by naked-eye readout. Based on the significant enhanced binding stability and sensitivity, the PDA NPs-based LFIA is of certain spreading value for detecting other analytes.

Immunomagnetic separation-based nanogold enhanced surface plasmon resonance and colloidal gold test strips for rapid detection of Vibrio parahaemolyticus

Nanogold enhanced surface plasmon resonance (SPR), colloidal gold immunochromatographic test strips (ICTS), and polymerase chain reaction (PCR), combined with immunomagnetic separation (IMS) were established in this study for the rapid detection of Vibrio parahaemolyticus (VP). The sensitivities of SPR, ICTS, and PCR was determined to be 10¹, 10³, and 10³ CFU/mL for VP, respectively. After separation and enrichment by IMS, the sensitivities of SPR, ICTS, and PCR were 10⁰, 10¹, and 10² CFU/mL for VP, respectively, which were improved by 10-, 100-, and 10-fold compared to the direct detection by SPR, ICTS, and PCR, respectively. When the VP-polluted water samples were directly assessed by SPR, ICTS, and PCR, the results were negative. By contrast, after separation and enrichment for 45 min by IMS, the results were all positive. The IMS-SPR, IMS-ICTS, and IMS-PCR detection methods were able to yield results in approximately 1.5 h, 55 min, and 3.5 h, respectively. These combined detection methods have advantages in being high-throughput and easy to operate without the need for sophisticated equipment or specialized skills. These methods might aid in the development of SPR, ICTS, and PCR technologies for simultaneously examining multiple food-borne pathogens in food products.

Development of an Immunochromatographic Strip for Rapid Detection of Canine Adenovirus

Although canine adenovirus (CAdV) is highly prevalent in dogs, there is currently a lack of a quick diagnostic method. In this study, we developed a rapid immunochromatographic strip (ICS) assay using colloidal gold coupled to CAdV-2-specific monoclonal antibodies (mAbs). BALB/c mice were immunized with a purified CAdV-2 suspension, and four mAbs (belonging to two different epitopes) were generated and designated as 2C1, 7D7, 10D1, and 4G1. Western blot and protein spectral analysis indicated that the hexon protein of CAdV-2 recognized all four mAbs. The colloidal gold-coupled 7D7 and 2C1 mAbs were chosen for inclusion in the rapid ICS assay. The optimal concentrations of the coating antibody (2C1), the capture antibody (7D7), and the goat anti-mouse antibody were 1.0 mg/ml, 10 μg/ml, and 2.0 mg/ml, respectively. The limit of detection was approximately 2.0 × 10² tissue culture infective dose (TCID₅₀)/ml. Other common canine viruses were tested to evaluate the specificity of the ICS, and positive results were observed for only CAdV-1 and CAdV-2. The ICS test was conducted on 360 samples to detect CAdV, and the results were compared with those of polymerase chain reaction (PCR) tests. The ICS test was found to be a sufficiently sensitive and specific detection method for the convenient and rapid detection of CAdV.

Fluorescent ZnO quantum dots synthesized with urea for the selective detection of Cr6+ ion in water with a wide range of concentrations

Nearly monodisperse Zinc oxide (ZnO) quantum dots (QDs) displayed yellow fluorescence were synthesized using urea as dispersant. In this paper, urea-ZnO QDs were used as fluorescent probe to detect Cr⁶⁺ in solution. The emission from the as-synthesized urea-ZnO QDs is selectively quenched when Cr⁶⁺ ions were added. Moreover, there are two linear relationships between the quenching of fluorescence intensity and the Cr⁶⁺ concentrations ranging from 4 μM to 1000 μM, with the detection limit for Cr⁶⁺ at 19.53 nM (on basis of 3σ/slope criterion). The quenching of fluorescence is attributed to aggregation of the QDs and charge transfer between the QDs and Cr⁶⁺ by measurements of transmission electron microscopy (TEM) images, UV-visible absorption spectra and fluorescence lifetime.

Quantitative assessment of disease markers using the naked eye: point-of-care testing with gas generation-based biosensor immunochromatographic strips

BACKGROUND

Immunochromatographic strips (ICSs) are a practical tool commonly used in point-of-care testing (POCT) applications. However, ICSs that are currently available have low sensitivity and require expensive equipment for quantitative analysis. These limitations prohibit their extensive use in areas where medical resources are scarce.

METHODS

We developed a novel POCT platform by integrating a gas generation biosensor with Au@Pt Core/Shell nanoparticle (Au@PtNPs)-based ICSs (G-ICSs). The resulting G-ICSs enabled the convenient and quantitative assessment of a target protein using the naked eye, without the need for auxiliary equipment or complicated computation. To assess this platform, C-reactive protein (CRP), a biomarker commonly used for the diagnosis of acute, infectious diseases was chosen as a proof-of-concept test.

RESULTS

The linear detection range (LDR) of the G-ICSs for CRP was 0.05-6.25 μg/L with a limit of detection (LOD) of 0.041 μg/L. The G-ICSs had higher sensitivity and wider LDR when compared with commonly used AuNPs and fluorescent-based ICSs. When compared with results from a chemiluminescent immunoassay, G-ICS concordance rates for CRP detection in serum samples ranged from 93.72 to 110.99%.

CONCLUSIONS

These results demonstrated that G-ICSs have wide applicability in family diagnosis and community medical institutions, especially in areas with poor medical resources.

Rapid visual sensing and quantitative identification of duck meat in adulterated beef with a lateral flow strip platform

A novel high-sensitivity authentication method has been demonstrated for the rapid visual detection of adulterated meat based on both the lateral flow strip (LFS) platform and on polymerase chain reaction (PCR). After the rapid extraction of genomic components from meat, the on-site amplification of the target DNA of adulterated duck meat is carried out with the rationally designed functional FITC- and biotin-modified primer set, thereby producing numerous double-stranded DNA (dsDNA) products dually labelled with FITC and biotin. The FITC-labelled terminal end of the products binds to the pre-immobilized FITC antibody on the test line of the strip, and the biotin-labelled terminal end binds to the streptavidin-conjugated gold nanoparticles, resulting in a visible test line on the LFS for the rapid identification of duck meat in adulterated beef. After optimization, an adulteration ratio as low as 0.05% can be easily measured, which is more sensitive than other common adulteration authentication methods and is even comparable to instrumental methods. Moreover, 22 commercial processed meat samples were tested with this new strategy, and 4 adulterated samples were successfully identified by both the classic method and our method. In essence, the present authentication method is simple in design, convenient in operation, and can be easily extended to the identification of other adulteration components just by replacing the modified primers.

A lateral flow assay for copper(II) utilizing catalytic and stem-loop based signal amplification

A DNAzyme-based catalytic and stem-loop based amplification scheme is used in a Cu(II)-specific lateral flow assay (LFA). Three test lines with given cut-off value on the test strip are set as the signal indicating zone for semiquantitative analysis by the number of red color bands that appear after lateral flow. The colored bands are generated by accumulation of gold nanoparticles. Four detection ranges can be visualied: (a) 0-2 ng·mL^-1 (= negative); 2-50 ng·mL^-1; 50-200 ng·mL^-1 and > 200 ng·mL^-1 of Cu(II) (= positive). The visual detection limit is thus considered as being 2 ng·mL^-1 which is much lower than the U.S. EPA limit in drinking water (1.25 μg·mL^-1). The highly specific DNAzyme, the strong multiple-turnover catalytic target recycling property and highly efficient amplification strategy warrant the high specificity, sensitivity and rapidity of this LFA. Conceivbly, this detecton scheme can be extended to other metal ions by proper choice of the ion-specific DNAzyme. Graphical abstract Schematic presentation of a semiquantitative lateral flow test strip for Cu²⁺ analysis by three visual cut-off value test lines using catalytic and stem-loop based signal amplification strategy.

Practical immune-barometer sensor for trivalent chromium ion detection using gold core platinum shell nanoparticle probes

The technology progress of biosensors has markedly improved healthcare, disease diagnosis, environment monitoring, and food safety control over the past few decades. However, development of sensitive, robust, low-cost and portable assays for on-site bioanalysis is still a great challenge. In this study, we described a portable, feasible and miniaturized immune-barometer sensor (IBS), which can be used to sensitively measure the changes in a pressure signal, and we applied this IBS in the detection of Cr(iii). In this system, a competitive immunoassay was incorporated as a signaling technique for Cr(iii) detection. To generate a signal of pressure changes (ΔP), Au@PtNPs (gold core platinum shell nanoparticles) were prepared for decomposing H₂O₂ to generate O₂ in a sealed chamber. The expansion of gas volume was accurately detected using a sensitive barometer in the sealed reaction chamber. The ΔP correlated well with Cr(iii) concentrations ranging from 0.39 to 25 ng mL^-1. The limit of detection (LOD) of the IBS was estimated to be as low as 0.35 ng mL^-1. Furthermore, the IBS has high specificity and high recovery for Cr(iii) detection in tap water samples (97.5%-108.7%) and in the Pearl River water samples (95.6%-110.2%). Compared with the traditional enzyme-linked immunosorbent assay (ELISA), the IBS was observed to be more sensitive, of low-cost and portable for the on-site detection of Cr(iii). Therefore, the IBS is a promising potential method for the detection of heavy metals in aqueous solutions and many other fields.

Nanomaterial enabled sensors for environmental contaminants

The need and desire to understand the environment, especially the quality of one's local water and air, has continued to expand with the emergence of the digital age. The bottleneck in understanding the environment has switched from being able to store all of the data collected to collecting enough data on a broad range of contaminants of environmental concern. Nanomaterial enabled sensors represent a suite of technologies developed over the last 15 years for the highly specific and sensitive detection of environmental contaminants. With the promise of facile, low cost, field-deployable technology, the ability to quantitatively understand nature in a systematic way will soon be a reality. In this review, we first introduce nanosensor design before exploring the application of nanosensors for the detection of three classes of environmental contaminants: pesticides, heavy metals, and pathogens.

A test strip for ochratoxin A based on the use of aptamer-modified fluorescence upconversion nanoparticles

An aptamer-based test strip is described for visual and instrumental determination of the mycotoxin ochratoxin A (OTA). It is based on the use of NaYF₄:Yb,Er upconversion nanoparticles (UCNPs) as a label for the aptamer and on the competition between OTA and its complementary sequence for an OTA-specific aptamer. To improve the analytical performance, the optical properties of the UCNPs, the fluidity of the UCNP-aptamer conjugate, and the migration rate on the nitrocellulose membranes were investigated. Under the optimal experimental conditions and by using a 980-nm laser, the relative fluorescence intensity (test line value/control line value) is proportional to the logarithm of the OTA concentration over a range from 5 to 100 ng·mL^-1 (R² = 0.9955). The limit of the detection is 1.86 ng·mL^-1. This aptamer based flow assay can be performed within 15 min and has no serious cross-sensitivity to potentially interfering species. It was successfully applied to the determination of OTA in spiked wheat and beer samples. Graphical abstract An aptamer-based upconversion fluorescent strip based on the use of NaYF₄:Yb,Er nanoparticles was developed for sensitive detection of Ochratoxin A. The limit of the detection was determined as 1.86 ng·mL^-1. The assay can be performed within 15 min, indicating its great potential in point-of-care testing.

A simple and compact smartphone-based device for the quantitative readout of colloidal gold lateral flow immunoassay strips

Colloidal gold lateral flow immunoassay strips (AuNPs-LFIS) have been widely applied as qualitative diagnostic tools for point-of-care tests (POCT). If strip readers were incorporated, their use could be extended to quantitative analysis. However, their cost and non-portability render commercial strip readers unavailable for use in either home testing, community or rural hospital diagnosis. This is particularly true for on-site testing. Here, a smartphone-based reader was designed and 3D-printed for quantitatively assess AuNPs-LFIS. The basic principle of the devise was relying on a smartphone's ambient light sensor (SPALS). This sensor was harnessed to measure the transmitted light intensities originating from the T-lines on the strips, the transmitted light intensities vary with concentration of AuNP on the T-lines. To validate this approach, our newly developed smartphone's ambient light sensor-based reader (SPALS-reader) was used to readout AuNPs-LFIS of three analytical targets: cadmium ion (Cd²⁺; limit of detection (LOD) was 0.16 ng/mL), clenbuterol (CL; LOD was 0.046 ng/mL), and porcine epidemic diarrhea virus (PEDV; LOD was 0.055 μg/mL). The result showed good consistency with the results of conventional image analysis approaches, indicating that the smartphone-based device is appropriate for use in AuNPs-LFIS readouts. Compared with the traditional analysis method, the developed AuNPs-LFIS reader is easier operated, lower cost and more portable, which provided an on-site quantitative analysis tool for AuNPs-LFIS and enhances the applied range of AuNPs-LFIS.

A Novel Diagnostic Method to Detect Duck Tembusu Virus: A Colloidal Gold-Based Immunochromatographic Assay

Duck Tembusu virus (DTMUV) is an emerging pathogenic flavivirus that has resulted in large economic losses to the duck-rearing industry in China since 2010. Therefore, an effective diagnostic approach to monitor the spread of DTMUV is necessary. Here, a novel diagnostic immunochromatographic strip (ICS) assay was developed to detect DTMUV. The assay was carried out using colloidal gold coated with purified monoclonal antibody A12D3 against envelope E protein. Purified polyclonal C12D1 antibodies from BALB/c mice against the envelope E protein were used as the capture antibody. Goat anti-mouse IgG was used to detect DTMUV, which was also assembled on the ICS. Results showed that the ICS could specifically detect DTMUV within 10 min. It also could be stored 25 and 4°C for 4 and 6 months, respectively. The sensitivity of the ICS indicated that the dilution multiples of positive allantoic fluid of DTMUV (LD50: 10^4.33/0.2 ml) was up to 200. Its specificity and sensibility showed no significant change under the above storage situations. Fifty clinical samples were simultaneously detected by ICS and reverse-transcription polymerase chain reaction with a 93.9% coincidence rate between them. It proved that the ICS in the present study was highly specific, sensitive, repeatable, and more convenient to rapidly detect DTMUV in clinical samples.