Visual Detection Limit Research Articles

Simultaneous generation and immobilization of silver nanoparticles on cellulose membranes by hydrogen bond-assisted in-situ reaction for colorimetric detection of mercury ions and hydrogen peroxide

The present study has verified that silver nanoparticles (AgNPs) can be simultaneously generated and immobilized in the micro-nanopores of regenerated cellulose membranes (CMs) via a simple in-situ synthesis, which can be used for colorimetric detection of mercury ions (Hg2+) and hydrogen peroxide (H2O2). The findings showed that the high-loose interpenetrating porous structure and abundant hydroxyl groups of CMs can serve as both micro-reaction spaces and immobilized sites for the in-situ synthesis of AgNPs. The Ag@CMs, composed of well-dispersed, firmly-fixed, and quantity controlled AgNPs functionalized CMs, have excellent Hg2+ colorimetric detection capabilities with a visual limit of detection (VLOD) as low as 5 nM. It can efficiently complete early-warning and semi-quantitative Hg2+ recognition, and exhibits high storage stability for more than 180 days. Moreover, the Ag@CMs exhibited peroxidase mimic behavior and catalyzed the oxidation reaction of 3,3,5,5-tetramethylbenzidine (TMB) by H2O2 to produce a blue solution. This work proposes a simple “green” approach for the heterogeneous synthesis of controllable and stable AgNPs immobilized on CMs and explores their application in chemosensing.

Cost-efficient and ultrasensitive hydrogel-based visual point-of-care sensor integrated with surface patterning and strongly emissive carbon dots directly from Prunus mume Carbonisatus

Point-of-care (POC) sensors possess significant potential for various applications such as environmental monitoring and clinical diagnosis. However, POC sensors often encounter challenges regarding accuracy and sensitivity. Herein, we present a facile, cost-efficient and high-yield synthesis strategy of strongly blue-emitting carbon dots (CDs) from Prunus mume Carbonisatus (PMC) for fabricating surface patterned fluorescent hydrogel POC sensors with ultra-high sensitivity and accuracy. By rationally integrating Fe3+-responsive PMC-CDs with surface patterning enhanced visualization (SPEV) strategy, we achieve accurate POC detection of Fe3+ ions with a visual detection limit of 0.1 μM using the pseudo-color-assisted patterned POC sensors. Benefiting from more diverse and well-controlled visual information provided by the pseudo-color images of patterned hydrogels, the ultrasensitive and accurate visual POC detection of Fe3+ in iron supplements and human serum samples could be easily achieved without using any expensive instruments. This single emitting fluorophore-based surface patterned hydrogel sensing platform exhibits exceptional visual quantitative capability and remarkable convenience, thus holding great promise for visual POC testing.

High Specific and Rapid Detection of Cannabidiol by Gold Nanoparticle-Based Paper Sensor.

In order to facilitate monitoring of cannabidiol (CBD), we devised a gold immunochromatographic sensor based on a specific monoclonal antibody (mAb). To prepare the antigen, a novel hapten with CBD moiety and a linear carbon chain was employed. By utilizing hybridoma technology, a specific mAb was screened and identified that exhibited a 50% maximal inhibitory concentration against CBD ranging from 28.97 to 443.97 ng/mL. Extensive optimization led to the establishment of visual limits of detection for CBD, achieving a remarkable sensitivity of 8 μg/mL in the assay buffer. To showcase the accuracy and stability, an analysis of CBD-spiked wine, sparkling water, and sports drink was conducted. The recovery rates observed were as follows: 88.4-109.2% for wine, 89.9-107.8% for sparkling water, and 83.2-95.5% for sports drink. Furthermore, the coefficient of variation remained impressively low, less than 4.38% for wine, less than 2.07% for sparkling water, and less than 6.34% for sports drink. Importantly, the developed sensor exhibited no cross-reaction with tetrahydrocannabinol (THC). In conclusion, the proposed paper sensor, employing gold nanoparticles, offers a user-friendly and efficient approach for the precise, rapid, and dependable determination of CBD in products.

Recognition-Activated Primer-Mediated Exponential Rolling Circle Amplification for Signal Probe Production and Ultrasensitive Visual Detection of Ochratoxin A with Nucleic Acid Lateral Flow Strips.

We proposed a visual strategy for rapid and ultrasensitive detection of ochratoxin A (OTA) by integration of primer-mediated exponential rolling circle amplification (P-ERCA) with a designed nucleic acid lateral flow strip (LFS). The recognition component was preimmobilized in the tube by hybridization between the immobilized functionalized aptamer and complementary ssDNA. Recognition of OTA induces the release of complementary ssDNA from the tube, which will also act as the primer of the designed P-ERCA. Three nicking sites on the template P-ERCA could contribute to the production of enormous signal probes based on the simultaneous amplification-nicking model, which can be visually measured directly with the constructed nucleic acid LFS. Importantly, the nicked signal probe can also act as the trigger of the new-round RCA, achieving exponential growth of signal probes for measurement and signal enhancement. Taking advantage of the extraordinary amplification efficiency of P-ERCA and the simplicity of LFS, this P-ERCA-LFS method demonstrates ultrasensitive detection of OTA with a visual limit of detection as low as 100 fg/mL for qualitative screening and a limit of detection of 35 fg/mL for semiquantitative analysis. This designed strategy could also be utilized as a universal method for detection of other chemical analytes with the replacement of the aptamer for recognition, and the nucleic acid LFS unit could also be a useful protocol for direct ssDNA analysis.

Comparative analysis of three immunochromatographic test strips for rapid detection of cadmium ion in Asparagus

SummaryCurrently, there is increasing concern regarding the presence of cadmium ion (Cd2+) residues in Asparagus, necessitating the development of a rapid, sensitive and effective detection method. Immunochromatographic detection techniques offer a swift and efficient primary screening approach, significantly reducing labour and material resources compared to traditional detection methods. In this study, we aimed to construct and optimise an immunochromatographic test strip method for precise determination of Cd2+ content in Asparagus. To achieve this, monoclonal cadmium antibody (4A9) was prepared and conjugated with colloidal gold nanoparticles (AuNPs), latex microspheres (LM) and polydopamine (PDA) to create immunoprobes for test strip construction. We optimised key factors, such as probe parameters, strip assembly conditions and sample pretreatment methods. The sensitivity and detection capabilities of the three test strips were evaluated using actual Asparagus samples. The results demonstrated that all three immunochromatographic test strips exhibited high sensitivity, efficiency and rapidity in detecting Cd2+ levels in Asparagus. Notably, the LM‐based and PDA‐based test strips showed outstanding performance, with a visual limit of detection (vLOD) of 0.1 ng mL−1 and an elimination value of 2.0 ng mL−1. These findings underscore the promising potential of these test strips for practical cadmium detection in Asparagus samples.

Establishment of ultrasensitive immunoassay strip based on colloidal gold-McAb probe for detecting cyproheptadine hydrochloride and six phenothiazines in feed

An ultrasensitive and broad-specific monoclonal antibody recognising cyproheptadine hydrochloride and six phenothiazines was produced. The 50% inhibition concentration against cyproheptadine hydrochloride was 0.036 ng/mL, and the cross-reactivities for six phenothiazines were from 6.33% to 63.16%. Based on the developed monoclonal antibody, an immunochromatographic strip was established, with the visual detection limits (cut-off values) of seven drugs ranging from 5 to 100 ng/g in feedstuffs. With the strip reader, the 50% inhibition concentration of the developed immunochromatographic strip for seven drugs ranged from 0.570 to 7.750 ng/g. The intra-assay recoveries were from 79.8% to 103.4% with the highest coefficient of variation of 11.3%. The inter-assay recoveries were from 79.0% to 96.6% with the highest coefficient of variation of 12.7%. In summary, the proposed immunochromatographic strip was considered suitable for simultaneously monitoring cyproheptadine hydrochloride and phenothiazines in feedstuffs.

Original-structure-based hapten design strategy and development of a derivatization-free gold-based paper lateral-flow immunoassays for detecting furaltadone metabolite in shrimp

Veterinary drug residues in food-producing animals pose a threat to human health and public safety, and accurate measurement of these drug residues is necessary. However, detecting nitrofuran metabolite residues is challenging because of their low molecular weight and the long derivatisation time required for their indirect detection. Current antibodies produced against these metabolites have limited accuracy and sensitivity owing to the traditional and ineffective hapten design based on the reaction of 3-amino-5-morpholinomethyl-2-oxazolidone (AMOZ) with nitrobenzaldehyde. In this study, a new antigen strategy was adopted using an original-structure-based hapten design combined with a new carrier protein with immunosynergistic effects to produce a monoclonal antibody that could recognise the metabolite of furaltadone (AMOZ) directly without derivatisation with excellent analytical performance. Finally, a gold-based paper lateral flow immunoassay for AMOZ without derivatisation was established with a visual limit of detection of 5 ng/mL, IC50 of 0.97 ng/mL and linear range (IC20∼IC80) of 0.45–2.07 ng/mL. The method was sensitive and accurate, and detection was completed within 10 min. This new antigen design strategy provides a theoretical basis and reference for antibody production of other ultrasmall molecules.

Detection of Listeria monocytogenes using an immunochromatographic point of care test based on anti-internalin A and B antibodies and a nano-biotinylated detection complex

The detection of Listeria monocytogenes, a Gram-positive food-borne bacterium, helps prevent listeriosis outbreaks, an invasive disease with high mortality rates among immunocompromised individuals. Microbiological culture methods are time-consuming, requiring laboratory infrastructure while molecular techniques are expensive and require complex equipments. We have developed a point of care test (POCT) based on lateral flow immunochromatography, combining anti-Internalin A and B antibodies and the biotin-streptavidin system into a nano-biotinylated detection complex. The new lateral flow prototype presented the following visual limit of detection (LOD):102 CFU/mL in pure cultures of L. monocytogenes; 102 CFU/mL or/25 g in samples of artificially contaminated milk, lettuce, mozzarella cheese, hamburger. Quantitative analysis indicated LOD between 102–10 CFU/mL in pure cultures of L. monocytogenes. The prototype showed 100% specificity when tested with pure cultures of Listeria innocua, Bacillus cereus, Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Micrococcus luteus, Serratia marcescens, Enterobacter aerogenes, Enterococcus faecalis, Enterobacter cloacae Salmonella Enteritidis, Salmonella Typhimurium and Klebsiella pneumoniae. Unlike commercially available tests, this prototype showed detection capacity closer to the minimum L. monocytogenes infectious dose. Therefore, this prototype represents a promising POCT candidate allowing the quick, specific, and sensitive detection of L. monocytogenes in food matrices and on food production platforms.

A simultaneous qualitative and quantitative lateral flow immunoassay for on-site and rapid detection of streptomycin in pig blood serum and urine

Veterinary antibiotic residues are major contaminants in animal-derived foods and dairy products, and the consumption of contaminated products is associated with severe health risks. Among the wide range of veterinary antibiotics, streptomycin (STR, an aminoglycoside commonly used to treat bacterial infections) is widely administered to livestock. Hence, efficient on-site sensing strategies are required to detect veterinary antibiotics. Using gold nanoparticles (AuNPs), we fabricated a one-step lateral flow immunochromatographic assay (LFIA) for the simultaneous quantitative and qualitative detection of STR in pig serum and urine samples. A specific anti-streptomycin monoclonal antibody was conjugated with AuNPs to fabricate LFIA test strips. Several key parameters were optimized to enhance the sensitivity of the LFIA sensor. The visual limit of detection of the sensor was 5 ng/mL for both serum and urine spiked samples, and cut-off values for serum and urine were 20 ng/mL and 22 ng/mL, respectively, which demonstrated the developed LFIA sensor is highly sensitive for detecting STR. Furthermore, test strips had good reliability and produced results within 10 min without the need for professional personnel or specialized equipment. We also combined the LFIA test strips with an LFIA reader to obtain quantitative results and assess risk ranges. The success rates of the LFIA reader for serum and urine sample testing were 95.5 % and 91 %, respectively. These results indicate the test strips could be utilized as a significant sensing strategy for semi quantitative, qualitative, and quantitative on-site detection of STR in pig serum and urine samples before slaughter.

Development of a Lateral-Flow Immunochromatographic Strip for the Detection of Oxytetracycline Residues in Biological Fluids.

Oxytetracycline (OTC) is extensively used in veterinary medicine and for growth promotion around the globe. The indiscriminate use of OTC in food-producing animals leaves residues in animal products. The presence of these residues in animal products causes economic losses and harmful effects on consumers. Different regulatory bodies set maximum residue limits (MRLs) for different tetracyclines. To avoid harmful effects, there is a need for a simple, fast, and economical method for the screening of animal products. In this study, a fast, economical, and user-friendly lateral-flow immunochromatographic (LFIC) assay based on gold nanoparticles (AuNPs) was developed to detect the presence of OTC residues in biological fluids. AuNPs provided visual results as red lines in 6-15 min. Polyclonal rabbit IgG antibodies were produced using the immunogen of OTC. These antibodies were purified by the combined ammonium sulfate-octanoic acid precipitation method. Antibodies were conjugated to AuNPs as recognition biomolecules. A LFIC strip was optimized using borate buffer spiked with different concentrations of the OTC. The visual limit of detection (LOD) in different biological samples (milk, serum, and urine) was determined using samples spiked with OTC. The LOD was found to be 15 μg/L, which is very low from the MRL (100 μg/L) set by different regulatory authorities. This LFIC strip can be used to detect OTC residues in biological fluids for point-of-care testing (POCT). These strips are easy to use, cost-effective, and portable and provide quick results without the use of laboratory instruments.

A hydrazine-based unsymmetrical bis-imine-Schiff base as a chemosensor for turn-off fluorescence and naked-eye detection of Cu2+ ion: Application in aqueous media using test strips

A new hydrazine-based unsymmetrical bis-imine-Schiff base 1-((((5-bromothiophen-2-yl)methylene)hydrazono)methyl)naphthalen-2-ol (L1) was synthesized and characterized with FT-IR, 1H NMR, 13C NMR, UV–visible spectroscopy, ESI-MS, and elemental analysis. The solution of L1 in dichloromethane/methanol (9.8:0.2,v/v) mixture shows a rapid change in color from yellow to yellowish brown in the presence of Cu2+ ions. In addition, L1 displays “turn-off” fluorescence preferentially for Cu2+ ions which was attributed to the Chelation Enhanced Quenching (CHEQ) effect caused due to the reversible binding of L1 to paramagnetic Cu2+ in a 2:1 stoichiometric ratio. No interference was caused in the sensing process by other metal ions such as Ag+, Na+, Ni2+, Co2+, Hg2+, Cr3+ Ba2+, Ca2+, Cd2+, Pb2+, Sn2+, Zn2+, Fe3+, Al3+, K+, and Sr2+. The limit of detection was determined to be 2.809 µM. Furthermore, the test strips coated with L1 show a change in color from pale yellow to brownish-yellow in the presence of Cu2+ions in the aqueous medium, and the limit of visual detection was found to be 15 µM, which is well under the maximum recommended limit (31.5 µM) of Cu2+ for drinking water as per WHO guidelines. These observations establish L1 as an efficient reversible chemosensor for sensing Cu2+ in both aqueous and non-aqueous media with high sensitivity and selectivity.

Highly sensitive lateral flow immunoassays based on Ag@Au nanoflowers with marine medaka (Oryzias melastigm) vitellogenin as a target analyte

In order to improve the sensitivity of lateral flow immunoassays (LFIAs) for the detection of piscine vitellogenin (Vtg), a well-established biomarker for environmental estrogens, Au coated Ag nanoflowers (Ag@Au NFs) were used as labeling probes to develop a LFIA for marine medaka Vtg. The synthesized Ag@Au NFs with good monodispersity had an average diameter of 44.1 nm and absorbance peak of 524 nm. When the concentration of goat anti-mouse IgG and anti-Vtg polyclonal antibody (anti-Vtg PAbs) were 1.3 and 0.4 mg/mL, respectively, the detection range of the LFIA was 0.19–25 ng/mL, and the visual detection limit was 0.1 ng/mL, which was approximately 80 times lower than that of LFIAs based on other nanoparticles (Au NPs, Ag NPs, Au NFs, and FM). After evaluation of its specificity and robustness, the usefulness of Ag@Au NFs labeled LFIA was validated by measuring Vtg induction in the plasma of marine medaka exposed to bisphenol A, a weak estrogenic chemical. This highly sensitive lateral flow immunoassay could detect Vtg biomarker within 15 min without the need of expensive and complicated instruments, and thus offered an ultrasensitive and robust on-site detection method for estrogenic activity in field environment.

Capillary flow-driven immunoassay platform for COVID-19 antigen diagnostics

Over the last few years, the SARS-CoV-2 pandemic has made the need for rapid, affordable diagnostics more compelling than ever. While traditional laboratory diagnostics like PCR and well-plate ELISA are sensitive and specific, they can be costly and take hours to complete. Diagnostic tests that can be used at the point-of-care or at home, like lateral flow assays (LFAs) are a simple, rapid alternative, but many commercially available LFAs have been criticized for their lack of sensitivity compared to laboratory methods like well-plate ELISAs. The Capillary-Driven Immunoassay (CaDI) device described in this work uses microfluidic channels and capillary action to passively automate the steps of a traditional well-plate ELISA for visual read out. This work builds on prior capillary-flow devices by further simplifying operation and use of colorimetric detection. Upon adding sample, an enzyme-conjugated secondary antibody, wash steps, and substrate are sequentially delivered to test and control lines on a nitrocellulose strip generating a colorimetric response. The end user can visually detect SARS-CoV-2 antigen in 15–20 min by naked eye, or results can be quantified using a smartphone and software such as ImageJ. An analytical detection limit of 83 PFU/mL for SARS-CoV-2 was determined for virus in buffer, and 222 PFU/mL for virus spiked into nasal swabs using image analysis, similar to the LODs determined by traditional well-plate ELISA. Additionally, a visual detection limit of 100 PFU/mL was determined in contrived nasal swab samples by polling 20 untrained end-users. While the CaDI device was used for detecting clinically relevant levels of SARS-CoV-2 in this study, the CaDI device can be easily adapted to other immunoassay applications by changing the reagents and antibodies.

Impact of High-Pressure Homogenization on Enhancing the Extractability of Phytochemicals from Agri-Food Residues.

The primary objective of the Sustainable Development Goals is to reduce food waste by employing various strategies, including the reuse of agri-food residues that are abundantly available and the complete use of their valuable compounds. This study explores the application of high-pressure homogenization (HPH), an innovative nonthermal and green treatment, for the recovery of bioactive compounds from agri-food residues. The results demonstrate that the optimized HPH treatment offers advantages over conventional solid/liquid extraction (SLE), including shorter extraction time, solvent-free operation, low temperatures, and higher yields of phenol extraction (an approximately 20% improvement). Moreover, the micronization of agri-food residue-in-water suspensions results in a decrease in the size distribution to below the visual detection limit, achieved by disrupting the individual plant cells, thus enhancing suspension stability against sedimentation. These findings highlight the potential of HPH for environmentally friendly and efficient extraction processes.

The use of Au@Pt nanozyme to perform ultrasensitive immunochromatographic detection of banned pork additives in meat products

In this study, an ultrasensitive immunochromatographic determination of the muscle tissue of pork was developed. Myoglobin (MG), a protein contained in skeletal muscles, was proposed as a molecular identifier of pork via the application of specific monoclonal antibodies (MAb) recognizing the porcine form of this protein. The immunochromatographic analysis (ICA) was based on the sandwich format with specific MAb labeled by a nanozyme – core@shell Au@Pt nanoparticles having peroxidase-mimicking catalytic properties. Several MAb–Au@Pt conjugates were synthesized by varying ratios of components; the one ensuring the best analytical parameters of the ICA was chosen. The enhancement of bands’ coloration on the test strips was promoted by the product of the reaction catalyzed by the nanozyme, which enabled the lowering visual limit of detection (LOD) of MG in the buffer down to 0.15 ng/mL. The amplification enabled to decrease in the LOD of MG by ∼30 times compared to the ICA based on gold nanoparticles as a traditional label and more than 3 times compared to the ICA based on the colorimetric detection of the nanozyme. The duration of the enhanced analysis was 23 min, including the reaction with the substrate. The rapid and simple procedure of sample preparation for extracting MG from meat samples before the ICA was proposed. The specificity of the developed test system was high: no interaction was detected upon analyzing other meat samples except pork. Testing of raw meat mixtures showed ultrasensitive detection of pork additives in beef, chicken, and turkey meat – down to 0.005%.

A multimode detection of silver ions based on peroxidase-like activity and photothermal effect of Prussian blue nanoparticles

Silver ion (Ag+), as a heavy metal ion easily absorbed by organisms, can be enriched through the food chain. This study present a novel multimodal detection system for Ag+ using Prussian blue nanoparticles (PB NPs) with excellent photothermal effect and peroxidase-like activity. The PB NPs undergo a dissolution-precipitation equilibrium, converting blue PB NPs into colourless silver ferrocyanide ions in the presence of Ag+. The color, photothermal effect, and peroxidase-like activity of the PB NPs change with the concentration of Ag+, making them an effective probe for detecting Ag+. The key parameters that affect the performance of multimode detection assay were optimized. Under optimal conditions, the detection limit of visual detection was estimated to be 2.94 μM. Based on catalytic color development and the photothermal effect of PB NPs, the detection limit of color development detection and photothermal analysis were reduced to 0.57 μM and 0.23 μM, respectively. And the detection range was also broadened than visual direct detection. Besides, the multimode detection of Ag+ improves the accuracy of detection by mutual verification. The promising multimode system exhibited good repeatability and specificity of Ag+ in different sample implementations, which has great potential for applications in food safety regulation and environmental monitoring.

Nanozyme-immobilized cellulose membranes designed by a simple hydrogen bond-dominated for colorimetric detection of hydrogen peroxide and uric acid

Nanozymes are considered promising replacement materials for natural enzymes. The application limitations of nanozymes in separation and purification, quantitative utilization, and recycling can be solved by immobilization technology. Herein, a cellulose membrane-based nanozyme immobilization platform was designed and successfully applied for the colorimetric detection of hydrogen peroxide (H2O2) and uric acid (UA). Gold nanoclusters (AuNCs), which can mimic peroxidase and catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2, were immobilized on cellulose membranes (CMs) by hydrogen bonding to prepare AuNCs functionalized CMs (Au@CMs) with firm immobilization and uniform dispersion. TMB (colorless) in solution was oxidized to oxTMB (blue) after collision with hydroxyl radicals (∙OH) formed by H2O2 decomposition on the surface of Au@CMs. The oxTMB generated on Au@CMs was immediately in-situ immobilized under the combined action of cellulose hydroxyl groups and AuNCs. This enabled the dispersion of the colored molecules on the Au@CMs without diffusing into the solution, therefore the colorimetric response was retained to the maximum. Au@CMs were used to effectively colorimetric H2O2 with high selectivity and sensitivity, its visual limit of detection (VLOD) was 7 μM. Experiment results proved that Au@CMs were stable, convenient, and recyclable. It was worth noting that in the presence of uricase, the sensor could also be used for the colorimetric detection of UA, which had a gradient colorimetric response to UA in the concentration range of 50–500 μM. The design and preparation of Au@CMs provided an effective method for immobilizing nanozymes, promising for early-warning and semi-quantitative analysis.

A Comparable icELISA and Lateral Flow Immunoassay for the Sensitive and Rapid Detection of 4,4'-Dinitrocarbanilide in Chicken.

4,4'-dinitrocarbanilide (DNC) is a key component and marker residue of nicarbazin, which forms residues in edible tissue and then causes nephrotoxicity and hepatotoxicity in humans if used excessively. To simplify sample preparation and monitor the DNC rapidly and accurately, a comparable icELISA and lateral flow immunoassay (LFIA) was developed in this study. Briefly, the reaction parameters were explored for improving the sensitivity of icELISA and LFIA. Under the optimal conditions, methanol was selected as the extracting solvent for DNC in chicken, and 20- and 10-fold dilutions of sample extraction eliminated the matrix effect for icELISA and LFIA, separately. After sample pretreatment, the analysis properties of icELISA and LFIA were compared. The limit of detection of icELISA for DNC was 0.8 μg/kg, and the visual and quantitative limits of detection of LFIA were 8 and 2.5 μg/kg. Compared with icELISA, LFIA showed lower sensitivity but obvious advantages in terms of matrix tolerance and detection time (within 15 min). The sensitivity, specificity, and accuracy of the developed assays satisfied the detection requirement even if using simple sample pretreatment. This comparable icELISA and LFIA provided mutual verifiability methods for the accurate detection of DNC in chicken.

Development of a Gold Nanoparticle-Based Immunochromatographic Strip for Rapid Detection of Porcine Circovirus Type 2.

Porcine circovirus type 2 (PCV2) is an important swine infectious pathogen that seriously threatens the global swine industry. PCV2 Cap protein is the only structural and the main immunogenic protein constituting the viral capsid. In this study, a gold nanoparticle-based immunochromatographic strip with high sensitivity and specificity was developed which could be used for rapid detection of PCV2 virions or Cap protein in research. The visual detection limit of the strip was 103.18 50% tissue culture infective does (TCID50)/mL for PCV2, and 2.03 μg/mL for PCV2 Cap protein. No cross-reactivity was observed with the PCV1 and PCV3 Cap proteins and other common swine pathogens such as porcine reproductive and respiratory syndrome virus, classical swine fever virus, pseudorabies virus, porcine epidemic diarrhea virus, porcine parvovirus, and swine influenza virus. The repeatability of the strip was good. The stability of the strip was perfect for 12 months in a dry state at room temperature. Visual results could be obtained within 5 min by simply inserting the strip into the diluted sample. The strip is a time-saving, labor-saving, and reliable tool for testing of PCV2 virions or Cap protein in research. The idea of this study might open a new perspective for the application of the strip. IMPORTANCE Porcine circovirus type 2 (PCV2) Cap protein is the only structural and the main immunogenic protein constituting the viral capsid. Although many methods can be used to identify PCV2 or PCV2 Cap protein in vaccine research, they usually require high workload and time. The developed strip can specifically detect PCV2 virions or Cap protein, and visual qualitative results can be obtained within 5 min by simply diluting the sample and inserting the strip into the sample. The final value of the strip is providing a simple and time-saving method for real-time monitoring of PCV2 antigen in vaccine research with reliable results, such as the different stages of PCV2 Cap protein expression and purification, as well as the different stages of PCV2 reproduction and purification.

Screening bisphenols in complex samples via a planar Arxula adeninivorans bioluminescence bioassay

The Arxula yeast bisphenol screen (A-YBS) utilizes the bioluminescent Arxula adeninivorans yeast–based reporter cells for tailored analysis of bisphenols, one of the major endocrine-disrupting compound groups. For the first time, this bioreporter has been applied on the high-performance thin-layer chromatography (HPTLC) adsorbent surface to develop a respective planar bioluminescence bioassay (pA-YBS). The goal was to combine the advantages of HPTLC with a more selective bioassay detection for bisphenols. The performance of this pA-YBS bioluminescence bioassay was demonstrated by calculating the half-maximal effective concentration (EC50) of bisphenols compared to references. The EC50 ranged from 267 pg/band for bisphenol Z and 322 pg/band for bisphenol A (BPA) to > 1 ng/band for other bisphenols (BPC, BPE, BPF, and BPS) and references (17β-estradiol and 17α-ethinylestradiol). The EC50 value of BPA was three times more sensitive in signal detection than that of 17β-estradiol. The visual or videodensitometric limit of detection of BPA was about 200 pg/zone. The higher signal intensity and sensitivity for BPA confirmed the tailored bioassay selectivity compared to the existing estrogen screen bioassay. It worked on different types of HPTLC silica gel plates. This HPTLC–UV/Vis/FLD–pA-YBS bioluminescence bioassay method was used to analyze complex mixtures such as six tin can migrates, five thermal papers, and eleven botanicals. The detected estrogenic compound zones in the tin can migrates were successfully verified via the duplex planar yeast antagonist estrogen screen (pYAES) bioassay. The two bisphenols A and S were identified in one out of five thermal papers and confirmed with high-resolution mass spectrometry. No bisphenols were detected in the botanicals investigated via the pA-YBS bioluminescence bioassay. However, the botanicals proved to contain phytoestrogens as detected via the pYAES bioassay, which confirmed the tailored bioassay selectivity. This HPTLC–UV/Vis/FLD–pA-YBS bioluminescence bioassay is suited for cost-efficient analysis of BPA in complex samples, with no need for sterile conditions due to the fast workflow.