Sensitive immunoassays based on specific monoclonal IgG for determination of bovine lactoferrin in cow milk samples

Establishment of highly sensitive lateral flow immunochromatographic strips for quinclorac detection utilizing signal amplification nanoparticles

Highly selective herbicide quinclorac (Qui) is a type of quinoline carboxylic acid hormone herbicide, which has the characteristics of long half-life and difficulty for degradation, causing high risk to the environmental safety. In this study, anti-Qui 8A3 monoclonal antibody (mAb) with good specificity and high affinity (3.89 × 109 L/mol) was prepared, and two kinds of lateral flow immunochromatographic strips (LFICS) including nano-flower nanoparticles (AuNF) - and latex microsphere (LM)- based LFICS were established based on the antibody and signal amplification. The linear range of the AuNF- and LM- based LFICS were 5.31-345.48 ng/mL and 2.52-257.92 ng/mL, respectively. The limit of detection (LOD) of the AuNF- and LM- based LFICS were determined to be 5.31 ng/mL and 2.52 ng/mL, respectively. In summary, the developed LFICS using AuNF and LM as signal amplification reporters exhibited excellent sensitivity and provided the rapid on-site screening of Qui and other analytes in food safety field.

Self-Responsive Fluorescence Aptasensor for Lactoferrin Determination in Dairy Products

In this study, a self-responsive fluorescence aptasensor was established for the determination of lactoferrin (Lf) in dairy products. Herein, the aptamer itself functions as both a recognition element that specifically binds to Lf and a fluorescent signal reporter in conjunction with fluorescent moiety. In the presence of Lf, the aptamer preferentially binds to Lf due to its specific and high-affinity recognition by folding into a self-assembled and three-dimensional spatial structure. Meanwhile, its reduced spatial distance in the aptamer-Lf complex induces a FRET phenomenon based on the quenching of 6-FAM by amino acids in the Lf protein, resulting in a turn-off of the fluorescence of the system. As a result, the Lf concentration can be determined straightforwardly corresponding to the change in the self-responsive fluorescence signal. Under the optimized conditions, good linearities (R2 > 0.99) were achieved in an Lf concentration range of 2~10 μg/mL for both standard solutions and the spiked matrix, as well as with the desirable detection limits of 0.68 μg/mL and 0.46 μg/mL, respectively. Moreover, the fluorescence aptasensor exhibited reliable recoveries (89.5-104.3%) in terms of detecting Lf in three commercial samples, which is comparable to the accuracy of the HPCE method. The fluorescence aptasensor offers a user-friendly, cost-efficient, and promising sensor platform for point-of-need detection.

Human lactoferrin from breast milk: characterization by HPLC and its in vitro antibiofilm performance

Preterm infants are at high risk of infection due to opportunistic bacteria as Pseudomonas aeruginosa, causing infections among infants in neonatal intensive care units. Human lactoferrin (hLf) is a multifunctional protein and one of the most abundant in breast milk, and plays an important role in prevention of different infections in neonates. This work offers a strategy to obtain a lyophilisate of purified lactoferrin from breast milk. In addition, a reliable HPLC method for quantification of lactoferrin with a linear quantification range of 0.040-0.140 mg/mL with selectivity, accuracy and repeatability, is described. Lyophilized hLf was obtained by purification through a heparin affinity column followed by ultrafiltration with a 30 kDa membrane. The final solution was lyophilized and the product was analyzed using HPLC method, recovering about 70% of initial lactoferrin in the sample. This molecule was elucidated through FTIR spectroscopy and SDS-PAGE electrophoresis. In addition, the capacity against biofilm formation of P. aeruginosa was demonstrated with 75% of inhibition at 6 mg/mL. These results suggest that lyophilized hLf can be obtained by purification of breast milk and that it can provide antibiofilm activity against P. aeruginosa.

Enzyme-Linked Aptamer Kits for Rapid, Visual, and Sensitive Determination of Lactoferrin in Dairy Products

Lactoferrin (Lf), as a popular nutritional fortification in dairy products, has the ability regulate the body's immune system and function as a broad-spectrum antibacterial, which is of great significance to the growth and development of infants and children. Herein, an indirect competitive enzyme-linked aptamer assay (ELAA) kit was established for rapid, sensitive, and visual determination of Lf in dairy products. In the construction, the Lf aptamer was conjugated with horseradish peroxidase (HRP) as the recognition probe and aptamer complementary strand (cDNA) were anchored onto the microplate as the capture probe. The recognition probes were first mixed with a sample solution and specifically bound with the contained Lf, then added into the microplate in which the free recognition probes in the mixture were captured by the capture probe. After washing, the remaining complex of cDNA/Aptamer/HRP in the microplate was conducted with a chromogenic reaction through HRP, efficiently catalyzing the substrate 3, 3', 5, 5'-tetramethylbenzidine (TMB), therefore the color shade would directly reflect Lf concentration. Under the optimization conditions, a good linear relationship (R², 0.9901) was obtained in the wide range of 25-500 nM with the detection limit of 14.01 nM and a good specificity, as well as the reliable recoveries. Furthermore, the ELAA kits achieved the Lf determination with an accuracy of 79.71~116.99% in eleven samples, which consisted of three kinds of dairy products: including goat milk powder, cow milk powder, and nutrition drop. Moreover, the results were also validated by the high-performance capillary electrophoresis (HPCE) method. The ELAA kit provides a simple and convenient determination for Lf in dairy products, and it is highly expected to be commercialized.

Rapid and sensitive detection of tenuazonic acid in agricultural by-products based on gold nano-flower lateral flow

Tenuazonic acid (TA) is a highly toxic mycotoxin mainly generated by the fungi of Alternaria genus and widely contaminates agricultural by-products. Given the threat of TA to food-security, it is very important to develop rapid and sensitive detection methods for TA monitoring. In this study, gold nano-particles (AuNP) with average diameter near 17.25 nm were prepared, and the developed AuNP-based strip has an assay time of 15 min with visual limit of detection (LOD) of 12.5 ng/ml and threshold of 100 ng/ml. To further improve sensitivity, multi-branched gold nano-flowers (AuNF) with average diameter near 50 nm were prepared and characterized by UV-VIS and TEM, and the established AuNF-based strip has visual LOD of 0.78 ng/ml and threshold of 50 ng/ml within 15 min. Both assays were applied to determine TA in apple juice and tomato ketchup, and the results were consistent with that of UHPLC-MS/MS. Thus, these assays could be applied for rapid determination of trace TA in real samples.

Self-assembly and label-free fluorescent aptasensor based on deoxyribonucleic acid intercalated dyes for detecting lactoferrin in milk powder

Lactoferrin (Lf), an iron-binding glycoprotein, regulates the immune system. It has broad-spectrum antimicrobial activity and is critical for child physical growth and development. As a common additive in the dairy industry, it is crucial to quantify LF content. This study established a self-assembly and universal fluorescence aptasensor for detecting LF in milk powder based on structure-selective dyes of PicoGreen intercalated in the label-free aptamer. Herein, the aptamer functions as both a specific recognition element against targets and a fluorescent signal reporter integrated with structure-selective dyes. First, the aptamer folds into a three-dimensional spatial structure based on complementary base pairings and intermolecular weak non-covalent interactions. Then, the dye is intercalated into the minor groove structures of the aptamer and triggers its potential fluorescent property. When the target exists, the aptamer binds to it preferentially, and its space structure unfolds. This causes the freeing of the subsequent dye and decreases the corresponding fluorescence. Hence, the reflected fluorescence signals could directly determine the target concentrations. Under the optimum conditions, a good linear relationship (R2, 0.980) was obtained in the Lf range from 20 to 500 nM with a detection limit of 3 nM (2.4 mg/kg) and good specificity, as well as a reliable recovery of 95.8–105.1% in milk powder. In addition, the universality was also confirmed with a good performance by quickly changing the aptamers against other targets (chlorpyrifos, acetamiprid, bovine thyroglobulin, and human transferrin) or utilizing another fluorescence dye. Therefore, this self-assembly aptasensor provides a universal and concise strategy for effective detection.

Development of Immunochromatographic Strip for Detection of αB-VxXXIVA-Conotoxin Based on 5E4 Monoclonal Antibody

Given the application of αB-VxXXIVA-conotoxin (αB-CTX) in analgesics and cancer chemotherapeutics, and its threat to humans, it is urgent to develop a rapid, effective and accurate method for the analysis and detection of αB-CTX in real shellfish and medicine drug samples. In the present study, two different immunochromatographic strips were established for αB-CTX detection, based on the monoclonal antibody 5E4 against αB-CTX, and the visual limits of detection (vLOD) for the colloidal gold nanoparticles-based strip (AuNPs-based strip) and nanoflowers-based strip (AuNFs-based strip) were 4 μg/mL and 1.5 μg/mL, respectively. The developed AuNPs-/AuNFs-based strips have good specificity and accuracy, and the detection results were analyzed in less than 10 min, without using an instrument. In view of the excellent repeatability and usability, the established methods could be applied to detect and analyze the content of αB-CTX in real samples.

Detection of αB-Conotoxin VxXXIVA (αB-CTX) by ic-ELISA Based on an Epitope-Specific Monoclonal Antibody

In view of the toxicological hazard and important applications in analgesics and cancer chemotherapeutics of αB-CTX, it is urgent to develop an accurate, effective and feasible immunoassay for the determination and analysis of αB-CTX in real samples. In this study, MBP-αB-CTX4 tandem fusion protein was used as an immunogen to elicit a strong immune response, and a hybridoma cell 5E4 secreting IgG2b against αB-CTX was successfully screened by hybridoma technology. The affinity of the purified 5E4 monoclonal antibody (mAb) was 1.02 × 108 L/mol, which showed high affinity and specificity to αB-CTX. Epitope 1 of αB-CTX is the major binding region for 5E4 mAb recongnization, and two amino acid residues (14L and 15F) in αB-CTX were critical sites for the interaction between αB-CTX and 5E4 mAb. Indirect competitive ELISA (ic-ELISA) based on 5E4 mAb was developed to detect and analyze αB-CTX in real samples, and the linear range of ic-ELISA to αB-CTX was 117–3798 ng/mL, with a limit of detection (LOD) of 81 ng/mL. All the above results indicated that the developed ic-ELISA had high accuracy and repeatability, and it could be applied for αB-CTX detection and drug analysis in real samples.

Highly efficient and precise two-step cell selection method for tetramethylenedisulfotetramine-specific monoclonal antibody production

Monoclonal antibodies (mAbs) are useful biological tools for research, diagnostics, and pharmaceuticals. Here, we proposed a new mAb discovery platform named the two-step cell selection method (TCSM) for mAbs production of some small molecule haptens as antibiotic, toxins, and pesticides. The first step was performed by a fluorescence-activated cell sorter to enrich the hapten-specific B cells, the second step was an image-based precise pick of single hapten-specific hybridoma cells by confocal laser scanning microscopy. In this study, we used tetramethylenedisulfotetramine (TETS) as a model analyte, which is a highly lethal neurotoxic rodenticide. The TETS-specific hybridoma cells selection was completed within 10 days by the TCSM, compared with at least 40 days in the traditional hybridoma method (THM). The half maximal inhibitory concentration (IC₅₀) of the best mAb 1G6 for TETS in the TCSM was 1.98 ng mL^-1, and that of mAb 2B6 in the THM was 11.49 ng mL^-1. Antibody-TETS recognition also showed more interactions in mAb 1G6 than in mAb 2B6. Then, the mAb 1G6 was then successfully applied to develop an icELISA for TETS in biological samples with satisfactory sensitivity, accuracy and precision. The results demonstrated that the TCSM was a feasible and efficient method for mAb discovering of poisonous hapten molecules.

Comparative Assessment of Different Gold Nanoflowers as Labels for Lateral Flow Immunosensors

Many studies have found that gold nanoparticles with branched surfaces (nanoflowers) are markers for immunosensors that provide higher sensitivity gains than the commonly used spherical gold nanoparticles. Although the analytical characteristics of nanoparticle-using systems vary significantly depending on their size and shape, the question of choosing the best gold nanoflowers remains open. This work presents a comparative study of a panel of 33 preparations of gold nanoflowers formed by varying several parameters: the size of spherical nanoparticles-nuclei, the concentrations of nuclei, and tetrachloroauric acid during growth. The sizes of the resulting particles, their sorption capacity under antibody immobilization, mobility along membranes for lateral flow assays, and the effects of these parameters on the limits of detection of lateral flow immunoassay are characterized. The optimality of preparations obtained by growing a 0.2% v/v solution of nuclei with a diameter of 10 or 20 nm with tetrachloroauric acid at a concentration of 0.12 mM was shown. With their use, lateral flow immune tests were developed to determine markers of acute myocardial infarction-fatty acids binding protein and troponins I and T. The use of gold nanoflowers obtained under the proposed protocols led to significant gains in the limits of detection-3 to 10 times under visual detection and over 100 times under instrumental detection-compared to spherical gold nanoparticles. The significant increase under instrumental detection is due to the label's low nonspecific binding.

Logarithmic Data Processing Can Be Used Justifiably in the Plotting of a Calibration Curve

The article is a response to a recent opinion piece that log concentration values should not be applied in analytical chemistry. An essential aim in the development of analytical chemistry methods is to obtain more sensitive and accurate detection values. For the application of chemical analysis methods, the obtained experiment data need to fit with the mathematical functions in the first place. As influenced by different detection principles and analytical methods, data can be displayed in a coordinate system with two linear axes for linear function fitting, or the data can first be taken through a logarithmic transformation and then for function fitting. Using raw data or data after logarithmic transformation primarily depends on analytical principles, without special rules of data formats. For example, ultraviolet-visible spectrophotometric data are more suitable for direct linear fitting. However, enzyme-catalyzed reaction or electrochemical data in logarithmic form are more appropriate for function fitting. This transformation of data form will not affect the soundness of fit statistics; rather, it simplifies the complexity of function analysis and calculation, which are the essence of analytical chemistry. In this brief article, we provide justification and legitimacy of the application of logarithmic processing in various fields of quantitative analytical chemistry.

Recent Advances in Microfluidic Devices for Contamination Detection and Quality Inspection of Milk

Milk is a necessity for human life. However, it is susceptible to contamination and adulteration. Microfluidic analysis devices have attracted significant attention for the high-throughput quality inspection and contaminant analysis of milk samples in recent years. This review describes the major proposals presented in the literature for the pretreatment, contaminant detection, and quality inspection of milk samples using microfluidic lab-on-a-chip and lab-on-paper platforms in the past five years. The review focuses on the sample separation, sample extraction, and sample preconcentration/amplification steps of the pretreatment process and the determination of aflatoxins, antibiotics, drugs, melamine, and foodborne pathogens in the detection process. Recent proposals for the general quality inspection of milk samples, including the viscosity and presence of adulteration, are also discussed. The review concludes with a brief perspective on the challenges facing the future development of microfluidic devices for the analysis of milk samples in the coming years.

A high sensitive platinum-modified colloidal gold immunoassay for tenuazonic acid detection based on monoclonal IgG

Due to the threat of tenuazonic acid (TA) to public health, it is urgent to establish rapidly effective and sensitive assay methods for TA. In this study, a TA-specific IgG monoclonal antibody (McAb) with high affinity (Kaff was 1.72 × 10¹⁰ L/mol) was screened, and the developed icELISA for TA detection has IC₅₀ of 2.50 ng/mL and LOD of 0.17 ng/mL. Platinum-modified gold nanoparticle (Au@PtNP) was optimized as Au@Pt_0.4NP, and the resulted Au@Pt_0.4NP-McAb probe was designed to catalyze precipitation-type tetramethylbenzidine for visual detection of trace TA with visual LOD of 0.39 ng/mL. The sensitivity of this established Au@Pt_0.4NP-McAb strip was highly increased when compared with the existing colloidal gold strip. The developed strip was used to detect trace TA in apple juice and tomato ketchup which were consistent with the results from UHPLC-MS/MS. Therefore, this developed strip could be used for rapid detection of trace TA in real samples.

Oral fate and stabilization technologies of lactoferrin: a systematic review

Lactoferrin (Lf), a bioactive protein initially found in many biological secretions including milk, is regarded as the nutritional supplement or therapeutic ligand due to its multiple functions. Research on its mode of action reveals that intact Lf or its active peptide (i.e., lactoferricin) shows an important multifunctional performance. Oral delivery is considered as the most convenient administration route for this bioactive protein. Unfortunately, Lf is sensitive to the gastrointestinal (GI) physicochemical stresses and lactoferricin is undetectable in GI digesta. This review introduces the functionality of Lf at the molecular level and its degradation behavior in GI tract is discussed in detail. Subsequently, the absorption and transport of Lf from intestine into the blood circulation, which is pivotal to its health promoting effects in various tissues, and some assisting labeling methods are discussed. Stabilization technologies aiming at preserving the structural integrity and functional properties of orally administrated Lf are summarized and compared. Altogether, this work comprehensively reviews the structure-function relationship of Lf, its oral fate and the development of stabilization technologies for the enhancement of the oral bioavailability of Lf. The existing limitations and scope for future research are also discussed.