Development of sandwich ELISA for testing bovine β-lactoglobulin allergenic residues by specific polyclonal antibody against human IgE binding epitopes

A rapid immunomagnetic beads-based sELISA method for the detection of bovine αs1-casein based on specific epitopes

Although αs1-casein poses significant health risks to individuals with milk allergies, the availability of quantification methods for this allergen remains limited. In this study, we developed an immunomagnetic beads-based immunoassay (IMBs-ELISA) for the precise quantitative detection of bovine αs1-CN, specifically targeting epitope AA173-194. No cross-reactivity was observed with the other 7 food allergens including milk allergen. The linear detection range of the established IMBs-ELISA method was 0.125 μg/mL-2.000 μg/mL, with a limit of detection of 0.099 μg/mL. The accuracy of this method was 1.048 %, and the intra-plate and inter-plate precision achieved 4.100 % and 6.777 %, respectively. Notably, the entire IMBs-ELISA process could be completed within 75 min, representing a substantial time-saving advantage over traditional ELISA methods. These results proved the reliability and rapidity of the IMBs-ELISA method for detecting αs1-CN in real food.

A label-free fluorescent magnetic dual-aptasensor based on aptamer allosteric regulation of β-lactoglobulin

We presented a label-free fluorescent biosensor based on magnetic dual-aptamer allosteric regulation of β-lactoglobulin (β-LG) detection. The bovine serum albumin (BSA) acted as the bridge to connect amino-modified magnetic beads and aptamer, which synthesized pyramid-type probes (MBAP) with high capture and reduced nonspecific adsorption. Moreover, the original aptamer was tailored and then designed as a bivalent aptamer to fabricate allosteric signal probes (ASP). The ASP can both specifically capture β-LG and output the fluorescence signal. The detection mechanism is as follows. The combination of the dual-aptamer and β-LG triggered the allosteric change, resulting in the release of SYBR Green (SG I) from the allosteric signal probe and change signals. This method exhibits a broad linear detection range from 10 ng/mL to 1 mg/mL and the limit of detection reaches as low as 8.06 ng/mL. This study provides a highly generalizable strategy for protein biomolecular detection via replacing different target aptamers.

Sandwich assay for β-lactoglobulin in infant food formula based on a hierarchically architectured antifouling capture probe and fluorescent recognition probe

Tracing the presence of allergenic β-lactoglobulin (β-Lg) in infant foods is an urgent need, but the interference from the protein-rich matrix often hampered the detection accuracy. Here, we developed a sandwich assay for β-Lg in infant food formula based on a hierarchically architectured antifouling capture probe and fluorescent recognition probe. The antifouling capture probe was constructed from the polydopamine-coated magnetic particles (Fe3O4@PDA), which was modified with repeated glutamic acid-lysine (EK) antifouling peptide and aptamer towards β-Lg. The spatial arrangement of these ligands on the Fe3O4@PDA surface was carefully tailored. Furthermore, a fluorescent recognition probe based on aptamer-modified silica-doped carbon quantum dot was developed to explore a sandwich assay for β-Lg with the capture probe. The sandwich assay was proved to have high potential in detecting β-Lg in commercially available infant food samples. The work provided a new approach to developing detection methods with matrix interference-resistant properties.

Designing tannic acid-polyethyleneimine-modified electrode and novel affinity peptide for β-lactoglobulin detection in milk

Harmful substances that cause food allergies can pose a significant threat to consumers along with food safety. According to the World Health Organization (WHO), approximately 10 % of the global population is currently affected by food allergies. Therefore, there is an urgent need for the development of more accurate and precise biosensors capable of detecting these hazardous substances including beta-lactoglobulin. Although numerous detection and analysis methods have been developed, they still suffer from various limitations. In this study, a tannic acid-polyethyleneimine (TA-PEI) network modified screen-printed electrodes (SPE) are newly developed and the binding sequence of peptide against β-LG was successfully screened using random peptide library. A novel affinity peptide with the desired sequence of S-L-S-P-S-L-W-Q-V-S-M-L-G-G-G-G-E-P-L-Q-L-K-M against β-lactoglobulin (β-LG) is designed and synthesized. The synthesized affinity peptide was immobilized on TA-PEI modified SPE to develop peptide-based sensor against β-LG for the first time. Under successful optimization, the developed sensor exhibited a linear relationship between 50 and 750 ng, with a Kd of 213.9 ng. In addition, the sensor was able to detect β-LG in cow and goat milk, with average recoveries of 88.5 % and 92.2 %, respectively.

Enzymatic construction Au NPs-rGO based MIP electrochemical sensor for adulteration detection of bovine-derived allergen in camel milk

In this work, a high-performance molecularly imprinted polymer (MIP) sensor for the determination of β-lactoglobulin (β-LG) was fabricated by using trypsin as a template removal reagent. Gold nanoparticles (Au NPs) and reduced graphene oxide (rGO) designed for electrode modification accelerate the heterogeneous electron transfer rate to enhance the sensitivity of the prepared sensor. With enzymatic hydrolysis, β-LG templates were effectively digested into short peptides without damage to the MIP so that the imprinted cavities of the MIP were preserved with a complete spatial structure exhibiting high selectivity. Based on the optimization of the protein removal time and pH, the prepared MIP electrochemical sensor could recognize β-LG in the range of 4-100 ng/mL with a low detection limit (3.58 ng/mL). The sensor also expressed excellent selectivity and was successfully applied to real sample detection. The results demonstrate that the proposed MIP electrochemical sensor may be a promising candidate for camel milk adulteration detection.

A novel IgE epitope-specific antibodies-based sandwich ELISA for sensitive measurement of immunoreactivity changes of peanut allergen Ara h 2 in processed foods

Background

Peanut is an important source of dietary protein for human beings, but it is also recognized as one of the eight major food allergens. Binding of IgE antibodies to specific epitopes in peanut allergens plays important roles in initiating peanut-allergic reactions, and Ara h 2 is widely considered as the most potent peanut allergen and the best predictor of peanut allergy. Therefore, Ara h 2 IgE epitopes can serve as useful biomarkers for prediction of IgE-binding variations of Ara h 2 and peanut in foods. This study aimed to develop and validate an IgE epitope-specific antibodies (IgE-EsAbs)-based sandwich ELISA (sELISA) for detection of Ara h 2 and measurement of Ara h 2 IgE-immunoreactivity changes in foods.

Methods

DEAE-Sepharose Fast Flow anion-exchange chromatography combining with SDS-PAGE gel extraction were applied to purify Ara h 2 from raw peanut. Hybridoma and epitope vaccine techniques were employed to generate a monoclonal antibody against a major IgE epitope of Ara h 2 and a polyclonal antibody against 12 IgE epitopes of Ara h 2, respectively. ELISA was carried out to evaluate the target binding and specificity of the generated IgE-EsAbs. Subsequently, IgE-EsAbs-based sELISA was developed to detect Ara h 2 and its allergenic residues in food samples. The IgE-binding capacity of Ara h 2 and peanut in foods was determined by competitive ELISA. The dose-effect relationship between the Ara h 2 IgE epitope content and Ara h 2 (or peanut) IgE-binding ability was further established to validate the reliability of the developed sELISA in measuring IgE-binding variations of Ara h 2 and peanut in foods.

Results

The obtained Ara h 2 had a purity of 94.44%. Antibody characterization revealed that the IgE-EsAbs recognized the target IgE epitope(s) of Ara h 2 and exhibited high specificity. Accordingly, an IgE-EsAbs-based sELISA using these antibodies was able to detect Ara h 2 and its allergenic residues in food samples, with high sensitivity (a limit of detection of 0.98 ng/mL), accuracy (a mean bias of 0.88%), precision (relative standard deviation < 16.50%), specificity, and recovery (an average recovery of 98.28%). Moreover, the developed sELISA could predict IgE-binding variations of Ara h 2 and peanut in foods, as verified by using sera IgE derived from peanut-allergic individuals.

Conclusion

This novel immunoassay could be a user-friendly method to monitor low level of Ara h 2 and to preliminary predict in vitro potential allergenicity of Ara h 2 and peanut in processed foods.

"Fluorescence-wavelength" label-free POCT tandem with "fluorescence-photothermal" nanobody-immunosensor for detecting BSA and β-lactoglobulin

Two carbon dots (CDs) (λEm = 525 nm, G-CDs and λEm = 640 nm, R-CDs) were synthesized from citric acid and urea. The bovine serum albumin (BSA) responsiveness of the R-CDs was used to develop a "fluorescence-wavelength" label-free point of care testing (POCT) for the detection of the milk quality marker BSA with the detection limit (LOD) of 4.89 μg/mL for fluorescence mode and 3.38 μg/mL for wavelength mode. In addition, R-CDs were found to have hydroxyl radical (·OH)-dependent fluorescence quenching properties, and a "fluorescence-photothermal" immunosensor based on nanobodies was constructed by introducing the fluorescence signal of R-CDs@BSA and the photothermal signal of oxTMB for the detection of β-lactoglobulin (β-LG) with the LOD of 0.034 ng/mL for fluorescence mode and 0.075 ng/mL for photothermal mode. The tandem detection of POCT and immunosensor enables the simultaneous and highly sensitive detection of BSA and β-LG after only simple dilution of less than 5 µL of sample.

One-Step Purification of IgE Epitope-Specific Antibody Using Immunomagnetic Beads and Highly Sensitive Detection of Bovine β-Lactoglobulin for the Prediction of Milk Allergenicity in Foods

Bovine β-lactoglobulin (BLG) is a common allergen found in milk, and the immunoglobulin E (IgE) epitope plays a crucial role in cow milk allergy. Therefore, targeting the IgE epitope could be useful in accurately detecting BLG and assessing its allergenicity. However, producing an IgE epitope-specific antibody (IgE-EsAb) through traditional methods requires complex and time-consuming procedures. Here, IgE-EsAb was purified from rabbit anti-BLG sera by immunomagnetic beads in one step. Then, a sandwich ELISA (sELISA) based on the IgE-EsAb was developed to detect BLG and predict the potential milk allergenicity in foods. The obtained IgE-EsAb could specifically recognize the target IgE epitope of BLG and exhibited high affinity and specificity. The developed IgE-EsAb-based sELISA demonstrated an ultra-wide linear range of 3.9-1.28 × 105 ng/mL, with a limit of detection of 0.49 ng/mL for BLG. Additionally, the proposed immunoassay showed high specificity and recoveries (91.24-109.61%). The ability of the IgE-EsAb-based sELISA to evaluate the potential milk allergenicity in foods was validated using sera from cow milk allergy patients. These results suggest that immunomagnetic beads are an effective tool for rapidly obtaining the IgE-EsAb, and our proposed sELISA could be a reliable and user-friendly method for monitoring trace amounts of BLG and predicting the potential milk allergenicity of food samples.

Detection of β-lactoglobulin under different thermal-processing conditions by immunoassay based on nanobody and monoclonal antibody

The problems of inaccurate detection values of thermal-processed β-lactoglobulin (β-LG) content seriously affect the screening of allergens. A monoclonal antibody (mAb) against β-LG was successfully prepared and a highly sensitive sandwich ELISA (sELISA) was constructed with specific nanobody (Nb) as the capture antibody with detection limit of 0.24 ng/mL. Based on this sELISA, the ability of Nb and mAb to recognize β-LG and β-LG interacting with milk components was explored. Combined with protein structure analysis to elaborate the mechanism of shielding β-LG antigen epitopes during thermal-processing, thus enabling the differentiation between pasteurized and ultra-high temperature sterilized milk, the detection of milk content in milk-containing beverages, and the highly sensitive detection and analysis of β-LG allergens in dairy-free products. The method provides methodological support for identifying the quality of dairy products and reducing the risk of β-LG contamination in dairy-free products.

Highly Sensitive β-Lactoglobulin Fluorescent Aptamer Biosensors Based on Tungsten Disulfide Nanosheets and DNase I-Assisted Signal Amplification

β-lactoglobulin (β-Lg) is a protein found in milk that can cause severe allergic reactions, including rash, vomiting, and diarrhea. Thus, it is crucial to develop a sensitive β-Lg detection method to protect people who are susceptible to allergies. Here, we introduce a novel and highly sensitive fluorescent aptamer biosensor for detecting β-Lg. First, a fluorescein-based dye (FAM)-labeled β-lactoglobulin aptamer (β-Lg aptamer) is adsorbed on the surface of tungsten disulfide (WS₂) nanosheets via van der Waals forces, resulting in fluorescence quenching. When β-Lg is present, the β-Lg aptamer selectively binds to β-Lg, causing a conformational change in the β-Lg aptamer and releasing it from the surface of WS₂ nanosheets, which restores the fluorescence signal. Simultaneously, DNase I in the system cleaves the aptamer bound to the target, producing a short oligonucleotide fragment and releasing β-Lg. The released β-Lg then binds to another β-Lg aptamer adsorbed on WS₂, initiating the next round of cleavage, resulting in significant amplification of the fluorescence signal. This method has a linear detection range of 1-100 ng mL^-1, and the limit of detection is 0.344 ng mL^-1. Furthermore, this approach has been successfully used for detecting β-Lg in milk samples with satisfactory results, providing new opportunities for food analysis and quality control.

Accurate determination of the milk protein allergen β-lactoglobulin by on-line aptamer affinity solid-phase extraction capillary electrophoresis-mass spectrometry

An on-line aptamer affinity solid-phase extraction capillary electrophoresis-mass spectrometry (AA-SPE-CE-MS) method was developed to purify, preconcentrate, separate, and characterize the milk allergenic protein β-lactoglobulin (β-LG) in food samples. The sorbent to pack into the SPE microcartidges was prepared by immobilizing an aptamer against β-LG onto magnetic bead particles. After optimizing the SPE-CE-MS method, the sample (ca. 75 μL) was loaded in separation background electrolyte (BGE, 2 M acetic acid pH 2.2), while a solution of 100 mM NH₄OH (pH 11.2) (ca. 100 nL) was used for the protein elution. The linearity of the method ranged between 0.1 and 20 μg mL^-1 and the limit of detection (LOD) was 0.05 μg mL^-1, which was 200 times lower than by CE-MS. The method was repeatable in terms of relative standard deviation (RSD) for migration times and peak areas (<0.5% and 2.4%, respectively) and microcartridge lifetime was more than 25 analyses. The applicability of the method for the determination of low levels of β-LG was shown by analyzing milk-free foods (i.e. a 100% cocoa dark chocolate, a hypoallergenic formula for infants, and a dairy-free white bread) and milk-containing white breads. Results were satisfactory in all cases, thus demonstrating the great potential of the developed method for accurate food safety and quality control.

Exploration of Specific Nanobodies As Immunological Reagents to Detect Milk Allergen of β-Lactoglobulin without Interference of Hydrolytic Peptides

Milk proteins are widely used for food supplementation, despite the potential risk of food allergy, especially against β-lactoglobulin (BLG), which makes BLG surveillance critical. Possible interaction of detecting antibodies with BLG-derived peptides will result in unprecise inspection. Thus, in this study, it was proposed to generate nanobodies (Nbs) and validate the immunological detection of intact BLG rather than hydrolytic peptides. Nbs were successfully retrieved and characterized with high stability and target specificity. A competitive enzyme-linked immunosorbent assay (cELISA) was developed with a linear range from 39 to 10,000 ng/mL and a detection limit (LOD) of 4.55 ng/mL, with a recovery of 86.30%-95.09% revealed by analysis of spiked samples. Meanwhile, a sandwich ELISA (sELISA) was established with Nb82 and BLG polyclonal antibody (pAb-BLG) providing a linear range from 29.7 to 1250 ng/mL and an LOD of 13.82 ng/mL with a recovery of 87.82%-103.97%. The interaction of selected Nbs with BLG-derived peptides was investigated by Nb structure modeling and BLG docking. No binding on hydrolytic peptides was revealed, confirming the precision of Nb-mediated immunoassays. In summary, this study successfully identified BLG-specific Nbs for immunoassay development and guaranteed the monitoring of intact BLG without interference of hydrolytic peptides, providing experimental evidence that our Nbs recognize intact food allergen.

A Method for Screening Proteases That Can Specifically Hydrolyze the Epitope AA83-105 of αs1-Casein Allergen

Milk protein hydrolysates are common in infant formula, but some of them retain allergenicity due to incomplete hydrolysis of the epitopes for milk allergens. This study explored a method for screening proteases that could specifically hydrolyze the epitope of αs1-casein allergen. Firstly, the αs1-casein epitope AA83-105 was synthesized by the solid-phase synthesis method. Then, after purification and identification, the complete antigen was prepared through coupling with bovine serum albumin (BSA) and was used to raise monoclonal antibodies (mAb) in BALB/c mice. Additionally, an indirect competitive-enzyme-linked immunosorbent assay (icELISA) was established. The mAb raised against αs1-casein protein was used as a control. The results showed that the purity of the synthetic epitope was >90%, and the coupling rate with BSA was 6.31. The mAb subtype is IgG1, with a titer of 1:320,000. The mAb reacted specifically with αs1-casein but did not cross-react with soybean protein. The linear regression equation of the competitive inhibition curve was y = −9.22x + 100.78 (R2 = 0.9891). The detection limit of icELISA method was more sensitive, and the method showed good accuracy and repeatability. The amounts of antigen residues in papain protease hydrolysates were relatively small, and the epitope fragment was detected in papain hydrolysate via mass spectrometry. This study provides ideas and methods for screening proteases that specifically hydrolyze the epitopes of milk allergens and also provides a superior foundation for the development of an advanced hypoallergenic formula.

Enzyme-Linked Immunosorbent Assay (ELISA)

Enzyme-linked immunosorbent assay (ELISA) is one of the most specific and straightforward assays for detecting biomolecules in research and clinics. With advances in analytical methods, ELISA assay has been constantly optimized to improve its sensitivity, and different types of ELISA are now available to detect various biomarkers. This chapter provides an overall summary of the basic principle of ELISA, discusses different components of ELISA assay, and clearly outline protocols for different types of ELISA assays, including direct, indirect, sandwich, competitive, and nanoparticle-based ELISA.

Fluorescence detection of milk allergen β-lactoglobulin based on aptamers and WS2 nanosheets

β-Lactoglobulin (β-Lg), a food allergen, can easily cause allergic reactions in infants and young children. Therefore, it is necessary to develop a rapid, sensitive, and selective detection method to protect individuals prone to allergies. In this paper, a fluorescence assay based on WS₂ nanosheets and a fluorescent dye (FAM)-labeled β-Lg aptamer was designed to detect β-Lg rapidly with high sensitivity. In the sensing platform, the β-Lg aptamer is adsorbed on the WS₂ nanosheet surface by van der Waals forces, which trigger the phenomenon of fluorescence resonance energy transfer (FRET) and suppress the fluorescence signal in the system. When β-Lg is present, the conformation of the aptamer specifically bound to β-Lg changes. Therefore, the aptamer is separated from the WS₂ nanosheet surface, and the fluorescence signal is recovered. This method combines the high quenching efficiency of WS₂ nanosheets and good specificity of the β-Lg aptamer. The detection range of this method for β-Lg is 0.1-100 μg mL^-1. The detection limit is 20.4 ng mL^-1. This method exhibits high sensitivity, selectivity and good reproducibility, and it can be used for β-Lg detection in actual samples.

Dual signal light detection of beta-lactoglobulin based on a porous silicon bragg mirror

In this work, a new dual signal light detection method based on porous silicon Bragg mirror (PSBM) and biological labelling with quantum dots (QDs) is proposed for the detection of beta-lactoglobulin (β-lg). The first signal light is a probe light emitted by a laser with wavelength of 633 nm, which enters the PSBM and is reflected from the surface. The wavelength of the probe light is located at the edge of the PSBM band gap, where it has the lowest reflectivity. β-lg antibodies is labelled with CdSe/ZnS QDs and reacts with β-lg molecules have been fixed to the inner wall of the porous silicon pores. Due to the specific binding of biomolecules in PSBM, the refractive index of the device increases, resulting in the enhancement of detection reflected light. The QDs play the role of refractive index amplification. The second signal light is the fluorescence of QDs in immune reactants. QDs produce fluorescence at 630 nm when excited by a short-wavelength laser. The fluorescence signal is further enhanced by PSBM. The superimposed images of two kinds of light on the surface of PSBM are obtained by digital microscope at the same time. By calculating the average grey value change of the image before and after biological reaction, β-lg can be detected with high sensitivity. The detection limit of β-lg was 0.12 ng/mL. The experimental results showed that the PSBM-based dual signal light method could be used to detect the content of cow milk adulterated in β-lg free camel milk.

A UCMPs@MIL-100 based thermo-sensitive molecularly imprinted fluorescence sensor for effective detection of β-lactoglobulin allergen in milk products

In this study, a thermo-sensitive molecularly imprinted fluorescence sensor was developed for the specific detection of β-Lactoglobulin (β-LG) allergen in milk products. The metal–organic frameworks (MIL-100) with a high specific surface area was coated on the surface of upconversion micro-particles (UCMPs). As the core, an imprinted polymer layer allowing for swelling and shrinking with response to temperature was prepared, which exhibited high adsorption and mass transfer capabilities for β-LG allergen. The fluorescence intensity of UCMPs@MIL-100@MIP decreased linearly with the concentration of β-LG in the range of 0.1–0.8 mg mL⁻¹, and the limit of detection was 0.043 mg mL⁻¹. The imprinting factor reached 3.415, which indicated that excellent specificity of the UCMPs@MIL-100@MIP for β-LG allergen. In the analysis of β-LG allergen in actual milk samples, the proposed UCMPs@MIL-100@MIP fluorescence sensor produced reliable and accurate results (recovery: 86.0–98.4%, RSD: 2.8–6.8%), closely related to the results of standard HPLC method (correlation coefficient: 0.9949), indicating that its feasibility in the detection of β-LG allergen.

An Electrochemical Molecularly Imprinted Polymer Sensor for Rapid β-Lactoglobulin Detection

Facile detection of β-lactoglobulin is extraordinarily important for the management of the allergenic safety of cow's milk and its dairy products. A sensitive electrochemical sensor based on a molecularly imprinted polymer-modified carbon electrode for the detection of β-lactoglobulin was successfully synthesized. This molecularly imprinted polymer was prepared using a hydrothermal method with choline chloride as a functional monomer, β-lactoglobulin as template molecule and ethylene glycol dimethacrylate as crosslinking agent. Then, the molecularly imprinted polymer was immobilized on polyethyleneimine (PEI)-reduced graphene oxide (rGO)-gold nanoclusters (Au-NCs) to improve the sensor's selectivity for β-lactoglobulin. Under optimal experimental conditions, the designed sensor showed a good response to β-lactoglobulin, with a linear detection range between 10-9 and 10-4 mg/mL, and a detection limit of 10-9 mg/mL (S/N = 3). The developed electrochemical sensor showed a high correlation in the detection of β-lactoglobulin in four different milk samples from the market, indicating that the sensor can be used with actual sample.

Non-Specific Binding and Cross-Reaction of ELISA: A Case Study of Porcine Hemoglobin Detection

Different types of enzyme-linked immunosorbent assays (ELISA) have been widely used to control food safety and quality. To develop an accurate and reproducible ELISA, false immunodetection results caused by non-specific binding (NSB) and cross-reaction must be prevented. During the case study of sandwich ELISA development for the detection of porcine hemoglobin (P_Hb), several critical factors leading to NSB and cross-reaction were found. First, to reduce the NSB of the target analyte, the selection of microplate and blocker was discussed. Second, cross-reactions between enzyme-labeled secondary antibodies and sample proteins were demonstrated. In addition, the function of (3-aminopropyl)triethoxysilane (APTES) was evaluated. Overall, this study highlights the essence of both antibody and assay validation to minimize any false-positive/negative immunodetection results.

Development of a NanoMIPs-SPR-Based Sensor for β-Lactoglobulin Detection

Food manufacturers are aiming to manage the levels of cross-contamination of allergens within food processing plants and ultimately move away from precautionary labelling. Hence, the need for rapid methods to detect allergens cross-contamination. A sensitive and selective label-free nanoMIPs based sensor was developed and tested for the detection of β-lactoglobulin (BLG). NanoMIPs were synthesized using solid-phase synthesis and appeared as spherical nanoparticles with sizes ranging from 264–294 nm, using dynamic light scattering (DLS). The nanoMIPs were functionalized with amine groups and attached to the surface of the SPR gold chip via amine-coupling protocol. The SPR nanoMIPs-based sensor demonstrated a detection limit of 3 ng mL−1 (211 pM) over a linear range of 1–5000 ng mL−1, with binding affinity of 7.0 × 10−8 M and specificity towards BLG. With further testing and final optimization, the developed nanosensor can be integrated on-line or at-line cleaning-in-place (CIP) wash systems, allowing to effectively monitor milk protein allergens as a rapid, point-of-source methodology.

Parallel Reaction Monitoring Mass Spectrometry Method for Detection of Both Casein and Whey Milk Allergens from a Baked Food Matrix

Milk allergy is among the most common food allergies present in early childhood, which in some cases may persist into adulthood as well. Proteins belonging to both casein and whey fractions of milk can trigger an allergic response in susceptible individuals. Milk is present as an ingredient in many foods, and it can also be present as casein- or whey-enriched milk-derived ingredients. As whey proteins are more susceptible to thermal processing than caseins, conventional methods often posed a challenge in accurate detection of whey allergens, particularly from a processed complex food matrix. In this study, a targeted mass spectrometry method has been developed to detect the presence of both casein and whey allergens from thermally processed foods. A pool of 19 candidate peptides representing four casein proteins and two whey proteins was identified using a discovery-driven target selection approach from various milk-derived ingredients. These target peptides were evaluated by parallel reaction monitoring of baked cookie samples containing known amounts of nonfat dry milk (NFDM). The presence of milk could be detected from baked cookies incurred with NFDM at levels as low as 1 ppm using seven peptides representing α-, β-, and κ-casein proteins and three peptides representing a whey protein, β-lactoglobulin, by this consensus PRM method.

Generation of High Affinity Anti-Peptide Polyclonal Antibodies Recognizing Goat αs1-Casein

The chemical, technological and allergy properties of goat's milk are significantly affected by the level of αs1-casein. Detection and quantification of αs1-casein requires high-specificity methods to overcome high-sequence similarity between this protein and others in the casein family. Unavailability of antibodies with high affinity and specificity towards goat αs1-casein hinders the development of immuno-based analytical methods such as enzyme-linked immunosorbent assay (ELISA) and biosensors. Here, we report the generation of polyclonal antibodies (or immunoglobulins, IgGs) raised towards goat αs1-casein N- (Nter) and C-terminal (Cter) peptide sequences. The Nter and Cter peptides of goat αs1-casein were immunized in rabbits for the generation of antisera, which were purified using protein G affinity chromatography. The binding affinity of the antisera and purified IgGs were tested and compared using indirect ELISA, where peptide-BSA conjugates and goat αs1-casein were used as the coating antigens. The Nter antiserum displayed higher titer than Cter antiserum, at 1/64,000 and 1/32,000 dilutions, respectively. The purification step further yielded 0.5 mg/mL of purified IgGs from 3 mL of antisera. The purified Nter IgG showed a significantly (p < 0.05) higher binding affinity towards peptide-BSA and goat αs1-casein, with lower Kd value at 5.063 × 10-3 μM compared to 9.046 × 10-3 μM for the Cter IgG. A cross-reactivity test showed that there was no binding in neither Nter nor Cter IgGs towards protein extracts from the milk of cow, buffalo, horse and camel. High-quality antibodies generated will allow further development of immuno-based analytical methods and future in vitro studies to be conducted on goat αs1-casein.

Electrochemical detection of β-lactoglobulin based on a highly selective DNA aptamer and flower-like Au@BiVO4 microspheres

Beta-lactoglobulin is a natural milk protein and the main cause of infant milk allergy. In this work, a sensitive, selective and inexpensive electrochemical biosensor for the detection of β-lactoglobulin was developed. In this sensor, a DNA aptamer was used instead of an expensive antibody as the recognition group highly selective for β-lactoglobulin. The flower-like BiVO₄ microspheres were firstly found to have peroxidase mimic catalytic activity and used to amplify the electrochemical signal. The aptamer can bind β-lactoglobulin and fall off from the working electrode, after which the DNA2/Au/BiVO₄ probe can be fixed to the DNA1/AuNPs/ITO working electrode by the hybridization of DNA2 with DNA1. Therefore, a higher concentration of β-lactoglobulin leads to increased fabrication of the DNA2/Au/BiVO₄ probe on the surface of the working electrode, and thereby increases the electrochemical signal. This electrochemical biosensor exhibited a wide detection range from 0.01 to 1000 ng mL^-1, with a limit of detection (LOD) of 0.007 ng mL^-1, which indicates a good potential application in the field of food analysis.

Highly Sensitive Detection of Bovine β-Lactoglobulin with Wide Linear Dynamic Range Based on Platinum Nanoparticles Probe

Cow's milk allergy is one of the most frequent and severe IgE-induced food allergies for children, demanding sensitive analytical methods, and β-lactoglobulin (BLG) can be as an important biomarker for detection of milk protein. In this study, a highly sensitive sandwich enzyme-linked immunosorbent assay (sELISA) based on a specific polyclonal antibody against human IgE linear epitopes of BLG and an anti-BLG polyclonal antibody-platinum nanoparticles probe was described for detection of BLG. This sELISA exhibited an ultrawide linear range of 0.49-1.6 × 10⁴ ng/mL, covering more than four orders of magnitude. The limit of detection was 0.12 ng/mL, which was 16-fold lower than that using traditional sELISA with the same antibodies. Furthermore, the proposed approach showed high recoveries (93.53%-111.95%) and low coefficient of variation (1.49%-12.50%) after analysis of samples fortified with BLG. The presence of allergenic BLG residues also could be detected in partially hydrolyzed infant formulas. These results, in comparison with conventional and commercial BLG detection sELISAs, highlight that this proposed sELISA could be a reliable and user-friendly tool to monitor trace amounts of BLG and its potentially allergenic residues in foods.

Ultrasensitive Detection of Protein with Wide Linear Dynamic Range Based on Core-Shell SERS Nanotags and Photonic Crystal Beads

Detection of proteins in a wide concentration range from fg mL^-1 to sub mg mL^-1 is a challenge in the high throughput analysis of precision medicine. Herein, we proposed a biosensor consisting of core-shell surface-enhanced Raman scattering (SERS) nanotags as labels and photonic crystal beads (PCBs) as carriers for ultrasensitive detection of proteins. In practice, Raman dyes (RDs) were embedded in the interface of gold core and silver shell in the bimetal nanoparticles to form SERS nanotags. It was found that the sensitivity was significantly improved due to the enhanced Raman signal by the coupling of the core-shell structure and linear dynamic range (LDR) was extended owing to the high surface to volume ratio of PCBs as well. In addition, we also demonstrated that the biosensor exhibited fine stability and low background, which has great application potential in the detection of protein biomarkers.