Spectral data fusion in nondestructive detection of food products: Strategies, recent applications, and future perspectives.

In recent years, the food industry has shown a growing interest in the development of rapid and nondestructive analytical methods. However, the utilization of a solitary nondestructive detection technique offers only a constrained extent of physical or chemical insights regarding the sample under examination. To overcome this limitation, the amalgamation of spectroscopy with data fusion strategies has emerged as a promising approach. This comprehensive review delves into the fundamental principles and merits of low-level, mid-level, and high-level data fusion strategies within the domain of food analysis. Various data fusion techniques encompassing spectra-to-spectra, spectra-to-machine vision, spectra-to-electronic nose, and spectra-to-nuclear magnetic resonance are summarized. Moreover, this review also provides an overview of the latest applications of spectral data fusion techniques (SDFTs) for classification, adulteration, quality evaluation, and contaminant detection within the purview of food safety analysis. It also addresses current challenges and future prospects associated with SDFTs in real-world applications. Despite the extant technical intricacy, the ongoing evolution of online data fusion platforms and the emergence of smartphone-based multi-sensor fusion detection technology augur well for the pragmatic realization of SDFTs, endowing them with formidable capabilities for both qualitative and quantitative analysis in the realm of food analysis.

The specific biopanning of single-domain antibody against haptens based on a functionalized cryogel.

Phage display technology is commonly applied for high-throughput screening of single-domain antibodies (sdAbs), and the problem of non-specific adsorption caused by carrier proteins seriously affects the biopanning of single-domain antibodies specific to haptens. In this paper, enrofloxacin (ENR)-functionalized cryogels were prepared by the ethylenediamine (EDA) and carbodiimide methods for application in the biopanning of ENR-specific phages. To improve the efficiency of biopanning, double blocking, a wash solution flow rate of 1 mL/min, and phage pre-incubation were applied to the biopanning process through single-factor experiments. Results of flat colony counting showed that the phage output of AG-ENR cryogels was 15 times higher than that of AG cryogels for the same input amount. And seven complete sequences of ENR-specific shark sdAbs were obtained by monoclonal phage ELISA and sequence alignment. All these results indicate that functionalized cryogels could be used as a novel and efficient method for phage biopanning for single-domain antibodies to haptens.

Efficient Hapten-Specific Biopanning Strategy Based on the Fe3O4@ENR-Functionalized Core-Shell Magnetic Nanoparticles.

The biopanning of target-specific phages is one of the most critical steps in the preparation of single-domain antibodies. In the traditional biopanning of haptens, the nonspecific binding of library phages to macromolecular proteins is one of the most challenging problems in preparing single-domain antibodies. In this research, Fe3O4@ENR-functionalized core-shell magnetic nanoparticles (FMNPs) were silylated and aminated by tetraethyl orthosilicate and (3-aminopropyl)triethoxysilane, and target enrofloxacin was coupled onto the surface by the carbodiimide method. The magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy, particle size distribution, zeta potential, transmission electron microscopy observation, and indirect enzyme-linked immunosorbent assay (ELISA). A biopanning strategy based on Fe3O4@ENR FMNPs was then established to solve the problem in the traditional solid-phase biopanning process. The results showed that a considerable number of enrofloxacin (ENR)-positive phages were screened by only one round of biopanning. Finally, two ENR-specific shark-derived single-domain genes were identified and validated by monoclonal phage ELISA, gene sequencing, and biolayer interferometry technology. Our study provides a new biopanning strategy based on Fe3O4@ENR FMNPs for efficiently providing phages specific to haptens.

Study on Volatile Chemicals as Spoilage Indexes of Salmon by HS-SPME-GC-MS Technique during Non-Frozen Storage.

Freshness is the most fundamental and important factor to assess raw fish quality. The purpose of our study was to determine the potential spoilage indexes of salmon during non-frozen storage by using headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS). More than 300 volatile compounds in salmon were detected when sensory scores declined gradually following the quality changes of salmon at different temperatures. And there were 27 and 31 compounds that showed concentration variations when stored at 4 °C and 25 °C, respectively. Among them, the contents of 1,3-di-tert-butylbenzene, acetic acid, and 3-methyl-1-butanol increased significantly in the later storage period and were in accordance with the salmon's qualities. The present study provides valuable information on the volatile chemical spoilage indexes that are closely related to the freshness of salmon, which may provide an efficient alternative way for quality evaluation of salmon.

The effect of chlorophyll on the enzyme-linked immunosorbent assay (ELISA) of procymidone in vegetables and the way to overcome the matrix interference.

BACKGROUND: There is now an increasing demand for the immunoassay of procymidone residue in foodstuffs. However, the matrix interference could significantly affect the analysis. Till now there is no detailed information on the source of the interference and the mechanism involved, which greatly limits the real application of these techniques. RESULTS: Significant matrix effect was observed in the enzyme-linked immunosorbent assay (ELISA) of procymidone in negative vegetable samples (leek, broccoli and cucumber). By the investigation with both vegetable extracts and standard solutions, the chlorophyll was confirmed as an important source of the matrix effect. Therefore, a new strategy was proposed for the pretreatment based on the exploitation of 5-sulfosalicylic acid. It was demonstrated to effectively eliminate chlorophyll and exhibited little effect on procymidone and the competitive indirect ELISA (ci-ELISA) performance. The established technique was validated with different vegetables. With the spiking concentration of procymidone investigated, the recovery rate of ci-ELISA was 71.52-120.37%, and the relative standard deviation was 4.05-17.61%. CONCLUSION: Chlorophyll was for the first time illuminated as an important source of matrix interference to the immunoassay of procymidone in vegetables. A new pretreatment based on 5-sulfosalicylic acid was established to remove chlorophyll and therefore eliminate the matrix effect. Validated with different vegetable samples, the new technique was demonstrated much better efficiency in comparison to conventional methods, which indicated its promising application for the development of immunoassays of herb-origin samples. © 2021 Society of Chemical Industry.

Analysis of shark NCR3 family genes reveals primordial features of vertebrate NKp30.

Natural killer (NK) cells play major roles in innate immunity against viruses and cancer. Natural killer receptors (NKR) expressed by NK cells recognize foreign- or self-ligands on infected and transformed cells as well as healthy cells. NKR genes are the most rapidly evolving loci in vertebrates, and it is generally difficult to detect orthologues in different taxa. The unique exception is NKp30, an activating NKR in mammals that binds to the self-ligand B7H6. The NKp30-encoding gene, NCR3, has been found in most vertebrates including sharks, the oldest vertebrates with human-type adaptive immunity. NCR3 has a special, non-rearranging VJ-type immunoglobulin superfamily (IgSF) domain that predates the emergence of the rearranging antigen receptors. Herein we show that NCR3 loci are linked to the shark major histocompatibility complex (MHC), proving NCR3's primordial association with the MHC. We identified eight subtypes of differentially expressed highly divergent shark NCR3 family genes. Using in situ hybridization, we detected one subtype, NS344823, to be expressed by predominantly single cells outside of splenic B cell zones. The expression by non-B cells was also confirmed by PCR in peripheral blood lymphocytes. Surprisingly, high expression of NS344823 was detected in the thymic cortex, demonstrating NS344823 expression in developing T cells. Finally, we show for the first time that shark T cells are found as single cells or in small clusters in the splenic red pulp, also unassociated with the large B cell follicles we previously identified.

Production of egg yolk antibody against A.fumigatus and its therapeutic potential for treating A.fumigatus keratitis.

OBJECTIVE: To prepare specific IgY against A. fumigatus and verify its specificity and antifungal effect on A. fumigatus keratitis. METHOD: Lay hens were immunized with the suspension of inactivated A. fumigatus hyphae which mixed with Freund's complete adjuvant or incomplete Freund's adjuvant. The IgY protein specific for A. fumigatus was extracted by ammonium sulfate salting-out method at the fifth to eighth week after immunization. Bradford method and indirect ELISA were used to determine the concentration and titer of IgY. To verify the inhibitory effect of specific IgY on fungal growth, 1 × 105 CFU/mL A. fumigatus hyphae suspension and specific IgY of different concentrations were mixed and cultured for 24 h, 48 h and 72 h to measure the absorbance. Using specific IgY to treat A. fumigatus keratitis in mice, we observed the cornea under a slit lamp at 24 h, 72 h, and 120 h after treatment. Clinical score was used to assess the disease severity of fungal keratitis in mice cornea. The indirect ELISA method was used to determine the titer of specific IgY stored at room temperature and 4 °C for 1, 2, 3, 4, 5, 6, 7, 8, and 9 months. RESULTS: The protein concentrations of specific IgY at the fifth, sixth, seventh and eighth weeks after immunization were 5.46 mg/mL, 5.79 mg/mL, 26.98 mg/mL, 28.71 mg/mL. The titer of the specific IgY of A. fumigatus can reach 1:10000, and the antifungal effect of the specific IgY is dose dependent within a certain range. Specific IgY treatment alleviated the severity of fungal keratitis of mice and reduced the clinical score. Moreover, there were no significant change in the titer of specific IgY after storage at room temperature for 2 months and storage at 4 °C for 6 months. CONCLUSION: The specific IgY can be successfully prepared by ammonium sulfate salting-out method. And it has excellent stability and significant antifungal effect on A. fumigatus keratitis.

Quick and convenient construction of lambda-cyhalothrin antigen for the generation of specific antibody.

Lambda-cyhalothrin is a pyrethroid widely used in crop, fruit and vegetable production, but has potential health threats to human. Immunoassay is a cheap, rapid and facile method to detect lambda-cyhalothrin, yet wide application of this method still requires improvement in the construction of antigen. In this study, we developed a one-step lambda-cyhalothrin hapten synthesis that transformed the cyanide group in lambda-cyhalothrin to amide. Complete antigen was assembled by coupling the amide with succinic-anhydride-activated carrier proteins, and corresponding polyclonal antibodies were generated using Balb/c mice. Using antibody generated by the method in this paper, the competitive ELISA demonstrated the lowest detection limit of 3.772 µg/L for lambda-cyhalothrin, and no significant cross-reactivity for other pyrethroid pesticides was observed. All the results suggested we have established a more efficient technique of generating lambda-cyhalothrin antibody. Furthermore, since the activated proteins used in this study are highly controllable, we believe these proteins could potentially be the prototype of a series of standardized carrier proteins for the synthesis of complete antigens.

Extraction, Identification, Modification, and Antibacterial Activity of Histone from Immature Testis of Atlantic salmon.

In the present study, histone from immature testis of Atlantic salmon was extracted and identified, and its antibacterial activity after enzymolysis was investigated. Histone extracted from Atlantic salmon (Salmo salar) testis using the acid extraction method was successfully identified by LC-MS/MS, and revealed significant inhibitory activity on both the Gram-negative and Gram-positive bacteria. With a low concentration of 10 mg/mL, the observed inhibitory zone diameter (IZD) could significantly reach up to 15.23 mm. After modification of enzymatic hydrolysis by pepsin, histone could be digested to three fragments, while the antibacterial activity increased up to 57.7%. All the results suggested the leftovers from commercial fishing could be utilized for the extraction of antimicrobial peptides.

Boronic acid-functionalized agarose affinity chromatography for isolation of tropomyosin in fishes.

BACKGROUND: Tropomyosin is now receiving increasing attention because of its significant allergenic activity in various fishery products but its simple and effective isolation still remains a challenging task. RESULTS: An agarose-based boronate affinity chromatography was produced for the first time to isolate tropomyosin in various fishery products using 3,5-difluoro-4-formyl-phenylboronic acid as the functional monomer, tris(2-aminoethyl)amine as the multi-branched ligand, and agarose gel particles as supporting materials. The agarose concentration, binding pH, and the concentration of elution buffers demonstrated significant effects on separation performance. Under optimized conditions, the purity of the isolated tropomyosin was higher than 90%, with the column adsorption capacity over 1.85 mg mL-1 and the enrichment efficiency over 65%. Such efficiency was also validated with different fish samples including Paralichthys olivaceus, Thunnusthynnus, Oreochromis spp., and Lophius litulon. CONCLUSION: In comparison with conventional methods, the established affinity chromatography demonstrated excellent biocompatibility (without involving any organic solvent), better speed (from at least 1-2 days to 3-4 h), and simplicity (from at least five steps to three steps). This suggests that it is a novel and promising technique for the isolation of tropomyosin and other glycoproteins (including most allergens) in foodstuffs. © 2019 Society of Chemical Industry.

Determination of four different purines and their content change in seafood by high-performance liquid chromatography.

BACKGROUND: Seafood is regarded as a high-purine food that may induce gout, which has attracted extensive attention concerning its safety. Therefore, the aim of this study was to develop a simple and reliable method to determine the purine content in seafood and its change during storage to offer consumers healthy diet information. RESULTS: Chromatographic separation was carried out using Waters Atlantis dC18 column, and potassium phosphate monobasic solution (0.02 mol L-1 , pH 3.6) as a mobile phase. The average recovery yields of four purines were 91.5-105.0%, and relative standard deviation values were around 1.8-6.5%. Shrimp and snail contained higher amounts of purine than fish and bivalves; the livers and skins of fish contained higher amounts of purine than muscles; and the main purine varied depending on the type of seafood. Also, purine content of seafood changed during storage. CONCLUSION: The purine content of seafood differed depending on species, body part and degree of freshness, which could recommend consumers a healthy diet, especially for people with hyperuricemia and gout. © 2016 Society of Chemical Industry.

5-Sulfosalicylic acid dihydrate-based pretreatment for the modification of enzyme-linked immunoassay of fluoroquinolones in fishery products.

A simple, rapid sample extraction method for the determination of FQs was developed. Fishery samples were extracted with 2% of 5-sulfosalicylic acid dihydrate and the extracts were analyzed directly without any further purification or clean-up procedures. The FQs were determined with standards of 2% of 5-sulfosalicylic acid dihydrate in the concentration range of 0.1-25.6 µg L(-1), and the limit of detection (LOD) was 0.1 µg L(-1). The matrix interference originated from fishery samples was eliminated by 2% of 5-sulfosalicylic acid dihydrate and did not interact with horseradish peroxidase (HRP) labeled IgG in western blotting. No significant matrix interference was observed as samples extracted with 2% of 5-sulfosalicylic acid dihydrate. Recoveries of FQs in fishery muscle were between 72.37-94.35% in the concentrations range of 10-50 µg kg(-1).This extraction procedure was much rapider and simpler to conventional ELISA extraction procedure and could be used as a time-saving and cost-effective method for FQs monitoring in fishery samples.

Effects of Fab' fragments of specific egg yolk antibody (IgY-Fab') against Shewanella putrefaciens on the preservation of refrigerated turbot.

BACKGROUND: In our previous studies the specific egg yolk antibody (IgY) against Shewanella putrefaciens (one of the specific spoilage organisms for marine products during aerobic chilling storage) demonstrated significant activity to prolong the shelf life of refrigerated fish. The exploitation of the antigen-binding fragment plus the hinge region (IgY-Fab') is now considered a promising method for improving the efficiency of such natural antimicrobial agents. RESULTS: The antimicrobial activity of IgY-Fab' against S. putrefaciens was investigated using refrigerated turbot as samples. By microbial, chemical and sensory tests, it was shown to be able to effectively inhibit bacterial growth and prolong the shelf life of samples, with an efficiency evaluated significantly higher than that of whole IgY with the same molarity. The interaction between IgY agents and S. putrefaciens cells was also investigated, and the IgY-Fab' showed a much greater ability to damage cell membranes than the whole IgY. CONCLUSION: Compared to whole IgY with the same molarity, IgY-Fab' demonstrated higher and more durable antimicrobial efficiency. Such a result was assumed to be closely related to its structural properties (such as the much lower molecular weight), which may enhance its ability to influence physiological activities of antigen bacteria, especially the property or/and structure of cell membranes.

Nano-gold capillary immunochromatographic assay for parvalbumin.

A novel non-instrumental bioanalysis based on colloidal-gold immunochromatography in a modified glass capillary was developed and named capillary immunochromatographic assay (CICA). In this report, glass capillary was proposed as a support in immunochromatographic assay because of its excellent characteristics. Goat anti-rabbit IgG and parvalbumin (PV) were immobilized on the inner wall of the glass capillary as control zone and test zone, respectively. The CICA was constructed, and main variables for the performance were optimized. Using an important allergen of fish products (parvalbumin, PV) as the target, the analytical efficiency of the developed technique was investigated and the visual detection limit (VDL) and semi-quantitative limit of detection (LOD) were estimated to be 70 ng mL(-1) and 40 ng mL(-1), respectively. The coefficient of variation (CV) for the intra-assay and inter-assay was calculated for the PV concentration of 50 ng mL(-1), and the entire operation, including sample preparation, was consistently performed in 30 min. The developed technique was implemented and validated with different foodstuffs, including Scophthalmus maximus (Linnaeus), surimi products, and livestock, confirming sufficient accuracy and precision of results and verifying the method to be efficacious. These results enabled us to propose CICA as a new and promising technique for simple, rapid, and on-site screening of PV in biological samples.

Bimetallic Fe/Ni metal organic framework-based hypoxanthine biosensor for early monitoring of freshness changes of aquatic products.

The timely detection of freshness changes of aquatic products is crucial. In this study, we have developed a reliable, cost-effective, and user-friendly method for rapidly detecting hypoxanthine using a xanthine oxidase (XOD)/nanozyme enzymatic cascade system. The nanozyme, derived from the Fe7/Ni3 metal-organic framework (Fe7Ni3MOF), exhibited good peroxidase-mimetic activity and stability. Our proposed XOD/Fe7Ni3MOF enzymatic cascade system demonstrated a linear response to hypoxanthine in the range of 3-70 µM, with a low detection limit of 1.39 µM. We also analyzed hypoxanthine in actual aquatic products, achieving spiked recoveries ranging from 90.04 % to 107.37 %. The correlation coefficient between our developed colorimetric method and the HPLC method was 0.98. Importantly, our proposed method holds several advantages over alternative techniques, particularly in terms of cost-effectiveness, precision, and speed. Consequently, this methodology shows great promise for the early detection of freshness changes in aquatic samples.

Seafood waste derived carbon nanomaterials for removal and detection of food safety hazards.

Nanobiotechnology and the engineering of nanomaterials are currently the main focus of many researches. Seafood waste carbon nanomaterials (SWCNs) are a renewable resource with large surface area, porous structure, high reactivity, and abundant active sites. They efficiently adsorb food contaminants through π-π conjugated, ion exchange, and electrostatic interaction. Furthermore, SWCNs prepared from seafood waste are rich in N and O functional groups. They have high quantum yield (QY) and excellent fluorescence properties, making them promising materials for the removal and detection of pollutants. It provides an opportunity by which solutions to the long-term challenges of the food industry in assessing food safety, maintaining food quality, detecting contaminants and pretreating samples can be found. In addition, carbon nanomaterials can be used as adsorbents to reduce environmental pollutants and prevent food safety problems from the source. In this paper, the types of SWCNs are reviewed; the synthesis, properties and applications of SWCNs are reviewed and the raw material selection, preparation methods, reaction conditions and formation mechanisms of biomass-based carbon materials are studied in depth. Finally, the advantages of seafood waste carbon and its composite materials in pollutant removal and detection were discussed, and existing problems were pointed out, which provided ideas for the future development and research directions of this interesting and versatile material. Based on the concept of waste pricing and a recycling economy, the aim of this paper is to outline current trends and the future potential to transform residues from the seafood waste sector into valuable biological (nano) materials, and to apply them to food safety.

Improving the detection accuracy of the dual SERS aptasensor system with uncontrollable SERS "hot spot" using machine learning tools.

BACKGROUND: Simultaneous detection of food contaminants is crucial in addressing the collective health hazards arising from the presence of multiple contaminants. However, traditional multi-competitive surface-enhanced Raman scattering (SERS) aptasensors face difficulties in achieving simultaneous accurate detection of multiple target substances due to the uncontrollable SERS "hot spots". In this study, using chloramphenicol (CAP) and estradiol (E2) as two target substances, we introduced a novel approach that combines machine learning methods with a dual SERS aptasensor, enabling simultaneous high-sensitivity and accurate detection of both target substances. RESULTS: The strategy effectively minimizes the interference from characteristic Raman peaks commonly encountered in traditional multi-competitive SERS aptasensors. For this sensing system, the Au@4-MBA@Ag nanoparticles modified with sulfhydryl (SH)-CAP aptamer and Au@DTNB@Ag NPs modified with sulfhydryl (SH)-E2 aptamer were used as signal probes. Additionally, Fe3O4@Au nanoflowers integrated with SH-CAP aptamer complementary DNA and SH-E2 aptamer complementary DNA were used as capture probes, respectively. When compared to linear regression random forest, and support vector regression (SVR) models, the proposed artificial neural network (ANN) model exhibited superior precision, demonstrating R2 values of 0.963, 0.976, 0.991, and 0.970 for the training set, test set, validation set, and entire dataset, respectively. Validation with ten spectral groups reported an average error of 244 µg L-1. SIGNIFICANCE: The essence of our study lies in its capacity to address a persistent challenge encountered by traditional multiple competitive SERS aptasensors - the interference generated by uncontrollable SERS "hot spots" that hinders simultaneous quantification. The accuracy of the predictive model for simultaneous detection of two target substances was significantly improved using machine learning tools. This innovative technique offers promising avenues for the accurate and high-sensitive simultaneous detection of multiple food and environmental contaminants.

Data fusion of near-infrared and Raman spectroscopy: An innovative tool for non-destructive prediction of the TVB-N content of salmon samples.

Total volatile basic nitrogen (TVB-N) serves as a crucial indicator for evaluating the freshness of salmon. This study aimed to achieve accurate and non-destructive prediction of TVB-N content in salmon fillets stored in multiple temperature settings (-20, 0, -4, 20 °C, and dynamic temperature) using near-infrared (NIR) and Raman spectroscopy. A partial least square support vector machine (LSSVM) regression model was established through the integration of NIR and Raman spectral data using low-level data fusion (LLDF) and mid-level data fusion (MLDF) strategies. Notably, compared to a single spectrum analysis, the LLDF approach provided the most accurate prediction model, achieving an R2P of 0.910 and an RMSEP of 1.922 mg/100 g. Furthermore, MLDF models based on 2D-COS and VIP achieved R2P values of 0.885 and 0.906, respectively. These findings demonstrated the effectiveness of the proposed method for precise quantitative detection of salmon TVB-N, laying a technical foundation for the exploration of similar approaches in the study of other meat products. This approach has the potential to assess and monitor the freshness of seafood, ensuring consumer safety and enhancing product quality.

Multifunctional metal-organic framework-enhanced sodium alginate-based intelligent indicator: Mechanism and application for freshness monitoring.

Intelligent food packaging has recently gained significant attention due to the heightened consumer awareness regarding food quality. Although anthocyanins avoid safety issues, the instability and leakage of anthocyanins restrict their utilization in freshness indicator labels. In this study, we introduced an innovative metal-organic framework (UiO-66-NH2) synergistic pH-colorimetric label with fast ammonia-responsive, incorporating sodium alginate, red cabbage anthocyanin, and UiO-66-NH2. The cross-linked sodium alginate substrate enabled the label to possess superior insolubility. The microscopic morphology of the labels was intricately analyzed, while their sensitivity was rigorously tested utilizing ammonia as a representative gas. Due to the remarkable UV absorption capability of UiO-66-NH2 and various molecular interactions with anthocyanins, the label exhibited good UV absorption, enhanced stability, and optimized performance in reducing anthocyanin leakage, ensuring the stability and effectiveness of the labels in practical applications. The prepared label exhibited good specificity for volatile amines and ammonia gases, and robust anti-interference properties, enabling visualization and early detection of shrimp spoilage during storage at different temperatures. The strategy employed in this study presents promising new possibilities for developing intelligent packaging solutions for food products.

The effect of fish matrix on the enzyme-linked immunosorbent assay of antibiotics.

BACKGROUND: The matrix effect is considered to be a problem in the immunoassay of foodstuffs. However, information on the interference from aquatic products, as well as the mechanism involved, is very limited. In this study, using three flatfishes (Scophthalmus maximus, Paralichthys olivaceus and Cymoglossus robustus) as samples, the effect of the fish matrix on the competitive indirect enzyme-linked immunosorbent assay (ci-ELISA) of antibiotic (norfloxacin) residues was investigated. The mechanism of the observed matrix effect is also preliminarily discussed. RESULTS: Within the working range of the calibration curves, a significant (P = 0.05) but irregular variation in the inhibition ratio was observed in the presence of fish extracts. Further experiments revealed that such a matrix effect could be caused by some water-soluble fish proteins with a wide range of molecular weight (from below 14.4 kDa to about 116.0 kDa), and the ions from fish muscles may also contribute to the interference. The results of western blotting indicated that some fish protein components might effectively bind with antibody reagents used. CONCLUSION: Significant interference in the immunoassay of norfloxacin was observed in the presence of fish matrix. Some proteins and ions were demonstrated to contribute to the matrix effect investigated. Although the detailed mechanism is still unclear, the non-specific interaction between fish proteins and immunoglobulin G (IgG) or horseradish peroxidase (HRP) labelled IgG was assumed to be an important source of the matrix effect in immunoassays.