Development of Sandwich Double-Competitive ELISA for Sulfonamides. Comparative Analytical Characteristics and Matrix Effect Resistance

Development of alkaline phosphatase-linked single-chain variable fragment fusion proteins for one-step immunodetection of deoxynivalenol in cereals

Deoxynivalenol (DON) is a mycotoxin that widely distributes in various foods and seriously threatens food safety. To minimize the consumers' dietary exposure to DON, there is an urgent demand for developing rapid and sensitive detection methods for DON in food. In this study, a bifunctional single-chain variable fragment (scFv) linked alkaline phosphatase (ALP) fusion protein was developed for rapid and sensitive detection of deoxynivalenol (DON). The scFv gene was chemically synthesized and cloned into the expression vector pET25b containing the ALP gene by homologous recombination. The prokaryotic expression, purification, and activity analysis of fusion proteins (scFv-ALP and ALP-scFv) were well characterized and performed. The interactions between scFv and DON were investigated by computer-assisted simulation, which included hydrogen bonds, hydrophobic interactions, and van der Waals forces. The scFv-ALP which showed better bifunctional activity was selected for developing a direct competitive enzyme-linked immunosorbent assay (dc-ELISA) for DON in cereals. The dc-ELISA takes 90 min for one test and exhibits a half inhibitory concentration (IC50) of 11.72 ng/mL, of which the IC50 was 3.08-fold lower than that of the scFv-based dc-ELISA. The developed method showed high selectivity for DON, and good accuracy was obtained from the spike experiments. Furthermore, the detection results of actual cereal samples analyzed by the method correlated well with that determined by high-performance liquid chromatography (R2=0.97165). These results indicated that the scFv-ALP is a promising bifunctional probe for developing the one-step colorimetric immunoassay, providing a new strategy for rapid and sensitive detection of DON in cereals.

On-line preconcentration and determination of sulfadiazine in food samples using surface molecularly imprinted polymer coating by capillary electrophoresis

In this study, on-line preconcentration and selective determination of the trace sulfadiazine (SDZ) existing in milk and hen egg white samples were realized by the capillary electrophoresis using molecularly imprinted polymer (MIP) coated capillary. The capillary coated with MIP was firstly prepared through the surface imprinted techniques, using SDZ as template molecule and dopamine as function monomer and crosslinker, and then amine-terminated poly(2-methyl-2-oxazoline) (PMOXA-NH₂) was introduced onto polydopamine layer to reduce the non-specific adsorption. Successful preparation of SDZ-MIP-PMOXA coating was verified by zeta potential, as well as water contact angle. The SDZ-MIP-PMOXA coated capillary performed well on-line preconcentration of SDZ and the obtained peak area of SDZ was 46 times higher than that one obtained in bare capillary using the same procedure. Then the proposed on-line preconcentration method was fully validated and displayed good linear behavior in the concentration from 5.0 to 100.0 ng/mL, with the limit of detection was low to 1.5 ng/mL; and this method presented excellent accuracy and robustness. The prepared SDZ-MIP-PMOXA coated capillary also showed high selectivity with the imprinting factor of 5.85 and good repeatability during five consecutive runs with the relative standard deviation value of peak area was 1.6%. At last, the application of the prepared SDZ-MIP-PMOXA coated capillary in the detection of SDZ in spiked food samples was investigated, and good recoveries of 98.7-109.3% were obtained.

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.

Development of ELISA formats for polymyxin B monitoring in serum of critically ill patients

Treating infections in critically ill patients often requires the use of last-line antibacterial drugs such as polymyxins with a narrow therapeutic window and high toxicity. In critically ill patients, the drug pharmacokinetics changes significantly, and as a result, the antibiotic concentrations in blood and infection foci become suboptimal, which leads to therapeutic failures or toxic manifestations. For timely dosage adjustments, a competitive ELISA-based method using antibodies to polymyxin В (PMB) was developed. Among the several considered assays, a direct antibody-coated format was selected for its short duration (1.5 h) and the best agreement with the LC-MS/MS data (R² = 98 %). The assay dynamic measurement range (IC₂₀-IC₈₀) could be substantially shifted by changing the ratio of immunoreagents. To conveniently measure the therapeutic range of PMB concentrations, it was adjusted to 5.0-192 ng/mL, allowing the samples to be analyzed after a simple 100-fold dilution with the assay buffer. The ELISA sensitivity expressed in half-inhibition concentration (IC₅₀) and the limit of detection were 30.6 and 1.8 ng/mL, respectively. The assay cross-reactivity towards the related analogue colistin (COL) was 95 %, and this compound could also be adequately quantified by the same assay. The PMB and COL recovery from the spiked serum samples was similar and constituted 98-109 %. The trial drug monitoring was carried out in 3 patients with Gram-negative sepsis, and the established pharmacokinetic profiles of PMB revealed the necessity for individual dosage adjustment.

Simultaneous immunodetection of ionophore antibiotics, salinomycin and narasin, in poultry products and milk

Rabbit polyclonal antibodies were generated against the ionophore antibiotic salinomycin (SAL) as a determinant of the BSA-SAL conjugate. The homologous ELISA format was found to be preferred for similar recognition of SAL and narasin (NAR) with IC₅₀ values of 0.55 and 0.57 ng mL^-1, respectively. Both analytes could be determined in the range of 0.1-2.7 ng mL^-1 (IC₂₀-IC₈₀) with a detection limit of 0.03 ng mL^-1. To analyze matrices, individual pretreatment of samples was required. For chicken muscles, simple buffer extraction was sufficient to recover 87-110% of ionophores. Extraction with acetonitrile followed by evaporation of the solvent was best for recovering 67-108% SAL and NAR from egg homogenate. A feature of the extraction of ionophores from milk was the elimination of fat-mediated interference by organic solvation. It was found that the absence of Na⁺ and K⁺ ions during reconstitution of sample extracts was a key factor contributing to the increase in the average recovery of ionophores from 32% to 93%. Thanks to this special pretreatment and improved recovery, the developed immunoassay method was suitable for the analysis of ionophore antibiotics SAL and NAR in a milk matrix, which has not been previously reported.