Sensitive enzyme immunoassay for screening methandienone in dietary supplements

Isolation of atrazine nanobodies enhanced by depletion of anti-carrier protein phages and performance comparison between the nanobody and monoclonal antibody derived from the same immunogen

Nanobody, a single domain antibody, has been shown a great promise for immunoassay (IA) applications. To improve the panning efficiency so as to obtain a valuable nanobody, anti-carrier protein phages in a phage display library were depleted to enhance the selection of nanobodies against the herbicide atrazine by using immunomagnetic beads conjugated with bovine serum albumin (IMB-BSA). The depletion of anti-carrier protein phages from the atrazine phage display library tripled the number of atrazine positive phage clones after four rounds of panning. One of the most sensitive phage clones Nb3 selected from the IMB-BSA depleted library was used to compare the performance with the monoclonal antibody (mAb 5D9) developed from the same immunogen. The Nb3-based IA exhibited similar specificity with the mAb 5D9-based IA, but greater thermostability and organic solvent tolerance. The half-maximum inhibition concentration (IC₅₀) of the former was 3.5-fold greater than that of the latter (36.7 ng/mL versus 10.2 ng/mL). Because the Nb3-based IA was more robust than the mAb 5D9-based IA, the method detection limit of the two assays was 7.8 ng/mL of atrazine in river samples. The depletion strategy can increase the chance to acquire high quality nanobody and can be applicable for effective development of nanobodies against other small molecules.

Advances in the Determination of Anabolic-Androgenic Steroids: From Standard Practices to Tailor-Designed Multidisciplinary Approaches

Anabolic-androgenic steroids (AASs), a group of compounds frequently misused by athletes and, unfortunately, also by the general population, have lately attracted global attention; thus, significant demands for more precise, facile, and rapid AAS detection have arisen. The standard methods ordinarily used for AAS determination include liquid and gas chromatography coupled with mass spectrometry. However, good knowledge of steroid metabolism, pretreatment of samples (such as derivatization), and well-trained operators of the instruments are required, making this procedure expensive, complicated, and not routinely applicable. In the drive to meet current AAS detection demands, the scientific focus has shifted to developing novel, tailor-made approaches leading to time- and cost-effective, routine, and field-portable methods for AAS determination in various matrices, such as biological fluids, food supplements, meat, water, or other environmental components. Therefore, herein, we present a comprehensive review article covering recent advances in AAS determination, with a strong emphasis on the increasingly important role of chemically designed artificial sensors, biosensors, and antibody- and fluorescence-based methods.

Tailor-Made Immunochromatographic Test for the Detection of Multiple 17α-Methylated Anabolics in Dietary Supplements

In recent years, the undeclared presence of various anabolic androgenic steroids (AAS) in commercial supplements has been confirmed. This fact can be a potential threat to all athletes using these supplements, and therefore, there is of increased interest in the implementation of rapid methods for the detection of AAS. The presented study describes the development of an immunostrip test for the detection of multiple 17α-methylated AAS based on direct and indirect competitive principle using gold nanoparticles as a label. As a capture reagent on test lines conjugated stanazolol to rabbit serum albumin (RSA/ST-3) was used, the intensity of color formed in the test line of the AAS-positive sample was visually distinguishable from that of negative sample within 10 min. The optimized closed direct and indirect format of the test provided a similar visual detection limit (0.7 and 0.9 ng/mL, respectively). The most commonly orally abused AAS (17α-methyltestosterone, methandienone, methyldihydrotestosterone, oxandrolone and oxymetholone) showed a strong cross-reaction. Developed immunostrips were successfully applied to analysis of artificially contaminated dietary supplements with 17α-methylated AASs. The developed immunostrips offer potential as a useful user-friendly method for capturing suspicious dietary supplement samples with different contents of AAS at levels far below the usually used concentrations of AAS.

Highly specific nanobody against herbicide 2,4-dichlorophenoxyacetic acid for monitoring of its contamination in environmental water

2,4-dichlorophenoxyacetic acid (2,4-D), a widely used herbicide, is a small organic chemical pollutant in the environment. To develop a nanobody-based immunoassay for monitoring trace levels of 2,4-D, a step-wise strategy for the generation of nanobodies highly specific against this small chemical was employed. Firstly, we synthesized three novel haptens mimicking 2,4-D and assessed their influence on the sensitivity and specificity of the existing antibody-based assay. Polyclonal antibodies (pAb) from rabbits showed good sensitivity and moderate specificity for 2,4-D, pAb from llama based on selected haptens showed similar performance when compared to those from rabbits. Secondly, nanobodies derived from llama were generated for 2,4-D by an effective procedure, including serum monitoring and one-step library construction. One nanobody, NB3-9, exhibited good sensitivity against 2,4-D (IC₅₀ = 29.2 ng/mL) had better specificity than the rabbit pAb#1518, with no cross-reactivities against the 2,4-D analogs tested. Thirdly, one-step fluorescent enzyme immunoassay (FLEIA) for 2,4-D based on a nanobody-alkaline phosphatase (AP) fusion was developed with IC₅₀ of 1.9 ng/mL and a linear range of 0.4-8.6 ng/mL. Environmental water samples were analyzed by FLEIA and LC-MS/MS for comparison, and the results were consistent between both methods. Therefore, the proposed step-wise strategy from hapten design to nanobody-AP fusion production was successfully conducted, and the resulting nanobody based FLEIA was demonstrated as a convenient tool to monitor 2,4-D residuals in the environment.