Development of competitive and noncompetitive lateral flow immunoassays for pendimethalin using synthetic peptides

Dimer peptidomimetics-based non-toxic immunoassay for bongkrekic acid in food and biosamples compatible with smartphone demonstration

Non-toxic immunoassays are effective analytic methods that offer enhanced safety and cost efficiency by substituting toxins with peptidomimetics. Bongkrekic acid (BA), a highly lethal bacterial toxin, has recently garnered significant attention due to its toxicity. This work isolated a phage-borne peptide (CFSFQVGDC) with a strong binding affinity to an anti-BA monoclonal antibody (mAb) from a peptide phage library. Monomer and dimer peptidomimetics were synthesized to achieve a phage-free peptide. ELISA revealed a detection sensitivity of 0.63 ng/mL for the dimer, which is 120-fold higher than that of the monomer. Meanwhile, computer-aided simulations revealed that the enhancement of the hydrogen bonding network of the dimer was the key factor driving its stronger binding affinity. Then, a sensitive immunochromatographic assay (ICA) based on the dimer peptidomimetic was developed to detect BA, compatible with smartphone demonstration. The visible limit of detection (vLOD) was 2.50 μg/kg, while the quantitative limit of detection (qLOD) was 0.12 μg/kg. The recovery rates for real samples, including blood and urine, ranged from 85.00 % to 115.20 %, consistent with standard LC-MS/MS. Importantly, the dimer restored binding capacity to levels comparable to the native toxin, laying a robust foundation for further optimization of toxin-free peptide designs via directed evolution. The developed ICA platform also provided an alternative method for the non-toxic, sensitive, and on-site detection of BA.

Preparation of peptides against immunocomplex of deltamethrin and application in noncompetitive lateral flow immunoassay

Lateral flow immunoassay (LFIA) has the advantages of simplicity and rapidness, and is widely used for the rapid detection of pesticides and other analytes. However, small molecule compounds such as pesticides are often analyzed using competitive LFIA (CLFIA), whose sensitivity often does not meet the actual needs. In this study, a noncompetitive LFIA (NLFIA) for deltamethrin (DM) with high sensitivity was developed by using anti-immunocomplex peptides (AIcPs). A total of 21 unique AIcPs were identified through the screening of phage-displayed cyclic peptide libraries. The AIcP containing the CYFDGAWYAC sequence in noncompetitive phage enzyme-linked immunosorbent assays (P-ELISA) exhibited a half signal saturation concentration (SC50) of 1.49 ng/mL, achieving a remarkable 209-fold sensitivity enhancement compared to antigen-based competitive ELISA. The AIcP, in the form of CYFDGAWYACGGGSSK-biotin, was synthesized to prepare AIcP-conjugated gold nanoparticles (AuNPs) by reacting with streptavidin (SA)-labeled AuNPs and subsequently assembled into the NLFIA strip. After optimization, the NLFIA achieved a visual limit of detection (vLOD) of 6.25 ng/mL in Tris-HCl buffer and 0.5 mg/kg in wheat, Chinese cabbage, and celery within 8 min. Furthermore, NLFIA detection results for blind wheat samples matched those of a reference liquid chromatography method.

Formation of anisotropic nanoparticle structure for nanoplasmonic biosensing

A novel anisotropic nanoparticle structure consisting of a single gold nanorod and nanospheres is designed. The optical properties, especially the scattering under polarized light, are studied. The signal readout is conducted using dark-field microimaging techniques in a microfluidic chip. The formation of this novel structure is induced by the intermediate biomolecules. Therefore, it demonstrates potential applications in the ultrasensitive detection of biomarkers. As an example, the detection of vascular endothelial growth factor (VEGF165) is demonstrated, and the specificity is also investigated. This unique approach not only effectively reduces background interference but also provides a new approach for accurate sensing of targeted tumor markers.

Development of a gold nanoparticle-based lateral flow immunochromatographic assay for the rapid and quantitative detection of thymidine kinase 1 in human serum

Thymidine kinase 1 (TK1) is a marker of cell proliferation that can be used for early screening, treatment monitoring, and evaluating the prognosis of patients with tumors. The main purpose of this study was to develop clinically applicable TK1 antibodies, establish an appropriate detection method, and provide material and technical support for the research and clinical application for different types of tumors. Experimental mice were immunized with the C-terminal 31 peptide of human TK1 to screen monoclonal cell lines capable of stably secreting specific antibodies. Monoclonal antibodies were then prepared, purified and screened for optimal pairing following the identification of purity and isotype. Finally, based on the principles adopted by the double-antibody sandwich detection method, we constructed a lateral flow immunochromatographic assay (LFIA) to quantify the concentration of TK1 in serum samples when using a gold nanoparticle-labeled anti-TK1 monoclonal antibody as a probe. The limit of detection for TK1 in serum was 0.31 pmol/L with a detection range of 0.31-50 pmol/L. The spiked recoveries ranged from 97.7% to 109.0% with an analytical precision of 5.7-8.2%; there was no cross-reactivity with common proteins in the serum. The established LFIA also exhibited good consistency with commercially available chemiluminescent immunoassay kits for the detection of clinical samples. The LFIA developed in this study has the advantages of high sensitivity, accuracy, reproducibility and strong specificity, and provides a new technical tool for the quantitative detection of TK1.