(1) Background: Rapid on-site testing is an effective method for the detection of Escherichia coli O157: H7(E. coli O157: H7) in food ingredients and the environment. (2) Methods: In this study, we developed colorimetric loop-mediated isothermal amplification (LAMP) and immunochromatographic test strips (ICTs) for the rapid and visual detection of E. coli O157: H7. This study designed new specific LAMP primers for E. coli O157: H7 virulence island genes. After the LAMP amplification, the double-stranded DNA target sequence labeled with digoxin and fluorescein isothiocyanate (FITC) at both ends was bound to the anti-digoxin antibody on the gold nanoparticles. Subsequently, it was further bound to the anti-FITC antibody at the T line of the ICTs, forming a positive test result. Hydroxynaphthyl blue dye was directly added to the LAMP amplification product. A blue color indicated positive results, while a purple color indicated negative results. (3) Results: Two visualization methods showed high specificity for the target strains. The visualization tests had sensitivities of 5.7 CFU mL⁻¹, and the detection limit of the Escherichia coli O157: H7 in artificially contaminated milk samples was 5.7 × 10² CFU mL⁻¹, which was consistent with the results of the standard method (LAMP-electrophoresis method) used in commercial inspection. (4) Conclusions: Both methods could be useful in remote and under-resourced areas.

In order to improve the weak optical performance of gold nanoparticles and realize the signal amplification of lateral flow chromatography test strips, individual gold nanoparticles (AuNPs) were aggregated into gold nanoparticle aggregates through functional groups around polyamidoamine (PAMAM) dendrimers. A signal-amplified aptamer-based lateral flow chromatography test strip was constructed for the rapid determination of ochratoxin A (OTA). Under optimal conditions, the visual detection limit of this test strip was 0.4 ng mL⁻¹ and the semi-quantitative limit of detection (LOD) was 0.04 ng mL⁻¹. Compared with other traditional aptamer lateral flow chromatography test strips, its sensitivity was improved about five times. The whole test could be completed within 15 min. The aptamer-based strip was applied to the detection of OTA in red wine; the average recoveries ranged from 93% to 105.8% with the relative standard deviation (RSD) varying from 3% to 8%, indicating that the test strip may be a potentially effective tool for the on-site detection of OTA.