Paraquat is a widely used herbicide for controlling weeds and grasses in agriculture, and its contaminated residues in agricultural areas are of increasing concern. This work reports the development of the sensitive and easy‐to‐use colorimetric aptasensor for screening paraquat residues in agricultural soil. The short DNA fragments derived from the original aptamer were analyzed for their capability to interact with paraquat by molecular dynamic simulation. The paraquat‐aptasensor was developed using the selected DNA fragment and gold nanoparticles. Its limit of detection (LOD) for paraquat is 2.76 nM, which is more sensitive than the aptasensor with long‐length aptamer (LOD = 12.98 nM). The developed aptasensor shows the selectivity to paraquat, but not to other tested herbicides; ametryn, atrazine, difenzoquat, 2,4‐D‐dimethyl ammonium, and glufosinate. The recovery rates of paraquat detection in the spiked soil samples were in a range of 99.5%–105.1%, with relative standard deviation values of <4%. The developed aptasensor was used to screen for paraquat residues in agricultural soils, and three out of 23 soil samples were tested positive for paraquat, which was confirmed by a high‐performance liquid chromatography analysis. These results suggested the potential application of the developed aptasensor to detect paraquat residues in agricultural sites.

Trace of 17β‐estradiol (E2) contamination in food has been a concern for its negative impacts on human health, leading to the need for an E2‐monitoring system. This work reported a new simple, sensitive, and colorimetric E2 detection based on the designed repetitive‐loop aptamer and gold nanoparticles (AuNPs). The designed aptamers (L2–L5) exhibited a higher binding capability to E2 than the original truncated aptamer (L1). Although L3–L5 aptamers exhibited the highest binding capability, only L3‐aptasensor demonstrated the sensitive detection of E2 in a range of 0.05−0.8 nM, with the limit of detection at 13.1 pM. The developed L3‐aptasensor was 7.7‐folds more sensitive for E2 detection than the L1‐aptasensor. It selectively detected E2, but not the other tested chemicals with similar structures: progesterone, genistein, diethylstilbestrol, bisphenol A, and chloramphenicol. The L3‐aptasensor efficiently detected E2 spiked in milk samples within the precision acceptance criterion of recovery rates (100.1%−113.0%) and the relative standard deviations (5.24%−11.06%). These results demonstrated the development of a new aptasensor based on the designed repetitive‐loop aptamer that could enhance E2‐detection sensitivity and be potentially used for detecting E2 in milk samples with high accuracy and reliability.

The contamination of paraquat in vegetables is widely connected with human health risks, leading to the research interest in developing a paraquat sensing system. This work reports a simple detection method of paraquat based on the electrostatic interaction of paraquat and the negatively charged gold nanoparticles (AuNPs), resulting in the changes of colors from red to blue and the shifting of localized surface plasmon resonance (LSPR) peaks of AuNPs. The limit of detection concentration (C LOD ) of this system was 100 μM paraquat. Moreover, among eight cationic salts tested, NaCl was selective to enhance the detection sensitivity of the system, resulting in the reduction of C LOD to 0.10 μM. This system selectively detected paraquat, but not other tested herbicides (ametryn, atrazine, glyphosate, and 2,4-D-dimethyl ammonium). The paraquat-spiking experiment in kale demonstrated the significant recovery rate of paraquat at 96.0-103.0%, and the relative standard deviations were less than 4%. The developed system was efficient for screening contaminated paraquat in vegetables under unwashed and washed conditions. Three out of five unwashed vegetables had a significant level of paraquat as determined by LSPR values. These results suggested the potential application of this system for a simple screening of contaminated paraquat in vegetables.• Simple paraquat-screening system was developed based on the negatively charged gold nanoparticles.• The limit of paraquat detection of this system was 0.10 μM.• This system was potentially used for a simple screening of contaminated paraquat in vegetables.

Paraquat has been widely used in agriculture due to its efficient herbicidal activity. However, its remaining residues in the environment have caused eco-toxicity to live organisms and humans. Therefore, a portable and sensitive sensing system is required for field-monitoring paraquat towards eco-friendly usage. Toward this goal, citrate-capped silver nanoparticles (AgNPs) on a microfluidic paper analytic device (µPAD) were used to detect paraquat, accompanied by smartphone detection. Capillary action through paper fibers enabled the distribution of pre-loaded AgNPs across paper microfluidic channels and allowed rapid citrate-paraquat binding, which led to rapid, reproducible, and sensitive detection of paraquat. Full extents of color changes were recorded within 1 min using a smartphone camera, using only 2 µL samples. The assay's linear range was from 2.5 to 20 ppm, and the limit of detection was 2.3 ppm (8.94 µM) paraquat. Successful selectivity was also demonstrated using several different ions and herbicides, without substantial non-specific aggregation. Moreover, paraquat was further assayed with co-existing ions and field water samples, with satisfactory analytical recoveries of 95−117%, demonstrating its potential application towards on-site and field-ready assay of paraquat.