Development of a Homologous Fluorescence Polarization Immunoassay for Diisobutyl Phthalate in Romaine Lettuce

A review on solution- and vapor-responsive sensors for the detection of phthalates

Phthalic acid esters, largely referred to as phthalates, are today acknowledged as important pollutants used in the manufacture of polyvinyl chloride (PVC)-based plastics, whose use extends to almost every aspect of modern life. The risk of exposure to phthalates is particularly relevant as high concentrations are regularly found in drinking water, food-contact materials and medical devices, motivating an immense body of research devoted to methods for their detection in liquid samples. Conversely, phthalate vapors have only recently been acknowledged as potentially important atmospheric pollutants and as early fire indicators; additionally, deposition of these vapors can pose significant problems to the proper functioning of spacecraft and diverse on-board devices, leading to major space agencies recognizing the need of developing vapor-responsive phthalate sensors. In this manuscript we present a literature survey on solution- and vapor-responsive sensors and analytical assays for the detection of phthalates, providing a detailed analysis of a vast array of analytical data to offer a clear idea on the analytical performance (limits of detection and quantification, linear range) and advantages provided by each class of sensor covered in this review (electrochemical, optical and vapor-responsive) in the context of their potential real-life applications; the manuscript also gives detailed fundamental information on the various physicochemical responses exploited by these sensors and assays that could potentially be harnessed by new researchers entering the field.

Self-corrected dual-optical immunosensors using carbon dots@SiO2@MnO2 improving diethyl phthalate detection accuracy

The traditional immunoassay is widely used for pollutant detection and bioanalysis, but there are still some challenges in ensuring its sensitivity and reliable accuracy. Dual-optical measurement can prove mutual evidence to effectively improve the accuracy of the method by self-correction, which will overcome this problem. In this study, we developed a "visualization and sensing" dual-modal immunoassay based on blue carbon dots@SiO₂@MnO₂ (B-CDs@SiO₂@MnO₂) as "color and fluorescence" immunosensors. Here, MnO₂ nanosheets have the activity of simulating oxidase. 3,3', 5,5'-Tetramethylbenzidine (TMB) can be oxidized to TMB²⁺ under acidic conditions and the color of the solution from colorless to yellow. On the other hand, the MnO₂ nanosheets can quench the fluorescence of B-CDs@SiO₂. After adding ascorbic acid (AA), MnO₂ nanosheets were reduced to Mn²⁺, thereby the fluorescence of B-CDs@SiO₂ was restored. Under the optimum conditions, as the concentration of target substance (diethyl phthalate) increased from 0.05 to 100 ng/mL, the method showed a good linear relationship. The fluorescence measurement signal and the color change signal of the solution visualization support each other and give the information of the corresponding material content. The results of the dual-optical immunoassay maintain good consistency, which proves the accuracy of the developed dual-optical immunoassay for detection of diethyl phthalate is reliable. Additionally, it is demonstrated that the dual-modal method exhibits high accuracy and stability in the assays, pointing to a broad range of application prospects in pollutant analysis.

A sensitive bio-barcode immunoassay based on bimetallic Au@Pt nanozyme for detection of organophosphate pesticides in various agro-products

Organophosphate pesticides (OPs) are often used as insecticides and acaricides in agriculture, thus improving yields. OP residues may pose a serious threat, duetoinhibitionof the enzymeacetylcholinesterase(AChE). Therefore, a competitive bio-barcode immunoassay was designed for simultaneous quantification of organophosphate pesticide residues using AuNP signal amplification technology and Au@Pt catalysis. The AuNP probes were labelled with antibodies and corresponding bio-barcodes (ssDNAs), MNP probes coated with ovalbumin pesticide haptens and Au@Pt probes functionalized with the complementary ssDNAs were then prepared. Subsequently, pesticides competed with MNP probes to bind the AuNP probes. The recoveries of the developed assay were ranged from 71.26 to 117.47% with RSDs from 2.52 to 14.52%. The LODs were 9.88, 3.91, and 1.47 ng·kg^-1, for parathion, triazophos, and chlorpyrifos, respectively. The assay was closely correlated with the data obtained from LC-MS/MS. Therefore, the developed method has the potential to be used as an alternative approach for detection of multiple pesticides.

Fluorescence polarization immunoassay for the determination of diclofenac in wastewater

Pharmacologically active compounds are often detected in wastewater and surface waters. The nonsteroidal anti-inflammatory drug diclofenac (DCF) was included in the European watch list of substances that requires its environmental monitoring in the member states. DCF may harmfully influence the ecosystem already at concentrations ≤ 1 μg L-1. The fast and easy quantification of DCF is becoming a subject of global importance. Fluorescence polarization immunoassay (FPIA) is a homogeneous mix-and-read method which does not require the immobilization of reagents. FPIA can be performed in one phase within 20-30 min, making it possible to analyse wastewater without any complicated pre-treatment. In this study, new tracer molecules with different structures, linking fluorophores to derivatives of the analyte, were synthesized, three homologous tracers based on DCF, two including a C6 spacer, and one heterologous tracer derived from 5-hydroxy-DCF. The tracer molecules were thoroughly assessed for performance. Regarding sensitivity of the FPIA, the lowest limit of detection reached was 2.0 μg L-1 with a working range up to 870 μg L-1. The method was validated for real wastewater samples against LC-MS/MS as reference method with good agreement of both methods. Graphical abstract.

Development of an Ultrasensitive and Rapid Fluorescence Polarization Immunoassay for Ochratoxin A in Rice

Ochratoxin A (OTA) is a known food contaminant that affects a wide range of food and agricultural products. The presence of this fungal metabolite in foods poses a threat to human health. Therefore, various detection and quantification methods have been developed to determine its presence in foods. Herein, we describe a rapid and ultrasensitive tracer-based fluorescence polarization immunoassay (FPIA) for the detection of OTA in rice samples. Four fluorescent tracers OTA-fluorescein thiocarbamoyl ethylenediamine (EDF), OTA-fluorescein thiocarbamoyl butane diamine (BDF), OTA-amino-methyl fluorescein (AMF), and OTA-fluorescein thiocarbamoyl hexame (HDF) with fluorescence polarization values (δFP = FPbind-FPfree) of 5, 100, 207, and 80 mP, respectively, were synthesized. The tracer with the highest δFP value (OTA-AMF) was selected and further optimized for the development of an ultrasensitive FPIA with a detection range of 0.03-0.78 ng/mL. A mean recovery of 70.0% to 110.0% was obtained from spiked rice samples with a relative standard deviation of equal to or less than 20%. Good correlations (r² = 0.9966) were observed between OTA levels in contaminated rice samples obtained by the FPIA method and high-performance liquid chromatography (HPLC) as a reference method. The rapidity of the method was confirmed by analyzing ten rice samples that were analyzed within 25 min, on average. The sensitivity, accuracy, and rapidity of the method show that it is suitable for screening and quantification of OTA in food samples without the cumbersome pre-analytical steps required in other mycotoxin detection methods.