Dispersive solid-phase extraction and immunoassay with internal reference calibration using fatty acid-coated inorganic fluorescent nanoparticles.

Dispersive solid-phase extraction (dSPE) using fatty acid-coated Eu2O3 nanoparticles (NPs) was developed, and a direct immunoassay was carried out employing these NPs as support. Secondary antibodies labeled with fluorophore groups were used as reporters, and the intrinsic optical properties of the Eu2O3 NPs were employed as an internal calibration of the detection system. The methodology was optimized for both dSPE—NP amount, sample volume, extraction time, ionic strength, and pH—and immunoassay–immunoreagent concentrations, ionic strength, and incubation time. As proof of concept, the methodology was applied to the bovine serum albumin (BSA)/anti-BSA system, and precision of the method was between 5% and 17% with an IC50 of 100nM. Then, water samples with high saline content (sea water) were assayed to observe the matrix effect, and average recoveries (n=3) between 78% and 108% were obtained, demonstrating the reliability of the developed analytical method. Finally, the simultaneous dSPE–immunoassay methodology was applied to other compounds with very different chemical characteristics such as an oligonucleotide, the antibiotic sulfamerazine, and the pesticide chlorpyriphos. Although the IC50 values for sulfamerazine were approximately 2400nM, satisfactory standard curves were obtained. However, poor reproducibility and sensitivity results were obtained for the oligonucleotide and chlorpyriphos preliminary assays.