Immunoaffinity monolithic capillary microextraction coupled with ICP-MS for immunoassay with quantum dot labels

Abstract

A sensitive and selective method of immunoaffinity monolithic capillary microextraction (CME) based on a sandwich immunoreaction with quantum dots (QDs) labels coupled with micro-concentric nebulizer inductively coupled plasma mass spectrometry (MCN-ICP-MS) was proposed for the determination of antigen human IgG in human serum. Aminopropyltriethoxysilane (APTES)-silica hybrid monolithic capillary which was prepared by room temperature ionic liquid (RTIL)-mediated sol–gel method was immobilized with primary goat-anti-human antibody. After a complete immunoreaction among primary antibody, IgG antigen and secondary antibody labeled with CdSe QDs in monolithic capillary, the concentration of IgG was quantified by MCN-ICP-MS simultaneous analysis of Cd and Se released from captured QDs labels with an acid-dissolution (pH 2.0) step. With consumption of only 50 μL sample solution, the established method presented a limit of detection of 0.058 μg L⁻¹ based on the Cd signal and 0.097 μg L⁻¹ based on the Se signal for human IgG antigen, with the relative standard deviations (RSDs) of 7.2% based on the Cd signal and 13% based on the Se signal (c_{humanIgGantigen} = 5 μg L⁻¹, n = 7), respectively. The response of CME-MCN-ICP-MS method for human IgG was linear over a dynamic range from 0.2 to 10 μg L⁻¹ based on the Cd signal and from 0.5 to 10 μg L⁻¹ based on the Se signal, respectively. The proposed method was successfully applied for the determination of IgG in real human serum with good recoveries. For validation, the same sample was also analyzed by the commonly used clinical method of immunoturbidimetry, and the analytical result obtained by the proposed method is in good agreement with that the result obtained by immunoturbidimetry. By using CdSe QDs labels, the quantification of human IgG antigen could be performed by ICP-MS determination of both Cd and Se, and the analytical results for human IgG antigen could be validated in one run. The developed method was fast, sensitive, selective, versatile and could be easily extended to other protein quantification schemes as well as in DNA analysis.