Detection of CEA in human serum using surface-enhanced Raman spectroscopy coupled with antibody-modified Au and γ-Fe₂O₃@Au nanoparticles

Highlights

• A rapid and simple SERS method to detect CEA was developed with high selectivity.

• The method built was successfully applied to the determination of CEA in healthy and patients’ serum

• The detection results of CEA in real samples by the present method were in accordance with those by ECLI.

Abstract

In this present work, a rapid and simple method to detect carcinoembryonic antigen (CEA) was developed by using surface-enhanced Raman spectroscopy (SERS) coupled with antibody-modified Au and γ-Fe₂O₃@Au nanoparticles. First, Au@Raman reporter and γ-Fe₂O₃@Au were prepared, and then modified with CEA antibody. When CEA was present, the immuno-Au@Raman reporter and immuno-γ-Fe₂O₃@Au formed a complex through antibody-antigen-antibody interaction. The selective and sensitive detection of CEA could be achieved by SERS after magnetic separation. Under the optimal conditions, a linear relationship was observed between the Raman peak intensity and the concentration of CEA in the range of 1–50 ng mL⁻¹ with an excellent correlation coefficient of 0.9942. The limit of detection based on two times ratio of signal to noise was 0.1 ng/mL. The recoveries of CEA standard solution spiked with human serum samples were in the range of 88.5–105.9% with the relative standard deviations less than 17.4%. The method built was applied to the detection of CEA in human serum, and the relative deviations of the analysis results between the present method and electrochemiluminescence immunoassay were all less than 16.6%. The proposed method is practical and has a potential for clinic test of CEA.

Introduction

Colorectal cancer is classified as a common gastrointestinal malignancy, and ranks secondly in the causes of death in America. There is also a high incidence of colorectal cancer in North America and Western Europe. The mortality of colorectal cancer has got the fifth place of the total cancers in China, and has been rising in recent years. Early diagnosis of colorectal cancer is particularly important to the survival of patients due to the unknown etiology of colorectal cancer. Carcinoembryonic antigen (CEA) is a specific marker for colorectal cancer, and has been widely accepted as a diagnostic adjunct to colorectal cancer [1], [2], [3]. Various methods to detect CEA have been reported, such as polymerase chain reaction that requires a cumbersome process like signal amplification or labeling [4], [5], and electrochemiluminescence immunoassay (ECLI). Now, ECLI is normally used to determine CEA in hospital tests. However, there are still some defects for ECLI, such as time-consuming and false positive results. So, it is very necessary to improve the method of detecting CEA.

Many literatures have reported a lot of modified magnetic nanoparticles used in the diagnosis, treatment and other areas. In 2012, Mariana et al. used anti-CEA loaded maghemite nanoparticles as a diagnostic device for colorectal cancer [6]. Santos et al. used amphotericin B wrapped magnetic nanoparticles to detect the fungal infection in mice lungs [7]. In 2015, Ferreira et al. assessed the physicochemical properties of the surface-functionalized magnetic nanoparticles [8].

Recently, surface enhanced Raman spectroscopy (SERS) labeled immunoassay has been paid more and more attentions. Since it was discovered in 1974 [9], SERS has been one of the most widely pursued spectroscopic tools for identification and detection of biological species with the integration of high sensitivity, unique spectroscopic fingerprint, and nondestructive data acquisition [10], [11]. Rohr et al. used goat anti-mouse and goat anti-rabbit immunoglobulin labeled with Raman report to detect mouse and rabbit immunoglobulin [12]. Hwang et al. used a sandwich immunoassay based on SERS to detect alphafetoprotein, a kind of tumor marker [13]. Typically, SERS often uses a standard sandwich immunoassay structure. In 2009, Chon et al. developed a SERS-based immunoassay technique to detect CEA, using hollow gold nanospheres as a SERS-active substrate and magnetic beads as a separation technique, without the need of the assembly of standard structure onto a solid surface [14]. Although this method is quick and reproducible, it is very difficult to prepare the hollow gold nanoparticles, and this method was not used to determine CEA in real samples.

Herein, we developed a simple and rapid SERS method to detect CEA through easily preparing Au nanoparticles (AuNPs) coupled with magnetic core-shell AuNPs. The method was validated and made a partial least square analysis by TQ Analyst software, and finally applied to the detection of CEA in health and patients’ serum with satisfactory results.