Boronic acid recognition based-gold nanoparticle-labeling strategy for the assay of sialic acid expression on cancer cell surface by inductively coupled plasma mass spectrometry

Sialic acids are special sugars widely expressed at the termini of glycan chains on the cell surface, and their expression level on the cancer cell surface is much higher than on the normal cell surface. Herein, we reported an inductively coupled plasma mass spectrometry (ICP-MS) based method with elemental tags for the analysis of sialic acids on the cancer cell surface. The method is based on the selective recognition of sialic acids by biotinylated phenylboronic acid (biotin-APBA) at physiological pH and signal enhancement of gold nanoparticles (AuNPs) in ICP-MS when AuNPs were used as elemental tags labeled on biotin-APBA. A specificity test reveals that the proposed method has high specificity towards cancer cells. Taking HepG2 and MCF-7 cells as two model cancer cells, competitive experiments were performed to estimate the expression level of sialic acids on the cancer cell surface, and it was found that the average numbers of sialic acids expressed on the single MCF-7 and HepG2 cell surface were 7.0 x 10(9) and 5.4 x 10(9), respectively. With sialic acid as the biomarker for cancer cells, the method was further used for cell detection. The limits of detection in terms of cell number for HepG2 and MCF-7 cells were 120 and 64, respectively. And the relative standard deviations for nine replicate determinations of ca. 1000 HepG2 and MCF-7 cells were 9.6% and 8.9%, respectively. The linear ranges for HepG2 cells and MCF-7 cells were 300-10 000 and 170-11 000, respectively. The proposed approach is sensitive as well as selective for the analysis of sialic acids on the cancer cell surface, and is potentially applicable for the study of tumor malignancy and metastasis, which is helpful for biological research and clinical diagnostics.