Abstract
The protein mucin1 (MUC1) is an attractive target for cancer biomarkers because it is overexpressed in most adenocarcinomas. In this study, we exploited a MUC1-binding aptamer (AptMUC1) as a targeting agent for nanoparticle-based imaging systems coupled with laser desorption/ionization mass spectrometry (LDI-MS). We found that AptMUC1-conjugated gold nanoparticles immobilized, through hydrophobic and π–π interactions, on graphene oxide (AptMUC1–Au NPs/GO) bound effectively to MUC1 units on tumor cell membranes. The ultrahigh density and high flexibility of AptMUC1 on the GO surface enhanced the platform’s cooperative and multivalent binding affinity for MUC1 on cell membranes. After we had labeled MUC1-overexpressing MCF-7 cells (human breast adenocarcinoma cell line) with AptMUC1–Au NPs/GO, we used LDI-MS to monitor Au cluster ions ([Aun]+; n = 1–3), resulting in the detection of as few as 100 MCF-7 cells. We also employed this AptMUC1–Au NPs/GO–LDI-MS system to analyze four different MUC1 expression cell lines. In addition, the AptMUC1–Au NPs/GO platform could be used further as a labeling agent for tumor tissue imaging when coupled with LDI-MS. Thus, Apt–Au NPs/GO can function as a highly amplified signal transducer through the formation of large Au clusters ions during LDI-MS analysis.
Highlights
Biological imaging enables the morphological features of organs to be correlated with pathological symptoms; this process is important for finding biomarkers and subsequently using them for the diagnosis of diseases[1]
We found that graphene oxide (GO) modified with Mucin[1] (MUC1) binding aptamer– conjugated gold nanoparticles (AptMUC1–Au NPs/GO) coupled with laser desorption/ionization mass spectrometry (LDI-mass spectrometry (MS)) is a facile platform for the detection of tumor cells and for tissue imaging (Fig. 1)
Atomic force microscopy (AFM) and transmission electron microscopy (TEM) images revealed that the average size of a single-layer GO was approximately 235 nm
Summary
Using our AptMUC1–Au NPs/GO–LDI-MS detection system, we observed an apigenin-induced downregulation of MUC1 expression: the intensity of the [Au1]+ signals decreased upon increasing the concentration of apigenin used for treatment of the MCF-7 cells (Fig. 4a). This downregulation of MUC1 in MCF-7 cells was consistent with the results of western blotting (Fig. 4c), revealing that our LDI-MS–based assay has great potential for use in the analysis of membrane protein expression levels after labeling with functional Au NPs. Compared with western blotting analysis, our assay is relatively simple, sensitive, and capable of high throughput. This high-throughput LDI-MS imaging system has great potential for the diagnosis of cancer
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