Anti-nucleolin aptamer mediated specific detection of cancer cells by Localized Surface Plasmon Resonance-based U-bent optical fiber

Abstract

The detection of Circulating Tumor Cells (CTCs) is of profound importance for cancer diagnosis and monitoring in diseased patients. In the presented work, an aptasensor for CTC detection was developed using AS1411 aptamer specific for nucleolin on cancer cells’ surface as receptor on Gold NanoParticles (GNPs) decorated U-bent optical fiber. The aptamer binds to target upon folding into a parallel G-quadruplex structure, and therefore, components of folding and running buffer were optimized to 50 mM tris buffer and 100 mM KCl with and without 5 mM Mg+2 based on Circular Dichroism spectroscopy (CD) and bright field microscopy respectively. Further, the binding of aptamer and MCF-7 cells to GNP coated U-bent fiber were validated by fluorescence microscopy. The aptasensor showed significantly higher absorbance for 104 cancer cells (retinoblastoma, meningioma, breast, cervical, and colon cancer cells) as compared to non-cancer cells (MCF-10A and WBCs) with a t-test p-value of 0.0012. On an optical bench, aptasensor was able to detect as low as 500 cells/mL. To develop a portable and small CTC detection system, aptasensor was integrated with a hand-held opto-electronic device μSens (custom developed in our lab) and was able to detect 50 cells/mL. This is the first time a portable sensing system based on U-bent optical fiber was tested for sensing cancer cells. The ability to detect diverse types of cancer cells by AS1411 aptamer is promising and paves the way for the detection of circulating tumor cells in blood samples, with relative ease and low cost.