Nucleic Acid Aptamers-immobilized Nanoparticle Flexible Scaffolds And Their High Efficiency Capture For Circulating Tumor Cells

In this paper, anionic polyelectrolyte polyacrylic acid (PAA) has been used as cross-linking agent to build the rough surface of three layers of SiO2 nanoparticles on the glass substrate, and then connect PAA chemically to obtain three-layer-nanoparticle flexible scaffolds (FTLS). Flexible scaffolds modified by multiple aptamer (Apt-FTLS) have been successfully assembled by chemically connecting TD05 aptamers to PAA of FTLS.Electron microscope and AFM (atomic force microscope) were used to characterize morphology features of the scaffolds and it showed that the scaffolds had the stratified structure of three-layer-nanoparticle. The specificity capture efficiency of Apt-FTLS was 17 times as one-layer-nanoparticle rigid scaffolds while FTLS-based non-specific absorption was only 11.1% of one-layer-nanoparticle rigid scaffolds. This article realized assembly of ordered multilayer flexible scaffolds of simple, rapid and controllable nanoparticles. The scaffolds had nanoparticle structure and flexible structure, and also represented the advantage of high roughness.Based on the aforementioned analysis, we constructed the multiple-aptamer-modified flexible scaffolds with PAA-cross-linked three-layer nanoparticle-structure, i.e. the multiple aptamer flexible scaffolds, which consisted of multiple-aptamer-modified polymer PAA and the three-layer nanoparticles. The scaffold was assembled as following:at first, the PAA molecules of large molecular weight with activated carboxyl groups were chemically connected on the rough carrier substrate with the PAA-cross-linked three-layer nanoparticle structures, and then many of amino-modified aptamers were simultaneously connected with multiple-carboxyl of one polymer PAA molecule. Here, the multivalent aptamer flexible scaffolds have the two aspects of the structural advantages and the corresponding ones of capturing cells.At first, the scaffold-assembled carrier surface has higher roughness owing to the three-layer-nanoparticle structure. When the roughness obviously increased, the length of the spacers (i.e. the height of the scaffolds between the multiple aptamers and the carrier substrate) was greatly increased, and then the steric hindrance from the carrier substrate for the multiple aptamers capturing flow target cells was greatly decreased. Secondly, the scaffolds consisting of three-layer nanoparticles and PAA have the flexible structure. Since this kind of the flexible scaffold has some bent capability with a degree, the multiple ligands modified on the scaffolds should more easily bend and enfold to form a suitable three-dimensional stereo-structure for better interaction with the multiple receptors on same cell, that is, to more easily form good multivalent binding. Then the capture forces of the scaffolds for flow target cells were greatly increased. For target cells, the scaffolds showed lower non-specific absorption and the scaffolds modified by multivalence aptamer had higher specificity capture efficiency.