Multifunctional Surface-enhanced Raman Scattering Nanoprobe and Encoding Materials for Ligand Screening

Abstract

Surface-enhanced Raman scattering (SERS) has been widely utilized in bio applications due to its great advantages in multiplex detection. By controlling the structure of SERS active materials, effective SERS nanoprobes have been developed with additional functionality and strong SERS signals. In chapter 1, the fabrication of multilayered tri-functional magnetic-fluorescence-SERS nanoprobes (MF-SERS dots) containing superparamagnetic Fe3O4 nanoparticles (NPs) clusters, assembled Ag NPs, and fluorescent silica layer is described. The MF-SERS dots exhibite both superparamagnetism and fluorescence properties, and can also generate strong SERS signals from the assembled Ag NPs after treating four kinds of Raman reporter molecules

4-fluorobenzenethiol (4-FBT), 4-chlorobenzenethiol (4-CBT), 4-bromobenzenethiol (4-BBT), and 3,4-dichlorobenzenethiol (3,4-DCT). The MF–SERS dots were internalized into cells, allowing successful separation of cells using an external magnetic field, and SERS and fluorescence signals were successfully detected from the NPs-containing cells. Also, CD44 antibody-conjugated MF-SERS dots were selectively bound to MDA-MB-231 cells. These results prove that MF-SERS dots are useful nanoprobes for multiplex detection and separation of cells. In chapter 2, the application of silica based disk type encoding material (micro-encoder) using graphical patterns and SERS signal is presented. The size and thickness of micro-encoders is 5 µm and 1 µm respectively, and 1 µm-sized holes are located on the micro-encoders. Each encoders can be distinguished by the number of holes and characteristic SERS signals of three kinds of Raman reporter molecules (4-FBT, 4-CBT, and 4-BBT) from the assembled Ag NPs on the micro-encoders. During solid-phase peptoid synthesis, the peptoid side chain can be encoded by the absorption of micro-encoders on the bead which is 100 µm in size. And the sequence and the type of peptoid side chain can be decoded with the number of holes in each micro-encoder and the SERS signals, respectively. The amount of absorbed micro-encoders on bead is dependent on the amount of treated micro-encoders, and for practical application, 10% of treated micro-encoders were introduced on the bead. The conditions of peptoid coupling reaction are optimized for maintaining appropriate amount of micro-encoders on the bead during peptoid synthesis. Thus, the appropriate amounts of bromoacetic acid and primary amine are determined to be 10 equivalent of the amine functional groups on the bead. Finally, the pepoid sequences, which are composed of 2-methoxyethylamine (Nmea), N-(3-aminopropyl)-2-pyrrolidinone (Napp), 1-naphtylmethylamine (Nnap), piperonylamine (Npip), and isobutylamine (Nleu), are synthesized, and the last three sequences are encoded using the micro-encoders. Then, the streptavidin bound beads are analyzed by the graphical pattern and the SERS signals of the micro-encoders on the beads, as a decoding process, which can effectively provide the information about the peptoid sequence. These results prove that the graphical and SERS dual modal micro-encoders can be utilized as an effective agent for screening of peptoid as well as small molecule ligands on bead by simple encoding-decoding processess.