다공성 금/은 나노구조체를 통한 향상된 광음향 영상화 및 DNA를 이용한 나노입자 표면 개질

Abstract

Photoacoustic(PA) imaging is an emerging tool that can solve the traditional problems of optical imaging such as imaging depth and resolution. Using the acoustic waves generated in response to the absorption of pulsed laser light, PA imaging can provide non-invasive images of live species. In addition, PA imaging shows several centimeters of penetration depth and a few hundred micrometers of resolution, due to lower scattering of acoustic waves in tissue than photons. Because of these advantages, PA imaging shows great potentials for clinical research and application. Porous AuAg alloy nanoparticles(NPs) for PA contrast agent with large surface area, which is advantageous in terms of thermal conduction and heat conversion. Colloidal porous AuAg alloyed nanoparticles (pAuAgNPs) were synthesized by galvanic replacement reaction from Ag nanocubes. pAuAgNPs have 50 nm exterior diameter and half of their inner space consists of voids that have a bimodal size distribution with peaks at 21 nm and 8.3 nm. pAuAgNPs showed a plasmonic peak at 750 nm, which was exploited for PA imaging. Gold nanorods (AuNRs) were prepared and used as the control: they have a strong plasmonic peak at 720 nm. In in vitro experiments at respective plasmonic peak excitations, pAuAgNPs gave stronger PA signals than AuNRs by 8.9 times per particle, and 11.7 times per dosage by exogenous atom. The high surface area per volume as a result of the inner voids amplified the PA signals by efficient thermo-acoustic conversion. In experiments of chicken-tissue phantoms, pAuAgNPs showed PA signals through 4.5 cm thick tissue, whereas AuNRs gave no detectable signal. In whole-body in vivo experiments, pAuAgNPs injected into the body showed 2.7 times stronger PA signals than did AuNRs. Coating the pAuAgNPs with a silica layer additionally increased their PA signal by 1.8 times when compared to the uncoated. DNA is composed of sugar, nitrogenous base and phosphate group. Because of the phosphate group, DNA is negatively charged. As a surface molecule, DNA can provide sufficient electrostatic repulsion. Otherwise, DNA is an outstanding material for the preparation of nano- and micro-scale assembles due to their Watson-Crick base pairing interactions. DNA is negatively charged molecule due to phosphate group. Using above-mentioned characteristics of DNA, two types of nanoparticles were prepared in this thesis. First, pH-responsive AuNPs modified ssDNA and cytochrome C (CytC/ssDNA-AuNPs) were prepared by simply mixing 10 nm citrate AuNPs, single stranded DNA and cytochrome C. The DNA has been chosen to form a consistently negative charged layer. Cytochrome C has been employed as a zwitterionic moiety with isoelectric point (pI) of around 9.6 resulting increase of the positively charged portion by raising the pH values. pH responsive gold nanoparticles which are designed to aggregate in acidic condition similar to cancer environment and returned to its original disassembled states in a physiological pH. The pH responsive behavior of the particles is derived by change of electrostatic interaction among the particles where attraction and repulsion play a major role in low and high pH of the environment, respectively. Since different electrostatic interaction behavior of the particles in varied pH is induced not by irreversible chemical change but by simple protonation differences, the pH responsive process of assembly and disassembly is totally reversible. The low pH specific aggregation of gold nanoparticles resulted in red shift of plasmonic absorption peak and showed higher photothermal efficacy in acidic pH than in normal physiological pH. The low pH specific photothermal effect with long wave laser irradiation was directly applied to cancer specific photothermal therapy and resulted higher therapeutic effect for melanoma cancer cells than non-pH responsive gold nanoparticles. Second, DNA valence controlled QDs were prepared by enzymatic cleavage. CdSe/CdS/ZnS QDs were chosen because of their ease of synthesis and optical analysis. Hexahistidine tag (His6-tag) was used as a moiety connecting QD and DNA. His-tag was introduced through a azide-alkyne cycloaddition reaction at one end of the DNA. This reaction was fast, stable and especially bio-orthogonal. So, His6-tag attached DNA has advantages for bioapplication. The other side of DNA was introduced biotin molecule. His-tag-DNA-biotin was introduced to streptavidin coated micro-sized magnetic bead by simple agitating. Next, QD was introduced into magnetic bead through His-tag-QD coordination. Finally, monovalent QD was obtained by enzymatic cleavage reaction. To confirm the monovalency, two types of monovalent QDs, which have complementary DNA sticky, were prepared and QD dimers were synthesized by hybridization reaction. QD dimers were statistically analyzed by TEM images, 65% dimerization rate was confirmed. Through additional study, it will be possible to form the more complex structures such as QDs with multi-valence or QD-DNA machine.