Development of ultrasensitive plasmonic nanosensor for early-diagnosis of disease

Abstract

In this study, we have fabricated highly reliable nano-plasmonic sensors with ultrasensitivity employ-ing single-crystalline noble metal nanostructures. For clear demonstration, This thesis consists of two main parts with 4 chapters. The first and main part demonstrates the early-diagnosis studies of acute myocardial infarction (chapter 1) and rheumatoid arthritis (chapter 2) employing Au particle-on-plate SERS sensor. Sin-gle-crystalline Au nanopate with ultraflat and ultraclean surface provides only very weak zero-signal due to highly reduced non-specific bindings, playing an important role in preparation of ultrasensitive sensor. The second and preliminary part reports fabrication of unique plasmonic platforms employing single-crystal AuAg nanowire (chapter 3) and Ag nonoplate optical antenna (chapter 4). The optical properties of AuAg alloy nanowires allow us to find a simple method to combine good plasmonic character of Ag and good corrosion resistant character of Au. Single-crystal Ag nanoplate can naturally involve plasmonic nano-antennas and SPP-active surface on a built-in platform. The detailed descriptions for each chapter are as follows. In chapter 1, we firstly discovered single strand DNA aptamers that can bind a cTnI as 77 times stronger than typical troponin antibodies using Systematic Evolution of Ligands by Exponential enrichment (SELEX) method and fabricated ultrasensitive SERS aptasensor with sub-fM of detection limit from troponin aptamer modified single-crystalline Au NPL-Au NP assembly. Since an ultra-flat surface of Au NPL is able to introduce a highly well-ordered self-assemble monolayer (SAM) of probe aptamers, non-specific binding is notably suppressed compared to NPs aggregation system so that zero-signal intensity at 0 M of cTnI detection can be extremely reduced. As a result, the Au NPL based SERS aptasensor will play an important role in development of a system for prognosis or prophylaxis against AMI from its reliable ultra-sensitivity and selectivity. In chapter 2, we reports ultrasensitive sensor with fM level of detection limit for anti-CCP, the best bi-omarker for rheumatoid arthritis, employing CCP modified Au particle-on-plate SERS platform. The anti-CCP was captured by sandwich method inserted at between Au NPL and Au NPs, creating hot spot from them to enhance Raman signal strongly. Especially, on ultraflat surface of Au, until 40 aM of anti-CCPs could be analyzed quantitatively with SEM observation, which was impossible on rough surface of Au film. We expect that such a highly well-defined SERS platform combining Au NPL and Au NPs can contribute importantly to fabrication of early-diagnosis tool against rheumatoid arthritis. In chapter 3, topotaxial growth of $Au_xAg_{1- x}$ alloy NWs by postepitaxial deposition of Ag vapor on Au NWs and investigation of their plasmonic properties are reported. Ag vapor is supplied onto the epitaxially grown Au NWs, topotaxially turning them into $Au_xAg_{1- x}$ alloy NWs. The original geometries and alignments of the Au nanostructures are well preserved, while the composition of the alloy NWs is controlled by varying the Ag vapor supply time. The $Au_{0.5}Ag_{0.5}$ NWs show high SERS activity comparable to that of Ag NWs as well as highly increased oxidation resistance. The plasmon-active wavelength range of the $Au_{0.5}Ag_{0.5}$ NW is significantly extended to the blue region compared to Au NWs. The $Au_xAg_{1- x}$ alloy NWs that have plasmonic activity in the blue region in addition to high corrosion resistance will make a superb material for practical plasmonic devices including SERS sensors and optical nanoantennas. In chapter 4, we have epitaxially synthesized twin-free single-crystal Ag nanoplates on $SrTiO_3$ sub-strates. Unlike the nanoplates synthesized in a solution phase, these nanoplates have perfectly clean surfaces as well as a quite large size of tens of micrometers. As-synthesized defect-free single-crystal Ag nanoplates have an atomically flat surface and sides with well-defined angles, allowing long distance propagation of surface plasmons and highly-reliable plasmonic integration. By spatially separating receiving and transmit-ting antennas and plasmonically interfacing them, it can highly improve the signal quality of transmis-sion/reception. Furthermore, by combining sub-dimensional nanostructures onto the two-dimensional space it can build up effective hierarchical plasmonic nano-complexes. Theoretical simulations well reproduced unique experimental results of coupling between SPPs and free-space radiation by the nanoplate antenna sides, low-loss long-range SPP propagation, and tunneling or scattering of SPPs at a nano-gap as well as a nano-structure introduced on the nanoplate. The single-crystal Ag nanoplate will find superb applications in plasmonic nano-circuitry and lab-on-a-chip for biochemical sensing.