Construction Of Core-Satellite Plasmonic Nanostructured Substrate For Biomolecular Detection

Plasmonic noble metal nanoparticles are widely used in the field of chemical sensing and biosensing, due to the special phenomenon of Localized Surface Plasmon Resonance (LSPR), which is highly sensitive to the changes of local dielectric environment around the plasmonic nanoparticles result from the interaction with the component to be determined. LSPR phenomenon is generally accompanied by two important effects:First, LSPR can enhance the incident light resonant absorption of plamonic nanoparticles selectively, which is usually affected by the component, size, shape and local dielectric environment of plasmonic nanoparticles, and this effect can be applied in the construction of colorimetric sensor. Second, LSPR could result in the enhancement of localized electromagnetic field, which would be further used in Surface Enhanced Raman Scattering (SERS) detection for chemical and biological molecule. On the basis of LSPR phenomenon and the subsequent two effects, we choose different sized and component plasmonic nanoparticles to fabricate core-satellites nanostructure assembly on substrates, which would enhance the signal of spectra due to its special morphology and structure, with DNA or glucose as detecting target and the linker between core and satellite nanoparticle. With the assistance of UV-vis and SERS spectra, we can obtain the signal changes before and after the assembly of core-satellite to accomplish the detection for target molecules. Since the assembly and detection were operated on the substrate, false positive signal caused by interference of impurity and pH changes would be avoided, which usually happened in solution. Besides, recycled operation and reproducible detection could be realized on substrates based on the reversible assembly and disassembly.(1) We made use of DNA as the assembly linker to construct a core-satellite nanoassembly on a two-dimensional substrate and demonstrated its functionality as a colorimetric biosensor. This colorimetric substrate also presented reproducible detection ability based on the reversible assembly and disassembly. First, different sized Au nanoparticles were modified with thiol-DNA, and then hybridization was accomplished for assembling core-satellite nanostructure through the introduction of complementary target DNA. With the decreasing concentration of target DNA, we found that the number of satellite nanoparticles assembled around core decreased and the corresponding peak intensity and peak position of UV-vis spetra reduced and blue-shift. The result showed that the detection limit was as low as 1 nM and single base mismatch of nucleic acid could also be distinguished clearly during our detection process. Compared with the detection treated in solution, detection carried out on substrate is advantageous as the false positive signal resulted from interference of impurity and pH changes could be avoided and reproducible detection could be achieved. In addition, compared to electron beam lithography method, this self-assembly method of DNA-functionalized nanoparticles was relatively simple and cost-effective for the construction of regular and orderly nanostructure.(2) A facile and sensitive sandwich glucose sensor based on Surface Enhanced Raman Scattering (SERS) has been developed through the specific binding between a-D-glucose molecule and two group of cis-coplanar dihydroxy provided by phenylboronic acid modified on the surface of core and satellite nanoparticles. Ag nanoparticles as core were immobilized on the substrate firstly, followed by the modification of p-mercaptophenylboronic acid (MPBA), and Au nanoparticles as satellite were also functionalized with MPBA molecule for the subsequent assembly. After the successive introduction of target glucose and satellite nanoparticles on the core immobilized substrate, heterogonous core-satellite nanostructure assembly was successfully fabricated due to a-D-glucose molecule as linker. Here, MPBA molecule could be identified as recognition site for specific assembly and Raman reporter. Compared with individual core nanoparticles on substrates, the core-satellite nanostructure assembly would lead to multiple electromagnetic enhanced active "hot spots", and subsequently amplified SERS intensity of MPBA, due to the enhanced LSPR effect resulted from the binding event of glucose molecules brings the core and satellite nanoparticles into close proximity. Correspondingly, the detection of α-D-glucose molecules was accomplished according to the changes of SERS signal intensity before and after the core-satellite assembly.