Using The Localized Surface Plasmon Resonance Of Gold Nanoparticles To Reversibly Sensing PH In Micro/Nano Spaces

Gold nanoparticles(AuNPs)exhibit internal parameters and external condition dependent localized surface plasmon resonance(LSPR)light scattering properties.Gold nanoparticles effectively scatter visible light and do not suffer from blinking or photobleaching,coupled with prominent biocompatibility and low cytotoxicity,which have great potential in bioanalysis application.The distance dependence of plasmon coupling in the gold nanoclusters can be used to monitor the chemical processes in micro/nano spaces.pH is an essential factor that regulates many cellular behaviors.Cell proliferation and apoptosis,as well as enzyme activity and protein degradation,are closely related to the change of intracellular pH.Disruptive variation of pH may lead to dysfunction of the organelles.Sensing and monitoring pH changes inside living cells are thus of great importance for studying cellular metabolisms and gaining insights into physiological and pathological processes.We here assemble homogeneous and stable gold nanoclus-ters based on hybridization of i-motif DNA and MO linkers at low salt concentration,probing pH in micro/nano spaces by monitoring the single-particle scattering spectra of the gold nanoclusters.The specific experiment can be divided into two parts:1.Construction of Au dimers based on i-motif DNA/MO hybridization Self-assembly of 40 nm Au dimers for pH sensing in mico/nano spaces.i-motif DNA and MO were modified onto 40 nm AuNPs respectively to prepare i-motif DNA-Au(40)and MO-Au(40)conjugates.The two functionalized AuNPs were mixed at molar ratio 1:1 to prepare 40 nm Au dimers.The introduction of HS-PEG-COOH protected MO-Au(40),while reducing the proportion of large clus-ters in the final assembly.The experimental conditions such as the molar ratio of i-motif DNA/MO to AuNPs,salt concentration and the method of salt addition were optimized.Balancing between low hybridization efficiency and formation of large clusters the two extremes,gold nanoclusters with dimers as main prod-ucts were thus obtained.The structure and optical properties of Au dimers were characterized by UV-visible spectroscopy and transmission electron microscopy.Dark-field microscopy was used to characterize the LSPR light-scattering prop-erties of a single Au dimer.The application feasibility of Au dimers in pH sens-ing in micro/nano spaces was analyzed.2.Construction and characterization of pH-responsible Au core-satellite nan-oclusters based on i-motif DNA/MO hybridizationSelf-assembly of Au core-satellite nanoclusters for pH sensing in mico/nano s-paces.15 nm and 50 nm AuNPs were synthesized respectively.We then as-sembled core-satellite nanoclusters from DNA-Au(50)+ MO-Au(15)and MO-Au(50)+ DNA-Au(15)two ways.UV-visible spectroscopy and transmission electron microscopy characterization confirmed DNA-Au(50)+ MO-Au(15)bet-ter choice to prepare core-satellite nanostructure.The single-particle scattering spectra of the surface immobilized core-satellite nanoclusters verified their pH response performance and response reversibility.A control experiment was car-ried out to confirm the pH response property of core-satellite nanoclusters was originated from the folding of i-motif DNA.