NIR laser induced TPA enhancement of Zn(II)-terpyridine capped gold nanoparticles for targeting mitochondria
Graphical abstract
A new type of mitochondrial identification of Nano fluorescent dyes.
Introduction
Over past decades, the interactions between organic chromophore and metal nanoparticles (NPs) have attracted considerable attention of the scientists who deal with problems of the organic-metal nanohybrids and endeavor to improve their overall application performance [1], [2], [3], [4], [5], [6]. Au NPs could be utilized to enhance the optical responses of nearby chromophores, including localized surface plasma resonance (LSPR) [7], [8], [9], extremely large extinction coefficients, enhanced second-harmonic generation (SHG) and two-photon photoluminescence (TPPL) [10], [11], [12], [13], [14], surface-enhanced Raman scattering (SERS) [15], [16] and metal-enhanced fluorescence(MEF) [17], [18]. In addition to the aforementioned optical properties, Au also has a variety of inherent attributes that make its nanostructures an attractive platform for biomedical applications [19], [20], [21]. In TPPL, the electron is excited by two photons of half the energy relative to the photon in single photon fluorescence (SPPL) and longer excitation wavelength could greatly reducing the level of phototoxicity. Some nonlinear optical materials (NLOM) modified by Au particles resulting in better electronic structure, fine optical properties and good biocompatibility, could apply to the bioimaging.
Mitochondria targeting has been reported over past few decades [22], [23], [24], [25], [26]. It is essential organelles that are required for cellular energy production and involved in many other cellular activities, such as lipid modification, maintenance of redox balance, maintenance of calcium balance, and controlled cell death [27], [28].Fluorescence imaging with subcellular resolution offers a unique approach for visualizing morphological details in tissue or cell that cannot be resolved by other medical imaging techniques [29]. As we all known, Mitochondria is polarized as the negative electric potential differences across the inner membranes. In contrast, depolarization, i.e. loss of the electric potential, is an indicator of mitochondrial dysfunction. The general trend of mitochondrial depolarization has a close association with cellular apoptosis and thus, is a pathological feature for some major diseases, e.g. Parkinson’s disease and Alzheimer’s disease [30], [31]. Therefore, this nano gold modified complex particles targeting mitochondria may cause by the surface excess of Au3+.
Our previous work [32] formed a composite material of teryridyl conjugated with nano silver via coordination interaction, but the one-photon fluorescence quenching phenomenon and lifetime attenuation make it cannot be better applied to bioimaging. In this work, “fine particles” Au was chose to replace silver nanoparticles simultaneously with the LSPR properties, nonreactivity and bioinert [33]. Despite its extraordinary inertness under most conditions, Au is well-known for its ability to form a relatively strong gold-thiolate (AuS) bond with compounds containing the thiol (-SH) or disulfide group (SS) [34]. Herein, as continue our previous work, a D-π-A type terpyridyl ligand is chose to coordinate to Zn(SCN)2, then the two sulfur-terminal metal complex was presented, and Nano gold is used to modified the NLOM through the traditional method for Au particles. Fortunately, a novel Au-complex composite material has been obtained with longer lifetime, two-photon absorption (TPA) coefficient (β), TPA cross section (σ), nonlinear refractive index (γ) and third order nonlinear optical susceptibility (χ(3)) than the original complex. This material can be effectively penetrated into cellular mitochondria with phenomenon in two-photon fluorescence microscopy towards HepG2 cells in vitro.
Section snippets
Apparatus
All chemicals were purchased as reagent grade and used without further purification. The solvents were dried and distilled according to standard procedures. IR spectra (4000-400 cm−1), in KBr pressed pellets, were recorded on a Nicolet FT-IR 170 SX spectrophotometer. 1H NMR spectra were performed on a Bruker 500 Hz Ultrashield spectrometer and reported as parts per million (ppm) from TMS (δ). Coupling constants J are given in Hertz. UV–vis absorption spectra were measured on a UV-265
Characterization of SAu NPs
TEM image of SAu NPs with particle sizes of 5 nm was shown in Fig. 1. From the image, the surface of the Au particles was obviously capped with S. FT-IR of SAu NPs was shown in Fig. 2. The peak 2167 cm−1, identified as characteristic peak of SCN−1, blue shifts to 2085 cm−1 after the formation of complex S, then blue shifts to 2078 cm−1 and the intensity reduces when capped with Au particle. Moreover, in Fig 3 the Raman spectra of S and SAu NPs, the peaks 1174.3 cm−1, 1190.3 cm−1 identified as
Conclusions
A novel nanostructure was designed with intensity of one-photon fluorescence was approximately 2.5 times than that of S. Lase irradiation induce charge transfer from S to Au, leading to the enhancement of a series of nonlinear optical properties. Lase induced coagulation, fragmentation and dissolution of metal nanoparticles make it can penetrate into living cells and stained with mitochondria, which providing the nanomaterial with potential application in optical device and bio-imaging.
Acknowledgements
This work was supported by a grant for the National Natural Science Foundation of China (21271004, 51372003, 21271003, 51432001, 21101001), and the Anhui Provincial Natural Science Foundation (1308085MB24), and Scientific Innovation Team Foundation of Educational Commission of Anhui Province of China (KJ2012A025, 2006KJ007TD).
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