Department of Mechanical and Aerospace Engineering, WVNano Initiative, West Virginia University, Morgantown, WV 26506, USA.
Nanotechnology. 2012 Mar 23;23(11):115501. doi: 10.1088/0957-4484/23/11/115501.
To meet the requirement of Raman probes (labels) for biocompatible applications, a synthetic approach has been developed to sandwich the Raman-probe (malachite green isothiocyanate, MGITC) molecules between the gold core and the silica shell in gold-SiO₂ composite nanoparticles. The gold-MGITC-SiO₂ sandwiched structure not only prevents the Raman probe from leaking out but also improves the solubility of the nanoparticles in organic solvents and in aqueous solutions even with high ionic strength. To amplify the Raman signal, three types of core, gold nanospheres, nanorods and nanostars, have been chosen as the substrates of the Raman probe. The effect of the core shape on the surface-enhanced Raman scattering (SERS) has been investigated. The colloidal nanostars showed the highest SERS enhancement factor while the nanospheres possessed the lowest SERS activity under excitation with 532 and 785 nm lasers. Three-dimensional finite-difference time domain (FDTD) simulation showed significant differences in the local electromagnetic field distributions surrounding the nanospheres, nanorods, and nanostars, which were induced by the localized surface plasmon resonance (LSPR). The electromagnetic field was enhanced remarkably around the two ends of the nanorods and around the sharp tips of the nanostars. This local electromagnetic enhancement made the dominant contribution to the SERS enhancement. Both the experiments and the simulation revealed the order nanostars > nanorods > nanospheres in terms of the enhancement factor. Finally, the biological application of the nanostar-MGITC-SiO₂ nanoparticles has been demonstrated in the monitoring of DNA hybridization. In short, the gold–MGITC-SiO₂ sandwiched nanoparticles can be used as a Raman probe that features high sensitivity, good water solubility and stability, low-background fluorescence, and the absence of photobleaching for future biological applications.
为满足拉曼探针（标签）的生物相容性应用要求，开发了一种在金-二氧化硅复合纳米粒子中将拉曼探针（孔雀石绿异硫氰酸酯，MGITC）分子夹在金核和硅壳之间的合成方法。金-MGITC-SiO₂夹心结构不仅防止了拉曼探针的泄漏，而且提高了纳米粒子在有机溶剂和高离子强度水溶液中的溶解度。为了放大拉曼信号，选择了金纳米球、纳米棒和纳米星三种类型的核作为拉曼探针的基底。研究了核形状对表面增强拉曼散射（SERS）的影响。胶体纳米星表现出最高的 SERS 增强因子，而纳米球在 532nm 和 785nm 激光激发下表现出最低的 SERS 活性。三维有限差分时域（FDTD）模拟表明，纳米球、纳米棒和纳米星周围的局部电磁场分布存在显著差异，这是由局域表面等离子体共振（LSPR）引起的。纳米棒的两端和纳米星的尖锐尖端周围的电磁场得到了显著增强。这种局部电磁场增强对 SERS 增强做出了主要贡献。实验和模拟都表明，增强因子的顺序为纳米星>纳米棒>纳米球。最后，纳米星-MGITC-SiO₂纳米粒子在 DNA 杂交监测中的生物应用得到了证明。总之，金-MGITC-SiO₂夹心纳米粒子可用作拉曼探针，具有高灵敏度、良好的水溶性和稳定性、低背景荧光和无光漂白等特点，可用于未来的生物应用。
