Ag@oxides Core-shell Nanoprisms: From Synthesis To Applications

Nanostructured materials, especially noble metal nanoparticles(NPs), such as silver(Ag), have been a research focus in recent decades because of their unique physical, chemical, and biological properties. These materials have attracted considerable attention due to their potential applications in the fiels of catalysis, biosensing, drug delivery, and nanodevice fabrication. Previous studies on Ag NPs have clearly demonstrated that their electromagnetic, optical, and catalytic properties derived from the surface plasmon resonance are strongly influenced by their shape, size, and size distribution. Although the synthesis and applications of Ag NPs have been investigated extensively, it is still a challenge for precisely controlling their morphology and stability. In this paper, we synthesize Ag@oxides core-shell nanopisms, and study their applications in organic solar cells, surface enhanced Raman scattering(SERS) and photothermal therapy(PTT).First,we use a two-step-method to synthesize anisotropic Ag nanoprisms, and then Ag@oxides core-shell nanopisms were prepared via a simple sol–gel route at room temperature. The oxides shell coating process was controlled by changing the reaction variables to precisely tune the thickness of Ti O2 shell in the range of 1-15 nm(1-10 nm for Si O2). Those indicate that the red-shift of plasmon resonance absorption peak of core-shell nanoparticles strongly depends on the increase of the thickness of the shell.Second, Ag@oxides nanoprisms are transfered from ethanol to 1, 2- dichlorobenzene(1, 2- DCB) through changing surface capping group, so that it could be directly blended into the active layer of polymer solar cells. Compare to bare Ag nanoprisms, a significant absorption and PL enhancement in the P3HT/ Ag@oxides nanoprisms film are observed, due to the local surface plasmon resonance(LSPR) of Ag nanoprisms which could enhance the absorption capability of the active layer in the solar cell. The light absorption enhancement could be transferred into the increment of the photogenerated exciton of P3 HT. Through the transient absorption spectrum, a long-lived photogenerated polaron are observed in the P3HT/Ag@oxides nanoprisms film, those indicate that the oxides layer can effectively avoid the exciton recombination. When the Ag@oxides nanoprisms are introduced into the active layer of P3HT: PCBM photovoltaic devices, about 31% of power conversion efficiency enhancement is obtained relative to the reference cell. All these results indicate that the ultrathin oxides shell dose not depress the LSPR effect of the Ag nanoprisms, and can effectively prevent from the recombination of the holes and electrons on the site of Ag nanoprisms.Third, surface-enhanced Raman spectroscopy(SERS) is a powerful vibrational spectroscopy technique that allows the highly sensitive structural detection of low-concentration analytes(chemicals and biomolecules) through the amplification of electromagnetic fields generated by the excitation of localized surface plasmons. However, poor chemical and structural stability of Ag nanoprisms have been a serious issue, limiting the further practical applications. We introduce a uniform ultrathin layer of oxide(Si O2 or Ti O2) on the Ag surface through a simple sol- gel route, and the shell not only could considerably improve the stability of the Ag nanoprisms in the oxidant, normal saline, phosphate buffer solution and under high temperature. The oxides also provide an excellent platform for binding all kinds of molecules that contain a COOH group in addition to a SH group. We demonstrate that Ag@oxides have high performance with respect to the typical SERS molecule 4-aminothiophenol(4-ATP), which contains a typical SH group, the enhancement factor(EF) reaches 1.08 × 106. Ag@oxides also can be directly employed for the SERS detection of amino acids, such as Glycine, and EF is 3.27 × 105. That will extend the SERS technique to a large group of biomolecules such as amino acids, DNA, and protein.Finally, we study the photothermal therapy by Ag@oxides nanoprisms based on surface plasmon resonance. Compare to Ag nanoprisms, Ag@oxides nanoprisms show the high structure stability under the laser irradiation(808 nm, 2 W cm-2). We measure the photothermal effect of different solution concentration,, and the photothermal conversion effiency of Ag@Si O2 and Ag@Ti O2 nanoprisms are 67.5% and 65% at a concentration of 200 μg m L-1, respectively. Toxicity experiments confirm their excellent biocompatibility and low toxicity. Furthermore, they showed strong NIR absorption and could efficiently kill cancer cells and suppress tumor growth with less damaging normal tissues after the irradiation with laser of 808 nm.