Silicon Nanowires-based Fluorescence Chemosensors

In this dissertation, Si nanowires(SiNWs) were prepared by chemical vapor deposition (CVD) and chemical etching methods. Different fluorescent sensing molecules were synthesized and immobilized on the surface of the SiNWs. Optical sensors based on the modified SiNWs were obtained in the first time. The main results are summarized as follows:1. SiNWs-based fluorescence sensors for pH were realized by covalently immobilizing photoinduced electron transfer (PET) fluorophores 3-[N,N-bis (9-anthrylmethyl)amino]-propyltriethoxysilane(DiAn) on the surface of the SiNWs synthesized by chemical vapor deposition. Fluorescence properties of the SiNWs-based sensors were studied. And experimental results showed that fluorescence intensity of the sensors depended on pH and strong fluorescence could be obtained only at low pH value. A linear relationship between fluorescence intensity and pH value was found. Based on these results, the DiAn-modified SiNWs could be employed as pH sensor. And this sensor may be reproductive by washing with water and filtration.2. A chemical INH logic gate based on silicon nanowires was realized by covalently immobilizing dansylamide on the surface of the SiNWs. Fluorescence properties of dansylamide-modified SiNWs were investigated. The experimental results indicated that the presence of Hg(II) quenched the fluorescence of the dansylamide-modified SiNWs, which were not interfered by other familiar metal ions such as Cu(II), Zn(II), Cd(II), Fe(II), Co(II), Ni(II) and Ag(I) etc. Moreover, anions interfering experiment demonstrated that the fluorescence quenching resulted from Hg(II) could be recovered by introducing Cl-, Br-or I-. However, addition of excess Ag(I) could effectively avoid the interference from the Cl-, Br- or I-. Accordingly, the dansylamide-modified SiNWs could serve as a Hg(II) sensor. Considering the effect of Hg(II) and anions such as Cl-, Br-or I- on the fluorescence of the dansylamide-modified SiNWs, a new type of chemical INH logic gate could be set up, in which the Hg(II) and Cl-, Br-or I- were defined as two Inputs and the fluorescence from the dansylamide-modified SiNWs was regarded as Output, respectively. This new kind of logic gate structure could extend to other logic operation and make it possible to assemble various logic operation arisen from different modification of individual SiNW in a SiNWs array.3. SiNWs were covalently modified by fluorescence ligand, N-(quinoline-8-yl) -2-(3-triethoxysilyl-propylamino)-acetamide (QlOEt), and finally formed an optical sensor to realize a high sensitive and selective detection for Cu(II). The QlOEt-modified SiNWs sensor has sensitivity for Cu(II) down to 5×10-8 M, which is more sensitive than QlOEt alone. Other metal ions have no observable effect on the sensitivity and selectivity of the QlOEt-modified SiNWs sensor. The SiNWs-based fluorescence sensor is reversible by addition of acid to replace Cu(II). The sensing mechanisms of the QlOEt-modified SiNWs to Cu(II) and the rationale for the enhancement in the sensitivity and selectivity of the QlOEt-modified SiNWs over QlOEt on Cu(II) are discussed. The current sensor structure may be extendable to other chemo- and bio-sensors, and even to nanosensors for directly detecting specific materials in intracellular environment.