IntroductionNanoscale titania (TiO 2 ) has a wide range of properties -from optical to electronic, chemical, and even structural -that make it an especially versatile material for performing chemical analysis. For example, TiO 2 has a fi nite resistance as a semiconductor that can change with adsorption of other species. This property has been used to build effective chemical -electrical transducers that form the basis of many chemical sensors [1 -5] . TiO 2 (formally Ti IV ) is also susceptible to oxidation and its conversion into Ti III is accompanied by a signifi cantly increased con ductance and redshift in adsorption wavelength. This behavior has been used for the analysis of certain oxidizing or reducing agents by monitoring changes in electrical [4, 6 -8] and optical properties [9 -13] . Other properties of TiO 2 nanomaterials that are favorable for trace analysis include high thermal and chemical stability, optical transparency in the visible and near -IR domain, photovoltaic properties, photo -cleaning capability, strong adsorption characteristics, and pH -dependent surface charges.Under UV illumination, the electrons of TiO 2 nanomaterials can be pumped into a conduction band, leaving holes in a valence band. This photovoltaic effect has been used for voltammetric sensing when the nanomaterials are placed in an electrical circuit under light irradiation [13 -16] . Alternatively, photo -generated electrons and holes can also act as strong reducing and oxidizing agents in the absence of an electric circuit and can participate in surface reactions. A useful application of this property, from the standpoint of analysis, is the photo -cleaning and recovery of titania -based sensors that have been poisoned by adsorption of organic contaminants [17 -19] .The strong adsorption characteristics of nanostructured TiO 2 are attributed to the high chemical activities of these surfaces and result primarily from their amphiprotic nature [20 -22] . While strong adsorption can sometimes lead to matrix interferences and poisoning issues, this property has been widely exploited to preconcentrate analytes by solid -phase extraction [20, 23 -25] and to design sensitive platforms for trace analysis. For similar reasons, the surface of nanostructured TiO 2 can be readily functionalized and charges on the surface can be altered by