| Liquid/liquid interface, or the so-called the interface between two immiscible electrolyte solutions (ITIES), with capability of detecting both ions and electrons, enables the label-free detection of non-redox molecules based on the current signal caused by the ion transfer across the interface. A miniaturized ITIES has advantages of minimized charging current and suppressed ohmic drop. If the size of ITIES is reduced to the nanoscale, the mass transport at the interface can be further improved. Two main approaches have been reported so far to build nanoscopic ITIES (nano-ITIES), either by establishing it at the orifice of a nanopipette or by supporting it with nanoporous materials. In the latter case, ion transfer will be dominated by the molecular properties, such as size and charge, ascribing to the sufficiently small nanochannels. Thus, at the nanoscopic ITIES, selective detection of molecules can be achieved with high sensitivity. Herein we report a detailed electrochemical study on the silica isoporous membrane (SIM)-supported nano-ITIES array (SIM/nano-ITIES) by ion transfer voltammetry. The main content of this thesis contains following four parts.In chapter 1, we introduced the basic theories of the micro/nano-interface. Then, different preparation methods of micro/nanopipettes and micro/nanoporous membranes as well as their application in electroanalysis were summarized. The methods of preparing micro/nanoporous membranes can be divided into two kinds, i.e., by means of physical/chemical fabrication and chemical synthesis. The former one employs ultraviolet eximer laser photoablation processing, deep reactive ion etching, electron beam lithography, focused ion beam, track etching or other fabrication methods to prepare nanochannels on different substrates, while the latter one contains silica zeolite, anodic aluminum oxide, in-situ silica deposition and hybrid mesoporous silica membranes. The application of micro/nano-ITIES focused on studying ion transfer reaction and kinetics, molecular detection and so on.In chapter 2, the free-standing SIM were used to pattern the nano-ITIES array for selective ion transfer study. Thanks to its excellent geometric features of regularly aligned nanochannels, ultrasmall pore size (2-3 nm) and ultrathin membrane thickness of ca.80 nm, the SIM can support a stable nano-ITIES array with well-defined interface structure, mass transport geometry and permselectivity. Importantly, at the nano-ITIES array the trans-membrane resistance caused by the SIM was found to be pretty small, due to the high nanochannel density and ultrathin membrane thickness. The permselectivity allowed of studying the transfer of specific ions in term of their charge and size. The charge and size permselectivity could be facilely modulated by the supporting electrolyte concentration, aqueous solution pH and channel surface modification. Finally, facilitated ion transfer was also studied to clarify its mechanism.In chapter 3, we designed a portable amperometric strip-sensor with SIM supported nanopore array-water/polyvinylchloride-1,2-dichloroethane (PVC-DCE) organogel interfaces (SIM/nano-W/Gel) for the measurement of choline, acetylcholine, benzoylcholine and atropine quantitatively and qualitatively. Via gellifying the organic phase, the defect of interface instability can be minimized. Geometry of the gellified ITIES established in SIM seemed to be similar with the non-gellified ITIES supported by SIM. Cyclic voltammetry (CV) was also performed for analyzing the transfer behavior of choline compounds at the SIM/nano-W/Gel. For quantitative detection, differential pulse stripping voltammetry (DPSV) was utilized. Thanks to the selective permeation behavior, the sensor was also applied to detect choline compounds in real samples, such as urine and blood.Last chapter summarized the work presented in this thesis and foreseen the prospect of nano-ITIES arrays supported by the SIM. |
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