Herein, we present an electrochemical sensing platform based on nanochannel-confined graphene quantum dots (GQDs), which is able to detect a spectrum of small analytes in complex samples with high sensitivity. Vertically-ordered mesoporous silica-nanochannel film (VMSF) is decorated on the supporting electrode, conferring the electrode with excellent anti-fouling and anti-interference properties through steric exclusion and electrostatic repulsion. The synthesized GQDs with different functionalities are confined in the nanochannels of VMSF through electrophoresis, serving as the recognition element and signal amplifier. Without the usual need of tedious pretreatment, ultrasensitive and fast detection of Hg 2+ , Cu 2+ and Cd 2+ (with limit of detection or LOD of 9.8 pM, 8.3 pM and 4.3 nM, respectively) and dopamine (LOD of 120 nM) in complex food (Hg 2+ -contaminated seafood), environmental (soil leaching solution), and biological (serum) samples are realized as the proof-of-concept demonstrations.
Direct electrochemical detection in human whole blood remains challenging due to electrode surface fouling and passivation by abundant biological substances. In this work we report that the isoporous silica-micelle membranes (designated as iSMM) can effectively function as antibiofouling layer for electrochemical detection of drug molecules in human whole blood without pretreatment. The iSMM possesses molecular sieving capacity, charge/lipophilicity selectivity, and preconcentration ability. Only small and neutral/lipophilic analytes can permeate the iSMM, be concentrated, and subsequently be detected at the underlying electrode. It is however impermeable to big sized substances and those small but charged and hydrophilic. We first investigated the molecular permeability of iSMM by electrochemical impedance spectroscopy (EIS) and then demonstrated its application in the quantitative determination of chloramphenicol (CAP) in the unprocessed human whole blood. The analytical sensitivity and long-term stability of iSMM based electrochemical sensors are apparently better than bare electrodes.
The rapid and sensitive detection of nitroaromatic compounds is of great significance for human health, the environment, and public security. The present work reports on the extraction and electrochemical analysis of trace nitroaromatic compounds, such as explosives and organophosphate pesticides (OPs), using the indium tin oxide (ITO) electrodes modified with a highly ordered and aligned binary assembly of silica mesochannels and micelles (BASMM). With a pore diameter of ca. 2-3 nm, silica mesochannels (SMs) perpendicularly oriented to the ITO electrode surface can provide hard and robust supports to confine the soft cylindrical micelles formed by the aggregation of cationic surfactants, namely, cetyltrimethylammonium bromide (CTAB). Due to the organized self-assembly of hydrocarbon tails of CTAB surfactants, each micelle has a hydrophobic core, which acts as an excellent adsorbent for rapid extraction and preconcentration of trace nitroaromatic compounds from aqueous solutions via the hydrophobic effect. Furthermore, the cylindrical micelles are directly in contact with the underlying electrode surface, to which extracted compounds can freely diffuse and then be reduced therein, thus allowing their determination by means of voltammetry. Using the BASMM/ITO sensor, electrochemical analysis of trace nitroaromatic explosives, including 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitrophenol, 2,6-dinitrotoluene, 3-nitrophenol, and nitrobenzene, and OPs, such as paraoxon, methyl parathion, and fenitrothion, was achieved with a fast response, wide linear range, high sensitivity, and low detection limit at the ppb level. TNT and paraoxon in real apple, tea, and water samples were also determined. By combining the heterogeneous extraction and determination in one ordered binary nanostructure, the BASMM sensor provides a very simple, rapid, and cost-effective way for analysis of nitroaromatic compounds and can be extended to a wide range of lipophilic yet redox-active analytes.
Mesoporous silica films consisting of highly ordered and vertically aligned nanochannels (abbreviated as VMSFs) have received considerable attention because of their high surface area, long-range order, thermal and mechanical stability, controllable pore size and more importantly good molecular accessibility for rapid mass transport. These characteristics are ideal for electroanalytical chemistry and separation science. In this review, we firstly present briefly the strategies for the synthesis of VMSFs on the electrode surface, mainly the electrochemically assisted self-assembly and Stöber-solution growth approaches, as well as the surface modification of channel walls with diverse terminal groups for various functionalities. In the next section, recent progress on the applications of VMSFs in electroanalytical chemistry and sensing is summarized, in terms of the spatial confinement and permselective effects (size, charge and lipophilicity selectivity of the mesochannels). We then present the preparation and application of perforated free-standing VMSFs for fast and precise molecular sieving/separation. The review ends with an outlook and perspective on the future applications of VMSFs.
An ultrathin and highly porous silica isoporous membrane was employed as a nanofluidic power source to harness osmotic energy from salinity gradients.
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