Nanopore sensing is blooming due to its label-free and high sensitivity features. As a novel nanopore, a droplet is formed at the orifice of a dual-nanopipette, which allows for the translocation of analytes through the two channels at a relatively low speed and the promotion of signal-to-noise ratio. However, nanopore sensing based on the principle of current blockage requires the pore size to be comparable to that of the single entity, which poses a huge challenge for the direct detection of small molecules. In this work, gold nanoparticles (Au NPs) modified with sulfhydryl poly(ethylene glycol) (PEG-SH) or aptamers were detected successfully. The size difference of Au NPs and the interaction between Au NPs and dual-nanopipettes could be distinguished sensitively. Furthermore, Au NPs modified with designed aptamers will produce different blocking current after capturing the corresponding small molecules (e.g., dopamine and serotonin). Even non-electroactive ions, such as potassium ions, can also be detected, which is difficult to sense based on redox reactions, and further illustrates that the change of surface properties of nanoparticles is responsible for the detection. This work expands the application of nanopipette sensing for Au NPs and provides a universal platform for the small-molecule detection, which has the potential application in biosensing.
As one phase constituting of a liquid/liquid (L/L) interface, suitable organic solvents are of great significance for the study of electrochemistry at a L/L interface. In this work, the thermodynamic and kinetic parameters of simple ion transfer (IT) at the water/trifluorotoluene (W/TFT) interface were measured using micro-and nanopipettes voltammetry, respectively. In addition to the study of model ions, we have also explored some ions whose transfer potentials are close to the two ends of the potential window. Inspired by the work of the W/TFT interface, we also further developed two novel L/L interfaces and investigated various simple IT reactions based on the W/oand p-methylbenzotrifluoride (W/o-and p-MBTF) interfaces. The transfer potential and Gibbs energy of ITs across the W/o-and p-MBTF interface were determined by the analysis of the electrochemical voltametric curves. Special attention should be paid to that we can observe the IT peak or steady-state of tetraamyl ammonium (TAA + ) at W/o-and p-MBTF interfaces with no difficulty, which is rather challenging at other L/L interfaces. Compared to the classical W/1,2-dichloroethane (DCE) and W/ nitrobenzene (NB) interfaces, the W/TFT and its derivatives interfaces exhibit low toxicity, favourable stability, and wider potential windows, which can be better choices for replacing the traditional organic solvents in the electrochemical study at a L/L interface.
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