Ion current rectification dependent on the concentration gradient of KCl solutions was systematically investigated in polyethyleneimine modified glass nano-pipettes with inner diameter of 105 nm. Peak shape dependence of the rectification factor on outer KCl solution concentration was observed when inner KCl solution with concentration from 1 mM to 500 mM was used. The peak shape dependence was also observed when the concentrations of the inner and outer KCl solutions were identically controlled. The peak shape in the ion current rectification could be explained by the ion conductance changes through the conical nano-pipette, which result from modulation of ion concentration.

Surface-enhanced Raman scattering (SERS) spectroscopy is attractive in various detection analysis fields. However, the quantitative method using SERS spectroscopy remains as an area to be developed. The key issues in developing quantitative analysis methods by using SERS spectroscopy are the fabrication of reliable SERS-active materials such as nanoparticle-based structures and the acquisition of the SERS signal without any disturbance that may change the SERS signal intensity and frequency. Here, the fabrication of seamless multilayered core–shell nanoparticles with an embedded Raman label compound as an internal standard (MLRLC dots) for quantitative SERS analysis is reported. The embedded Raman label compound in the nanostructure provides a reference value for calibrating the SERS signals. By using the MLRLC dots, it is possible to gain target analyte signals of different concentrations while retaining the Raman signal of the internal standard. The ML4‑BBT dots, containing 4-bromobenzenethiol (4-BBT) as an internal standard, are successfully applied in the quantitative analysis of 4-fluorobenzenethiol and thiram, a model pesticide. Additionally, ratiometric analysis was proved practical through normalization of the relative SERS intensity. The ratiometric strategy could be applied to various SERS substrates for quantitative detection of a wide variety of targets.

Cyclodextrins (CDs) have beneficial characteristics for drug delivery, including hydrophobic interior surfaces. Nanocarriers with β-CD ligands have been prepared with simple surface modifications as drug delivery vehicles. In this study, we synthesized β-CD derivatives on an Ag-embedded silica nanoparticle (NP) (SiO2@Ag NP) structure to load and release doxorubicin (DOX). Cysteinyl-β-CD and ethylenediamine-β-CD (EDA-β-CD) were immobilized on the surface of SiO2@Ag NPs, as confirmed by transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) spectrophotometry, and Fourier transform infrared (FTIR) spectroscopy. DOX was introduced into the β-CD on the SiO2@Ag NPs and then successfully released. Neither cysteinyl-β-CD and EDA-β-CD showed cytotoxicity, while DOX-loaded cysteinyl-β-CD and EDA-β-CD showed a significant decrease in cell viability in cancer cells. The SiO2@Ag NPs with β-CD provide a strategy for designing a nanocarrier that can deliver a drug with controlled release from modified chemical types.

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It has been increasingly important to develop a highly sensitive and selective technique that is easy to handle in detecting levels of beneficial or hazardous analytes in trace quantity. In this study, mono-6-deoxy-6-aminopropylamino-β-cyclodextrin (pr-β-CD)-functionalized silver-assembled silica nanoparticles (SiO2@Ag@pr-β-CD) for flavonoid detection were successfully prepared. The presence of pr-β-CD on the surface of SiO2@Ag enhanced the selectivity in capturing quercetin and myricetin among other similar materials (naringenin and apigenin). In addition, SiO2@Ag@pr-β-CD was able to detect quercetin corresponding to a limit of detection (LOD) as low as 0.55 ppm. The relationship between the Raman intensity of SiO2@Ag@pr-β-CD and the logarithm of the Que concentration obeyed linearity in the range 3.4–33.8 ppm (R2 = 0.997). The results indicate that SiO2@Ag@pr-β-CD is a promising material for immediately analyzing samples that demand high sensitivity and selectivity of detection.