Studying the Adsorption Process of Riboflavin on Silver-Deposited Fe3O4 Nanoparticles

The adsorption characteristics of riboflavin onto silver-deposited iron oxide magnetic nanoparticles (Ag/Fe3O4) have been described. Characterization of the synthesized Ag/Fe3O4 nanoparticles was achieved by FTIR spectra, TEM image and XRD pattern. The influence of several experimental parameters such as nanoparticles dosage, pH of the sample solution, different orientations of the riboflavin molecules toward Ag/Fe3O4 surface, riboflavin concentration, contact time of the reagents, temperature, ionic strength and presence of halide anions were studied. Experimental data indicated that Ag/Fe3O4 nanoparticles adsorb more than 90% of riboflavin under the optimum experimental conditions of the adsorbent dosage of 4.0 mg, a pH of 6.0, and a contact time of 2.0 min, when an initial riboflavin concentration of 0.02 mM is used. The results revealed that the presence of halide anions lower the adsorption of riboflavin on the surface of nanoparticles due to dissolution of the silver layer of the nanoparticles. It was found that the adsorption isotherm is best fitted to Dubinin-Radushkevich and Freundlich models and kinetic model followed a pseudo-second-order adsorption rate

An All-in-One Solid State Thin-Layer Potentiometric Sensor and Biosensor Based on Three-Dimensional Origami Paper Microfluidics

An origami three-dimensional design of a paper-based potentiometric sensor is described. In its simplest form, this electrochemical paper-based analytical device (ePAD) is made from three small parts of the paper. Paper layers are folded on each other for the integration of a solid contact ion selective electrode (here a carbon-paste composite electrode) and a solid-state pseudo-reference electrode (here writing pencil 6B on the paper), which are in contact with a hydrophilic channel fabricated on the middle part (third part) of the paper. In this case, the pseudo-reference and working electrodes are connected to the two sides of the hydrophilic channel and hence the distance between them is as low as the width of paper. The unmodified carbon paste electrode (UCPE) and modification with the crown ether benzo15-crown-5 (B15C5) represented a very high sensitivity to Cu (II) and Cd2+ ions, respectively. The sensor responded to H2O2 using MnO2-doped carbon paste electrode (CPE). Furthermore, a biosensor was achieved by the addition of glucose oxidase to the MnO2-doped CPE and hence made it selective to glucose with ultra-sensitivity. In addition to very high sensitivity, our device benefits from consuming a very low volume of sample (10.0 µL) and automatic sampling without need for sampling devices