In this work, we designed a visual biosensor for dopamine (DA) detection using magnetic Fe3O4 particles and dithiobis(sulfosuccinimidylpropionate)-modified gold nanoparticles (DTSSP-AuNPs) as the recognition elements. Specifically, DA molecules were assembled onto the surface of DTSSP-AuNPs via the amine coupling reaction between the amino group of DA and activated carboxyl group of DTSSP. Accordingly, DA-anchored DTSSP-AuNPs were captured by Fe3O4 through the interaction of catechol and iron. In a magnetic field, the formed Fe3O4-DA-DTSSP-AuNPs conjugates were easily removed from the solution, leading to fading of the AuNPs suspension and decrease of the UV/Vis signal. As a result, a detection limit of 10 nM for DA was achieved. The theoretical simplicity and high selectivity demonstrated that the sandwich-type strategy based on Fe3O4 and AuNPs would lead to many colorimetric detection applications in clinical study by rationally designing the surface chemistry of AuNPs and Fe3O4.

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Octahedral Ni x S y nanoparticles and Ni x S y /PVDF nanocomposites are successfully prepared by solvothermal method. The electromagnetic absorption performance of Ni x S y /PVDF with different filler content is investigated in the range of 2-18 GHz. An optimal reflection loss value of −32.75 dB at 10.48 GHz is achieved for the filler content of 20 wt%, and the bandwidth <−10 dB can reach up to 4.48 GHz with a thickness of 3 mm. Furthermore, fundamental mechanisms of electromagnetic absorbing is discussed, indicating that the interface polarization, electric dipole polarization, Debye relaxation and impedance matching are the main factors affecting the absorption performance of Ni x S y /PVDF composites.

The superparamagnetic Fe 3 O 4 single nanocrystals with diameters of 10-15 nm have been synthesized via a simple method. Several characterizations such as SEM, TEM and XRD are used to obtain the morphology and crystallinity of Fe 3 O 4 nanoparticles. The investigation about wave absorption property indicates that Fe 3 O 4 nanocrystals is an excellent absorber, the effective frequency band (RL<-5.30 dB) of absorbers are obtained in a broad frequency range from 2.0 GHz to 15.40 GHz and the minimum reflection losses and the peak frequencies are-10.5 dB and-7.7 dB at the frequency of 10.4 GHz and 14.1 GHz, respectively.