Core–shell Fe3O4@Ag magnetic nanoparticles (MNPs) integrated with a Wheatstone bridge-giant magnetoresistance (GMR) sensor provide access to GMR-based biosensors. The Fe3O4 nanoparticles synthesized using the coprecipitation method demonstrated 77 emu g−1 of magnetization saturation (M S), 51 Oe of coercivity (H C), and particle size of 11 nm. Furthermore, core–shell Fe3O4@Ag MNPs prepared by the aqua-solution method possessed 53 emu g−1 of M S, 145 Oe of H C, and 17 nm of particle size. This high M S of nanoparticles not only offer a large induced magnetic field but is sufficient for particle penetration within the biofilms. It was discovered that the sensor can distinguish between the bare Fe3O4 with the Fe3O4@Ag nanoparticles through an output voltage increase corresponding to a decrease in M S. The output signal of the sensor responds linearly to an increase in the core–shell Fe3O4@Ag nanoparticle concentration, owing to an increase in the induced-field. The sensor exhibits better sensitivity when applied in detecting less than 2 g L−1 of nanoparticle concentration, that is, 0.76 mV per unit of concentration (g/L).

Kelimpahan plankton pada budidaya udang vaname (Litopenaeusvannamei) dengan kepadatan berbeda di tambak lahan pasir (Plankton abundance on white leg shrimp (Litopenaeus vannamei) cultivation with different stocking densities in sand land)

The objective of this research is to advance the affectability of Surface Plasmon Resonance (SPR) biosensor utilizing core-shell Fe3O4@Ag nanoparticles (Fe3O4@Ag NPs) with a variation of Ag concentration (20, 40, 60, 80, 100) mM. Fe3O4@Ag NPs were synthesized by the aqueous solution method. The characterization by utilizing X-ray Diffractometer (XRD) depicts that the crystal structure of Fe3O4 compares to the cubic inverse spinel structure and based on Transmission Electron Microscopy (TEM) estimation, the particle size average of Fe3O4@Ag NPs is 14.45 nm. The magnetic properties of Fe3O4@Ag NPs were evaluated by Vibrating Sample Magnetometer (VSM), the result appears that the more concentration of Ag increases, the more remanent magnetization (Mr), saturation magnetization (Ms), and coercitivity field (Hc) diminishes. In this research, a Fe3O4@Ag NPs, a spherical nanoparticle consisting of a spherical Fe3O4 core covered by an Ag shell, was used as an active material to enhance the signal detection of SPR, with a wavelength of 632.8 nm in the Kretschmann configuration. The system consists of a four-layer material, i.e., prism/Au film/ Fe3O4@Ag NPs. The results show that the SPR angle shifted to the larger angle of incident light by using Fe3O4@Ag NPs. However, the effect of Ag concentration appears that the more concentration of Ag extends, the lower angle of SPR shifts. The addition of a core-shell in the conventional SPR-based biosensor leads to the enhancement of the SPR biosensor sensitivity if the fractional volume of the core-shell is large.

The magneto-optic surface plasmon resonance (MOSPR) properties of core-shell Fe3O4@Ag nanoparticles (NPs) were successfully investigated using the Kretschmann configuration. The four layer configuration system consists of prism/Au/Fe3O4@Ag/air. At the plasmon resonance frequency, a prominent resonant enhancement of magneto-optical activity was observed. An external magnetic field of 40, 50 and 60 Oe was applied in the longitudinal, polar, and transversal configurations with variation in the positive and negative directions in the longitudinal configuration. In the longitudinal configuration, the SPR angle shifted to the larger and lower angles when an external magnetic field was applied in the positive and negative directions, respectively. Under an external magnetic field, the SPR angle shifted to the larger angle for polar and transversal configurations. The non-reciprocal reflection of light was exploited under an external magnetic field applied to core-shell Fe3O4@Ag magnetic NPs. The SPR angle shift is observed in each configuration. The results indicated that the MOSPR system might be used for next generation of biosensor application.

Peda merupakan salah satu produk hasil pengolahan secara tradisional yang digolongkan sebagai ikan asin basah. Perinsip pengolahannya adalah dengan memberikan sejumlah garam dengan konsentrasi tertentu pada ikan segar, kemudian difermentasi, dijemur dan difermentasi kembali sampai tercium aroma khas ikan peda. Tujuan penelitian ini untuk mrngetahui pengaruh konsentrasi garam dan lama fermentasi terhadap kandungan histamine peda, Penelitian ini dilakukan dalam dua tahap yaitu penelitian pendahuluan yang dimaksudkan untuk mengetahui proses pengolahan peda secara tradisional dan penelitian utama, dimana dilakukan pembuatan peda secara laboratoris dengan metode modifikasi dan hasil survey lapang dan kaji pustaka. Produk yang dihasilkan selanjutnya dianalisa kadar histamine, kadar air, dan pHnya, dengan parameter perlakuan konsentrasi garam 20% dan 30% dengan lama masing-masing fermentasi 5-7 hari. Hasil analisa produk peda tersebut menunjukkan bahwa dengan konsentrasi garam 30% dengan lama fermentasi 5 hari memiliki kadar histamine (29,65 mg/100 gr), kadar air (53,44%), dan pH (5,4) yang lebih rendah dibandingkan dengan perlakuan konsentrasi garam 20% dengan fermentasi 5 hari dan 7 hari.