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).

The paper porosity study has been done by observing microscopically.The purpose is provide airborne porosity data on various paper types, so that we can rank the ability of liquid absorption on the same paper type. This porosity analysis is done by using ImageJ, with converting the image to binary, set the threshold limit, and clarify the watershed limit. The result of the porosity of filter paper A=51,50586 , B=18,30719 ,C=21,68076 ,D=29,72028 ; tissue paper A=9,174071 ,B=20,96931 ,C=32,76454 ; HVS paper A=23,31616 ,B=27,70944 . So it can be concluded that the ability of filter paper absorption A > filter paper D > filter paper C > filter paper B. Absorption ability tissue paper C > tissue paper B > tissue paper A. Absorption ability HVS B paper > HVS paper A. In general can be inferred that the higher the porosity value of the paper the greater ability to absorb liquids on paper.

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