Magnetite (Fe3O4) nanostructures and their modifications with other materials show proper characteristics to be implemented as a sensing material. This paper provides a brief review of the application of the Fe3O4 nanostructures and their modifications as sensitive material for pollutant gas sensors. Several studies were highlighted to explain the past-to-present progress of materials development. Various synthesis procedures of the materials were also clearly explained. The application of pure Fe3O4 nanostructures and their modification as sensitive materials in gas sensor devices to detect toxic gases is the main section of this paper. Last, the future prospects section summarized the materials’ development and provided a suggestion for future development.

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The purpose of this study is the characteristics of the indicator electrode which has been coated with a membrane with XRD, SEM-EDS, UV-Vis and FTIR. Research has been carried out using XRD, SEM-EDS, UV-Vis and FTIR tests on immobilized indicator electrodes 0.0350 g PVA-Enzyme coated with PVC-KTpClPB 0.0120 g and 0.0500 g. The method used was the biosensor potentiometric method with the urease enzyme immobilization technique in PVA coated with PVC-KTpClPB. To see the difference in the absorbance spectrum pattern of each PVA-Enzyme composition coated with PVC-KTpClPB against wavelength with UV-Vis, PVA-Enzim solution as a reference and PVC-KTpClPB solution as the first analysis 0.0120 g and as the second analysis 0,0500 g. To see the PVA-enzyme membrane coated with PVC-KTpClPB in the two compositions above was characterized by FTIR and SEM-EDS. To see the indicator electrode that had been immobilized by PVA-enzyme coated with PVC-KTpClPB in the two compositions above, it was characterized by XRD. It was concluded that the best results were found on the immobilization indicator electrode of 0.0350 g PVA-Enzyme coated with 0.0350 g PVC-0.0500 g KTpClPB.

Time-frequency analysis can provide useful information in digital signal seismic data processing and interpretation. The energy concentration of the spectrum depends on the consistency of function of the time-frequency analysis and instantaneous frequency variation digital signal. In this case, we used the digital signal seismic from selected seismometer broadband which deployed in Sumatera Island. The aim of this study to classify the waveform based on the time-frequency analysis using continuous wavelet transform (CWT). The sample data used the earthquake of 20 February 2018 in North Sumatera. The result indicated the classification between the horizontal and vertical components from the seismometer broadband is different. The classification of vertical is affected by seismic source and horizontal component affected the site effect.

Testing and analyzing the water quality had been conducted by combining several characteristics of sensors (temperature, turbidity and heavy metals) integrated in the wireless network system to determine the quality comparator parameters of water worth drinking in coastal areas. Using sensors made of chitosan compounds to detect heavy metals contained in water. Testing was also done using the DS18B20 sensor (temperature) and TDS (salt levels) by operating a wireless network to transmit data in real time to the web through the GPRS network with the automation system. The sampling used purposive sampling by seafront distance, ± 1 km distance and ± 3 km distance. Testing of copper chips with the addition of Chitosan showed a more stable reading result than without using copper plates (read: pure PCB). At Chitosan biosensors, the addition of CMC shows more varied readings compared to using chitosan biosensors alone. The Ds18b20 Sensor was able to work at high temperatures, with stable value readings. From Sensor readings TDS (EC meter), it’s obtained that the higher the water solution, the greater the reading from the TDS sensor. It was shown on a chart that describing the closer to the sea area, the higher the level of the dissolved substances. The tool was accessed in real time through the Thing Speak platform in accordance with the specified account.