The rGO/Fe3O4 composite is one type of composites that can be used as a biosensor material, especially glucose sensors. The main ingredients of the composite synthesis are graphite and iron sand. The synthesis process of Fe3O4 was done using the coprecipitation method, while the graphite oxidation process was accomplished using the modified Hummer's method. The composites were formed using the ex-situ wet mixing method. The formed iron sand and graphite were characterized using FTIR and XRD, and it was found that Fe3O4 was formed from the appearance of the Fe-O bond, the oxidation process of graphite was seen from the appearance of the C=O bond, and the detection of Fe peaks corresponded to the cubic crystal plane. Likewise, the composites formed were also characterized using FTIR and XRD for identification of the rGO/Fe3O4 composite formation. It was proven from the presence of Fe-O and C-O bonds and the appearance of an amorphous peak of rGO in the XRD results. The performance of the  rGO/Fe3O4 composites as the glucose biosensor was examined by varying the mass of Fe3O4 on the composite, using UV-Vis spectroscopy. The performance of the rGO/Fe3O4 composite biosensor in absorbing glucose reached optimum at a mass variation of 0.3 grams of Fe3O4, as demonstrated by by the lowest absorbance peak with an intensity of 0.0048 at a wavelength of 440 nm, corresponding to glucose entrappment of 7.1 mg/gram.

The development of composites as biosensors is very broad, one of them is biosensors to absorb glucose. Composite materials characteristic as biosensors must fulfill the criteria including nanomaterials that have magnetic properties, electrical conductivity, and good catalytic properties. One of the composites that fulfill those criteria is rGO/Fe3O4. By varying the addition of Fe3O4 in the making of rGO/Fe3O4 composites, the composition of composites that have the most effective performance in absorbing glucose will be known. The variation of Fe3O4 addition in this study is 0.1 gram - 0.5 gram, with 0.5 gram of RGO. The characteristics of rGO, Fe3O4 and the rGO/Fe3O4 composite are known by the XRD and FTIR analysed based on relevant previous studies. Glucose biosensor absorbance was tested by UV-Vis, a composite with mass variations of Fe3O4 0.1 gram, 0.2 gram, 0.3 gram, 0.4 gram, and 0.5 gram. Peak absorption of the composite of 0.1 gram Fe3O4 shows high glucose concentration, it can be seen that the composite does not absorb glucose properly. The 0.2 gram composite has the lowest absorption peak so that this composite is the best biosensor. Because with the addition of Fe3O4 mass shows the peak absorption is also higher. So, composites have a maximum limit in absorbing glucose.