**3.3 SiO2/GO/Ni(OH)2/GCE**

To the best of our knowledge, SiO2/GO/Ni(OH)2/GCE is not currently used in vitamin D sensing. SiO2/GO/Ni(OH)2/GCE is a composite material that has been shown to have excellent electrocatalytic properties, making it a promising platform for the detection of various analytes. The combination of silica nanoparticles and graphene oxide sheets provides a large surface area for electrochemical reactions to occur, while the nickel hydroxide nanoflowers act as a catalyst, facilitating the electron transfer process [49].

When it comes to vitamin D sensing, SiO2/GO/Ni(OH)2/GCE has the potential to be used in the development of electrochemical immunosensors for detecting 25OHD in serum samples. This could be achieved by functionalizing the material with specific antibodies that are designed to capture 25OHD from the sample matrix, followed by electrochemical detection using a suitable reagent [52].

One advantage of electrochemical immunosensors is that they offer several benefits over traditional methods for measuring 25OHD, such as immunoassays or liquid chromatography-mass spectrometry (LC–MS/MS) [53]. For example, electrochemical immunosensors are generally faster and less expensive, and require less sample volume than other methods. They also have the potential for on-site testing, which could be particularly useful in remote or resource-limited settings.

However, there are some challenges that need to be addressed before SiO2/GO/ Ni(OH)2/GCE can be used in practical applications for vitamin D sensing. One challenge is the development of specific and sensitive antibodies that are capable of capturing 25OHD from complex biological matrices, such as serum or plasma. Another challenge is the optimization of the electrochemical conditions, such as the choice of reagents and the applied potential, to achieve maximum sensitivity and selectivity.

Overall, SiO2/GO/Ni(OH)2/GCE is a promising material for electrochemical sensing applications, including vitamin D sensing. While further research is needed to optimize the conditions and validate the performance of this technology, the potential benefits of electrochemical immunosensors for vitamin D detection are clear and could have important implications for the diagnosis and management of vitamin D-related disorders.
