GO/ZnO Biosensor Synthesis and Characterization for Biosensors

In this study, GO/ZnO nanoparticles were synthesized using the solvothermal method and characterized for potential biosensor applications. The synthesized nanoparticles exhibited a high degree of crystalline structural purity, as confirmed by XRD analysis. The XRD pattern revealed characteristic peaks corresponding to the crystal planes of ZnO, indicating a typical wurtzite hexagonal structure. In addition, the synthesized nanoparticles were evaluated for their physical characteristics using transmission electron microscopy. The TEM analysis showed that the ZnO nanoparticles had a narrow size distribution, with an average particle size of approximately 25.19 ± 4.1 nm. The morphology of the nanoparticles was further examined, revealing that the ZnO nanoparticles were uniformly dispersed and localized within the GO sheets. Furthermore, the exfoliation of GO into single or few-layered sheets was achieved, as evidenced by its transparency in the TEM images. These findings suggest that the solvothermal synthesis method is effective in producing highly dispersed GO/ZnO nanoparticles with a narrow size distribution. The synthesized GO/ZnO nanoparticles showed promise for biosensor applications due to their uniform shape and distribution, as well as their small size.


Introduction
Graphene (GO) is a nanomaterial with a flat structure made up of carbon atoms arranged in a single layer.arranged in a honeycomb lattice, has garnered significant attention due to its exceptional properties [1][2][3].Since its isolation from graphite in 2004, researchers have been exploring the potential applications of GO in various fields such as electronics, energy storage, and biosensors.GO possesses exceptional properties including high electrical conductivity, a large surface area, and excellent mechanical strength making it an ideal candidate for biosensing applications [4].In addition to GO, zinc oxide nanoparticles have also been extensively studied for their unique properties in biosensor applications [5].Zinc oxide nanoparticles, like GO, exhibit high biocompatibility, low toxicity, good chemical stability, and high electron mobility.These properties make zinc oxide nanoparticles a promising material for use in biosensors [6].The development of biosensors has been further advanced using exceptional nanomaterials such as metal oxides and nanoparticles.One area of interest is the synthesis of GO/ZnO nanocomposites, which combine the unique properties of both materials.By combining GO and ZnO, researchers aim to create nanocomposites with enhanced performance and tailored properties.The synthesis of GO/ZnO nanocomposites has been attempted by many researchers in order to generate composites with special features for sensing purposes [3,7].
The combination of GO and ZnO in these nanocomposites has shown potential for various applications, including improved photocatalytic performance, thermal stability, and outstanding electrochemical properties [8].The synthesis of GO/ZnO nanocomposites for biosensor applications involves careful consideration of the methods and characterization techniques used.This process has gained significant interest among researchers due to its potential for creating nanocomposites with improved performance.Various methods, such as solvothermal synthesis and electrodeposition, are employed to combine GO and ZnO, resulting in composites with specific properties.The solvothermal method, demonstrated by Kavitha and colleagues, involves the in-situ generation of ZnO nanoparticles on GO using a reactant complex.In their study, zinc benzoate dihydrazinate complex was used to generate ZnO nanoparticles onto GO through a solvothermal synthesis process at high temperature and pressure.This resulted in the formation of a GO/ZnO nanocomposite.Another method, as shown by Palanisamy et al., involved the deposition of ZnO onto GO through electrodeposition using an electrolyte solution containing zinc ions.The synthesis methods mentioned above offer unique advantages and challenges.The fabrication of GO/ZnO nanocomposites through solvothermal synthesis and electrodeposition methods offers promising opportunities for the development of biosensors [3].These nanocomposites possess unique properties that make them suitable for biosensor applications.Firstly, the combination of GO and ZnO in a nanocomposite offers enhanced electrical conductivity, which is crucial for efficient sensing.The GO/ZnO nanocomposite provides a highly conductive platform for the detection of analytes, improving the sensitivity and accuracy of biosensors.Secondly, the flower-like structure of ZnO nanoparticles grown on the GO surface in the solvothermal synthesis method provides a large surface area for the immobilization of biomolecules, such as enzymes or antibodies, for biosensing purposes [9].The synthesis of GO/ZnO nanocomposites using solvothermal and electrodeposition methods has demonstrated potential for biosensor applications.These environmentally friendly approaches allow for the preparation of high-quality GO/ZnO nanocomposites with intact crystalline structures.

Synthesis of GO/ZnO Nanoparticles
To start the synthesis, 1.48 g of Zn(CH3COO)2 • 2H2O was dissolved in 63 ml of absolute ethanol in a 250 ml Schott bottle and heated under constant stirring at 60°C.Additionally, 0.74 g of KOH was dissolved separately in 33 ml of absolute ethanol in a similar condition as the Zn(CH3COO)2.The two solutions were mixed together by slowly adding dropwise KOH into the Zn(CH3COO)2.After complete dissolution, the mixture solution underwent vigorous stirring at 60°C for approximately three hours to ensure completion of the reaction.Next, the mixture was centrifuged at a speed of 4000 rpm for 10 minutes to separate and isolate ZnO, which appeared as a white precipitate.The ZnO obtained was then washed twice with acetone followed by one wash with ultrapure water to remove any impurities present.After allowing it to return to room temperature, we continued with our experiment [10].A composite of GO and ZnO was prepared by dispersing separate powders of GO and ZnO into an ethanol solution using a sonicator.The solutions were then combined, sonicated for 15 minutes, and mixed further with a magnetic stirrer for 4 hours.Subsequently, the solution underwent centrifugation at 2000 rpm for 30 minutes followed by washing with ethanol and distilled water.The resulting precipitate was subsequently dried at a temperature of 80°C [3].

Characterization
The synthesized GO/ZnO nanocomposites were characterized using various techniques to evaluate their structural and morphological properties.One of the techniques used was X-ray diffraction using X-Ray Diffractometer (XRD) Bruker D8 Advance, which provides information about the crystal structure of the nanoparticles.Transmission electron microscopy (TEM) using TEM HT7700 was employed to analyze the morphology and size distribution of the GO/ZnO nanoparticles.

Result and Discussion
ZnO nanoparticle synthesis was carried out using the solvothermal method.This method offers the advantage of producing nanostructures with varying morphologies based on reaction conditions, thereby enhancing nanoparticle dispersion, and facilitating an uncomplicated synthesis process [11].The synthesized ZnO nanoparticle results were characterized using XRD to determine product purity and TEM to assess particle size distribution.The XRD pattern shown in Figure 1a manifests peaks at 2θ = 31.67°,34.34°, 36.17°,47.42°, 56.46°, 62.73°, 67.84°, and 68.96° corresponding to the characteristic ZnO crystal planes of (100), ( 002), ( 101), ( 102), ( 110), ( 103), (112), and (201) respectively.The elevated peak intensity observed in the (101) plane indicates a favored tendency for the orientation of the (101) crystal plane, thus suggesting a higher propensity for the development of the (101) plane orientation within the hexagonal wurtzite structural framework of ZnO [12].This assertion gains corroborative backing through the comparison of the X-ray Diffraction (XRD) analysis results of the synthesized ZnO samples against the standardized JCPDS reference data for ZnO, as illustrated in Figure 1.Furthermore, the absence of any other discernible peaks implies that there are no additional observable peaks present.As a result, the formed ZnO exhibits a high degree of crystalline structural purity.In Figure 1b, the XRD outcomes for the GO/ZnO variations at ratios of 1:1, 1:2, and 2:1 reveal peaks that correspond to both the GO and ZnO constituents.Notably, there is a distinct peak observed at 26.29°, which aligns with the characteristic GO peak [13].The characterization of nanoparticles is typically accomplished using transmission electron microscopy (TEM), a widely accepted and reliable method for nanoparticle analysis.In Figure 2, the TEM images unveil the morphological properties of the synthesized ZnO nanoparticles through the solvothermal synthesis technique.This method has proven effective in producing particles with dimensions under 30 nm.An extensive measurement of approximately 200 randomly selected particles revealed an average size of roughly 25.19 ± 4.1 nm for the synthesized ZnO nanoparticles, as shown in Figure 2a.Furthermore, the distribution analysis, also presented in Figure 2a, affirms the capability of solvothermal synthesis to yield ZnO nanoparticles with a remarkably narrow size distribution.Remarkably, the transmission electron microscope images illustrate the GO/ZnO nanocomposite, clearly displaying the composite's composition, consisting of uniformly distributed two-dimensional GO sheets embellished with ZnO nanoparticles.The transparency of the GO indicates successful full exfoliation into single or few-layered sheets, and within these layers, the ZnO nanoparticles are discernibly localized, as shown in Figure 2b.Notably, no ZnO nanoparticles exist outside of the GO sheets, strongly indicating the effective synthesis and integration of the GO/ZnO nanocomposite.

Conclusion
In conclusion, the synthesis of GO/ZnO nanoparticles using the solvothermal method has been successfully achieved.The XRD analysis confirmed the crystalline structure of the synthesized ZnO nanoparticles, exhibiting characteristic peaks corresponding to the wurtzite hexagonal structure of ZnO.Furthermore, the presence of an additional peak at 26.29° confirmed the incorporation of GO in the nanocomposite.The characterization of the nanoparticles was conducted using a transmission electron microscope, which revealed that the synthesized ZnO nanoparticles had a mean size of approximately 25.19 ± 4.1 nm with a narrow size distribution.