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The nano-structured Zinc Oxide (ZnO) has been synthesized by using hydrothermal method and modified via doping of Cobalt (Co), Iron (Fe), a mixture of Co and Fe (Co-Fe) for glucose sensing. The formations of pristine ZnO and doped ZnO have been confirmed by X-Ray diffraction (XRD), which suggests the incorporation of doping elements into the ZnO Matrix. The doped samples show a decrement in photoluminescence intensity in comparison to pristine ZnO, which is an indicative of the formation of competitive pathways for the recombination process. (Co-Fe) doped electrode shows better conductivity than other electrodes, which was later modified with Glucose Oxidase (GOx) for the application of electrochemical sensor. GOx modified (Co-Fe) doped ZnO sensor exhibits enhanced 2-fold sensitivity ( $32.2~\mu \text{A}$ mM−1cm−2) in comparison to the pristine ZnO sensors following the linear range of 0–4 mM, response time 6.21 seconds and $K_{m}^{\textit {app}}$ value of 0.054 mM. This sensor would be a potential candidate in clinical diagnosis, industry, and food science.

Gastric cancer, as a complex heterogeneous disease, is one of the most widely recognized malignancies around the world. Gastric malignant growth is the fifth most common disease and the subsequent driving reason for the third leading malignant growth-related mortality (accounted for 8.2%) overall. Early gastric cancer can be cured with surgery, while advanced gastric cancer often needs combined multidisciplinary therapy. Besides early-stage diagnosis, an accurate preoperative staging also can reduce mortality. However, due to the lack of defined risk factors, gastric cancer is facing more challenges in its staging system, such as time constraints, problematic diagnosis, and inconvenient suffering among patients caused by gastroscopy or biopsy. Unfortunately, delayed diagnosis and inadequacies of the staging system may lead to increased mortality. Therefore, it is very demanding to develop a rapid and noninvasive diagnosis technique to realize early detection of gastric cancer and simultaneous staging, and biosensors have been recommended as a capable tool for the early diagnosis of Gastric cancer. This chapter presented a brief report on the role of biosensor for the early diagnosis of gastric cancer.

Zn1−xFexO nanoparticles with different doping concentration i.e. (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) were successfully synthesized via hydrothermal method. The crystal structure, morphology, optical and magnetic properties were studied by X-ray diffraction, field emission scanning electron microscope, UV–visible, photoluminescence spectra (PL) and vibrating sample magnetometer. The experimental results show that all the samples possess a single phase hexagonal wurtzite structure, no impurity phase was observed. The crystallite size decreases with the increase in Fe concentration. Optical absorption analysis by UV–visible exhibits a slight blueshift in the bandgap with increasing doping concentration. PL spectra shows that the emission peak in the UV region is absent for all the samples. All the emission peaks are in the visible region. Shifting of PL emission peaks is not observed indicating that the intrinsic defects are consistent. The magnetic observation indicated that all the samples including pure zinc oxide exhibit room temperature ferromagnetism (RTFM). The observed RTFM is attributed to the bound magnetic polaron that arises due to the presence of singly ionized oxygen vacancy (Vo) as indicated by PL spectra.