Novel sensitive, rapid and economical biosensors are being developed in a wide range of medical environmental and food applications. In this paper, we review some of the main advances in the field over the past few years by discussing recent studies from literature. A biosensor, which is defined as an analytical device consisting of a biomolecule, a transducer and an output system, can be categorized according to the type of the incorporated biomolecule. The biomolecules can be enzymes, antibodies, ssDNA, organelles, cells etc. The main biosensor categories classified according to the biomolecules are enzymatic biosensors, immunosensors and DNA-based biosensors. These sensors can measure analytes produced or reduced during reactions at lower costs compared to the conventional detection techniques. Numerous types of biosensor studies conducted over the last decade have been explored here to reveal their key applications in medical, environmental and food industries which provide comprehensive perspective to the readers. Overviews of the working principles and applications of the reviewed sensors are also summarized.

Coronavirus Disease‐19 (COVID‐19) is an infectious disease caused by severe acute respiratory syndrome‐coronaviruses‐2 (SARS‐CoV‐2), a highly pathogenic and transmissible coronavirus. Most cases of COVID‐19 have mild to moderate symptoms, including cough, fever, myalgias, and headache. On the other hand, this coronavirus can lead to severe complications and death in some cases. Therefore, vaccination is the most effective tool to prevent and eradicate COVID‐19 disease. Also, rapid and effective diagnostic tests are critical in identifying cases of COVID‐19. The COVID‐19 pandemic has a dynamic structure on the agenda and contains up‐to‐date developments. This article has comprehensively discussed the most up‐to‐date pandemic situation since it first appeared. For the first time, not only the structure, replication mechanism, and variants of SARS‐CoV‐2 (Alpha, Beta, Gamma, Omicron, Delta, Epsilon, Kappa, Mu, Eta, Zeta, Theta, lota, Lambda) but also all the details of the pandemic, such as how it came out, how it spread, current cases, what precautions should be taken, prevention strategies, the vaccines produced, the tests developed, and the drugs used are reviewed in every aspect. Herein, the comparison of diagnostic tests for SARS‐CoV‐2 in terms of procedure, accuracy, cost, and time has been presented. The mechanism, safety, efficacy, and effectiveness of COVID‐19 vaccines against SARS‐CoV‐2 variants have been evaluated. Drug studies, therapeutic targets, various immunomodulators, and antiviral molecules applied to patients with COVID‐19 have been reviewed.

Nanostructured metal oxides (NMOs) provide electrical properties such as high surface-to-volume ratio, reaction activity, and good adsorption strength. Furthermore, they serve as a conductive substrate for the immobilization of biomolecules, exhibiting notable biological activity. Capitalizing on these characteristics, they find utility in the development of various electrochemical biosensing devices, elevating the sensitivity and selectivity of such diagnostic platforms. In this review, different types of NMOs, including zinc oxide (ZnO), titanium dioxide (TiO₂), iron (II, III) oxide (Fe₃O₄), nickel oxide (NiO), and copper oxide (CuO); their synthesis methods; and how they can be integrated into biosensors used for medical diagnosis are examined. It also includes a detailed table for the last 10 years covering the morphologies, analysis techniques, analytes, and analytical performances of electrochemical biosensors developed for medical diagnosis.

A novel design optimization strategy is proposed to enhance the analytical performance of a biosensor by taking into consideration the constructional and experimental parameters as design variables. A detailed study on multiple nonlinear neuro-regression analysis has been performed methodically in order to overcome the insufficient approaches on modeling-design-optimization of a biosensor. For this aim, the data were selected from a literature study. A hybrid method is used to test the accuracy of the predictions of 12 candidate functional structures that were proposed for modeling the data. The boundedness of the candidate models is checked after the calculation of R²_training and R²_testing values to reveal whether the model is realistic or not. Then appropriate models were optimized by using the four different optimization algorithms in terms of three different optimization scenarios. The results show that all the models express the process well regarding R²_training. However, only four models are appropriate based on R²_testing, and two of them were selected as the objective function depending on to be a realistic value. This novel optimization approach is also feasible for another modeling-design-optimization problem in analytical applications.

The easy design of an enzyme electrode using tyrosinase immobilized magnetite chitosan nanobiocomposite film (TMCG) and its applicability for electrochemical sensing platform are reported in this work. The sensor components were characterized by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Stable biomaterial was obtained by chemical immobilization of the enzyme to chitosan structure with glutaraldehyde. Magnetite nanoparticles were homogeneously distributed on the chitosan surface. Nyquist curves revealed that, chitosan and tyrosinase enzyme exhibit higher resistance to the electron transfer while magnetite nanoparticles promote the electron transfer as a result of their nanostructure behaviors. In addition to well defined oxidation peak, new reduction peak was observed from CV analysis after magnetite modification as a result of electrochemical reduction of enzymatically produced o-quinone to the catechol. The developed biosensor (TMCG^*) selectively detected the catechol at a sensitivity of 0.057A/M in a linear range from 1 μM to 30 μM with a detection limit of 260 nM and K_m value of 22.5 μM. These findings strongly indicate that TMCG^* is applicable as an electrochemical sensing platform for detection of the sample that inhibits the tyrosinase enzyme in tap water.