A rapid and simple method for quantitative monitoring of Brucella melitensis using electrochemical impedance spectroscopy (EIS) is reported for the first time. The label-free immunosensors were fabricated by immobilizing Brucella melitensis antibody on the surface of gold nanoparticle-modified screen-printed carbon electrodes (GNP-SPCEs). Cyclic voltammetry (CV) and EIS were used to characterize the Brucella melitensis antigen interaction on the surface of GNP-SPCEs with antibody. A general electronic equivalent model of an electrochemical cell was introduced for interpretation of the impedance components of the system. The results showed that the change in electron-transfer resistance (R_ct) was significantly different due to the binding of Brucella melitensis cells. A linear relationship between the R_ct variation and logarithmic value of the cell concentration was found from 4 × 10⁴ to 4 × 10⁶ CFU/mL in pure culture. The label-free impedance biosensor was able to detect as low as 1 × 10⁴ and 4 × 10⁵ CFU/mL of Brucella melitensis in pure culture and milk samples, respectively, in less than 1.5 h. Moreover, a good selectivity versus Escherichia coli O157:H7 and Staphylococcus aureus cells was obtained for our developed immunosensor demonstrating its specificity towards only Brucella melitensis.

Methods that can be used to check the health of fish, determine their physiological condition and detect abnormalities at an early stage, have been attracting recent attention. The health of fish can be determined by the assessment of stress responses, prediction of spawning time, and highly sensitive detection of bacteria that cause diseases in fish, etc. However, it can be difficult to accurately measure these parameters due to factors such as sampling errors, uncontrollable aquaculture conditions and unsound methodological approaches. Also, the methods currently used are time-consuming and may involve complicated processes. Thus, there is a high demand for novel approaches for the assessment of fish health. We have thus focused on the development of a biosensor to measure target factors of fish health by combining biocatalytics and electronics technology. We believe that this technology can greatly improve the assessment of the health of fish produced for consumption. In this article, we described various biosensors that can both rapidly and easily measure indicators of fish health. Future applications of these techniques are also discussed.

Wireless biosensor systems were developed in our lab for monitoring blood glucose concentrations in fish as an indicator of fish stress. However, uniform immobilization of the enzyme on the surface of the electrode is difficult, so the sensor response is typically reduced at a range of high glucose concentrations during the stress monitoring. In this study, we attempted to enhance sensor response by using a self-assembled monolayer-immobilized enzyme. Glucose oxidase was immobilized on a working electrode modified with a self-assembled monolayer. The proposed biosensor showed a good correlation between the output current and the glucose concentration range of 10–3500 mg dL⁻¹ under an optimized working condition. The dynamic measurement range of this newly developed sensor is significantly improved, especially over a high concentration range, which helps the sensor to achieve better performance in dramatic changes in the stress response of fish. In addition, we used biological samples from test fish and obtained a good correlation coefficient between the sensor output current and the glucose concentration using a conventional method. The proposed wireless biosensor system was also applied to monitor fish stress responses in real time through different stressors and to obtain some precise data that reflect real fish stress responses.