Advances in enzyme-free electrochemical sensors for hydrogen peroxide, glucose, and uric acid

Endogenously produced pro-oxidant reactive species are essential to life, being involved in several biological functions. However, when overproduced (e.g. due to exogenous stimulation), or when the levels of antioxidants become severely depleted, these reactive species become highly harmful, causing oxidative stress through the oxidation of biomolecules, leading to cellular damage that may become irreversible and cause cell death. The scientific research in the field of reactive oxygen species (ROS) associated biological functions and/or deleterious effects is continuously requiring new sensitive and specific tools in order to enable a deeper insight on its action mechanisms. However, reactive species present some characteristics that make them difficult to detect, namely their very short lifetime and the variety of antioxidants existing in vivo, capable of capturing these reactive species. It is, therefore, essential to develop methodologies capable of overcoming this type of obstacles. Fluorescent probes are excellent sensors of ROS due to their high sensitivity, simplicity in data collection, and high spatial resolution in microscopic imaging techniques. Hence, the main goal of the present paper is to review the fluorescence methodologies that have been used for detecting ROS in biological and non-biological media.

Electrochemical biosensors combine the sensitivity of electroanalytical methods with the inherent bioselectivity of the biological component. The biological component in the sensor recognizes its analyte resulting in a catalytic or binding event that ultimately produces an electrical signal monitored by a transducer that is proportional to analyte concentration. Some of these sensor devices have reached the commercial stage and are routinely used in clinical, environmental, industrial, and agricultural applications. The two classes of electrochemical biosensors, biocatalytic devices and affinity sensors, will be discussed in this critical review to provide an accessible introduction to electrochemical biosensors for any scientist (110 references).

Wide-scale point-of-care diagnostic systems hold great promise for early detection of cancer at a curable stage of the disease. This review discusses the prospects and challenges of electrochemical biosensors for next-generation cancer diagnostics. Electrochemical biosensors have played an important significant role in the transition towards point-of-care diagnostic devices. Such electrical devices are extremely useful for delivering the diagnostic information in a fast, simple, and low cost fashion in connection to compact (hand-held) analyzers. Modern electrochemical bioaffinity sensors, such as DNA- or immunosensors, offer remarkable sensitivity essential for early cancer detection. The coupling of electrochemical devices with nanoscale materials offers a unique multiplexing capability for simultaneous measurements of multiple cancer markers. The attractive properties of electrochemical devices are extremely promising for improving the efficiency of cancer diagnostics and therapy monitoring. With further development and resources, such portable devices are expected to speed up the diagnosis of cancer, making analytical results available at patient bedside or physician office within few minutes.