Electrochemical biosensors for biomolecules

Biomolecules can be roughly divided into five categories: nucleic acids, proteins, lipids, carbohydrates, and other small molecules. They are always used as biomarkers or indicators for diseases diagnosis, pharmaceutical development, environmental monitoring, and food safety analysis. Many traditional analytical methods and tools have been employed to detect the biomolecules in vivo or in vitro, such as nuclear magnetic resonance (NMR) spectroscopy, chromatography-mass spectroscopy (MS), polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), fluorescence, and colorimetric detection. With advances in technologies, biosensors are popular and prevalent for biomolecules detection because of their simplicity, sensitivity, small size, and low cost. They can be alternative tools for early diagnosis, instant screening, medication guidance, treatment monitoring, and prognosis analysis of diseases, even in a noninvasive style. In general, sensors are one type of devices that detect physical quantities and convert them into signals that can be read by instruments or observers. Initially, they are mainly applied in factory operations, such as temperature sensors, vibration sensors, proximity sensors, and so on. In 1962, the first biosensor was proposed by Clark and Lyons to measure the glucose in biological samples. Glucose oxidase (GOx) was fixed on an electrode by a semipermeable membrane. Signals were recorded via the measurement of the oxygen consumption which occurred at the enzyme-catalyzed reaction.