MEMS hydrogel sensor. Coloured scanning electron micrograph of a MEMS (microelectromechanical systems) hydrogel sensor. MEMS devices are constructed on a microscopic scale using technologies such as wet and dry etching and thin film deposition. Applications include sensors and optical displays. Materials used to construct MEMS devices include silicon and polymers such as plastics. This device is used for very sensitive measurements, for example of pH, pC02 partial pressure of carbon dioxide) and glucose. Magnification: x748, when printed 10 centimetres wide.