An interdepartmental team of scientists at Oxford University has developed a new type of microelectrode electrochemical biosensor. The development marries an electrochemical enzyme selective analytical technique with semiconductor and materials processing technology.
Over the past five years the Dept of Engineering Science has been working with chemistry Professor Alan Hill to make an electrochemical sensor which is based on an array of tiny microelectrodes. The advantages of small charging capacitance, good radial diffusion kinetics, rapid response time and a simple and easily interpreted current-voltage behaviour outweigh the disadvantages of a small Faradaic current. This can be circumvented by making an array of 100-200 such electrodes, spaced far enough apart so that they behave independently and are connected in parallel.
Initially the team made devices which were based on a gold-silicon wafer technology and used conventional photolithography and semi-conductor device-processing techniques to make the arrays of micro-electrodes. While gold can be ‘functionalised’ with a variety of enzymes, it is far from the ideal electrode material. The team has been investigating cheaper materials and alternative technologies. Carbon is emerging as the favoured electrode material and is being made by a variety of methods, ranging from using screen-printable inks to sputtered graphite layers.
A technology based on making a glassy carbon electrode from a spin-coated sugar or polymer solution which is overcoated with an insulating glassy layer of silica in which holes are defined using polymer spheres has been patented recently by the team. This material reduces the cost of manufacture enormously and lends itself to the preparation of microelectrodes on a wide variety of curved and shaped surfaces.Thus, multi-analyte biosensors can be made which will detect a wide range of compounds in medical or environmental applications. The future looks exciting.