Electrochemical Sensors

Transcription

1 Introduction to BioMEMS & Medical Microdevices Sensor Principles and Microsensors Part 2 Companion lecture to the textbook: Fundamentals of BioMEMS and Medical Microdevices, by Prof., Electrochemical Sensors Potentiometric Sensors Ion selective electrodes (ISE) into the nanodimension range New ion recognition chemistries New ion selective membranes Importance of the reference electrode Voltametric Sensors Carbon paste electrodes (CPE) for organic molecule detection Micro and Ultramicro electrodes Environmental monitoring Carbon nanotubules Stripping voltammetry Privett, Benjamin J., Jae H. Shin, and Mark H. Schoenfisch Electrochemical Sensors. Analytical Chemistry 82, no. 12: Electrochemical Sensors Electrochemical Biosensors Selective and sensitive biological binding Aptamer-based biosensors Glucose, creatinine, pathologic bacteria, DNA Enzyme biosensors Immunosensors Bacteria, virus and cancer biomarkers Ion Selective Field Effect Transistors Based on the electrochemical phenomena occurring within the chemically sensitive membrane placed on top of the transistor gate and on electrical transduction of the signal by this semiconductor device. Privett, Benjamin J., Jae H. Shin, and Mark H. Schoenfisch Electrochemical Sensors. Analytical Chemistry 82, no. 12:

2 Ion Selective FET Photocurable polymers have been used for encapsulation of ion selective field effect transistors (ISFET) and for membrane formation in chemical sensitive field effect transistors (ChemFET). Charge Carriers In Charge Carriers Out G D G D S S P- Channel N- Channel Shown: Insulated Gate Field-Effect Transistor (IGFET). MOSFET (metal oxide is common). How a Field Effect Transistor Works Silicon (semiconductor) substrate. A B S G D A small signal on the plate above (gate) brings electrons to the surface, allowing current to flow and amplifying the original signal. ISFET Fabrication Polyimide covered by a standard photoresist and photocurable epoxy acrylate. The polymer layer after being applied to a wire bonded sensor glued to some substrate can be patterned using traditional photolithography techniques. Left: ISFET with photocurable encapsulate (1), with openings over the gate (2), contact pads (3) and scribing lines (4). Center and Right: Mounting, wire bonding and encapsulation. 3mm opening 2

3 Membrane Formation The best known method of ISFET membrane formation comes from traditional ion selective electrodes and is based on using a polymer matrix which is deposited over an ISFET gate and contains the required ion active components, like ionophore, plasticizer and lipophilic additives. Achievements in development of traditional ISE with liquid inner contact resulted in hundreds of different membrane compositions that can be used as well in case of ISFETs. Applied Polymer and Analyte 3

4 Optical Sensors Optical chemical sensors are usually configured as transducers, with transductions steps of electricaloptical-chemical-optical-electrical conversion: Boisde, G. and A. Harmer, Chemical and Biochemical Sensing with Optical Fibers and Waveguides, Artech House, Boston (1996) Optical Fiber Blood Pressure Sensor Esashi, Masayoshi Revolution of Sensors in Micro-Electromechanical Systems. Japanese Journal of Applied Physics 51, no. 8:

5 Optical Fibers An optical fiber consists of a solid cylindrical core of transparent material surrounded by a cladding of similar material but of lower refractive index than the core: Refractive Index & Snell s Law The refractive index is the ratio of the speed of light in a vacuum to the speed of light in the medium: c n c vacuum material 1 Snell s law defines the relationship between incident and refracted light, measured as an angle from a perpendicular to the surface: n sin I n sin R i r Critical Angle Refraction can not take place when the angle of incidence is too large, or greater than the critical angle. For air (refractive index of 1) and glass (refractive index of 1.5), the critical angle is defined as: arcsin( n / n ) 41.8 c r i ο 5

6 Acceptance Angle The acceptance angle is the angle over which light rays entering the fiber will be guided along its core: Numeric Aperture Numeric Aperture (NA) is the light gathering ability of a fiber. The material NA relates to the refractive indices of the core and cladding: sin 0 NA n n n sin Where n0 is the core index, n1 is the cladding index, and is half the acceptance angle, and is the confinement angle. c c Modes Light propagates through the core in a series of wave fronts or modes. Sterling, D.J., Technicians Guide to Fiber Optics, 3rd ed. Delmar Publishers, Albany, N.Y. (2000) 6

7 Applications in Medicine Glucose and anticoagulation monitoring: Images courtesy of LifeScan, Inc. and HemoSense, Inc. Temperature: Image courtesy of Braun Harsanyi, G., Sensors in Biomedical Applications, Technology and Applications. Technomic Pub. Co., Lancaster, PA (2000) Pressure: Fraden, J. Noncontact temperature measurement in medicine. Bioinstrumentation and Biosensors, D.L. Wise, Ed, Marcel Dekker (1991). 7

8 Intraocular pressure: Bergveld, A.P., The merit od using silicon for the development of hearing aid microphones and intraocular pressure sensors. Senors and Actuators 41:42, pp (1994) Pulse oximetry: Parker, D. Sensors for monitoring blood gasses in intensive care. J Phys. E. Sci. Instrum. 20, pp (1987). 8

9 Respiratory spirometry and CO 2 : Implanted pacemaker and rhythm monitor: Summary Electrochemical Sensors Potentiometry Sensors Voltametric Sensors Electrochemcial Biosensors Immunosensors Ion Selective Field Effect Transistors (ISFET) and Chemical Sensitive FET (ChemFET). Optical Sensors Optical chemical sensors Fiber optics Clinical Applications 9