Electrochemical Sensors

Transcription

1 Electrochemical Sensors Arthur Gildea ABC s of Electrochemistry 1/26/2012

2 Overview Introduction Reference electrode Biosensors and Immunosensors Potentiometric sensor Amperometric sesnor Conductometric sensor Electrochemical Sensors in CEER Lab Conclusion 2

3 Introduction Ohio University - Avionics Engineering Center 3

4 Introduction History Electrochemical sensors are the largest and oldest group of chemical sensors [1] With the oldest sensor dating back to 1950s, which was used for oxygen monitoring [2] Miniaturized electrochemical sensors that could measure a multitude of different chemical species have been industrially available since mid-1980s [2] Currently electrochemical sensors account for approximately 58% of all chemical sensors [3] 4

5 Introduction [4] 5

6 Introduction Cell Design Electrochemical sensors are electrochemical cell which employs a two or three electrode arrangement Measurements by electrochemical sensor can be taken at steady-state or transient conditions [5] 6

7 Introduction Cell Design In a two electrode system, there is a working and a reference electrode, while three cell system has a work, counter, and reference electrode The working electrode is the electrode where the chemical reaction of interest is taking place The counter electrode or auxiliary electrode allows current to flow between it and the working electrode without effecting the system The reference electrode remains at a constant potential, which allows it to behave independently of the working electrode or the solution being measured while maintaining a constant potential 7

8 Introduction Cell Design Physical size, shape, geometry, selection of electrode material, and construction of electrochemical sensor depends on intended use [2] Cell design effects performance parameters of the electrochemical sensor Examples of performance parameters are sensitivity, selectivity, working range, and limit of detection 8

9 Reference Electrode Ohio University - Avionics Engineering Center 9

10 Reference Electrodes Common Reference Electrodes Standard hydrogen electrode (SHE) Static mercury drop electrode (SMDE) Saturated calomel electrode (SCE) Mercury/mercury oxide electrode Silver/Silver chloride electrode 10

11 Reference Electrodes Current Research into Integrated Reference Electrodes Miniaturize reference electrode (Ag/AgCl electrodes) Hybrid electrodes that can working in acidic and alkaline solution Ex: silver tetramethylbis (benimidazolium) diiodide [6] Making disposable reference electrodes through techniques like screen printing Microfluidic electrochemical sensors Solid-state reference electrodes that do not require liquid junction 11

12 Biosensors and Immunosensors Ohio University - Avionics Engineering Center 12

13 Biosensors Introduction Biosensors utilize immobilized enzymes on an electrode surface They allow for very selective chemical reactions to be measured electrochemically Biosensor can measure a variety of different chemical species, such as glucose, lactate, and urea 13

14 Immunosensors Immunosensors transduce antigen-antibody interactions directly into electrical signals [7] Have become vital in determining biochemical targets relating to health concerns such as cancer [6] 14

15 Biosensors Current Research [6] Use of nano structures to immobilize enzymes, which allows electrodes to have high catalytic activity and high surface area (ex: graphene nano sheets) Protective film membranes, which allow extended life time, better selectivity, and sensitivity (ex: Nafion) New techniques which allow better immobilization of enzymes on nano structures, using other nano structures and ionic liquids 15

16 Immunosensors Current Research [6] Carbon nanotubes are being used to immobilize antigen, which protects and stabilizes species Cancer detection has been a driving force behind much of the research due to inherent specificity and accuracy of immunosensors Sandwich type sensors, which utilize immobilized antibodies to attach antigens to solid surface, while a second antibody carries a detection system, which is usually an enzyme 16

17 Potentiometric Sensors Ohio University - Avionics Engineering Center 17

18 Potentiometric Sensors Introduction Potentiometric sensor apply a current and measure the potential response Linear response used for calibration curve is given by the Nernst equation One of the most commonly used electrochemical sensors, which is the ph meter 18

19 Potentiometric Sensors Current Research [6] Ion selective electrode developments, which has allowed the measurement of minute amounts of ionic species (ex: multiwalled carbon nanotube membranes) Use of room temperature ionic liquids, instead of paraffin, which greatly increases sensor performance PVC membranes used as anion selective membrane 19

20 Amperometric Sensors Ohio University - Avionics Engineering Center 20

21 Amperometric Sensors Introduction Amperometric sensors apply a fixed potential and measure the current response, which is then related to analyte concentration [5,6] Charge and mass transfer at the working electrode surface directly affects the current response, therefore sensors must either be charge or mass transfer controlled 21

22 Amperometric Sensors Current Research [6] Improvements in nonenzyme based glucose and hydrogen peroxide sensors Use of novel new materials, such as nonamaterials and composite materials Screen printed microelectrode arrays, which allow for low cost disposable sensors 22

23 Conductmetric Sensors Ohio University - Avionics Engineering Center 23

24 Conductometric Sensors Introduction Conductometric sensors measures the conductivity change of the system in the presence of a give solute concentration [5] The measure of the conductivity of an electrolyte is often difficult due to polarization of the electrode at the operating potential [5] 24

25 Electrochemical Sensors in CEER Lab Conductiviy meter (Mettler Toledo) Ammonia sensor (Thermo Electron Corporation) ph meter (Oakton, Hanna Instruments) Urea sensor (Developed by CEER) 25

26 Conclusion Oldest and largest branch of chemical sensors Wide range of industrial and research application Designs of sensors are dependant on what is being monitored by the sensor Wide range of new research in order to solve inherent problems of different systems 26

27 References 1. Janata, Jir i. Principles of Chemical Sensors. New York: Plenum, Print. 2. "Electrochemical Sensors." International Sensor Technologies. Web. 25 Jan < 3. Janata, Jiri. "ELECTROCHEMICAL SENSORS." Electrochemistry Encyclopedia. Sept Web. 24 Jan < 4. Gushikem, Yoshitaka, and Simone S. Rosatto. "Metal Oxide Thin Films Grafted on Silica Gel Surfaces: Recent Advances on the Analytical Application of These Materials." Journal of the Brazilian Chemical Society 12.6 (2001). Print. 5. Liu, Chung-Chiun. "Electrochemical Sensors." CRC LLC, Print. 6. Kimmel, Danielle W., Gabriel LeBlanc, Mika E. Meschievitz, and David E. Cliffel. "Electrochemical Sensors and Biosensors." Analytical Chemistry (2011): Print. 7. Tiefenauer, L., and C. Padeste. "Immunosensor." Laboratory for Micro- and Nanotechnology. Paul Scherrer Institut, 23 July Web. 25 Jan < 27

28 For more information contact: