Altklausur

• Leland Clark

• gave the initial concept of an enzyme electrode for glucose determination

Simplification of analysis methods

at high pH

• other monovalent cations compete with H+ ions

• they partially reach the gel layer, hindering H+ ions to interact

• slope is smaller than theoretically described in Nernst equation

at low pH

• due to their high activity, some of the H+ ions will be “trapped” by anions and affect the signal

  • slope is smaller than theoretically described in Nernst equation

working electrode: Si, Ta2O5, SiO2

counter electrode: platin

reference electrode: Ag/AgCl

membrane: Teflon, GOD, ion-selective membrane containing ionophore

• consists of inner sensing element (e.g. pH-ISE and reference), surrounded by a gas-permeable membrane

• internal solution is weakly buffered

• if CO2 gas diffuses through the membrane, the pH of the internal solution changes

• CO2 determination in blood

• Enzymes

• DNA

• Antibodies/ Antigens

• Aptamers

• Microorganisms

• Cells

• synthetic polymers

• protein

• ionophore is a molecule that selectively binds and transports a given ion across the membrane, making the membrane only permeable to the ion of interesr

• ionophore is a complexation of primary ion by means of selective cavity

• optical

• electrical

• thermal

• magnetic

• electochemical

• mass-sensitive

• pH

• ionic strength -> Debye length

• surface charge of underlying gate

• ssDNA density

• ssDNA length

• immobilization methode

• length of linker molecules

• reference electrode

ISFET:

-> ion-sensitive field-effect transistor

• Si chip, which combines the pH-sensitive membrane of pH glass electrode with the amplification of a conventional metal-oxide-semiconductor FET

• varying pH results in potential shift

• potential shift affects the drain current flowing between source and drain of ISFET

• after calibration with standard solutions the variation of drain current can be used to determine the unknown H+-concentration

EIS:

-> electrolyte-insulator-semiconductor

• pH change leads to change of the width of depletion layer (p-SI: pH increase -> decrease width of depletion layer)

• change of space-charge capacity leads to shift of C-V curve

LAPS:

-> light-addressable potentiometric sensor

• capacitive field-effect sensor with additional light souce (e.g. laser, LED)

• applied voltage defines depletion layer

• LAPS is illuminated with light -> generation of electrone-hole pairs that diffuse into the space charge region to recombine or to be seperated in the electric field

• change in analyte concentration changes the space charge region -> change of photocurrent

• due to light addressability LAPS can be divided into different areas which function as indipendent sensors

• optical transducers use the variation of electro-magnetic radiation (e.g. fluorescence, absorption, reflectance, luminescence) due to interaction with analyte

• Surface plasmon resonance (SPR) is used

  -> charge-density oscillation that occurs at the interface of two media seperated by a thin metal layer in the conditions of total internal reflectance

  -> SPR is the consequence of the oscillation of mobile electrons (surface plasmons) on the metal surface

• QCM has a cross-sensitivity towards temperature and electromagnetic noise and has to be operated under thermostatic conditions and in Faraday cage

• because of the low depth of the surface waves, a more massive substrate can be used than with QCM

  -> higher mechanical strength

• oxidation is a way to produce a thin layer of oxide (SiO2) on the surface of a wafer

• for wet oxidation water vapor is used as oxidant

  -> Si + H2O -> SiO2 + 2H2

• for dry oxidation molecular oxygen is used as oxidant

  -> Si + O2 -> SiO2

• typical thicknesses are about 200 nm

  -> 1 µm SiO2 requires about 0,44 µm Si