A macro-organic molecule capable of specifically solubilizing an
inorganic ion of suitable size in organic mediums.
ISE (Ion selective electrode)
Ions in solution are quantified by measuring the change in voltage
(i.e. potentiometric) resulting from the distribution of ions (by
ion exchange controlled by the ion exchange current io) between a
sensing membrane (the ion selective membrane) and the
solution. This potential is measured at zero current with respect
to a reference electrode which is also in contact with the
solution. The potential measured is proportional to the logarithm
of the analyte concentration. The oldest and best known ISE is the
pH sensor based on a glass membrane. More recently, polymeric
membranes have been formed incorporating ionophores (see
ionophore) rendering the membrane specific to certain ions only.
ISFET
Ion Sensitive Field Effect Transistor: a logical extension of
ISE's. They can be conceptualized by imagining that the lead from
an ion-selective electrode, attached via a cable to a FET in the
high impedance input stage of a voltmeter, is made shorter until
no lead exists and the selective membrane is attached directly to
the FET. For an ISFET, the property measured is the lateral
conductivity between two opposing doped regions (the source and
drain) surrounding the active area. The underlying change is a
change in flat-band voltage.
Isomorphous
Having the same structure. In the phase diagram sense,
isomorphicity means having the same crystal structure
or complete solid solubility for all compositions.
Isothermal
At a constant temperature. In an isothermal process heat is, if
necessary, supplied or removed from the system at just the right
rate to maintain constant temperature.
Isotropic
Having identical values of a property in all crystallographic
directions.
Kilobyte (kB)
210 (= 1024, or about one thousand) bytes of information.
Kilohertz (kHz)
One thousand cycles per second (see also"frequency").
Kinetic molecular theory
A model that assumes that an ideal gas is composed of tiny
particles (molecules) in constant motion.
Label or marker
A problem endemic in immunoassays is the absence of a chemical
signal created by the antibody-antigen binding, in contrast with
an enzyme-substrate binding reaction which produces a chemical
reaction product. As a result of this absence, the use of a label
or marker is usually required to detect the bound antibody-antigen
complex. Several markers have been established for use in
immunoassays. Examples of such markers are:
