A simple, low cost & easy to build DIY apparatus is presented for measuring enzyme reaction rates that uses solution conductivity as the detection method.


Novel AC bridge uses two conductivity cells for enhanced differential sensitivity


The experimental device, its design, construction and use.


Don't expect it to look too tidy - it's simple breadboard DIY at present - but it works very well! Could easily be miniaturised



                        CONTENTS (see Menu above):



Intro (Basic & General) - can be skipped if you know about conductivity & enzymes


Intro (Specific & Technical)


The Kit (Equipment Design & Electronics)


Some Example Results - urease catalysed hydrolysis of urea


Potential Applications: enzyme assays & kinetics, clinical tests, school/university projects - works for most enzyme reactions




                            NEWS & UPDATES

             NEWS AND RECENT ADDITIONS      




Recently added is a new section detailing the construction of low cost electrodes made from pencil leads. Use of these in place of the original commercial (RS) electrodes saves some £50 in the overall cost of the apparatus. They are easy to construct, work very well and are robust & reliable in use.




OOps - The 1M ohm feedback resistor was missing from the original thermostat circuit - has now been included! Apologies.


Following a re-examination of the use of a 741 OPAMP in place of the long-tailed pair as the differential amplifier, it has been found to be better, particularly in the removal of common mode signals that (inevitably) arise from transients on the input square wave signal. A lower balance null voltage* is achieved and the noise is lower.

* Never quite zero owing to residual ac components that arise from electrode polarisation (see next section). NEW CIRCUIT SHOWN IN ELECTRONICS SECTION


The effects of electrode polarisation can be reduced by increasing the frequency of the input square wave. By changing just one resistor the frequency has been raised from 10.3 kHz to 27.8 kHz. A transient on the rising edge of the input waveform is effectively attenuated by the use of the 741 (above).


CALIBRATION, Linearity etc. [see sub-page to RHS of Results]


Following detailed studies of the above new information is being added to the calibration section. Guidelines have been evolved for allowing very sensitive measurements over a 100,000-fold range of conductivity.






















                                  TOP NEXT PAGE

                  Enzyme Assays,

simple widely applicable assays that measure changes in solution conductivity    






Site is configured as long pages, links underlined: BLUE

Equipment performance tests SUBPAGE to RHS of Results

Applications to RHS of HOME



NEWS & UPDATES at the bottom of this page for latest developments revisions etc.