a sample for delivery. Pre-wetting the tip influences
accuracy by increasing the humidity within the
tip, minimizing evaporation of the solution. This is
particularly important for solvents with high vapor
3. Work at room temperature: Allow liquids to ambient
temperature. Make sure the tips and solution are at
4. Use consistent plunger pressure and speed: Depress
and release the plunger smoothly and consistently for
each sample. The fatigue and strain caused due to this
is minimized in new generation pipettes due to their
5. Use the correct pipette tip: Securely attach a tip
designed for use with the pipette. Pick out fresh and
uncontaminated tips only. Do not reuse pipette tips. If
the shape of the pipette is disfigured, discard and use a
6. Storage and maintenance: Always store pipettes in an
upright position when not in use. Pipette stands are
ideal for this purpose. Check calibrations regularly,
Criteria for Choosing the Right Pipette
In order to maximize the accuracy and reproducibility
of volume delivery using micropipette, it is critical to
evaluate all of the components comprising the volume
delivery system. The choice of pipette, the selection of the
most appropriate instrument of the application, should
be based on prioritizing various criteria characterizing
instrument performance. The choice of pipette tip is also
critical to performance. The following is a list of criteria
that can be used in choosing a pipette.
The following are problems to watch out for when
reviewing pipette performance:
¾ Pipettes with advertised ranges that exceed the
performance tolerance provided by the manufacturer
¾ Pipettes whose tolerances are too tightly specified;
these will have trouble meeting the manufacturer’s
¾ Mulltichannel pipettes with tolerances that are
interchannel statistics as opposed to intrachannel
A pipettes’ durability is primarily a function of the
sturdiness of its components. In general, the thicker the
plastic the more durable the pipette.
Whatever pipette an end-user chooses, it is critical that
the end-user feels comfortable pipetting for the extended
periods of time typical of much of lab use. If a pipette is
too large for the end-users hand it is extremely likely that
it would cause repeat motion related injury to the hand.
In addition, it would be more difficult for the end-user
to develop proper technique that would deliver accurate
There are several types of pipettes designed for specific
applications. For example–autoclavibility. It is important
to check for the following information:
¾ Is the entire pipette autoclavable, or are only some
¾ What are the recommended conditions for autoclaving?
¾ Can the plastic used for the pipette’s body, shaft and tip
cones can withstand exposure to UV light?
¾ What are the chemical compatibilities and
incompatibilities of the pipette?
¾ How supportive the manufacturer and or the distributor
¾ How responsive is customer service on warranty issues?
¾ How knowledgeable is the technical staff in terms of the
mechanics and technical specifications of the pipette?
¾ How accessible is the manufacturer for visits?
Use of Multiple Brands of Pipettes
1. The need to train technical staff on each type of pipette
separately. Different brands may use different designs
for the pipetting mechanisms requiring differences
in pipetting technique. These pipettes may require
the application of different amounts of force while
pipetting which is a skill that requires training and
a single tip for all brands. Unfortunately the choice of
single tip ends up in a compromise given the variety
of shapes and plastic compositions of tips.
Streptavidin-Biotin Systems, Better than Traditional
Streptavidin-Biotin Based IEMA Systems use a biotinylated
antibody (biotin-labeled 1st antibody/capture). This is
because biotin can be attached to the FC portion of an
antibody in relatively high proportion without loss of
The binding ratio of Avidin to Biotin is 4:1. One molecule
of Streptavidin, which is a tetramer can bind with four
molecules of Biotin/Biotinylated 1st Antibody.
In a traditional enzyme immunoassay, a limited space
is normally available for coating the Capture/1st Antibody
in the bottom of the microwell/plastic tube.
Ideally, if one can increase the number of Capture/1st
Antibodies coated on the microwell, the assay sensitivity
goes up because more number of Antigen binding sites
are available in case of low concentration of analytes
(Antigens) present in the sample.
Streptavidin–biotin based systems coat streptavidin
on the microwell/plastic tubes instead of directly coating
the capture/1st antibody. Capitalizing the tetrameric
valency of streptavidin to biotin, each molecule of coated
streptavidin binds with four molecules of biotinylated
capture/1st antibody thus providing an excess of binding
sites to the system, which ensures four fold higher
sensitivity of the IEMA system.
In other words, the streptavidin-biotin system helps to
increase the number of binding sites and thus increasing
the chances and probability of binding an antigen to an
Streptavidin possess greater electrostatic attraction for
Streptavidin/avidin is more inert in assay systems.
Why Streptavidin-Biotin Based Lema Systems are a
Better Choice for Tropical Laboratories?
Stability: The binding of avidin and biotin is not disturbed
by extremes of salt, pH or temperature.
Specificity and sensitivity: Avidin has a very high binding
affinity for biotin and so the system avidin-biotin is highly
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