One of the problems that has arisen in spotting DNA onto membranes or glass
slides has been that the spotting solutions often have high surface tension
which results in variable volume hanging drops and therefore, variable spot
diameters. We had first noticed that distilled water has a very high
surface tension and when just used with dye (food coloring) to make practice
arrays this mixture produced very irregular spot sizes. We also found that
the irregular spot size
can be eliminated by adding a detergent such as Tween 20, Sarkosyl, or proteins,
carbohydrates or carrier DNA to the solution. However there are many
protocols where it is not possible to add these surface tension lowering compounds
to the solution.
Another way to address the problem of high surface tension liquids is
to clean the pins with our VP 110 solution (diluted before
use) which cleans the pin of proteins and
other residues and changes
the surface tension of the pin thus compensating for the high surface tension of
the liquid. Just dipping the pins into
this solution briefly cleans the pins and changes the surface tension of the pin. The pins are washed in
water and ethanol to remove any residual solution and used right away.
This pin cleaning treatment results in very uniform dispense volumes.
Another problem encountered with pin tools is that if they are not cleaned
after use or if they are contaminated by finger oil they will not deliver a consistent
volume. One 10 second treatment with the V&P Pin Cleaning Solution removes built
up protein and oils and dramatically improves delivery consistency.
Another similar problem with high surface tension buffer solutions is that they do
not wick and fill slot pins uniformly. This also results in variable spot
This phenomenon can also be over come by cleaning the slot pins with the V&P
Pin Cleaning Solution as above. The ability to have slots fill by capillary action is
very desirable when working with small volumes of DNA or PCR reaction products.
This wicking ability allows you to recover even the "dregs" at the
bottom of a PCR well.
The 2 ul slot blots to the right were made with a VP 408S2 Slot Pin Replicator
using just distilled water and 5% red food coloring on Hybond-N
Nylon membrane (Amersham Pharmacia, P/N RPN 1510 N) illustrates the problem.
Once the V&P Pin Cleaning Solution has cleaned the slots and modified the surface tension of the
pin, the modified surface tension
remains even after 15 rinses in 100% ETOH or distilled
water. It even remains on the pins after treatment with 5% bleach. Thus the replicator pins can be used for many blots or transfers without
re-treatment. We recommend that the V&P Pin Cleaning Solution be diluted 1
to 5 and used at the beginning of each spotting session. After dilution
and use, the V&P Pin Cleaning Solution can be stored and used again and again.
V&P Pin Cleaning Solution, concentrated solution, 30 ml/bottle.....VP
When it comes to keeping pins clean the type of blotting paper used is also
very important. Cheap blotting paper contains lint which can stick to the
pin tips and interfere with pickup of liquid on the pins. We strongly recommend
lint free blotting paper.
We also have a super absorbent polypropylene pad in a tray covered by lint free
that will hold up to 27 ml of liquid. This means you can make 100-10,000
blots with out changing the blotting paper.
We have also found you can significantly lower the surface tension on the pin by flaming**
from ETOH or isopropanol. This also results in very uniform drop size and slot
filling. This is convenient if you can accommodate flaming in your
replicating or spotting procedure.
* Triple dipping entails removing the pins from the bath and
immediately dipping back in 3 times. This gives a thorough washing of the
** Flaming just entails igniting the alcohol on the pin and
NOT heating the pins directly in a Bunsen burner which can damage the corrosion
resistant properties of the stainless steel pins.
Pin Cleaning Solution Treatment
Pin Cleaning Solution Treatment