SPI-Mark™ Unconjugated Colloidal Gold Probes
Some further considerations on stability of the unconjugated gold
Unconjugated colloids are unstable in salt solutions. They will not
immediately collapse but at 150mm there will be a gradual moving together of
the particles as the ionic distribution around the particles is altered.
There is nothing keeping the particles from touching.
One can coat the particles and then add salt. If you want to avoid protein,
then a polymer will work, but it must be remembered that unless the polymer
is adsorbed onto the surface it will merely be keeping the particles apart
by intervention and will only delay the collapse by salt solution. Polymers
which may be suitable for adsorbing onto the surface will include any which
have a hydrophobic or sulphur content. Many polymers have been used
historically with mixed results, eg PVP, PVA, PEG. A polymer which
incorporates a thiol group could prove the best because of the interaction
between sulphur and gold.
A description of the binding forces between gold particles and molecules is
given in the IVD article "The Place of Gold in Rapid Tests", J Chandler,
T Gurmin and N Robinson, IVD Technology, March/April, 2000, p37-49.
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Sunday March 21, 2010
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