SPI-Mark™ Cationic Colloidal Gold Conjugates
Conjugates
Conjugates
The colloidal gold is made cationic by careful conjugation to poly-Llysine,
a highly positively charged amino acid chain. For conjugates
of 5nm and larger the product is supplied in a Tris buffer containing
1% BSA and 20% glycerol at pH 7.
The glycerol content allows the gold conjugate to be frozen for long term storage.
The SPI-Mark 1nm cationic gold conjugate contains no glycerol but 1%
polyethylene glycol and is provided at pH 3 for extra stability. It
should not be frozen. Good stability of any of the gold conjugates is
achieved by storage at 4°C.
SPI-Mark Cationic Gold is available for electron microscope studies in
ultrathin sections and for light microscope sections in paraffin wax,
resin or cryo sections. As with detection of antigens by
immunolabeling, the preparation of the specimen may determine
the final results. Best results to date have been achieved using
acrylic resins such as LR White or Unicryl.
Cationic gold works by inducing, at low pH, a greater net positive
charge on the lysine coating the gold particles (due to its high
isoelectric point) than on the tissue. All proteins in the tissue take on
a more positive charge at low pH but the lysine is most likely to be
more positively charged than most components and is attracted to
the most anionic sites first. Adjustment of the pH will govern the
range of anionic sites that can be labeled. The anionicity of the
tissue components is determined by the amino acids that make up
the restive proteins.
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