Bead diluent

Carboxylated 2.7 μm paramagnetic beads (∼4
× 10⁸) were washed three times with 200 μL of
bead wash buffer
(0.1% Tween 20 in 1x PBS, pH 7.4) and twice with 200 μL of MES
buffer (50 mM MES, pH 6.2). EDC and sulfo-NHS were reconstituted in
MES buffer to a final concentration of 25 mg/mL. EDC and sulfo-NHS
(100 μL each) were added to the beads. The beads were activated
on a shaker for 30 min. After activation, the beads were washed three
times with bead wash buffer. The activated beads were dispersed in
150 μL of bead wash buffer, and subsequently, 50 μL of
2 mg/mL Abltide or Srctide or EA2 in water were added. For the preparation
of telomerase substrate beads, 10 nmol of the substrate DNA was diluted
into 200 μL of bead wash buffer and added to the activated beads.
The beads were incubated at room temperature with shaking for 3 h,
washed three times with bead wash buffer, and incubated in 200 μL
of Bead Diluent (Quanterix) with shaking for 1 h. The beads were then
washed three times with bead wash buffer and resuspended in 200 μL
of Bead Diluent for further use. Histone H3 protein-coated beads and
antiphosphotyrosine antibody-coated capture beads were prepared according
to a previously published method.^{23 (link)} The
beads were counted using a Beckman-Coulter multisizer.