Assay buffer, compositions containing the same, and methods of using the same

A method of conducting an electrochemiluminescence (ECL) assay for detecting a phosphorylated peptide or protein or phosphorylation of a peptide or protein in a sample, said method comprising:

• (a) contacting an assay electrode with said sample and a phospho-specific antibody comprising an ECL label, said assay electrode including a binding domain comprising a binding reagent immobilized thereto, wherein said binding reagent is specific for said phosphorylated peptide or protein, said contacting step thereby forming a complex immobilized to said electrode, said complex comprising said binding reagent, said phosphorylated peptide or protein, and said phospho-specific antibody;
• (b) contacting said electrode with an ECL assay buffer, wherein said ECL assay buffer has a concentration of less than 5 mM inorganic phosphate and comprises an ECL coreactant, glycylglycine and an organic co-solvent;
• (c) applying electrochemical energy to said electrode under conditions suitable to induce ECL labels on said antibody to emit electrochemiluminescence;
• and
• (d) measuring emitted electrochemiluminescence;
• wherein a phosphorylated peptide or protein, or phosphorylation of a peptide or protein, is detected by an increase in electrochemiluminescence.