Ultrasensitive assay for tau and methods of use thereof for assessing traumatic brain injury in tissues and biofluids

An ultrasensitive assay for quantifying total tau (T-tau) and/or phosphorylated tau (P-tau) in a biological sample, comprising:

• a) obtaining a biological sample from a subject;
• b) contacting said sample with capture antibodies that are immunologically specific for P-tau or T-tau, said capture antibodies binding said T-tau or P-tau when present in the sample;
• c) contacting said antibody-bound total tau or phosphorylated tau with a biotinylated detection antibody;
• d) contacting antibody-tau complexes formed in step c) with streptavidin;
• said streptavidin binding any biotinylated antibody in said antibody complexes;
• e) contacting the streptavidin-biotin-antibody complexes of step d) with a biotinylated primer, a T4 DNA ligase-pretreated DNA template, DNA polymerase reaction buffer, bovine serum albumin, nucleotide triphosphates supplemented with dUTP-sulforhodamine 101 acid chloride and DNA polymerase thereby forming a reaction mixture, under conditions suitable for rolling circle amplification (RCA) to occur, thereby generating a fluorescent signal;
• f) neutralizing said reaction mixture;
• and
• g) subjecting the mixture of step f) to fluorescence analysis using surround optical detection, thereby quantifying the levels of total tau and/or phosphorylated tau in said sample.