Sentence:  Secondary goat anti-rabbit antiserum coupled to horseradish peroxidase at a dilution of 1:500 in <WSD>blotto</WSD> was then incubated with the blot for 1 hour. Again the unbound antibodies were removed by three rinses in 10% <WSD>blotto</WSD> for 15 minutes. 
Meaning of the word marked with <WSD> tags:  A reagent made from non-fat dry milk, phosphate buffered saline, and sodium azide, which is used to block protein binding sites for laboratory techniques such as blots and the enzyme-linked immunosorbent assay (ELISA).