BlockOut® allows for superior signal detection and lower background noise in colorimetric, chemiluminescent, and fluorescent western blotting and other applications making it a convenient general purpose blocking agent. Antibody conjugates prepared with IRDye® 800 and IRDye® 700DX (Licor), Cy2™, Cy3™, Cy3.5™, Cy5™ and Cy5.5™ (Cytiva), DyLight™405, DyLight™ 549, DyLight™ 649, DyLight™ 680, and DyLight™ 800 (Thermo Fisher/Pierce) and Alexa Fluor® 488, Alexa Fluor® 532, Alexa Fluor® 546, Alexa Fluor® 647 and Alexa Fluor® 680 (Invitrogen/Molecular Probes) and ATTO (Atto-Tec) have been validated on various platforms using this product with superior results compared to other commercially available products. In the infrared range, where little to no autofluorescence occurs, specific signal is sharply evident from any background giving the best possible signal-to-noise ratio. This allows for detection levels in the picogram range which rivals the sensitivity of chemiluminescence on film for western blotting. Superior results are also seen when this product is used for simultaneous labeling (multiplex) in western blots or microscopy using various fluorochrome combinations for multicolor imaging. Membranes blocked with BlockOut® can be dried and are very stable.