Efficient small-scale conjugation of DNA to primary antibodies for multiplexed cellular targeting

The combination of the specificity of antibodies and the programmability of DNA nanotechnology has provid-ed the scientific community with a powerful tool to label and unambiguously distinguish a large number of subcellular targets using fluorescence-based read-out methods. While primary antibodies are commercially available for a large class of targets, a general stoichiometric site-specific DNA labelling strategy for this affinity reagent is lacking. Here, we present a universal, site-selective, conjugation method using a small photocross-linkable protein G adaptor that allows labelling of antibodies of different host species with a controlled number of short oligonucleotides (ODNs). Importantly, we illustrate that this conjugation method can be directly performed on commercially-available primary antibodies, on a small scale and without cross-reactivity towards other proteins, such as bovine serum albumin. In addition, we present a general, benchtop-compatible strategy to purify DNA-labeled antibodies without loss of function. The application of protein G-ODN labelled primary antibodies is demonstrated by employing three well-known methods for detecting subcellular targets using fluorescent read-out, including flow cytometry, DNA-PAINT, and dSTORM. This work thus establishes a general and efficient platform for the synthesis of a library of unique ODN-antibody conjugates, facilitating the broader use of DNA-based programmable tags for multiplexed labelling to identify subcellular features with nanometer-precision, improving our understanding of cellular structure and function.