AgarFix: simple and accessible stabilization of challenging single-particle cryo-EM specimens through crosslinking in a matrix of agar

•Fragile protein complexes can be cross-linked while embedded in agarose.•The agarose matrix prevents formation of aggregates upon crosslinking.•Crosslinking in agarose is easy, fast, and requires no expensive equipment.•The sample can directly be used for negative stain or cryo-EM grid preparation.