Recently, by taking advantages of the drastically enhanced PL of inorganic Ln3+‐nanoprobes in the enhancer solution, we developed a unique bioassay method, namely, DELBA, for the ultrasensitive in vitro detection of several important tumor markers such as CEA, PSA and AFP, with LODs several orders of magnitude improvement on those of either commercial TRFIA or the assays utilizing the PL of the original Ln3+‐nanoprobes (Table1), as exemplified in the following subsections. Here, CEACAM5 is linked to neoplasm.