A bifunctional immunosensor based on osmium nano-hydrangeas as a catalytic chromogenic and tinctorial signal output for folic acid detection.

As a neglected member of the platinum group elements, osmium, the metal with the highest density in the earth, is very suitable for the preparation of a peroxidase with high catalytic activity and stability, and can also be associated with the development of a sensor. In this study, we accessed Os nano-hydrangeas (OsNHs) with one-pot synthesis and utilized them in a bifunctional immunosensor that can present both catalytic chromogenic and tinctorial signal for nanozyme-linked immunosorbent assay (NLISA) and lateral flow immunoassay (LFIA) for use in folic acid (FA) detection. In the OsNHs-NLISA, the linear range is from 9.42 to 167.53 ng mL. The limit of detection (LOD) is 4.03 ng mL and the IC value is 39.73 ng mL. In OsNHs-LFIA, the visual cut-off value and limit of detection (v-LOD) are 100 ng mL and 0.01 ng mL, respectively. Additionally, the outcome from the specificity and spiked sample analysis offered recovery from the spiked milk powder sample ranging from 93.9 to 103.6% with a coefficient of variation under 4.9%, compared with UPLC-MS/MS for a correlation of = 0.999 and admirable validation. The promising application of the OsNHs can also be used in other bioprobes, and this bifunctional immunosensor analysis mode is suitable for diversified analytes.