A fluorometric and magnetic resonance (MR) dual-modal detection scheme is presented for determination of ascorbic acid (AA). It is based on the use of a blended Au/MnO@BSA mixture that was prepared via a biomimetic strategy, using bovine serum albumin (BSA) as the template at physiological temperature. The MnO@BSA fraction (one part of the composite) is not susceptible to MR but can be degraded to MR-active compounds upon a redox reaction with even ultralow concentrations of AA. In parallel, the blended Au/MnO@BSA recovers its fluorescence because MnO@BSA acts as a quencher of the fluorescence of circumjacent Au@BSA (the other part of the composite). Fluorescence typically is measured at excitation/emission wavelengths of 470/625 nm. Leveraging on this redox reaction between MnO and AA, a dual-mode detection scheme for AA was developed. Both the fluorescence and the MR signal increase with the concentration of AA. The lowest limit for the detection of AA is 0.6 μM in the fluorometric mode and 0.4 μM in the MR mode. Analysis of AA-spiked serum samples showed that the recoveries obtained by either the fluorometric and MR mode can reach 94%. This is the first report of the use of blended nanoparticles with their inherent cross-validation regularity. Graphical abstract Schematic presentation of the biomimetic synthesis of blended Au/MnO@BSA nanoprobes and fluorometric/MR cross-validation dual-modal detection of ascorbic acid.