Blended gold/MnO.sub.2@BSA nanoparticles for fluorometric and magnetic resonance determination of ascorbic acid

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.sub.2@BSA mixture that was prepared via a biomimetic strategy, using bovine serum albumin (BSA) as the template at physiological temperature. The MnO.sub.2@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.sub.2@BSA recovers its fluorescence because MnO.sub.2@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.sub.2 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 [mu]M in the fluorometric mode and 0.4 [mu]M 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.