Abstract: A novel paramagnetic ions-mediated magnetic relaxation switching biosensor was developed to detect hypoxanthine and histamine for the evaluation of fish freshness and quality. With the catalysis of xanthine oxidase or diamine oxidase, hypoxanthine and histamine can be decomposed to generate hydrogen peroxide. Hydrogen peroxide can act as a reductant or oxidant to induce the conversion of paramagnetic ions of different valence (Mn (VII)/Mn (II) and Fe (II)/Fe (III)), leading to an obvious change in magnetic signals. Herein, paramagnetic ions and hydrogen peroxide were employed to fabricate a magnetic signal readout system for the quantitative analysis of hypoxanthine and histamine. As a result, this biosensor allowed highly sensitive detection of hypoxanthine and histamine. The linear ranges for hypoxanthine and histamine were 0.525–1 050 and 5–1 000 μmol/L, the limits of detection were 0.17 and 2.34 μmol/L, respectively. The results of this biosensor for crucian carp samples were in good agreement with those of high performance liquid chromatography (HPLC). The proposed biosensor is sensitive, rapid, low cost and promising for fish freshness detection and quality control.

Key words: hypoxanthine; histamine; fish freshness; paramagnetic ions; magnetic relaxation switching biosensor