Monitoring of the levels of 5-hydroxyindole-3-acetic acid (5-HIAA) is of significant importance for diagnostics of carcinoid tumors. We propose simple catalytic electrochemical sensors for the determination of 5-HIAA in urine using laccase and its mimetics. Laccase-like nanozymes (LacNZs) were synthesized via a chemical reduction, and resulting PtMn and MnO2 nanoflowers (NFs) demonstrated laccase-like activity similar to the laccase from the Trametes zonata. In addition, these LacNZs showed enhanced stability under a wide range of pH (3.0-7.5), temperatures (4-70 °C), and ionic strengths (up to 500 mM NaCl). The developed PtMn NF/graphite electrode, similar to a laccase/graphite electrode, can detect 5-HIAA with a high sensitivity (25 000 ± 12 A·M-1·m-2 and 1900 ± 9 A·M-1·m-2, respectively) and have linear ranges of 0.3 - 15 μM and 2 - 50 μM. The sensors work at low working potentials with a detection limit of 0.16 and 1.4 μM, covering the normal and pathologic ranges of 5-HIAA (1 - 50 μM) content in urine. They have been successfully applied to 5-HIAA assay in urine samples of people with various diseases and revealed good recovery values and reproducibility. Additionally, the LacNZ-sensor has the best stability and can be used up to 20 days.
Keywords: 5-Hydroxyindole-3-acetic acid assay; Amperometric sensor; Laccase; Laccase-like nanozyme; Nanoflowers.
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