Highly sensitive nanozyme strip: an effective tool for forensic material evidence identification

During criminal case investigations, blood evidence tracing is critical for criminal investigation. However, the blood stains are often cleaned or covered up after the crime, resulting in trace residue and difficult tracking. Therefore, a highly sensitive and specific method for the rapid detection of human blood stains remains urgent. To solve this problem, we established a nanozyme-based strip for rapid detection of blood evidence with high sensitivity and specificity. To construct reliable nanozyme strips, we synthesized CoFe₂O₄ nanozymes with high peroxidase-like activity by scaling up to gram level, which can be supplied for six million tests, and conjugated antibody as a detection probe in nanozyme strip. The developed CoFe₂O₄ nanozyme strip can detect human hemoglobin (HGB) at a concentration as low as 1 ng/mL, which is 100 times lower than the commercially available colloidal gold strips (100 ng/mL). Moreover, this CoFe₂O₄ nanozyme strip showed high generality on 12 substrates and high specificity to human HGB among 13 animal blood samples. Finally, we applied the developed CoFe₂O₄ nanozyme strip to successfully detect blood stains in three real cases, where the current commercial colloidal gold strip failed to do. The results suggest that the CoFe₂O₄ nanozyme strip can be used as an effective on-scene detection method for human blood stains, and can further be used as a long-term preserved material evidence for traceability inquiry.