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<p>A novel colorimetric sensing platform was developed for rapid detection of L-cysteine (L-Cys) in human serum and milk samples, utilizing L-glutamic acid-coated Fe<sub>3</sub>O<sub>4</sub> quantum dots (Glu-Fe<sub>3</sub>O<sub>4</sub> QDs) with enhanced peroxidase-like activity. The Glu-Fe<sub>3</sub>O<sub>4</sub> QDs were synthesized via a two-step hydrothermal method, where L-glutamic acid modification significantly improved both catalytic performance and stability compared to unmodified Fe<sub>3</sub>O<sub>4</sub> nanoparticles. Characterization by TEM, XPS, and FTIR confirmed the ultrasmall size (2.57 ± 0.78&#xa0;nm) and successful surface functionalization with carboxyl/amino groups. The nanozymes catalyzed the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H<sub>2</sub>O<sub>2</sub>, generating a blue color change measurable at 652&#xa0;nm. L-Cys suppressed this reaction by competitively consuming hydroxyl radicals, enabling quantitative detection with a linear range of 5–50 µM (R<sup>2</sup> = 0.997) and a low detection limit of 0.73 µM. The method exhibited high selectivity against interfering amino acids and ions, and achieved recoveries of 96.99–107.59% in spiked serum and milk samples with RSDs &lt; 3.86%. This work provides a simple, cost-effective tool for monitoring L-Cys in complex biological matrices, with potential applications in food safety and clinical diagnostics.</p> Graphical abstract <p></p>

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Enhanced peroxidase-like activity of L-glutamic acid-coated Fe3O4 quantum dots for colorimetric detection of L-cysteine in serum and milk

  • 期刊论文

  • 发表日期：

    2026年5月28日

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  • Shipei Cheng,
  • Jinhua Liang,
  • Guidan Huang,
  • Hongying Ye,
  • Mengdan Yang,
  • Bingjian Lin,
  • Jinfang Nie,
  • Wenyuan Zhu,
  • Yun Zhang

摘要

A novel colorimetric sensing platform was developed for rapid detection of L-cysteine (L-Cys) in human serum and milk samples, utilizing L-glutamic acid-coated Fe3O4 quantum dots (Glu-Fe3O4 QDs) with enhanced peroxidase-like activity. The Glu-Fe3O4 QDs were synthesized via a two-step hydrothermal method, where L-glutamic acid modification significantly improved both catalytic performance and stability compared to unmodified Fe3O4 nanoparticles. Characterization by TEM, XPS, and FTIR confirmed the ultrasmall size (2.57 ± 0.78 nm) and successful surface functionalization with carboxyl/amino groups. The nanozymes catalyzed the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2, generating a blue color change measurable at 652 nm. L-Cys suppressed this reaction by competitively consuming hydroxyl radicals, enabling quantitative detection with a linear range of 5–50 µM (R2 = 0.997) and a low detection limit of 0.73 µM. The method exhibited high selectivity against interfering amino acids and ions, and achieved recoveries of 96.99–107.59% in spiked serum and milk samples with RSDs < 3.86%. This work provides a simple, cost-effective tool for monitoring L-Cys in complex biological matrices, with potential applications in food safety and clinical diagnostics.

Graphical abstract