Synthesis and Design of Magnetic Nanocomposites for Biosensing Applications

Abstract

Immunoassays such as immuno-polymerase chain reaction (iPCR) are very essential for both clinical and research purposes owing to its ultrahigh sensitivity and selectivity. However, thermal cyclers used in iPCR are heavy, expensive, energy- and time- consuming peltier-based heat block modules, which limit their application to point of care (POC) diagnosis.

To this end, a plasmonic magnetic nanocomposite composed of Fe₃O₄ magnetic core and Au plasmonic shell (Fe₃O₄@Au) was designed as a multifunctional platform for fast and sensitive quantification of biomarkers by a plasmonic photothermal (PPT)- iPCR method. Compared to most PCR-based immunoassays, the PPT-iPCR assay proposed here significantly reduced the required thermal cycling time (less than 10 mins) without compromising the superior sensitivity of iPCR, by using the nanocomposites with photothermal effect as a heat source for thermal cycling. To the best of our knowledge, this is the first report of iPCR technology combined with nanoparticle-based photothermal heating system.

On the other hand, the wide utilization of Fe₃O₄ in biosensing is also inseparable from their intrinsic enzyme activity. In 2007, Yan et al. discovered that Fe₃O₄ nanoparticles can mimic peroxidase reaction. Since then, many transition metal oxides as peroxidase nanozymes have been developed for a wide range of fields, but the mechanism is still not very clear. Recently, there has been some controversy regarding Fe₃O₄ as peroxidase mimetics. Accordingly, disclosing the catalytic mechanism behind them is imperative.

Herein, an atomic insight into the confusion and the origin of Fe₃O₄ nanoparticles as peroxidase mimetics were provided. The reduction of H₂O₂ by metal cations bearing a lower oxidation state was found to be the key step. In subsequent biosensing applications, polycrystalline Fe₃O₄ bearing a higher Fe(II)/Fe(III) ratio and more reactive Fe(II) species (cf. single crystalline Fe₃O₄) also showed more than 10 times higher in glutathione sensitivity. This study thus highlights the importance of understanding the surface chemical state of nanozymes, the insights provided here can guide the future design of other peroxidase nanozymes with high activity.

Date of Award	2 Aug 2023
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yung-kang PENG (Supervisor) & Jung-hoon LEE (Co-supervisor)