Functional catalytic nanoparticles (nanozymes) for sensing

Nanoparticles exhibiting diverse shapes, high porosity and chemical stability reveal, upon appropriate chemical engineering, enzyme-like catalytic activities, "nanozymes", providing a plethora of nanomaterials for diverse applications. The present review article addresses the sensing applications of the catalytic functions of nanozymes consisting of metal nanoparticles, metal oxides, metal sulfides and cyanometallate nanoparticles, carbon-based nanomaterials and metal-organic-framework nanoparticles. The nanozymes emulate catalytic functions of oxidases or peroxidases and are employed as amplifying agents for sensing diverse analytes such as glucose, dopamine, NADH, thiols, phosphates and more. Moreover, the immobilization of nanozymes on electrodes provides versatile means to develop electrochemical sensing platforms. Different principles of the electrochemical sensing platforms, synthetic methodologies to deposit nanozymes on electrodes, and methods to establish electrical communication between the bulk conductive support and nanozyme particles are introduced. Electrochemical sensing platforms applying nanozyme-modified electrodes for the detection of analytes such as organophosphates, glucose and more are discussed. In particular, the application of nanozymes as amplifying labels for biosensor devices detecting proteins, DNA and microRNAs are addressed. Finally, the uses of nanozymes as functional constituents to design sense-and-treat systems are discussed. This is exemplified with the assembly of a bioreactor system for the sensing of glucose, the nanozyme-promoted generation of reactive oxygen species as cytotoxic agents towards cancer cells, and the autonomous nanozyme-based glucose-controlled release of insulin from nanocarrier devices. The future challenges in developing nanozyme-based sensors and sense-and-treat systems are presented.