**Prefaceto "Biosensors with Magnetic Nanocomponents"**

The book you have in your hands is a result of the special efforts of an international team from Brazil, China, Italy, Russia, Spain, and the United States of America. The works of all the members of this multidisciplinary team are especially appreciated, as the last 5 months of the Issue coincided with the coronavirus world tragedy. We all learned from this new experience and started to realize the need for extra efforts in the field of biomedical applications and public health. This book contains peer-reviewed contributions from the Special Issue "Magnetic Materials Based Biosensors" in MDPI's Sensors. The works herein were submitted to the journal in the period from February 2019 to June 2020. This book contains nine research works and one topical review. PhD students, researchers, and the educational community working in the fields of magnetic nanomaterials and biomedical applications of nanocomposites with magnetic components will find this book useful.

The selective and quantitative detection of biocomponents is greatly requested in biomedical applications, clinical diagnostics, and the development of new composites from biotechnological roots. On one hand, many traditional magnetic materials are not suitable for the ever-increasing demands of these processes. On the other hand, the list of requested applications is rapidly growing. The push for a new generation of microscale sensors for biomedical applications continues to challenge the materials science and engineering communities to work together in close collaboration with medical teams aiming to develop novel compact analytical devices that are suitable for such purposes.

The principal requirements of a new generation of nanomaterials for sensor applications are based on well-known demands: high sensitivity, small size, low power consumption, stability, quick response, resistance to aggressive media, low price, and easy operation by nonskilled personnel. In addition, the possibility of integration of on-chip sensitive elements with nanoscale components is also expected for the next generation of devices.

There are different types of magnetic effects capable of creating sensors for biology, medicine, and drug delivery, including magnetoresistance, spin valves, Hall and inductive effects, magnetoelastic resonance, and giant magnetoimpedance. Although many geometries are still under testing, thin films and nanostructured multilayers are preferable, as they are most compatible with semiconductor electronics and existing electronic circuit fabrication technologies. There are different reasons contributing to the delay of the competitive integration of high-frequency nanostructured thin film elements into the global market. One of them is the need for additional understanding of basic concepts of microwave radiation absorption by nanostructured multilayered elements. Another is the need for the elaboration of simple, fast, and cheap characterization of materials with high dynamic permeability.

The present goal is to design nanomaterials both for magnetic markers and sensitive elements as synergetic pairs working in one device with adjusted characteristics of both materials. Synthetic approaches using the advantages of simulation methods and synthetic materials mimicking natural tissue properties can be useful, as can the further development of modeling strategies for magnetic nanostructures.

In fact, one of the most interesting cases greatly requested for cancer therapies, the detection of magnetic nanoparticles incorporated into biological tissues, has not been yet properly addressed. Biological tissues present a huge variety of morphologies, and therefore the development of magnetic biosensors is conditioned by the fabrication of reliable samples. One of the strategies for solving this problem is to substitute biological samples at a certain stage of the development of the biosensor by synthetic hydrogel (experimental model of the cytoskeleton) with a certain amount of magnetic nanoparticles, which is capable of mimicking the main properties of living tissues. Here, special attention was also paid to the remarkable multimodal properties of magnetic nanoparticles, as they are very important in resolving challenges slowing the progression of biotechnology.

> **Galina V. Kurlyandskaya** *Editor*

*Review*
