*Review* **MXenes-Based Bioanalytical Sensors: Design, Characterization, and Applications**

#### **Reem Khan and Silvana Andreescu \***

Department of Chemistry and Biomolecular Science, Clarkson University, Potsdam, New York, NY 13676, USA; rekhan@clarkson.edu

**\*** Correspondence: eandrees@clarkson.edu

Received: 23 August 2020; Accepted: 18 September 2020; Published: 22 September 2020

**Abstract:** MXenes are recently developed 2D layered nanomaterials that provide unique capabilities for bioanalytical applications. These include high metallic conductivity, large surface area, hydrophilicity, high ion transport properties, low diffusion barrier, biocompatibility, and ease of surface functionalization. MXenes are composed of transition metal carbides, nitrides, or carbonitrides and have a general formula Mn+<sup>1</sup>Xn, where M is an early transition metal while X is carbon and/or nitrogen. Due to their unique features, MXenes have attracted significant attention in fields such as clean energy production, electronics, fuel cells, supercapacitors, and catalysis. Their composition and layered structure make MXenes attractive for biosensing applications. The high conductivity allows these materials to be used in the design of electrochemical biosensors and the multilayered configuration makes them an efficient immobilization matrix for the retention of activity of the immobilized biomolecules. These properties are applicable to many biosensing systems and applications. This review describes the progress made on the use and application of MXenes in the development of electrochemical and optical biosensors and highlights future needs and opportunities in this field. In particular, opportunities for developing wearable sensors and systems with integrated biomolecule recognition are highlighted.

**Keywords:** MXenes; 2D nanomaterials; biosensors; wearables
