Flexible electrochemical sensors integrated with nanomaterials for in situ determination of small molecules in biological samples: A review

Flexible biosensors have aroused research enthusiasm due to their potential for in situ quantification of chemical constituents in the human body, which perform a vital function in health monitoring and disease diagnosis. Especially, flexible electrochemical biosensors based on different advanced nanomaterials combine the merits of electrochemical analysis with unique structural/chemical properties of flexible electrode materials, and have exhibited excellent performance for in situ biomarkers detection toward different biological samples. These flexible electrochemical sensors can be integrated into implantable/wearable devices, which demonstrate great promise in invasive/noninvasive in-situ analysis. Consequently, the development of flexible electrochemical biosensors is of great significance for both scientific research and clinical application. In this review, we focus on the state-of-the-art progress in flexible electrochemical biosensors integrated with a wide spectrum of nanomaterials, which are aimed at in situ sensitive detection of small molecule metabolites in different biological specimens including live cells, tissues, body fluids (e.g., human blood, cerebrospinal fluid (CSF), and interstitial fluid (ISF)), and exudate secretion liquors (e.g., human saliva, tear, sweat, and urine). From the perspectives of flexible electrochemical biosensors toward different biological samples, we discuss their innovations in nanomaterials with diverse structures. We also introduce the research status of integrated flexible implantable and wearable electrochemical sensing devices with various types and functionalities for practical application. Furthermore, we share our opinions on the recent progress of flexible electrochemical sensors based on nanomaterials and look forward to applying flexible electrochemical sensors in medical diagnosis and healthcare.