Wearable devices are becoming widespread in a wide range of applications, from healthcare to biomedical monitoring systems, which enable continuous measurement of critical biomarkers for medical diagnostics, physiological health monitoring and evaluation. Especially as the elderly population grows globally, various chronic and acute diseases become increasingly important, and the medical industry is changing dramatically due to the need for point-of-care (POC) diagnosis and real-time monitoring of long-term health conditions. Wearable devices have evolved gradually in the form of accessories, integrated clothing, body attachments and body inserts. Over the past few decades, the tremendous development of electronics, biocompatible materials and nanomaterials has resulted in the development of implantable devices that enable the diagnosis and prognosis through small sensors and biomedical devices, and greatly improve the quality and efficacy of medical services. This article summarizes the wearable devices that have been developed to date, and provides a review of their clinical applications. We will also discuss the technical barriers and challenges in the development of wearable devices, and discuss future prospects on wearable biosensors for prevention, personalized medicine and real-time health monitoring.

Putrescine and cadaverine are important volatile indicators for the evaluation of food spoilage. In this study, a metal-organic framework (MOF)-coated surface-enhanced Raman scattering (SERS) paper platform for the detection of putrescine and cadaverine is developed. Au@ zeolite imidazolate framework-8 (ZIF-8) SERS paper is fabricated by the coating of ZIF-8 layer on a Au nanoparticle-impregnated paper that is prepared by dry plasma reduction. The Au@ZIF-8 SERS paper is characterized by scanning electron microscope, energy-dispersive X-ray spectroscopy, X-ray diffraction, and N2 sorption isotherm. The ZIF-8 layer enables the accumulation of gaseous molecules and also provides enhancement of SERS signals. The fluorescence, SERS, and simulation results prove the improved detection ability of the Au@ZIF-8 platform for the volatile molecules. For the selective detection of putrescine and cadaverine, the Au@ZIF-8 SERS paper is functionalized with 4-mercatobenzaldehyde (4-MBA). The 4-MBA molecule acts as a Raman reporter and also a specific receptor for the volatile amine molecules. Using the intensity ratiometric detection of 4-MBA-functionalized Au@ZIF-8 SERS paper, putrescine and cadaverine are quantitatively detected with detection limits of 76.99 and 115.88 parts per billion, respectively. Furthermore, the detection of volatile amine molecules released from spoiled salmon, chicken, beef, and pork samples is demonstrated. It is anticipated that the MOF-coated SERS paper platforms will be applicable not only in food safety but other applications including disease diagnosis and environmental monitoring.