Photonic crystal colorimetric sensing in heart-on-a-chip systems

As an emerging modeling platform for cardiac cells and tissues, heart-on-a-chip systems have aroused great interest and made remarkable progress in recent decades. To expand the practical values of such microphysiological systems, various biosensing modules have been integrated into microfluidic chips to realize real-time monitoring of cardiomyocytes or cardiac tissues under different stimulations. Among them, photonic crystal colorimetric sensors are popular because of their intrinsic biocompatibility, visual characteristics, and lack of need for complex instrumentation. In this review, we will provide an overview of research concerning heart-on-a-chip systems integrated with photonic crystal colorimetric sensors, ranging from the natural structural colors, the fabrication of artificial photonic crystal materials, to their colorimetric sensing principle. The emphasis will be put on how the photonic crystal colorimetric sensors address the current limitations of heart-on-a-chip systems through visual optical signals and thus expand their biomedical applications. Finally, the remaining challenges of colorimetric sensing strategy will be summarized, with its future directions for organs-on-chips being discussed.