Two decades on, this rapidly growing, multidisciplinary field has evolved from the study of single-particle motion to the study of emergent behavior, from directional chemotactic motility to dynamic assembly based on interactions amongst themselves and with the environment . The potential applications of these synthetic active materials are vast. They would be capable of remodeling themselves and transforming their environment, they could self-organize and evolve their structures and functions to improve their performance, accomplishing tasks collectively. Practical applications including sensing , directed cargo and drug delivery , in vivo imaging , theranostics , and environmental remediation are being actively explored. From a fundamental standpoint, energy-harvesting nanomotors have emerged from scientific curiosities to powerful models for the study of complex systems .