Issues related to global energy and environment as well as health crisis are currently some of the greatest challenges faced by humanity, which compel us to develop new pollution-free and sustainable energy sources, as well as next-generation biodiagnostic solutions. Optical functional nanostructures that manipulate and confine light on a nanometer scale have recently emerged as leading candidates for a wide range of applications in solar energy conversion and biosensing. In this review, recent research progress in the development of photonic and plasmonic nanostructures for various applications in solar energy conversion, such as photovoltaics, photothermal conversion, and photocatalysis, is highlighted. Furthermore, the combination of photonic and plasmonic nanostructures for developing high-efficiency solar energy conversion systems is explored and discussed. We also discuss recent applications of photonic–plasmonic-based biosensors in the rapid management of infectious diseases at point-of-care as well as terahertz biosensing and imaging for improving global health. Finally, we discuss the current challenges and future prospects associated with the existing solar energy conversion and biosensing systems.

Plasmon-enhanced photo/electrocatalysis using hetero-nanostructures has emerged as a promising approach for boosting the efficiency and selectivity of photo/electrocatalytic reactions. Plasmonic nanostructures (PNSs), with their unique properties including localized surface plasmon resonance (LSPR), play a vital role in enhancing photo/electrocatalytic activities. By leveraging LSPR, PNSs can concentrate incident light, facilitate charge separation, and induce surface reactions, leading to improved catalytic performance. In this review, we provide a comprehensive analysis of the current state of knowledge in this field. We discuss the rational design and synthesis of hetero-nanostructures, focusing on the optimization of composition, size, shape, and interface properties. Furthermore, we explore various combinations of plasmonic sources with semiconductors of diverse morphologies to achieve enhanced photocatalytic activity. The reviewed research encompasses applications in water splitting, removal of organic pollutants, CO2 reduction, and energy conversion. We also address the challenges that need to be overcome, including optimization of materials, reproducibility, stability, band alignment, and understanding plasmon–material interactions in hetero-nanostructures. The review of future perspectives includes the integration of multiple functionalities, the exploration of novel plasmonic materials, and the translation of plasmon-enhanced photo/electrocatalysis into practical applications. The combination of plasmonics and nanotechnology can be used to advance green technologies and address pressing global issues.