Perspective on recent developments of near infrared-emitting gold nanoclusters: applications in sensing and bio-imaging

Fluorescent gold nanoclusters (AuNCs) have received enormously vast attention over the past several decades due to their extremely small size (<2 nm), supreme luminescence behavior, undemanding accessibility, and incredible bio-compatibility. These inherent properties of AuNCs are highly attractive for application in the fields of sensors and bio-imaging. To date, several high-quality reviews have focused on the topic of the developments of AuNCs that exhibit emission in the visible region. This current review deals with up-to-date progress in the synthesis, surface modification, and characterization of near infrared (NIR)-emitting fluorescent AuNCs and their broad applications in monitoring, detection, and imaging of heavy metal ions, anions, amino thiols, and environmental changes (e.g., pH and temperature). Additionally, we introduce the strategies used to enhance the quantum yields of NIR-emitting AuNCs that have low QYs as compared to visible-emitting AuNCs. Finally, some exciting examples are discussed to emphasize the potential of AuNCs for application in sensors and bio-imaging.