Introduction Thiol groups, are functional groups found in many proteins, that play key roles in various physiological processes and are closely related to a multitude of diseases. Amongst these protein thiols, some protein thiols are sufficiently proximal to form a disulfide bond under an oxidative environment, and exhibit bond cleavage in a reductive environment. These spatially adjacent thiol groups are called vicinal dithiols. And vicinal dithiol-containing proteins (VDPs) are thiol-containing proteins that possess at least one pair of vicinal thiols. Vicinal dithiols on VDPs are of considerable importance in regulating the cellular redox sate using characteristic reversible inter-conversion reactions of dithiols and disulfides. The high sensitivity and rapid reactivity of vicinal dithiols on VDPs empowers them with the ability to work as a redox buffer, indicating that they may play a key role in the maintenance of redox homeostasis and signalling pathways, and ultimately maintain the viable microenvironment of living cells. For instance, the alternation of VDPs in response to the change of ROS levels in the surrounding environment suggests that protein vicinal dithiols may be involved in cellular signaling systems, particularly in regulating the mitochondria where multiple core metabolic machineries utilizing redox reactions exist, such as calcium release from mitochondria and tuning of the mitochondrial membrane sensitivity. Another important role of vicinal dithiols is stabilizing the structures of VDPs, which prevent and manage protein misfolding and aggregation. A variety of diseases, for instance, cancer, human immunodeficiency virus (HIV) and neurodegeneration are considered to be closely associated with VDPs. Recently, protein vicinal dithiols were confirmed to play key role in regulating the interaction between the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, or simply COVID-19) and angiotensin-converting enzyme 2 (ACE2). However, limited information is available for the detailed behavior of vicinal dithiols on VDPs due to their highly dynamic nature and the lack of a direct visualization methods.