Reactive oxygen species (ROS) contain at least one oxygen atom and one or more unpaired electrons and include singlet oxygen, superoxide anion radical, hydroxyl radical, hydroperoxyl radical, and free nitrogen radicals. Intracellular ROS can be formed as a consequence of several factors, including ultra-violet (UV) radiation, electron leakage during aerobic respiration, inflammatory responses mediated by macrophages, and other external stimuli or stress. The enhanced production of ROS is termed oxidative stress and this leads to cellular damage, such as protein carbonylation, lipid peroxidation, deoxyribonucleic acid (DNA) damage, and base modifications. This damage may manifest in various pathological states, including ageing, cancer, neurological diseases, and metabolic disorders like diabetes. On the other hand, the optimum levels of ROS have been implicated in the regulation of many important physiological processes. For example, the ROS generated in the mitochondria (mitochondrial ROS or mt-ROS), as a byproduct of the electron transport chain (ETC), participate in a plethora of physiological functions, which include ageing, cell growth, cell proliferation, and immune response and regulation. In this current review, we will focus on the mechanisms by which mt-ROS regulate different pathways of host immune responses in the context of infection by bacteria, protozoan parasites, viruses, and fungi. We will also discuss how these pathogens, in turn, modulate mt-ROS to evade host immunity. We will conclude by briefly giving an overview of the potential therapeutic approaches involving mt-ROS in infectious diseases.

The substitution of semiconductor quantum dots (QDs) by a small number of transition-metal ions with magnetic properties gives rise to magnetic-doped semiconductors. With a balance of optical and magnetic properties, these magnetic semiconductors are widely used in spintronics, bioimaging and magnetic resonance imaging (MRI) applications. To facilitate their usage in bio-applications, it is critical to synthesize water-soluble magnetic QDs with a stabilized structure while maintaining their optical and magnetic properties. Here in our work, we have developed a facile substituted synthetic route to achieve Cr-doped CdSe (Cr-CdSe) via hydrothermal method. The effects of doping on the structural, optical, and magnetic properties of Cr-CdSe were studied using X-ray diffraction, UV-visible spectroscopy, and photoluminescence lifetime. We then explored their chemical nature and change in morphology with an increase in doping concentration via X-ray photoelectron spectroscopy and transmission electron microscopy. Water-soluble QDs have been used as bioimaging probes for the past few decades due to their strong fluorescence, photostability and improved tissue or cellular penetration. However, incorporating magnetic material into a fluorescent entity harnesses the ability to control the strengths of both modalities, which enhances diagnostic accuracy and facilitates its application in bio-systems, especially in early accurate diagnosis. Finally, we demonstrate the competency of Cr-CdSe as a dual-imaging probe with fluorescent cellular imaging and MRI applications.