The present invention generally relates to systems and methods for determining oxygen in a sample, or in a subject. In one aspect, the present invention is generally directed to an article exhibiting a determinable feature responsive to oxygen, such as oxygen-sensitive particles. The particles may exhibit a determinable change with a change in oxygen concentration, and such particles can accordingly be used to determine oxygen. For example, in one set of embodiments, the particles may be at least partially coated with a protein, such as hemoglobin, that is able to interact with oxygen. In some cases, the protein may aggregate under certain conditions (e.g., under relatively low oxygen concentrations), and such protein aggregation may be used, for example, to cause the particles to become aggregated, which can be determined in some way. In some cases, such aggregation may be irreversible; i.e., the degree of aggregation corresponds to the most extreme oxygen concentrations that the proteins were exposed to. Such articles may be used, for example, to determine oxygen within a sample, or within a subject, such as a human subject. For instance, the article may be formed as a skin patch, or administered to the skin of a subject, e.g., on the surface of the skin, within the dermis or epidermis, etc., to determine oxygen within the subject.