Phenylarsine oxide is primarily used in biochemical research as a selective inhibitor of enzymes, particularly those involved in redox reactions. It is often employed to study the role of thiol groups in enzymatic activity, as it forms stable complexes with cysteine residues, effectively blocking their function. This property makes it useful in investigating cellular processes like oxidative stress and signal transduction pathways. Additionally, it has applications in analytical chemistry as a reagent for detecting trace amounts of certain metals due to its ability to form specific complexes. In some cases, it is also explored for its potential in developing therapeutic agents targeting specific biochemical pathways. Due to its high toxicity, handling requires strict controls in well-equipped laboratories.