Isotachophoresis-Enhanced Immunoassays: Challenges and opportunities

Protein detection and quantification is a crucial part of many clinical, research, and preparatory applications . Protein biomarkers, such as prostate-specific antigen (PSA) and carcinoembryonic antigen (CEA), are regularly detected and quantified for cancer diagnosis and treatment monitoring. On the other hand, cardiac troponin 1 (CTn1) is the most important protein to quantify to detect cardiac injury and myocardial infarction. The detection of protein biomarkers such as PSA, CEA, and CTn1 requires specific identification and quantification of the protein, eliminating detection techniques that enable only size-based quantification of proteins in general, such as silver staining and simple gel electrophoresis. Isoelectric focusing depends on the isoelectric point of an analyte, whereas isotachophoresis (ITP) is based on changes in the analytes' velocity under an electric-field gradient. In particular, ITP has been shown to be an effective protein-preconcentration approach that can lead to a thousand-fold higher concentration of the target analytes within a couple of minutes, although some obstacles prevent it from becoming a prevalent concentration technique. We summarize the basics of ITP and briefly discuss its robust applications in nucleic-acid (NA) analysis and other applications in single -cell examination and detection. Most importantly, we cover the progress that has been made to integrate ITP into microfluidic immunoassays, analyze the process's benefits and challenges, and discuss possible directions for research in this field.