Biomarker detection for disease diagnosis, prognosis, and therapeutic response is becoming increasingly reliable and accessible. Particularly, the identification of circulating cell-free chemical and biochemical substances, cellular and subcellular entities, and extracellular vesicles has demonstrated promising applications in understanding the physiologic and pathologic conditions of an individual. Traditionally, tissue biopsy has been the gold standard for the diagnosis of many diseases, especially cancer. More recently, liquid biopsy for biomarker detection has emerged as a non-invasive or minimally invasive and less costly method for diagnosis of both cancerous and non-cancerous diseases, while also offering information on the progression or improvement of disease. Unfortunately, the standardization of analytical methods to isolate and quantify circulating cells and extracellular vesicles, as well as their extracted biochemical constituents, is still cumbersome, time-consuming, and expensive.
To address these limitations, researchers from Princeton Biochemicals and UCSF have developed a prototype of a portable, miniaturized instrument that uses immunoaffinity capillary electrophoresis (IACE) to isolate, concentrate, and analyze cell-free biomarkers and/or tissue or cell extracts present in biological fluids. Isolation and concentration of analytes is accomplished through binding to one or more biorecognition affinity ligands immobilized to a solid support, while separation and analysis are achieved by high-resolution capillary electrophoresis (CE) coupled to one or more detectors. When compared to other existing methods, the process of this affinity capture, enrichment, release, and separation of one or a panel of biomarkers can be carried out on-line with the advantages of being rapid, automated, and cost-effective. Additionally, it has the potential to demonstrate high analytical sensitivity, specificity, and selectivity. As the potential of liquid biopsy grows, so too does the demand for technical advances. The researchers discuss applications and limitations of liquid biopsy and hope to introduce the idea that this affinity capture-separation device could be used as a form of point-of-care (POC) diagnostic technology to isolate, concentrate, and analyze circulating cells, extracellular vesicles, and viruses.
Schematic diagram of two designs of on-line immunoaffinity analyte concentrator-microreactor (IACE) devices
(A) Unidirectional IACE design; and (B) orthogonal IACE design. The unidirectional IACE design is operated without the presence of microvalves, whereas the orthogonal IACE design requires the presence of microvalves, as depicted in (B) with green circles. The orthogonal IACE device has four microvalves positioned at each entrance-exit port. These microvalves are crucial in controlling the path of fluids through the transport capillary or separation capillary. Black arrows indicate flow direction of buffers in the separation capillary, and migration direction of the separated analytes within the separation capillary; purple arrows indicate the flow direction of sample and cleaning buffers introduced into the transport capillary. Biorecognition affinity capture ligands or affinity capture selectors are immobilized to a beaded or monolithic structure positioned within the cavity of the “analyte concentrator-microreactor” (ACM) devices, or immobilized directly to the inner surface of the cavity of the ACM device. The affinity capture selectors can be antibodies, antibody fragments, lectins, aptamers, enzymes, phages, receptors, protein A, protein G, or a variety of substances having affinities for different kind of substances.