On-Chip Indirect Detection of Non-Fluorescent Analytes Using Fluorescent Spacers

We present a technique that accomplishes on-chip preconcentration, separation and indirect detection of nonfluorescent analytes by leveraging isotachophoresis (ITP) and a set of fluorescent species termed spacers. The non-fluorescent analyte zones are detected as dark zones/gaps between fluorescent spacer zones. The length of this gap quantifies the initial concentration of the non-fluorescent analyte and mobilities of the fluorescent spacers on either side provide the upper and lower bound for the analyte mobility. We have successfully demonstrated separation and detection of amino acids, serine and phenylalanine, as well as other organic acids, acetic acid and phenylpropionic acid with this technique. Using three fluorescent spacers, we were able to detect ∼10 μM concentration of non-fluorescent analytes.