Affinity capture and detection of immunoglobulin E in human serum using an aptamer-modified surface in matrix-assisted laser desorption/ionization mass spectrometry.

Capture and detection of immunoglobulin E (IgE) in simple solution and in human serum using an aptamer-modified probe surface for affinity matrix-assisted laser desorption/ionization mass spectroscopy detection is reported. Detectable signals were obtained for 1 amol of IgE applied either in a single, 1microL application of 1 pM IgE or after 10 successive, 1-microL applications of 100 fM IgE. In both cases, the surface was rinsed after each application of IgE to remove sample concomitants including salts and free or nonspecifically associated proteins. Detection of native IgE, which is the least abundant of the serum immunoglobulins and occurs at subnanomolar levels, in human serum was demonstrated and interference from the high-abundance immunoglobulins and albumin was investigated. The aptamer-modified surface showed high selectivity toward immunoglobulins in serum, with no significant interference from serum albumin. Addition of IgE to the serum suppressed the signals from the other immunoglobulins, confirming the expected selectivity of the aptamer surface toward IgE. Dilution of the serum increased the selectivity toward IgE; the protein was detected without interference in a 10,000-fold dilution of the serum, which is consistent with detection of IgE at amol (pM) levels in standard solutions.