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Label-Free Impedimetric Detection of Glycan-Lectin Interactions Jeffrey T. La Belle,† Jared Q. Gerlach,‡ Sergei Svarovsky,*,§ and Lokesh Joshi*,‡
Center for Bioelectronics and Biosensors, Center for Innovations in Medicine, The Biodesign Institute, and Harrington Department of Bioengineering, Arizona State University, 1001 South McAllister Avenue, Tempe, Arizona 82287-6001
A compact biosensor for a label-free, rapid ( 1 MDa) on breast epithelial cells; currently it is most (31) Kumar, S. R.; Sauter, E. R.; Quinn, T. P.; Deutscher, S. L. Clin. Cancer Res. 2005, 11 (19), 6868-6871.
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widely used marker for BC detection.32 Mucins found on the surface of cancer cells are not only overexpressed but also aberrantly glycosylated. For example, in normal breast epithelia, MUC1 is heavily glycosylated with the core-2 glycans masking underlying core-1 structures. At the onset of BC, the shorter, core-1 glycans become unmasked exposing several tumor-associated carbohydrate antigens (TACAs), which include the TFantigens and its precursor, Tn-antigens.2 These TACAs have been proposed as useful BC glycobiomarkers because of their specific occurrence in BC but rarely in normal tissues.33 Recently, an ELISA was developed to measure levels of both TF- and Tn-antigens expressed on MUC1 from nipple aspirate fluid (NAF).31 It was shown that nearly 90% of breast cancer NAF samples contained measurable quantities of TF- and Tn-antigens in contrast to the vast majority of noncancerous samples that did not contain detectable levels of these carbohydrates. The usefulness of these immunochemical tests is however limited by their marginal sensitivity and overall time-consuming (>6 h/assay) laboratory-based procedure. The ultrasensitive and simple gold nanoparticle-based EIS assay for the TF-antigen developed here may become an attractive point-of-care testing alternative to the currently used enzymelinked immunochemical assays. Nanoparticles have received wide attention in the past few years in electrochemical sensing applications mainly due to their extraordinary optical, electronic, and electrocatalytic properties that can be used as additional means for further signal amplification in biosensors.34 The recent availablity of efficient glycoblotting35 technology to transfer glycans from the surface of cells and biomolecules onto the surface of (32) Martin, A.; Corte, D.; Alvarez, A. M.; Rodriguez, J. C.; Andicoechea, A.; Bongera, M.; Junquera, S.; Pidal, D.; Allende, M. T.; Muniz, J. L. G.; Vizoso, F. Anticancer Res. 2006, 26 (5B), 3965-3971. (33) Brokhausen, I. EMBO Rep. 2006, 7 (6), 599-604. (34) Merkoc¸ i, A. FEBS J. 2007, 274, 310-316. (35) Shimaoka, H.; Kuramoto, H.; Furukawa, J.; Miura, Y.; Kurogochi, M.; Kita, Y.; Hinou, H.; Shinohara, Y.; Nishimura, S. Chem. Eur. J. 2007, 13 (6), 1664-1673.
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nanoparticles can further facilitate the nanoparticle-based approach. CONCLUSIONS In this report, we demonstrate that EIS can be used to reliably detect glycan-lectin interactions in a label-free fashion. The technique was shown to be fast and sensitive. The obtained quantitative and qualitative information was essential for the understanding of affinity and specificity of interactions between glycans and their cognate protein receptors, lectins. Such novel methods for label-free glycan detection may be of value for the point-of-care early cancer detection since many established tumor biomarkers including CEA, CA125, PSA, and MUC1 (CA15-3) are heavily glycosylated. The ability to rapidly differentiate their glycosylation states may provide additional information on the status of the disease. In the past few years, it has become increasingly clear that no single biomarker can be reliably used for cancer diagnosis. Further improvements using more specific carbohydrate-binding receptors and their integration into multiplexed electrode arrays with computer-assisted pattern analysis are needed before this impedimetric approach can be advanced into clinical studies. ACKNOWLEDGMENT We are grateful to Dr. Joseph J. Barchi of the National Cancer Institute for kindly supplying us with the PEGylated TF-antigen. Thanks are due to Aaron Fairchild, Kinjal Bhavsar, Alex Perry, Daniel Bishop, and Eric Alonas for assistance with the experiments and Drs. Veer Bhavanandan and Joseph Wang for valuable discussions. This work was supported by a grant from the Wallace Foundation, Ira Fulton School of Engineering and the Biodesign Institute. Received for review April 2, 2007. Accepted June 13M, 2007. AC070651E
