Immunomagnetic Diffractometry highlighted in Analytical Chemistry and ACS Journal of Proteome Research

Immunomagnetic diffractometry for biomarker detectionIn the quest for an improved biomarker detection method, Cagri Savran and colleagues at Purdue University and the Mayo Clinic have designed a new technique called immunomagnetic diffractometry. Their approach combines the immunomagnetic capture of an analyte on beads, in situ assembly of an optical diffraction grating, and measurement of the diffraction. In this method, magnetic beads capture the target from the serum sample and bind to a surface to form the diffraction gratings. By virtue of their size, the beads enhance the diffraction signal, so no further signal amplification or labeling is needed. The target chosen for the proof-of-principle study was the folate receptor (FR), a potential serum biomarker for cancer. With microcontact printing, the researchers deposited alternating 15 μm lines of folate-coupled bovine serum albumin (F–BSA) onto a gold surface. Magnetic beads derivatized with the FR antibody (FR–beads) captured FR from serum and subsequently bound to the F–BSA lines. The bound molecules and beads effectively formed a grating that diffracted the incident laser radiation. The researchers observed that the FR–beads attached specifically to the F–BSA on the surface. The packing density of the bound FR–beads intensified with increasing FR concentrations (700 fM to 11 nM). After creating a calibration curve, the researchers measured the FR concentration in the serum of cancer patients. The detection limit of immunomagnetic diffractometry was lower than that of several other biomarker assays such as ELISAs. Immunomagnetic diffractometry has the additional advantages of speed, robustness, low cost, and ease of miniaturization. The researchers say that the assay is applicable to other biomarkers. (J. Am. Chem. Soc. 2007, 129, 15,824–15,829)

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