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Bioassay of prostate-specific antigen (PSA) using microcantilevers

Abstract

Diagnosis and monitoring of complex diseases such as cancer require quantitative detection of multiple proteins. Recent work has shown that when specific biomolecular binding occurs on one surface of a microcantilever beam, intermolecular nanomechanics bend the cantilever, which can be optically detected. Although this label-free technique readily lends itself to formation of microcantilever arrays, what has remained unclear is the technologically critical issue of whether it is sufficiently specific and sensitive to detect disease-related proteins at clinically relevant conditions and concentrations. As an example, we report here that microcantilevers of different geometries have been used to detect two forms of prostate-specific antigen (PSA) over a wide range of concentrations from 0.2 ng/ml to 60 μg/ml in a background of human serum albumin (HSA) and human plasminogen (HP) at 1 mg/ml, making this a clinically relevant diagnostic technique for prostate cancer. Because cantilever motion originates from the free-energy change induced by specific biomolecular binding, this technique may offer a common platform for high-throughput label-free analysis of protein–protein binding, DNA hybridization, and DNA–protein interactions, as well as drug discovery.

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Figure 1: Diagram of interactions between target and probe molecules on cantilever beam.
Figure 2: Detection of free PSA (fPSA).
Figure 3: Detection of complex PSA (cPSA).
Figure 4: Steady-state cantilever deflections as a function of fPSA and cPSA concentrations for three different cantilever geometries.
Figure 5: Surface stress as a geometry-independent parameter for assaying PSA.
Figure 6: Schematic diagram of the experimental setup showing a fluid cell within which a microcantilever beam was mounted.

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Acknowledgements

This work was supported by the Innovative Molecular Analysis Technologies (IMAT) program of the National Cancer Institute (NIH) (Grant R21 CA86132). G.W. and A.M. would also like to thank the Engineering Program of the DOE Basic Energy Sciences (Grant DE-FG03-98ER14870). K.H., H.J., and T.T. were supported by the Office of Biological and Environmental Research (OBER), US Department of Energy under contract DE-AC05-96OR22464 with Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corporation.

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Correspondence to Arun Majumdar.

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Wu, G., Datar, R., Hansen, K. et al. Bioassay of prostate-specific antigen (PSA) using microcantilevers. Nat Biotechnol 19, 856–860 (2001). https://doi.org/10.1038/nbt0901-856

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