Bioassay of prostate-specific antigen (PSA) using microcantilevers

Diagnosis and monitoring of complex diseases such as cancer require quantit ative detection of multiple proteins. Recent work has shown that when speci fic biomolecular binding occurs on one surface of a microcantilever beam, i ntermolecular nanomechanics bend the cantilever, which can be optically det ected. Although this label-free technique readily lends itself to formation of microcantilever arrays, what has remained unclear is the technologicall y critical issue of whether it is sufficiently specific and sensitive to de tect disease-related proteins at clinically relevant conditions and concent rations. As an example, we report here that microcantilevers of different g eometries 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 mug/ml in a b ackground of human serum albumin (HSA) and human plasminogen (HP) at 1 mg/m l, making this a clinically relevant diagnostic technique for prostate canc er. Because cantilever motion originates from the free-energy change induce d by specific biomolecular binding, this technique may offer a common platf orm for high-throughput label-free analysis of protein-protein binding, DNA hybridization, and DNA-protein interactions, as well as drug discovery.