Human blood serum contains various low-abundance biomarker proteins, the concentration of which can be correlated to the progress / existence of various common disease, including cancer. Accurate, reliable measurement of biomarker protein concentration holds promise as a mean to low-cost, on-site, early detection and warning method for cancer. However, technical challenges in sample preparation and detection have been limiting the use of protein biomarker in cancer prevention. While immunoassays such as ELISA are well established for antigen-based biomarker detection, the sensitivity and the detection dynamic range of the assay is inherently governed by the quality of the antibody-antigen complex. If the antigen concentration is significantly below Kd, then the binding kinetics are slow and readout precision of the antigen-antibody complex can be degraded by noise. Also, there is evidence to suggest that the next generation of cancer screening tests may employ not just one, but a small panel of less than ten biomarkers that together add statistical power to the detection of specific cancers.

We are proposing a general approach for improving the performance of immunoassays for biomarker detection. The approach is based on a nanofluidic device that controllably concentrates a dilute sample and an ultra-sensitive suspended microchannel resonant mass sensor that detects specific biomarkers within the concentrate. Since the amplification (or gain) of the concentrator is adjustable, the dynamic range and detection limit of the immunoassay can be governed by the properties of the concentrator and not Kd.
 >We have demonstrated that the nanochannel based preconcentrator can enhance sample concentration by many orders of magnitudes, and that the mass sensor can detect less than a femtogram in the aqueous environment. Provided 100 nm gold nanoparticles are used as mass enhancement labels within the ELISA-based sandwich assay, it should be possible to achieve single molecule resolution. Other tools for fractionating and separating complex protein mixtures are under development, which will effectively eliminate high-abundance protein species and therefore, enhance the sensitivity and selectivity of the downstream biosensor.
 >Our eventual goal is to integrate these micro/nanofluidic tools for biosensing and sample preparation tools in a microdevice, which could significantly reduce human error and labor cost, and can be made portable so that the bioassay can be performed on site. Since the integrated concentration/detection system is batch fabricated by conventional foundry-level processing techniques, the cost per device could potentially be less than ten dollars.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA