The optical interference signal is converted by a photodetector to an electrical signal. actively investigated1-4, with potentially important significance for PF-02575799 malignancy treatment. A number of reports have clearly established a relationship between the quantity of circulating tumor cells and patient end result for various cancers, particularly breast5,6and prostate7-9as well as other cancers . With respect to early markers for prostate malignancy (PCa), standard screenings for potential biomarkers such as prostate-specific antigen are generally not effective and other molecular biomarkers are needed10. However, a number of studies have established the power of CTC levels as a prognostic indication and/or a predictor of response to therapy in PCa4,7-9,11,12. CTCs have been detected using antibody-based methods targeting a global epithelial marker such as epCAM4,13. Such positive selections are complicated by the fact that certain common types of cancers (e.g., normal-like breast cancers) do not express epCAM14, and presently there is growing evidence that many CTCs have undergone the epithelial-to-mesenchymal transition, thereby losing expression of epCAM15,16. More commonly, CTCs for a given cancer type have been recognized using RT/PCR for pre-selected marker RNAs. In general, 2 markers appear to be PF-02575799 superior to one for detection of CTCs by increasing sensitivity17,18. Drawbacks to the approach of identifying CTCs based on pre-chosen PF-02575799 RNA markers are that the CTCs are being identified in patients only after they have been diagnosed with particular cancers, and that a relatively limited number of RNAs can be interrogated. In contrast, our approach is to develop a detection platform that would be useful for screening purposes, for early detection of multiple types of cancers, as well as for monitoring therapy. This approach is based on the original premise that metastasis is a relatively inefficient process19-21, and there is anecdotal but growing support for the usefulness of CTC detection in diagnosis of early-stage disease. A general relationship between CTC levels and stage appears to exist in many different cancers22but significant CTC levels are generally found even in early-stage cancers. For example, in one early study of breast cancer patients, 68% of patients with Stage N1 disease had detectable CTCs, but 46% of patients with Stage N0 disease also had detectable CTCs17. Others have found similar CTC NS1 levels in localized vs. advanced PCa patients23. Schmidt and co-workers24showed that even very small foci of PCa (0.2 cm3) give rise to CTCs, and recent work has also identified CTCs in PCa patients with low-volume tumors25. We intend to enrich CTCs from whole blood samples based on their decreased density using a simple porous membrane centrifugation device11, and RNA is then purified from the enriched CTC-containing fraction. This provides CTC enrichment of ~400:1 with respect to white blood cells. The platform we are developing consists of a chip-based device, which PF-02575799 utilizes antisense oligonucleotides (ASOs) covalently attached to metallic or silica-coated nanowires (NWs) to detect marker RNAs for various cancer types. NWs are first prepared off-chip and then assembled in a bottom-up manner from suspension and integrated to fabricate an array of NW-resonator (NR) devices. A hybridization sandwich is used, wherein target RNAs are bound to the ASO-derivatized NWs26. A 2ndASO, attached to a single 50 nm Au-nanoparticle (ASO:AuNP), is then hybridized to a different site on the bound target RNA; this requires a second stringent hybridization, which increases specificity, PF-02575799 and also provides a very substantial increase in mass which is important for NR sensitivity. Detection of the hybridization sandwich attached to the NW is accomplished by optically measuring the shift in resonance frequency of the NRs. Related recent work towards NR biosensor design describes the evaluation of resonator clamp quality27, elastic and dissipative properties of silicon27, gold and rhodium28, NW resonance in air27and programmed assembly of NWs29. We chose PCA3 (Gene ID#50652; also known as DD3) as a marker for PCa. PCA3 is an abundant, non-coding RNA; exon 4 is prostatespecific, and PCA3 is significantly up-regulated in PCa30,31. CTCs in PCa serve as a predictive biomarker in patients with hormone-sensitive PCa32as well as a surrogate marker for outcome33and clinical management12, and PCA3 is a prostate-specific marker for CTCs in peripheral blood13, and is of interest as a PCa-specific marker in urine34. NRs are attractive for biosensing applications because they offer high mass sensitivity35,36and can be incorporated onto integrated circuit chips for electrical transduction and/or actuation37. A recent critical review compares several nanobiosensor platforms38. NRs, with their small mass.