Arrays of highly ordered n-type silicon nanowires (SiNW) are fabricated using complementary metal-oxide semiconductor (CMOS) compatible technology, and their applications in biosensors are investigated. Peptide nucleic acid (PNA) capture probe-functionalized SiNW arrays show a concentration-dependent resistance change upon hybridization to complementary target DNA that is linear over a large dynamic range with a detection limit of 10 fM. As with other SiNW biosensing devices, the sensing mechanism can be understood in terms of the change in charge density at the SiNW surface after hybridization, the so-called "field effect". The SiNW array biosensor discriminates satisfactorily against mismatched target DNA. It is also able to monitor directly the DNA hybridization event in situ and in real time. The SiNW array biosensor described here is ultrasensitive, non-radioactive, and more importantly, label-free, and is of particular importance to the development of gene expression profiling tools and point-of-care applications.

A nanogapped microelectrode-based biosensor array is fabricated for ultrasensitive electrical detection of microRNAs (miRNAs). After peptide nucleic acid (PNA) capture probes were immobilized in nanogaps of a pair of interdigitated microelectrodes and hybridization was performed with their complementary target miRNA, the deposition of conducting polymer nanowires, polyaniline (PAn) nanowires, is carried out by an enzymatically catalyzed method, where the electrostatic interaction between anionic phosphate groups in miRNA and cationic aniline molecules is exploited to guide the formation of the PAn nanowires onto the hybridized target miRNA. The conductance of the deposited PAn nanowires correlates directly to the amount of the hybridized miRNA. Under optimized conditions, the target miRNA can be quantified in a range from 10 fM to 20 pM with a detection limit of 5.0 fM. The biosensor array is applied to the direct detection of miRNA in total RNA extracted from cancer cell lines.

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