Label-free electrical detection of cardiac biomarker with complementary metal-oxide semiconductor-compatible silicon nanowire sensor arrays.

Arrays of highly ordered silicon nanowire (SiNW) clusters are fabricated using complementary metal-oxide semiconductor (CMOS) field effect transistor-compatible technology, and the ultrasensitive, label-free, electrical detection of cardiac biomarker in real time using the array sensor is presented. The successful detection of human cardiac troponin-T (cTnT) has been demonstrated in an assay buffer solution of concentration down to 1 fg/mL, as well as in an undiluted human serum environment of concentration as low as 30 fg/mL. The high specificity, selectivity, and swift response time of the SiNWs to the presence of ultralow concentrations of a target protein in a biological analyte solution, even in the presence of a high total protein concentration, paves the way for the development of a medical diagnostic system for point-of-care application that is able to provide an early and accurate indication of cardiac cellular necrosis.

Highly sensitive measurements of PNA-DNA hybridization using oxide-etched silicon nanowire biosensors.

The highly sensitive and sequence-specific detection of single-stranded oligonucleotides using nonoxidized silicon nanowires (SiNWs) is demonstrated. To maximize device sensitivity, the surface of the SiNWs was functionalized with a densely packed organic monolayer via hydrosilylation, subsequently immobilized with peptide nucleic acid (PNA) capable of recognizing the label-free complementary target DNA. Because of the selective functionalization of the SiNWs, binding competition between the nanowire and the underlying oxide is avoided. Transmission electron microscopy was conducted to clearly differentiate the SiNW surface before and after removal of SiO(2). Fluorescence microscopy was used to further realize the selectivity of the oxide-etched chemistry on the SiNWs and sequence specificity of PNA-DNA hybridization. The concentration-dependent resistance change measurements upon hybridization of PNA-DNA show that detection limit down to 10fM can be obtained. The SiNW devices also reveal the capability of an obvious discrimination against mismatched sequences. Among several efforts being made to improve detection sensitivity, this work addresses one significant issue regarding surface functionalization which enables highly sensitive biomolecular sensing with SiNWs.

Fabrication and SERS performance of silver-nanoparticle-decorated Si/ZnO nanotrees in ordered arrays.

Highly ordered treelike Si/ZnO hierarchical nanostructures are successfully prepared in a large scale by combining two common techniques, viz., photolithography-assisted wafer-scale fabrication of Si nanopillars and bottom-up hydrothermal growth of ZnO nanorods. Silver nanoparticles are decorated onto the nanotrees by photochemical reduction and deposition. The Si/ZnO/Ag hybrid nanotrees are employed as SERS-active substrates, which exhibit good performance in terms of high sensitivity and good reproducibility. In addition to the SERS application, such ordered Si/ZnO arrays might also find potential applications in light-emitting diodes and solar cells.

Label-free direct detection of MiRNAs with silicon nanowire biosensors.

MicroRNA (miRNA), an 18-24-nucleotide (nt) noncoding RNA molecule in the genes of humans, plants and animals, is emerging as a key player in gene regulation. As a result, label-free, rapid, and sensitive detection for miRNA is of great significance. In this work, a label-free and direct hybridization assay for ultrasensitive detection of miRNA using silicon nanowires (SiNWs) device has been developed. Peptide nucleic acids (PNAs), which serve as a receptor to recognize miRNA directly without labeling the target miRNA, are immobilized on the surface of the SiNW device. Resistance change measured before and after hybridization correlates directly to concentrations of the hybridized target miRNA. Concentration-dependent measurements indicate that a detection limit of 1 fM was obtained using the optimized assay. The technique enables identification of fully matched versus mismatched miRNA sequences. Furthermore, the SiNW device is capable of detecting miRNA in total RNA extracted from Hela cells. This approach paves a way for label-free, early detection of miRNA as a biomarker in cancer diagnostics with very high sensitivity and good specificity.