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ABSTRACT: 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.
Analytical Chemistry 08/2009; 81(15):6266-71. · 5.86 Impact Factor
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ABSTRACT: 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.
Biosensors and Bioelectronics 07/2008; 23(11):1701-7. · 5.60 Impact Factor
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ABSTRACT: To provide a comprehensive understanding of the field effect in silicon nanowire (SiNW) sensors, we take a systematic approach to fine tune the distance of a charge layer by controlling the hybridization sites of DNA to the SiNW preimmobilized with peptide nucleic acid (PNA) capture probes. Six target DNAs of the same length, but differentiated successively by three bases in the complementary segment, are hybridized to the PNA. Fluorescent images show that the hybridization occurs exclusively on the SiNW surface between the target DNAs and the PNA. However, the field-effect response of the SiNW sensor decreases as the DNA (charge layer) moves away from the SiNW surface. Theoretical analysis shows that the field effect of the SiNW sensor relies primarily on the location of the charge layer. A maximum of 102% change in resistance is estimated based on the shortest distance of the DNA charge layer (4.7 A) to the SiNW surface.
Nano Letters 05/2008; 8(4):1066-70. · 13.20 Impact Factor
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ABSTRACT: 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.
Biosensors and Bioelectronics.
