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Recently, optical fibers comprising a crystalline semiconductor core in a silica cladding have been successfully drawn by a conventional drawing process. These fibers are expected to exhibit a photoconductive response when illuminated by photons more energetic than the band gap of the core. In the photoconducting state, such a fiber can be expected to support driven RF currents so as to function as an antenna element, much as a plasma antenna. In this paper, we report the first device-related results on a crystalline semiconductor core optical fiber potentially useful in a photoconducting optical fiber antenna array; namely, optically induced changes to the electrical conductivity of a glass-clad germanium-core optical fiber. Since DC photoconduction measurements were masked by a photovoltaic effect, RF measurements at 5 MHz were used to determine the magnitude of the induced photoconductive effect. The observed photoconductivity, though not large in the present experiment, was comparable to that measured for the bulk crystals from which the fibers were drawn. The absorbed pumping light generated photo-carriers, thereby transforming the core from a dielectric material to a conductor. This technology could thus enable a class of transient antenna elements useful in low observable and reconfigurable antenna array applications. OCIS codes: 160.2290, 160.6000, 060.2290, 060.2310, 160.5140, 260.5150.

A highly sensitive competitive immunosensor based on the electrochemiluminescence (ECL) of quantum dots (QDs) was proposed by coupling with an enzymatic amplification. The fabrication process of the immunosensor was traced with atomic force microscopic images and electrochemical impedance spectra. The strong cathodic ECL emission of the immobilized QDs could be detected at a relatively low emission potential. The reduction of dissolved oxygen during the cathodic process provided a self-produced coreactant, [H.sub.2][O.sub.2], for the ECL emission. Using human IgG (HIgG) as a model protein, upon the immuno-recognition of the immobilized HIgG to its antibody labeled simply with horseradish peroxidase, the ECL intensity decreased due to the steric hindrance of the proteins to electron Iransfer. The decrease could be greatly amplified by an enzymatic cycle to consume the self-produced coreactant, leading to a wide calibration range of 0.05 ng [mL.sup.-1] ~ 5 [micro]g [mL.sup.-1] and a low limit of detection for the competitive immunoassay of HIgG. This immunosensor showed good stability and fabrication reproducibility. The immunoassays of practical samples showed acceptable results. This facile immunosensing strategy opened a new avenue for detection of proteins and application of QDs in ECL biosensing. 10.1021/ac1013942

A novel electrocbemiluminescent (ECL) sensing system was constructed for low-potential detection of metal ion by immobilizing surface-unpassivated CdTe quantum dots (QDs) on a glassy carbon electrode. The surface-unpassivated CdTe QDs were prepared using meso-2,3-dimercaptosuccinic acid (DMSA) as a stabilizer to cap CdTe QDs and characterized with scanning electron micrograph and X-ray photoelectron spectroscopy. The immobilized QDs showed a strong cathodic ECL emission peak at -0.87 V with an onset potential at -0.64 V (vs Ag/AgCl/ saturated KCl) in air-saturated, pH 9.0 HC1--Tris buffer. On the basis of the competition of metal ion to the stabilizer, the quenching effect of metal ion on ECL emission was observed, which led to a sensitive chemical sensing application. Using cupric cation as a model analyte, the sensor showed a linear range from 5.0 nM to 7.0 [micro]M with a detection limit of 3.0 nM and had been successfully applied in the detection of copper in human hair. It could be extended to detect other metal ions with stronger metal--S interaction than with the Cd--S bond. As an example, the sensor could be used to detect [Hg.sup.2+] down to 1.4 nM. The bidentate chelate QD-basod sensor exhibited a promising platform for rapid detection of cations with strong metal--S interaction and could be further applied for development of other low-potential electrochemical sensing systems. 10.1021/ac100315a

A cascade signal amplification strategy was proposed for detection of protein target at ultralow concentration by combining the rolling circle amplification (RCA) technique with oligonucleotide functionalized quantum dots (QDs), multiplex binding of the biotin--strepavidin system, and anodic stripping voltammetric detection. The RCA product containing tandem-repeat sequences could serve as excellent template for periodic assembly of QDs, which presented per protein recognition event to numerous quantum dot tags for electrochemical readout. Both the RCA and the multiplex binding system showed remarkable amplification efficiency, very little nonspecific adsorption, and low background signal. Using human vascular endothelial growth factor as a model protein, the designed strategy could quantitatively detect protein down to 16 molecules in a 100 [micro]L sample with a linear calibration range from 1 aM to 1 pM and was amenable to quantification of protein target in complex biological matrixes. The proposed cascade signal amplification strategy would become a powerful tool for proteomics research and clinical diagnostics. 10.1021/ac100144g

Owing to their unique optical properties, quantum dots (QDs) with different colors have been applied for simultaneous detection of multiple analytes. However, the use of single QD for multiplex detection of analytes with single-molecule detection has not been explored. Here we report a single QD-based nanosensor for multiplex detection of HIV-1 and HIV-2 at single-molecule level in a homogeneous format. In this single QD-based nanosensor, the QD functions not only as a fluorescence pair for coincidence detection and as a fluorescence-resonance-energy-transfer (FRET) donor for FRET detection but also as a local nanoconcentrator which significantly amplifies the coincidence-related fluorescence signals and the FRET signals. This single-QD-based nanosensor takes advantage of a simple 'mix and detection' assay with extremely low sample consumption, high sensitivity, and short analysis time and has the potential to be applied for rapid point-of-care testing, gene expression studies, high-throughput screening, and clinical diagnostics. 10.1021/ac9026675

Advances in nanotechnology have led to the development of novel fluorescent probes called quantum dots. Quantum dots have revolutionalized the processes of tagging molecules within research settings and are improving [...]

Semiconductor nanocrystals (NCs) are increasingly being used as photoluminescen markers in biological imaging. Their brightness, large Stokes shift, and high photostability compared to organic fluorophores permit the exploration of biological [...]