We report direct, real-time electrical detection of single virus particles with high selectivity by using nanowire field effect transistors. Measurements made with nanowire arrays modified with antibodies for influenza A showed discrete conductance changes characteristic of binding and unbinding in the presence of influenza A but not paramyxovirus or adenovirus. Simultaneous electrical and optical measurements using fluorescently labeled influenza A were used to demonstrate conclusively that the conductance changes correspond to binding͞unbinding of single viruses at the surface of nanowire devices. pH-dependent studies further show that the detection mechanism is caused by a field effect, and that the nanowire devices can be used to determine rapidly isoelectric points and variations in receptor-virus binding kinetics for different conditions. Lastly, studies of nanowire devices modified with antibodies specific for either influenza or adenovirus show that multiple viruses can be selectively detected in parallel. The possibility of large-scale integration of these nanowire devices suggests potential for simultaneous detection of a large number of distinct viral threats at the single virus level.

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Integrating nanophotonics with electronics could enhance and/or enable opportunities in areas ranging from communications and computing to novel diagnostics. Light sources and detectors are important elements for integration, and key progress has been made using semiconducting nanowires and carbon nanotubes to yield electrically driven sources and photoconductor detectors. Detection with photoconductors has relatively poor sensitivity at the nanometre scale, and thus large amplification is required to detect low light levels and ultimately single photons with reasonable response time. Here, we report avalanche multiplication of the photocurrent in nanoscale p-n diodes consisting of crossed silicon-cadmium sulphide nanowires. Electrical transport and optical measurements demonstrate that the nanowire avalanche photodiodes (nanoAPDs) have ultrahigh sensitivity with detection limits of less than 100 photons, and subwavelength spatial resolution of at least 250 nm. Crossed nanowire arrays also show that nanoAPDs are reproducible and can be addressed independently without cross-talk. NanoAPDs and arrays could open new opportunities for ultradense integrated systems, sensing and imaging applications.

Coated quartz crystal microbalances were modified with a surface-imprinting process using whole yeast cells. These molded polymer and sol-gel surfaces show honeycomb-like structures as shown by atomic force microscopy. Reinclusion of cells allows a selective on-line monitoring of these microorganism concentrations in water over 5 orders of magnitude. The sensitivity to cells holds up in growth media up to 21 g/L. Even cell fragments can be detected in flowing conditions. The highly robust polymers on the sensor devices are suitable for biotechnological applications.