Nanobiosensors: probing the sanctuary of individual living cells

Recently, nanotechnology has been revolutionizing important areas in molecular biology, especially diagnostics and therapy at the molecular and cellular level. The combination of nanotechnology, biology, and photonics opens the possibility of detecting and manipulating atoms and molecules using nanodevices, which have the potential for a wide variety of medical uses at the cellular level. The nanoprobes were fabricated with optical fibers pulled down to tips with distal ends having sizes of approximately 30-50 nm. The nanoscale size of this new class of sensors, allows for measurements in the smallest of environments. One such environment that has evoked a great deal of interest is that of individual cells. Using these nanobiosensors, it has become possible to probe individual chemical species in specific locations throughout a cell. This article provides an overview of the principle, development, and applications of optical nanosensor systems for in vivo bioanalysis at the single-cell level. The fiberoptics nanoprobes were covalently bound with antibodies that are selective to target analyte molecules. Excitation light is launched into the fiber and the resulting evanescent field at the tip of the fiber is used to excite target molecules bound to the antibody molecules. The fluorescence emission from the analyte molecules is then collected via a microscope. The usefulness and potential of this nanotechnology-based biosensor systems in biological research and applications in single-cell analysis are discussed.