Optical nanosensors

Die study of individual cells or even compartments within a cell requires appropriately sized nanosensors. Optical nanosensors are usually grouped into chemical and biological nanosensors, depending on the probe being used. Both types of sensors have been used to measure chemicals in microscopic envuonments and to detect different entities within single cells. 

With the complex where L = pyridine an optical nanosensor was developed [135-137], the method used to fix the vapochromic material to the optical fiber was the electrostatic self assembling method (ESA) and the light source used was an 850 nm LED. The sensor was tested for two different alcohols (ethanol and methanol) and it was possible to distinguish between different concentrations. It was also possible to discriminate between the two different alcohols. 

Volatile alcoholic compounds fiber optic nanosensor. Sensors and Actuators B, 115, 444- 9. 

Kopelman et al.73 have prepared fiber optic sensors that are selective for nitric oxide and do not respond to most potential interferents. Both micro-and nanosensors have been prepared, and their response is fast (<1 s), reversible, and linear up to 1 mM concentrations of nitric oxide. The respective "chemistry" at the fiber tip was contacted with the sample, light was guided to the sample through the microfiber, and emitted light was collected by a microscope (without the use of fibers, however). 

Petersons pH probe also was modified in order to give a miniature fiber optic sensor potentially suitable for glucose measurements90. Kopelman et al.91 developed a fiber-optic pH nanosensor for physiological measurements using a dual-emission sensitive dye. The performance of a pH sensor was reported92. An unclad fiber was dip-coated with a thin layer of porous cladding within which a pH-sensitive dye was entrapped. The fundamental... 

Clark H.A., Kopelman R., Tjalkens R., Philbert M.A., Optical Nanosensors for Chemical Analysis inside Single Living Cells. 1. Fabrication, Characterization, and Methods for Intracellular Delivery of PEBBLE Sensors, Anal. Chem. 1999 71 4831— 4836. 

It is often desirable to immobilize different biomolecules on different sensing elements in close proximity on the same nanophotonic sensor in the development of a multiplexed sensor. This is the case in the example of parallel ID photonic crystal resonators described in Sect. 16.4. Cross-contamination of biomolecules must be avoided in order to preserve high specificity. We have found that a combination of parylene biopatteming and polydimethylsiloxane (PDMS) microfluidics is a convenient means to immobilized multiple biomolecules in close proximity without cross-contamination as shown in Fig. 16.8. Parylene biopatteming is first used to expose only the regions of highest optical intensity of the nanosensor for functionalization. Second, a set of PDMS microfluidics is applied to the parylene-pattemed nanophotonic sensor, and the biomolecules to be attached... 

Some bead materials possess porous structure and, therefore, have very high surface to volume ratio. The examples include silica-gel, controlled pore glass, and zeolite beads. These inorganic materials are made use of to design gas sensors. Indicators are usually adsorbed on the surface and the beads are then dispersed in a permeation-selective membrane (usually silicone rubbers). Such sensors possess high sensitivity to oxygen and a fast response in the gas phase but can be rather slow in the aqueous phase since the gas contained in the pores needs to be exchanged. Porous polymeric materials are rarer and have not been used so far in optical nanosensors. 

Similarly to bulk oxygen sensors, optical nanosensors rely on dynamic quenching of luminescence. Numerous indicators and polymeric materials were found suitable... 

Aylott JW (2003) Optical nanosensors-an enabling technology for intracellular measurements. Analyst 128 309-312... 

Borisov SM, Klimant I (2008) Optical nanosensors - smart tools in bioanalytics. Analyst 133 1302-1307... 

Borisov SM, Mayr T, Klimant I (2008) Poly(styrene-block-vinylpyrrolidone) beads as a versatile material for simple fabrication of optical nanosensors. Anal Chem 80 573-582... 

Clark HA, Hoyer M, Philbert MA, Kopelman R (1999) Optical nanosensors for chemical analysis inside single living cells. 1. Fabrication, characterization, and methods for intracellular delivery of PEBBLE sensors. Anal Chem 71 4831 1836... 

Park EJ, Brasuel M, Behrend C, Philbert MA, Kopelman R (2003) Ratiometric optical PEBBLE nanosensors for real-time magnesium ion concentrations inside viable cells. Anal Chem 75 3784-3791... 

Anderson, G. P., Jacoby, M. A., Ligler, F. S., and King, K. D. (1997). Effectiveness of protein A for antibody immobilization for a fiber optic biosensor. Biosens. Bioelectron. 12,329-336. Baeumner, A. (2004). Nanosensors identify pathogens in food. Food Technol. 58, 51-55. Balbus, J. M., and Embrey, M. A. (2002). Risk factors for waterborne enteric infections. Curr. Opin. Gastroenterol. 18, 46-50. 

Figure 19-20 Fluorescence from Oj-indicator beads showing constant intensity near 525 nm and variable intensity near 610 nm. The ratio of emission intensity at these two wavelengths is related to 02 concentration. [From H. Xu, J. W. Aylott, R. Kopelman, T. J. Miller, and M. A flhi/berf. "Real-Time Method for Determination of 02 Inside Living Cells Using Optical Nanosensors," And. Chem. 2001, 73,4124.]...

This construction results in signal enhancement when the composite particles are employed as optical nanosensors due to the possibility to exploit to this scope the Surface Enhanced Raman Scattering (SERS) by the embedded Au nanoparticles. 

Clark HA, Kopelman R, Tjalkens R, Philbert MA. Optical nanosensors for chemical analysis inside single hving cells. 2. Sensors for pH and calcium and the intracellular appbcation of PEBBLE sensors. Analytical Chemistry 1999, 71, 4837 1843. 

Advanced functional inorganic nanoparticles (NPs) have been studied intensively in the last couple of decades due to their unusual chemical and physical properties compared with their bulk materials, which enable them to be promising in applications as diverse as electronics,1 optics,2 optoelectronics,3 nanosensors,4 information storage,5 fuel cells,6 biomedicine,7 biological labeling,8 gene delivery,9 electrocatalysis,10 and surface enhanced Raman scattering (SERS).11,12 For instance, metal NPs with... 

Kneipp J, Kneipp H, Wittig B, Kneipp K (2007) One- and two-photon excited optical pH probing for cells using surface-enhanced Raman and hyper-Raman nanosensors. Nano Lett 7 2819... 

Baker SLR, Kopelman R, Meyer TE, Cusanovich MA (1998) Fiber optic nitric oxide selective biosensors and nanosensors. Anal Chem 70 971-976... 

Die constmction of nanosensors is cracially dependent on the constmction of nanometer-sized tips on optical fibers. Neai-field optical microscopy has spawned nanoscale optical fibers produced by either pulling with micropipette pullers or by chemical etching. 

Brian M. Cullum and Tuan Vo-Dinh, The development of optical nanosensors for biological meas-ui-ements, TIBTECH, 18 (2000), 388-393. 

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