Nanosensor design

El-Safty, S.A., Ismail. D. Prabhakaran. A. A., Matsunaga. H. and Muzukami. F. (2007) Nanosensor design packages a smart and compact development for metal ions sensing responses. Advanced Functiorud Materials, 17, 3731. 

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. 

Wu et al. [31] have recently presented a novel concept of designing oxygen nanosensors. They used the precipitation method to obtain polyfluorene beads (0 25 nm) doped with the oxygen indicator platinum(II) octaethylporphyrin. Poly (9,9-dihexylfluorene) belongs to materials widely used in OLEDs and has a bright blue emission when excited in the UV region. In beads, FRET-mediated red emission... 

Similarly to dyes, some fluorescent proteins can be incorporated into polymeric beads to be used as an alternative for ion sensing. For example, a reporter protein (composed of a phosphate-binding protein, a FRET donor (cyan fluorescent protein) and a FRET acceptor (yellow fluorescent protein)) was incorporated into polyacrylamide nanobeads by Sun et al. [46]. FRET was inhibited upon binding of phosphate. Kopelman and co-workers [47] used a similar approach to design a nanosensor for copper ions. They have found that fluorescence of red fluorescent protein DsRed (commonly used as a label) is reversibly quenched by Cu2+ and Cu+. Both DsRed and Alexa Fluor 488 (used as a reference) were entrapped into polyacrylamide nanobeads. Typically, up to 2 ppb of copper ions can be reliably measured. It should be mentioned, that in contrast to much more robust dyes, mild conditions upon polymerization and purification are very important for immobilization of the biomolecule to avoid degradation. 

Gouanve et al. [9] presented another approach to designing copper nanosensors. They prepared cross-linked polystryrene beads (0 14 nm) and functionalized the surface with 1,4,8,11-tetraazacyclotetradecane (Cyclam), which selectively bound copper ions. The core of the beads was stained with a lipophilic fluorescent dye 9,10-diphenylanthracene by swelling. Fluorescence of the dye was quenched in the presence of Cu2+ due to FRET. The particles were suitable for sensing Cu2+ in micromolar concentrations. 

De Novo Design Approach Based on Nanorecognition Functional Molecules/Materials and Nanosensors/Nanodevices... 

Varadan V. K, Linfeng Chen and Jining Xie. (2008). Nanomedicine design and applications of magnetic nanomaterials, nanosensors, wiley publisher, ISBN 978-0-470-03351-7. 

Design of Nanosensors The Ultimate in Sensors, Detection of a Single Molecule... 

---