**8. Cyclodextrin-nanoparticle hybrids as chemical sensors**

In recent years, scientific community has exploited the unique property of gold nanoparticle aggregation in the design and construction of various optical sensory

*Cyclodextrin-Based Sensors for the Recognition of Small Molecules DOI: http://dx.doi.org/10.5772/intechopen.108500*

#### **Figure 18.**

*Schematic illustration of fluorescence quenching of rhodamine B (64)* via *the* β*-CD-fullerene hybrid conjugate (63).*

**Figure 19.** *Schematic depiction of the formation of pyrene functionalized* β*-CD-SWCNT hybrid conjugate (67).*

devices where the sensing mechanism is perceived through color variation from red to purple/blue. In this regard, Kaifer and teammates have constructed *β*-CD functionalized gold nanoparticles (**68**) and noticed that the addition of ferrocene dimer (**69**) as a competitive guest to colloidal solutions of **68** primarily results in a red shift followed by the precipitation of a red solid (**Figure 20**) [85, 86]. These observations were not perceived in case of addition of ferrocene in methanol. This indicates that the ferrocene dimer operates as a linker between diverse gold nanoparticles, and hence helps in their aggregation. This aggregation in turn offers a color change, which signifies the sensing event with typical guest molecules. The same group also utilized the *γ*-CD in combination with gold nanoparticles for the sensing of well-known carbon nanomaterial known as fullerene (C60) through aggregation phenomenon [87]. In another event, Tang *et al.* constructed a highly selective as well as sensitive glucose

#### **Figure 20.**

*Schematic view of* β*-CD functionalized gold nanoparticles (68) aggregation upon addition of ferrocene dimer (69).*

#### **Figure 21.**

*Schematic illustration of FRET on/off mechanism operating in nanobiosensor (71) constructed from concanavalin A fabricated CdTe (QDs) and thiolated* β*-CD functionalized AuNps.*

nanobiosensor (**71**) in serum, which operates through FRET between concanavalin A fabricated CdTe quantum dots (QDs; energy donors) and thiolated *β*-CD functionalized gold nanoparticles (AuNps) acting as energy acceptors (**Figure 21**) [88]. Quite recently, Bindu and co-workers have functionalized gold nanoparticles by the *β*-CD in order to detect heavy metal ions in aquatic realm. Captivatingly, the sensitivity of the developed *β*-CD-gold nanoparticle hybrid conjugate toward copper was found to be 1.788 mM [89]. Elgamouz and teammates have functionalized silver nanoparticles by *β*-CD to develop a nanoprobe having the ability to encapsulate creatinine through the colorimetric response. The established *β*-CD-silver

*Cyclodextrin-Based Sensors for the Recognition of Small Molecules DOI: http://dx.doi.org/10.5772/intechopen.108500*

**Figure 22.** *Schematic representation of the detection of H2O2* via β*-CD-AgNP-based nano colorimetric probe (73).*

nanoparticle (AgNP)-based nano-colorimetric probe (**73**) has successfully been applied in the detection of reactive oxygen species *viz.* H2O2 in human urine samples by these authors (**Figure 22**) [90].
