Silicon-based calixarenes

FIG. 3 Comparison of membrane impedance among silicone-rubber-based ion-sensing membrane containing calixarene neutral carriers (5) (0) (6) ( ) and (2) (A)- (From Ref. 21.)... 

FIG. 4 Selectivity comparison among silicone-rubber-membrane Na -ISFETs based on calixarene neutral carriers (1), (2), and (5). 

Applicability in biological ion assay is an important factor for biocompatible potentio-metric ion sensors. Attempts were made to determine Na" " concentrations in human blood sera by using silicone-rubber membrane Na+-ISFETs based on (5) [Fig. 17(a)] [29]. The found values for Na concentration in undiluted, 10-fold diluted, and 100-fold diluted serum samples are in good agreement with the Na" " calibration plots. Even in the undiluted serum samples, only a slight potential shift was observed from the calibration. This indicates that the calixarene-based silicone-rubber-membrane Na+-ISFETs are reliable on serum Na assay. For comparison with the silicone-rubber membrane, Na -ISFETs with corresponding plasticized-PVC membrane containing (2) or (5) were also tested for the Na assay. The found values of Na" " concentration... 

SAMs of calixarene derivatives have been demonstrated to possess recognition properties towards ions [69-77] and small organic molecules [78-83]. For example, in 2012 Li reported on calix[4]azacrown-based SAMs that exhibit ion-pair recognition properties towards l-butyl-3-methylimidazolium chloride [84], The calixarene-based SAM was produced by a click reaction between the azido-modified silicon substrate and the calix[4]azacrown. The authors demtmstrated by contact angle (CA) measurements that the calixarene-modified surface is superhydrophobic (CA= 154.6 3°). Upon immersion of the calixarene-based SAM in a l-butyl-3-methylimidazolium chloride solution, the CA drops to 10.1 3° (Fig. 37.14). On the other hand, no changes in the CA of the surface are observed in the presence of 1-butyl-3-methylimidazolium bromide and l-butyl-3-methylimidazolium hexafluorophosphate. The calix[4]azacrown modified SAM was therefore demonstrated to possess selective wettability response towards the l-butyl-3-methylimidazolium chloride ion-pair. 

Zanoni reported on the assembly of AuNPs on calixarene-based SAMs [85]. A silicon surface (Si) was functionalized with a calix[6]arene derivative bearing three undecenyl chains on the lower rim and three phenylurea moieties on the upper rim (Ce). The so-produced SAMs form stable complexes with a redox-active molecule that consists of a 4,4 -bypiridinium unit linked by a dodecyl chain to another pyridinium ring (A). This surface showed binding towards AuNPs functionalized with a calix[4]arene derivative (C4) (Fig. 37.15). The presence of the di-topic guests allows for the reversible and hierarchical assembly of the AuNPs on the Si surface. Moreover, the nanoparticles were demonstrated to be electrochemically removed from the Si/Ce/A surface. 

---