Biosensing layers

With consideration to the quality of a bio or chemosensor it is therefore necessary to discuss the transduction principle, the quality of the sensitive layer and the data evaluation. These three issues will be discussed in this paper, with the focus on interferometric principles in the area of non-specific measurements using chemosensors and specific interaction processes in the case of biosensing. 

Gutes, A., C. Carraro, and R. Maboudian, Single-layer CVD-grown graphene decorated with metal nanoparticles as a promising biosensing platform. Biosensors and Bioelectronics,... 

Figure 3.1 — (A) Configuration of p-nitrophenyl phosphate biosensor (a) common end of bifurcated bundle b) retaining 0-ring (c) inner nylon mesh with enzyme (d) outer nylon mesh (not drawn to scale). (B) Processes occurring at the biosensing tip a enzyme/scatter layer S enzymatic substrate P light absorbing product. (Reproduced from [34] with permission of the American Chemical Society).

Because of this great flexibility in the design, fabrication, and readout, cantilever arrays for gaseous (Kim et al., 2001) and biosensing aqueous applications (Arntz et al., 2003) have been realized. Needless to say, the issues of selectivity, dynamic range, response time, and so on depend ultimately on the interactions of the analyte with the selective layer. What cantilevers can offer is a low instrumental detection limit and the possibility of avoiding experimental artifacts due to the effects not related to the chemical interactions. Because they are relatively new, it is too early to estimate their usefulness. They will have to stand the test of time. 

A.B.M. Ismail, T. Harada, T. Yoshinobu, H. Iwasaki, M.J. Schoning and H. Liith, Investigation of pulsed laser-deposited A1203 as a high pH-sensitive layer for LAPS-based biosensing applications, Sens. Actuators B Chem., 71(3) (2000) 169-172. 

In terms of biosensing applications using such layers, again cholera toxin detection on a porous silicon substrate [85] has been reported. Also biotin-avidin interaction by QCM [86], glutamate detection [87], as well as protein membrane interactions [88, 89] have been studied. 

Supramolecular and constitutional dynamic interfaces and layers have evidently not been consciously much employed to date in biosensing and transport applications. They may provide some initial chemical synthetic difficulties when compared to using naturally derived substances such as phospholipid and cholesterol based components but they may provide a route to nanostructured surfaces and particles demonstrating unknown specificities and behaviours. 

There may be instances where one wishes to detect die absorption of molecules from a liquid into a polymeric film on the plate surface. And in biosensing, one may wish to detect the adsorption or attachment of a layer of protein molecules, cells, bacteria or other organisms on a surface. Figure 3.48 (page 130) shows an exploded view of a three-chip FPW liquid flow cell made for such applications. 

---