Energy transfer glucose sensing

Figure 1.6. Glucose sensing by fluorescence resonance energy transfer (FRET).

Tolosa L, Szmacinski H, Rao G, Lakowicz JR. Lifetime-based sensing of glucose using energy transfer with a long lifetime donor. Analytical Biochemistry 1997, 250, 102-108. 

Duong HD, Rhee JI. Use of CdSe/ZnS core-shell quantum dots as energy transfer donors in sensing glucose. Talanta 2007 73 899-905. 

Facilitated diffusion is very similar to passive diffusion with the difference that transfer across membranes is assisted by the participation of carrier proteins embedded in the membrane bilayer. Again, the direction of passage will be from the side of the membrane with high concentration of a chemical to the side with low concentration this also occurs without energy expenditure by the cell. Such a process is somewhat specific in the sense that it applies to molecules that are able to bind to a carrier protein. Absorption of nutrients such as glucose and amino acids across the epithelial membrane of the gastrointestinal tract occurs by facilitated diffusion. Since a finite number of carriers are available for transport, the process is saturable at high concentrations of the transported molecules and competition for transport may occur between molecules of similar structure. 

---