Different geometries for introducing ALP. ALP can be either suspended in solution (S) or immobilized at the electrode surface (I). CdS QDs have been attached to the electrode surface via a BDT layer and spin coating. On top of the QD layer optionally polyelectrolyte layers out of PAH and PSS are added. Hereby i is the number of polyelectrolyte layers: S0, S1, S2, I0, I1. a) S0: immobilization of QDs via spin coating with ALP in solution. b) S1: a single layer of PAH is added on top of S0. c) S2: a layer of PSS is immobilized on top of S1. d) I1: ALP is immobilized on to of S1. e) I2: A second double layer of PAH and ALP is immobilized on top of I1.