We report a novel hybrid charge sensor realized by the deposition of phospholipid monolayers on highly doped n‐GaN electrodes. To detect the binding of recombinant proteins with histidine‐tags, lipid vesicles containing chelator lipids were deposited on GaN electrodes pre‐coated with octadecyltrimethoxysilane monolayers. Owing to its optical transparency, GaN allows the confirmation of the fluidity of supported membranes by fluorescence recovery after photo‐bleaching (FRAP). The electrolyte‐(organic) insulator‐semiconductor (EIS) setup enables one to transduce variations in the surface charge density ΔQ into a change in the interface capacitance ΔC p and, thus, the flat‐band potential ΔU FB. The obtained results demonstrate that the membrane‐based charge sensor can reach a high sensitivity to detect reversible changes in the surface charge density on the membranes by the formation of chelator complexes, docking of eGFP with histidine tags, and cancellation by EDTA. The achievable resolution of ΔQ ≥ 0.1 μC/cm2 is better than that obtained for membrane‐functionalized p‐GaAs, 0.9 μC/cm2, and for ITO coated with a polymer supported lipid monolayer, 2.2 μC/cm2. Moreover, we examined the potential application of optically active InGaN/GaN quantum dot structures, for the detection of changes in the surface potential from the photoluminescence signals measured at room temperature.

We investigated the electric-field dependence of the photoluminescence-emission properties of InGaN/GaN quantum dot multilayers in contact with an electrolyte. Controlled variations of the surface potential were achieved by the application of external electric fields using the electrolytic Schottky contact and by variation of the solution's pH value. Prior to characterization, a selective electrochemical passivation process was required to suppress leakage currents. The quantum dot luminescence is strongly affected by surface potential variations, i.e., it increases exponentially with cathodic bias and acidic pH values. The results cannot be explained by a modification of intra-dot polarization induced electric fields via the quantum confined Stark effect but are attributed to the suppression/enhancement of non-radiative recombination processes, i.e., mainly hole transfer into the electrolyte. The results establish a link between the photoluminescence intensity and the magnitude of electric fields at the semiconductor/electrolyte interface.