GaN-based heterostructures for gas and bio sensing (Conference Presentation)

Abstract

Recently, GaInN has found increasing interest in chemical sensors and biosensors. Such sensors are typically based on changes in the near-surface band bending caused by different adsorbates on the surface. Besides electrical structures, optochemical transducers have been demonstrated, where the sensor response is read out remotely by analyzing the photoluminescence of the sensor structures. Hence, no chemically vulnerable electric contacts are required. In biosensing using optical technologies, the attachment of fluorescent labels to biomolecules is a frequently applied method. Often these fluorophors suffer from photobleaching which limits applications. In our current studies, polar GaInN quantum wells (QWs) are applied for sensing different molecules adsorbed on the transducer surface. Instead of fluoro¬phors, adsorbate-caused changes of the GaInN quantum well photo¬lumi¬nescence (PL) are taken as chemical sensing signal. In particular, the band-bending influences the electric field in a near-surface quantum well and hence changes the emission wavelength owing to the quantum confined Stark effect (QCSE). The sensitivity depends on the design of the hetero structures like QW and cap layer thickness, as evaluated by band structure simulations. Besides gases such as oxygen and hydrogen, also biomolecules can be adsorbed on the semiconductor surface and studied by PL. As an example, we have studied the iron-storage protein ferritin. Ferritins with and without iron-load (the latter corresponds to apoferritin) are immobilized on hydroxylated polar GaInN quantum well surfaces. A spectral shift of the quantum well PL is found depending on the iron-load of the molecules which might enable sensing of ferritin-bound iron.