The three-dimensional structure of glycosidases and of their complexes and the study of transition-state mimics reveal structural details that correlate with mechanism. Of particular interest are the transition-state conformations harnessed by individual enzymes and the substrate distortion observed in enzyme-ligand complexes. 3D-structure in synergy with transition-state mimicry opens the way for mechanistic interpretation of enzyme inhibition and for the development of therapeutic agents.

Blending organic electron donors and acceptors yields intermolecular charge-transfer states with additional optical transitions below their optical gaps. In organic photovoltaic devices, such states play a crucial role and limit the operating voltage. Due to its extremely weak nature, direct intermolecular charge-transfer absorption often remains undetected and unused for photocurrent generation. Here, we use an optical microcavity to increase the typically negligible external quantum efficiency in the spectral region of charge-transfer absorption by more than 40 times, yielding values over 20%. We demonstrate narrowband detection with spectral widths down to 36 nm and resonance wavelengths between 810 and 1,550 nm, far below the optical gap of both donor and acceptor. The broad spectral tunability via a simple variation of the cavity thickness makes this innovative, flexible and potentially visibly transparent device principle highly suitable for integrated low-cost spectroscopic near-infrared photodetection.

Organic spectrometers are attractive for biomedicine and industrial process monitoring but are currently limited in terms of spectral selectivity and the accessible wavelength range. Here, we achieve narrowband enhancement of the below-gap near-infrared response of charge-transfer (CT) excitations in organic photodiodes by introducing them into a high-quality microcavity. The device architecture includes a nonconductive distributed Bragg reflector and thin metal electrodes, leading to the formation of sharp Tamm plasmon-polariton resonances. We demonstrate how to tailor the arising multimode spectra for spectroscopic photodetectors and present efficient single-resonance devices with remarkable line widths below 22 nm, which are partially transparent for visible wavelengths. Taking advantage of the spectrally broad CT band, we vary the resonator thickness to provide a proof of concept that benefits from the spectral selectivity of our high-quality microcavities. Finally, utilizing transfer-matrix calculations, we propose further improvements on the cavity architecture toward single-digit line widths.

Implementing large arrays of gold nanowires as functional elements of a plasmonic biosensor is an important task for future medical diagnostic applications. Here we present a microfluidic-channel-integrated sensor for the label-free detection of biomolecules, relying on localized surface plasmon resonances. Large arrays (∼1 cm) of vertically aligned and densely packed gold nanorods to receive, locally confine, and amplify the external optical signal are used to allow for reliable biosensing. We accomplish this by monitoring the change of the optical nanostructure resonance in the presence of biomolecules within the tight focus area above the nanoantennas, combined with a surface treatment of the nanowires for a specific binding of the target molecules. As a first application, we detect the binding kinetics of two distinct DNA strands as well as the following hybridization of two complementary strands (cDNA) with different lengths (25 and 100 bp). Upon immobilization, a redshift of 1 nm was detected; further backfilling and hybridization led to a peak shift of additional 2 and 5 nm for 25 and 100 bp, respectively. We believe that this work gives deeper insight into the functional understanding and technical implementation of a large array of gold nanowires for future medical applications.

We report on temperature-dependent Hall-effect measurements and secondary ion mass spectroscopy on unintentionally doped, n-type conducting GaN epitaxial films. Over a wide range of free carrier concentrations we find a good correlation between the Hall measurements and the atomic oxygen concentration. We observe an increase of the oxygen concentration close to the interface between the film and the sapphire substrate, which is typical for the growth technique used (synthesis from galliumtrichloride and ammonia). It produces a degenerate n-type layer of ≈1.5 μm thickness and results in a temperature-independent mobility and Hall concentration at low temperatures (<50 K). The gradient in free carrier concentration can also be seen in spatially resolved Raman and cathodoluminescence experiments. Based on the temperature dependence of the Hall-effect, Fourier transform infrared absorption experiments, and photoluminescence we come to the conclusion that oxygen produces a shallow donor level with a binding energy comparable to the shallow Si donor.