Despite the broad use of enzymes in electroanalytical biosensors, the influence of enzyme kinetics on the function of prototype sensors is often overlooked or neglected. In the present study, we employ amperometry as an alternative or complementary method to study the kinetics of tyrosinase, whose catalytic activity results in o-quinone products. We further compare our results for four monophenolic substrates with those obtained from ultravioletvisible spectrophotometry and show that the results from both assays are in good agreement. We also observe large variations in the enzyme kinetics for different monophenolic substrates depending on the R-group at the para position. To further study this effect, we investigate the stability of quinone products in the enzymatic assay. This information can in principle be utilized to discriminate between different phenolic species by monitoring the reaction rate.

We describe a novel and versatile method for the fabrication of poly(ferrocenylsilane) (PFS) based microspheres using microfluidics. Cross-linked microgel particles were obtained by UV-induced crosslinking of precursor droplets. By variations in the substitution of the silane units of PFS, organogel as well as hydrogel particles were prepared. Applications of these redox active microspheres to form in situ Ag nanoparticles, as well as loading and release of guest molecules were demonstrated.

Fluid and charge transport in micro-and nanoscale fluidic systems are intrinsically coupled via electrokinetic phenomena. While electroosmotic flows and streaming potentials are well understood for externally imposed stimuli, charge injection at electrodes localized inside fluidic systems via electrochemical processes remains to a large degree unexplored. Here, we employ ultramicroelectrodes and nanogap electrodes to study the subtle interplay between ohmic drops, streaming currents, and faradaic processes in miniaturized channels at low concentrations of supporting electrolyte. We show that electroosmosis can, under favorable circumstances, counteract the effect of ohmic losses and shift the apparent formal potential of redox reactions. This interplay can be described by simple circuit models, such that the results described here can be adapted to other micro-and nanofluidic electrochemical systems.

Nanoscale channels and electrodes for electrochemical measurements exhibit extreme surface-to-volume ratios and a correspondingly high sensitivity to even weak degrees of surface interactions. Here, we exploit the potential-dependent reversible adsorption of outer-sphere redox species to modulate in space and time their concentration in a nanochannel under advective flow conditions. Induced concentration variations propagate downstream at a species-dependent velocity. This allows one to amperometrically distinguish between attomole amounts of species based on their time-of-flight. On-demand concentration pulse generation, separation, and detection are all integrated in a miniaturized platform.

Abstract. The flower of Musa nana Lour., also named 'XiangJiaohua' in Chinese, is a commonly used herbal drug in traditional Chinese medicine (TCM). Musa nana Lour. flower and bract were usually discarded after banana fruit ripening, which leaded to resource waste and environmental pollution. It can not only protect the environment but also reduce the waste of resources to improve the utilization of the banana (Musa nana Lour.) flower and bract, so we analyzed volatile compounds of fresh, sun-dried and shade-dried Musa nana Lour. flowers and bracts by gas chromatography-mass spectrometry (GC-MS) technique with head-space solid micro-extraction (HS-SPME). The number of volatile ingredients from three kinds of Musa nana Lour. flowers were identified 29, 39 and 43, respectively. Thirteen common constituents were found in all of the three flowers. While three kinds of Musa nana Lour. bracts were identified 30, 36 and 37 volatile ingredients, respectively. In addition, twenties common constituents were found in all of the three bracts. It can be seen the compounds between flowers and bracts in different drying conditions were different apparently. This is the first ever report revealing the differences of volatile components between Musa nana Lour. flowers and bracts in different drying conditions.