Over the last couple of years, self-organizing nanotubes based on the dipeptide diphenylalanine have received much attention, mainly as possible building blocks for the next generation of biosensors and as drug delivery systems. One of the main reasons for this large interest is that these peptide nanotubes are believed to be very stable both thermally and chemically. Previously, the chemical and thermal stability of self-organizing structures has been investigated after the evaporation of the solvent. However, it was recently discovered that the stability of the structures differed significantly when the tubes were in solution. It has been shown that, in solution, the peptide nanotubes can easily be dissolved in several solvents including water. It is therefore of critical importance that the stability of the nanotubes in solution and not after solvent evaporation be investigated prior to applications in which the nanotube will be submerged in liquid. The present article reports results demonstrating the instability and suggests a possible approach to a stabilization procedure, which drastically improves the stability of the formed structures. The results presented herein provide new information regarding the stability of self-organizing diphenylalanine nanotubes in solution.
Abstract. Here we present a robust, stable and low-noise experimental set-up for performing electrochemical detection on a centrifugal microfluidic platform. By using a low-noise electronic component (electrical slipring) it is possible to achieve continuous, on-line monitoring of electrochemical experiments, even when the microfluidic disc is spinning at high velocities. Automated sample handling is achieved by designing a microfluidic system to release analyte sequentially, utilizing on-disc passive valving. In addition, the microfluidic system is designed to trap and keep the liquid sample stationary during analysis. In this way it is possible to perform cyclic voltammetry (CV) measurements at varying spin speeds, without altering the electrochemical response. This greatly simplifies the interpretation and quantification of data. Finally, real-time and continuous monitoring of an entire electrochemical experiment, including all intermediate sample handling steps, is demonstrated by amperometric detection of on-disc mixing of analytes (PBS and ferricyanide).
This study has evaluated self-assembled peptide nanotubes (PNTS) and nanowires (PNWS) as etching mask materials for the rapid and low-cost fabrication of silicon wires using reactive ion etching (RIE). The self-assembled peptide structures were fabricated under mild conditions and positioned on clean silicon wafers, after which these biological nanostructures were exposed to an RIE etching process. Following this treatment, the structure of the remaining nanotubes and nanowires was analyzed by scanning electron microscopy (SEM). Important differences in the behavior of the nanotubes and the nanowires were observed after the RIE process. The nanotubes remained intact while the nanowires were destroyed by the RIE process. The instability of the peptide nanowires during this process was further confirmed with focused ion beam milling experiments. The PNTS could stand energetic argon ions for around 32 s while the PNWS resisted only 4 s before becoming milled. Based on these results, selfassembled PNTS were further used as an etching mask to fabricate silicon wires in a rapid and low-cost manner. The obtained silicon wires were subjected to structural and electrical characterization by SEM and I-V measurements. Additionally, the fabricated silicon structures were functionalized with fluorescent molecules via a biotin-streptavidin interaction in order to probe their potential in the development of biosensing devices.
In this article we present a generalized theoretical model for the continuous separation of particles using the pinched flow fractionation method. So far the theoretical models have not been able to predict the separation of particles without the use of correction factors. In this article we present a model which is capable of predicting the separation from first principles. Furthermore we comment on the importance of the incorporation of the finite height of the micro fluidic channels in the models describing the system behavior. We compare our model with the experiment obtained by Seki et al. (J. Takagi, M. Yamada, M. Yasuda and M. Seki, Lab Chip, 2005, 5, 778-784).
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