Nanoscopic interactions of colloidal particles can suppress millimetre drop splashing.

The splashing of liquid drops onto a solid surface is important for a wide range of applications, including combustion and spray coating. As the drop hits the solid surface, the liquid is ejected into a thin horizontal sheet expanding radially over the substrate. Above a critical impact velocity, the liquid sheet is forced to separate from the solid surface by the ambient air, and breaks up into smaller droplets. Despite many applications involving complex fluids, their effects on splashing remain mostly unexplored. Here we show that the splashing of a nanoparticle dispersion can be suppressed at higher impact velocities by the interactions of the nanoparticles with the solid surface. Although the dispersion drop first shows the classical transition from deposition to splashing when increasing the impact velocity, no splashing is observed above a second higher critical impact velocity. This result goes against the commonly accepted understanding of splashing, that a higher impact velocity should lead to even more pronounced splashing. Our findings open new possibilities to deposit large amount of complex liquids at high speeds.

A novel ingestible electronic drug delivery and monitoring device.

BACKGROUND: We developed an ingestible electronic drug delivery and monitoring system. This system includes an electronic capsule comprising a drug reservoir, a pH and temperature sensor, a microprocessor and wireless transceiver, a stepper motor, and batteries. The location of the capsule in the gut derived from pH data can be monitored in real time. The stepper motor can be remotely actuated to expel the contents of the drug reservoir. OBJECTIVES: First human study. DESIGN: Two consecutive observational studies. SETTING: University medical center. SUBJECTS: Twenty healthy volunteers. INTERVENTIONS: Study I: Ingestion and passage of the capsule. Study II: Ingestion and passage of the capsule, loaded with (99m)technetium-pertechnetate ((99m)Tc); remotely actuated expulsion of (99m)Tc in the gut. MAIN OUTCOME MEASUREMENTS: Study I: Safety, tolerability, and functionality (wireless pH and temperature recording). Study II: Tracing of the capsule and expulsion and distribution of (99m)Tc from the drug reservoir by scintigraphy. Correlating location pH with scintigraphy. RESULTS: Study I: Ingestion and passage of the capsule was safe and well tolerated. Transmitted pH and temperature data were received by the recorder in 96.5% ± 3%. Study II: pH-determined passage of the esophagogastric, gastroduodenal, and ileocolonic junction correlated well with scintigraphy. Expulsion of (99m)Tc from the capsule was successful in 9 of 10 subjects. LIMITATIONS: Subjects with relatively low body mass index. CONCLUSIONS: This electronic drug delivery and monitoring system may be a promising tool for targeted delivery of substances to well-defined areas of the GI tract.

Immobilization of oligonucleotides with homo-oligomer tails onto amine-functionalized solid substrates and the effects on hybridization.

Microarrays have become important tools for the detection and analysis of nucleic acid sequences. Photochemical (254 nm UV) DNA immobilization onto amine-functionalized substrates is often used in microarray fabrication and Southern blots, although details of this process and their effects on DNA functionality are not well understood. By using Cy5-labeled model oligonucleotides for UV immobilization and Cy3-labeled complementary sequences for hybridization, we measured independently the number of immobilized and hybridized oligonucleotides on the microarray surface. By using a two-color fluorescence LED setup and a novel method to compile the data, a full analysis has been made of the effects of oligonucleotide composition (length and sequence) on both immobilization and hybridization. Short homo-oligomer sequences (tails) of uracils, thymines, and, to a limited extent, guanines attached to a hybridization sequence improve immobilization. We propose a possible mechanism explaining the grafting of these nucleotides to amine-functionalized substrates, and we found evidence that the DNA backbone is possibly involved in the immobilization process. Hybridization, on the other hand, greatly improves as a function of tail length regardless of tail composition. On the basis of statistical arguments, the probes increasingly bind via their tail, with the hybridization sequence becoming more accessible to its complement. We conclude that all tails, sequence independent, improve hybridization signals, which is caused by either improved immobilization (especially thymine and uracil) or improved hybridization (most pronounced with guanine tails).

Relaxation times in single event electrospraying controlled by nozzle front surface modification.

Single event electrospraying (SEE) is a method for on-demand deposition of femtoliter to picoliter volumes of fluids. To determine the influence of the size of the meniscus on the characteristics of the single event electrospraying process, glass capillaries were used with and without an antiwetting coating comprising a self-assembled 1H,1H,2H,2H-perfluorodecyltrichlorosilane-based monolayer to control the meniscus size. A large difference was found in driving single event electrospraying from a small meniscus compared to what is needed to generate a single event electrospraying from a large meniscus. Furthermore, after studying the different time constants related to the electrical and the hydrodynamic phenomena, we are able to explain the timing limitations of the deposition process from both a small and a large meniscus. The hydrodynamic relaxation time is significantly reduced in the case of the modified capillary, and the timing of SEE, which determines the deposition time, is limited by the resistor-capacitor RC time of the electrical circuit needed to drive the SEE. We have built a model that describes the almost one-dimensional motion of the liquid in the capillary during pulsing. The model has been used to estimate the hydrodynamic relaxation times related to the meniscus-to-cone and cone-to-meniscus transitions during SEE. By confining the meniscus to the inner diameter of the nozzle, we are able to deposit a volume smaller than 5 pL per SEE.

Fluid dynamical analysis of the distribution of ink jet printed biomolecules in microarray substrates for genotyping applications.

Oligonucleotide microarrays are tools used to analyze samples for the presence of specific DNA sequences. In the system as presented here, specific DNA sequences are first amplified by a polymerase chain reaction (PCR) during which process they are labeled with fluorophores. The amplicons are subsequently hybridized onto an oligonucleotide microarray, which in our case is a porous nylon membrane with microscopic spots. Each spot on the membrane contains oligonucleotides with a sequence complementary to part of one specific target sequence. The solution containing the amplicons flows by external agitation many times up and down through the porous substrate, thereby reducing the time delaying effect of diffusion. By excitation of the fluorophores the emitted pattern of fluorophores can be detected by a charge-coupled device camera. The recorded pattern is a characteristic of the composition of the sample. The oligonucleotide capture probes have been deposited on the substrate by using noncontact piezo ink jet printing, which is the focus of our study. The objective of this study is to understand the mechanisms that determine the distribution of the ink jet printed capture probes inside the membrane. The membrane is a porous medium: the droplets placed on the membrane penetrate in the microstructure of it. The three-dimensional (3D) distribution of the capture probes inside the membrane determines the distribution of the hybridized fluorescent PCR products inside the membrane and thus the emission of light when exposed to the light source. As the 3D distribution of the capture probes inside the membrane eventually determines the detection efficiency, this parameter can be controlled for optimization of the sensitivity of the assay. The main issues addressed here are how are the capture probes distributed inside the membrane and how does this distribution depend on the printing parameters. We will use two model systems to study the influences of different parameters: a single nozzle print head jetting large droplets at a low frequency and a multinozzle print head emitting small droplets at a high frequency. In particular, we have investigated the effects when we change from usage of the first system to the second system. Furthermore, we will go into detail how we can obtain smaller spot sizes in order to increase the spot density without having overlapping spots, leading eventually to lower manufacturing costs of microarrays. By controlling the main print parameters influencing the 3D distribution inside the porous medium, the overall batch-to-batch variations can possibly be reduced.