Current Fluctuations in Nanopores Reveal the Polymer-Wall Adsorption Potential.

Modification of surface properties by polymer adsorption is a widely used technique to tune interactions in molecular experiments such as nanopore sensing. Here, we investigate how the ionic current noise through solid-state nanopores reflects the adsorption of short, neutral polymers to the pore surface. The power spectral density of the noise shows a characteristic change upon adsorption of polymer, the magnitude of which is strongly dependent on both polymer length and salt concentration. In particular, for short polymers at low salt concentrations no change is observed, despite the verification of comparable adsorption in these systems using quartz crystal microbalance measurements. We propose that the characteristic noise is generated by the movement of polymers on and off the surface and perform simulations to assess the feasibility of this model. Excellent agreement with experimental data is obtained using physically motivated simulation parameters, providing deep insight into the shape of the adsorption potential and underlying processes. This paves the way toward using noise spectral analysis for in situ characterization of functionalized nanopores.

Surgical Emphysema in a Pediatric Tertiary Referral Center.

BACKGROUND: Laryngeal trauma in pediatrics is extremely rare; however, because of the smaller pediatric larynx, it can have catastrophic consequences. Following laryngeal trauma, surgical emphysema is a relatively common presentation. In pediatrics, it can be a life-threatening condition. Here we describe 2 cases of laryngeal trauma resulting in extensive surgical emphysema. CASES: The first case described involves bilateral pneumothoraces, airway compromise, and respiratory arrest and was managed with bilateral chest drains, intubation, and tracheostomy. The second case resulted in widespread surgical emphysema in a stable patient and was managed conservatively. Both cases were monitored closely for a period of time to ensure there were no further sequelae. DISCUSSION: Patients with laryngeal trauma resulting in surgical emphysema have the potential to deteriorate rapidly. Furthermore, surgical emphysema degrades the quality of ultrasound images, which may delay the diagnosis. If there are any concerns about the safety of the airway, then it should be secured definitively with either endotracheal intubation or emergency tracheostomy depending on clinical judgment. It is acceptable to monitor patients closely in a high-dependency unit setting if they are stable and do not show any evidence of laryngeal edema. CONCLUSIONS: We present 2 cases of laryngeal trauma that were dealt with effectively so that both patients made a full recovery. It is important to act quickly to secure the airway if there are any concerns about its patency. Stable patients with no evidence of laryngeal edema can be managed conservatively. Close monitoring is essential to prevent any potential airway compromise.

Observing capture with a colloidal model membrane channel.

We use video microscopy to study the full capture process for colloidal particles transported through microfluidic channels by a pressure-driven flow. In particular, we obtain trajectories for particles as they move from the bulk into confinement, using these to map in detail the spatial velocity and concentration fields for a range of different flow velocities. Importantly, by changing the height profiles of our microfluidic devices, we consider systems for which flow profiles in the channel are the same, but flow fields in the reservoir differ with respect to the quasi-2D monolayer of particles. We find that velocity fields and profiles show qualitative agreement with numerical computations of pressure-driven fluid flow through the systems in the absence of particles, implying that in the regimes studied here particle-particle interactions do not strongly perturb the flow. Analysis of the particle flux through the channel indicates that changing the reservoir geometry leads to a change between long-range attraction of the particles to the pore and diffusion-to-capture-like behaviour, with concentration fields that show qualitative changes based on device geometry. Our results not only provide insight into design considerations for microfluidic devices, but also a foundation for experimental elucidation of the concept of a capture radius. This long standing problem plays a key role in transport models for biological channels and nanopore sensors.

Ultra-rapid real-time microfluidic RT-PCR instrument for nucleic acid analysis.

The polymerase chain reaction (PCR) is paramount in nucleic acid amplification testing, and for many assays, the use of PCR or qPCR is considered the 'gold standard'. While instrumentation for executing PCR has advanced over the last two decades, a growing interest in point-of-need testing has highlighted the deficit that exists for 'rapid PCR' systems. Here, we describe a field-forward prototype instrument capable of ultra-fast thermal cycling for real-time PCR amplification of DNA and RNA. The custom-designed, injection-molded microfluidic chips interface with a novel mechatronic system to complete 40 cycles of real-time PCR in under 10 minutes, an 84% reduction in time compared to a standard 50 minute assay. Such rapid amplification is enabled by two thermoelectric Peltiers capable of efficiently heating and cooling the sample at 12 and 10 °C s-1, respectively. Judicious selection and strategic placement of the thermal cyclers and fluorescence detector relative to the microchip enable synchronized thermal cycling and fluorescence monitoring, further reducing time-to-result. Robust amplification and detection of DNA and RNA targets empowers laboratories to achieve rapid, actionable information in endless applications.