Upper Airway Complications in COVID-19: A Case Series.

Prolonged intubation is associated with several complications leading to upper airway obstruction, including tracheal stenosis and tracheomalacia. Tracheostomy may potentially decrease the risk of tracheal injury in patients with upper airway obstruction. The ideal timing to perform tracheostomy remains controversial. Prolonged intubations were particularly common during the initial phase of the coronavirus disease 2019 (COVID-19) pandemic. This study aimed to present a series of five cases of upper airway complications in patients who underwent mechanical ventilation in the setting of COVID-19 and discuss their clinical aspects, risk factors, and therapeutic strategies.

Noble metal nanostructure both as a SERS nanotag and an analyte probe.

We report nanotags encapsulated in Au-Ag nanostructure that are active in surface-enhanced Raman scattering. The Au-Ag nanoshells are filled with Ag via citrate reduction, entrapping label molecules in the process. The nanotags can be used for quantitative SERS measurements with the label molecules as internal reference.

Differential SERS activity of gold and silver nanostructures enabled by adsorbed poly(vinylpyrrolidone).

We report that poly(vinylpyrrolidone) (PVP), a common stabilizer of colloidal dispersions of noble metal nanostructures, has a dramatic effect on their surface-enhanced Raman scattering (SERS) activity and enables highly selective SERS detection of analytes of various type and charge. Nanostructures studied include PVP-stabilized Au-Ag nanoshells synthesized by galvanic exchange reaction of citrate-reduced Ag nanoparticles (NPs), as well as solid citrate-reduced Ag and Au NPs, both before and after stabilization with PVP. All nanostructures were characterized in terms of their size, surface plasmon resonance wavelength, surface charge, and chemical composition. While the SERS activities of the parent citrate-reduced Ag and Au NPs are similar for rhodamine 6G (R6G) and 1,2-bis(4-pyridyl)ethylene (BPE) at various pH values, PVP-stabilized nanostructures demonstrate large differences in SERS enhancement factors (EFs) between these analytes depending on their chemical nature and protonation state. At pH values higher than BPE's pK(a2) of 5.65, where the analyte is largely unprotonated, the PVP-coated Au-Ag nanoshells showed a high SERS EF of >10(8). In contrast, SERS EFs were 10(3)- to 10(5)-fold lower for the protonated form of BPE at lower pH values, or for the usually highly SERS-active cationic R6G. The differential SERS activity of PVP-stabilized nanostructures is a result of discriminatory binding of analytes within-adsorbed PVP monolayer and a subsequent increase of analyte concentration at the nanostructure surface. Our experimental and theoretical quantum chemical calculations show that BPE binding with PVP-stabilized Au-Ag nanoshells is stronger when the analyte is in its unprotonated form as compared to its cationic, protonated form at a lower pH.