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FRET (Fo¨rster resonance energy transfer) involves the transfer of energy from an excited donor fluorophore to an acceptor molecule in a manner that is dependent on the distance between the two. A biochemistry laboratory experiment is described that teaches students how to use FRET to evaluate distance changes in biological molecules. Students measured the apparent FRET between donor and acceptor fluorophores located on the ends of several DNAs of unknown lengths, enabling them to order the DNAs according to size. In addition, students investigated site-specific DNA cleavage by restriction endonucleases, using loss of apparent FRET to determine which enzyme cut sites were present in each of the DNAs. After completing this experiment, students understood the inverse relationship between changes in FRET and changes in distance, and understood how changes in FRET could be used to monitor a conformational change in a molecule. As an extension to the experiment, a tutorial is included that uses the same DNAs to illustrate the ability of single-molecule FRET measurements to resolve heterogeneity in a sample, which cannot be done via more traditional ensemble measurements.

Objective: Ketamine has been shown to decrease opioid utilization as an adjunct, but limited evidence is available on ketamine as a primary analgesic strategy., Design: A retrospective chart review., Patients and Participants: Mechanically ventilated adult patients (≥18 years) in the surgery-trauma intensive care unit (STICU) with continuous infusion ketamine or fentanyl with concomitant propofol for at least 12 hours were screened for inclusion. The final analysis included 22 patients in the ketamine/propofol (KP) group and 24 patients in the fentanyl/propofol (FP) group., Interventions: Patients in the STICU received KP or FP continuous infusions., Main Outcome Measures: The primary outcome compared opioid requirements between both groups during mechanical ventilation., Results: The median opioid requirement during mechanical ventilation was significantly higher in the FP group compared to the KP group (median 1,392 milligrams of morphine equivalents (MMEs) [interquartile range (IQR) 709.5-2,292] versus 206.3 MME [IQR 87-510], p < 0.001). After extubation, there was no difference in opioid utilization. Patients in the KP group spent less time at goal Critical Care Pain Observation Tool compared to the FP group (median 77.6 percent, IQR [71.9-85.2] versus 88.9 percent, IQR [76.9-97.4], p = 0.003). The proportions of patients developing adverse effects were not significantly different between the two groups., Conclusions: Among critically ill mechanically ventilated patients in the STICU, continuous ketamine resulted in signifi-cantly less opioids during mechanical ventilation. Further studies with a larger sample size are needed to assess the ap-propriate dosing strategy for ketamine to produce adequate analgesia when used as a primary analgesic in mechanically ventilated patients.