ABSTRACT
Quantum dots (QD) are rapidly making their way into several application sectors including optoelectronics, and there is a strong need to focus on non-toxic QDs. In this work, we have synthesized graphene QDs in the size range of 1.4-4.2 nm from inexpensive graphite by oxidative cleavage using a sulphuric and nitric acid mixture. A subsequent hydrogen peroxide oxidation step, investigated using two thermal budgets, has resulted in QDs with excellent photoluminescence (PL) intensity. Prolonged, higher temperature oxidation results in smaller size GQDs. X-ray photoelectron spectroscopy analysis confirmed the role of ·OH radicals in the oxidation process and Raman analysis revealed that the higher thermal budget oxidation results in lower defect density. To overcome the challenges in device adaptability due to the inherent acidity in the QDs, a post-synthesis neutralization process was devised. The neutralized GQDs were formed into a film to be used as the active layer in a photodetector device. Fluorescence decay analysis showed there is no significant change in lifetime because of the film formation process. The fabricated GQD photodetector device exhibited high photocurrent under ultraviolet illumination with an ON/OFF ratio of 400% at an applied bias of ±1 V. The device performance underlines the high potential for the non-toxic, top-down synthesized GQDs for application in optoelectronic devices.
ABSTRACT
BACKGROUND: This study compared the epidemiology of carbapenem-resistant (CRKP) and carbapenem-sensitive (CSKP) K. pneumoniae bloodstream infections (BSIs), and assessed risk factors for 28-day mortality of patients with K. pneumoniae BSIs. METHODS: A retrospective cohort study was conducted in a 2000-bed tertiary teaching hospital of Beijing between Jan 1st 2013 to Dec 31st, 2019. All patients with K. pneumoniae BSI were identified through the Hospital Information System. The endpoints included incidence rate, mortality and risk factors for mortality of patients with K. pneumoniae BSIs. RESULTS: 496 patients with K. pneumoniae BSIs were included in the analysis, with 108 CRKP BSIs. The incidence rate of K. pneumoniae BSI was 10.6 (CI: 9.7, 11.6) per 100 000 patient-days, with the rate for CRKP BSI was 2.3 (95% CI: 1.9, 2.8). The 28-day mortality was 38.0% for CRKP BSI and 8.8% for CSKP BSI, respectively. Logistic analysis showed, higher Charlson Comorbidity Index score (OR = 1.26, 95%CI 1.12-1.43, p < 0.001), respiratory failure (OR = 2.73, 95%CI1.28-5.84, p = 0.010), renal failure (OR = 4.13, 95%CI1.93-8.83, p < 0.001), septic shock (OR = 8.77, 95%CI3.60-21.32, p < 0.001), mechanical ventilation (OR = 4.41, 95%CI1.59-12.25, p = 0.004) and CRKP infection (OR = 3.04, 95%CI1.28-7.22, p = 0.012) were independently associated with 28-day mortality. CONCLUSIONS: Considerable incidence rate and remarkable mortality of patients with K. pneumoniae (especially CRKP) BSI was declared in the study. Patient conditions before (higher CCI) and after presentation (respiratory failure, renal failure, septic shock), and healthcare factors (mechanical ventilation and CRKP infection) were independently associated with 28-day mortality. Understanding these risks helps better establishment of infection control strategies.
