ABSTRACT
Small perturbations in the structure of materials significantly affect their properties. One example is single wall carbon nanotubes (SWCNTs), which exhibit chirality-dependent near-infrared (NIR) fluorescence. They can be modified with quantum defects through the reaction with diazonium salts, and the number or distribution of these defects determines their photophysics. However, the presence of multiple chiralities in typical SWCNT samples complicates the identification of defect-related emission features. Here, we show that quantum defects do not affect aqueous two-phase extraction (ATPE) of different SWCNT chiralities into different phases, which suggests low numbers of defects. For bulk samples, the bandgap emission (E11) of monochiral (6,5)-SWCNTs decreases, and the defect-related emission feature (E11*) increases with diazonium salt concentration and represents a proxy for the defect number. The high purity of monochiral samples from ATPE allows us to image NIR fluorescence contributions (E11 = 986 nm and E11* = 1140 nm) on the single SWCNT level. Interestingly, we observe a stochastic (Poisson) distribution of quantum defects. SWCNTs have most likely one to three defects (for low to high (bulk) quantum defect densities). Additionally, we verify this number by following single reaction events that appear as discrete steps in the temporal fluorescence traces. We thereby count single reactions via NIR imaging and demonstrate that stochasticity plays a crucial role in the optical properties of SWCNTs. These results show that there can be a large discrepancy between ensemble and single particle experiments/properties of nanomaterials.
ABSTRACT
Fluorophores that emit light in the near infrared (NIR) are advantageous in photonics and imaging due to minimal light scattering, absorption, phototoxicity and autofluorescence in this spectral region. The layered silicate Egyptian blue (CaCuSi4O10) emits as a bulk material bright and stable fluorescence in the NIR and is a promising NIR fluorescent material for (bio)photonics. Here, we demonstrate a surfactant-based (mild) exfoliation procedure to produce nanosheets (EB-NS) of high monodispersity, heights down to 1 nm and diameters <20 nm in large quantities. The approach combines planetary ball milling, surfactant assisted bath sonication and centrifugation steps. It avoids the impurities that are typical for the harsh conditions of tip-sonication. Several solvents and surfactants were tested and we found the highest yield for sodium dodecyl benzyl sulfate (SDBS) and water. The NIR fluorescence emission (λem ≈ 930-940 nm) is not affected by this procedure, is extremely stable and is not affected by quenchers. This enables the use of EB-NS for macroscopic patterning/barcoding of materials in the NIR. In summary, we present a simple and mild route to NIR fluorescent nanosheets that promise high potential as NIR fluorophores for optical applications.
ABSTRACT
BACKGROUND: CT head is commonly performed in the setting of delirium and altered mental status (AMS), with variable yield. We aimed to evaluate the yield of CT head in hospitalized patients with delirium and/or AMS across a variety of clinical settings and identify factors associated with abnormal imaging. METHODS: We included studies in adult hospitalized patients, admitted to the emergency department (ED) and inpatient medical unit (grouped together) or the intensive care unit (ICU). Patients had a diagnosis of delirium/AMS and underwent a CT head that was classified as abnormal or not. We searched Medline, Embase and other databases (informed by PRISMA guidelines) from inception until November 11, 2021. Studies that were exclusively performed in patients with trauma or a fall were excluded. A meta-analysis of proportions was performed; the pooled proportion of abnormal CTs was estimated using a random effects model. Heterogeneity was determined via the I2 statistic. Factors associated with an abnormal CT head were summarized qualitatively. RESULTS: Forty-six studies were included for analysis. The overall yield of CT head in the inpatient/ED was 13% (95% CI: 10.2%-15.9%) and in ICU was 17.4% (95% CI: 10%-26.3%), with considerable heterogeneity (I2 96% and 98% respectively). Heterogeneity was partly explained after accounting for study region, publication year, and representativeness of the target population. Yield of CT head diminished after year 2000 (19.8% vs. 11.1%) and varied widely depending on geographical region (8.4%-25.9%). The presence of focal neurological deficits was a consistent factor that increased yield. CONCLUSION: Use of CT head to diagnose the etiology of delirium and AMS varied widely and yield has declined. Guidelines and clinical decision support tools could increase the appropriate use of CT head in the diagnostic etiology of delirium/AMS.
