Quantum dots (QDs) are common as luminescing markers for imaging in biological applications because their optical properties seem to be inert against their surrounding solvent. This, together with broad and strong absorption bands and intense, sharp tuneable luminescence bands, makes them interesting candidates for methods utilizing Förster Resonance Energy Transfer (FRET), e. g. for sensitive homogeneous fluoroimmunoassays (FIA). In this work we demonstrate energy transfer from Eu<SUP>3+</SUP>-trisbipyridin (Eu-TBP) donors to CdSe-ZnS-QD acceptors in solutions with and without serum. The QDs are commercially available CdSe-ZnS core-shell particles emitting at 655 nm (QD655). The FRET system was achieved by the binding of the streptavidin conjugated donors with the biotin conjugated acceptors. After excitation of Eu-TBP and as result of the energy transfer, the luminescence of the QD655 acceptors also showed lengthened decay times like the donors. The energy transfer efficiency, as calculated from the decay times of the bound and the unbound components, amounted to 37%. The Förster-radius, estimated from the absorption and emission bands, was ca. 77 Å. The effective binding ratio, which not only depends on the ratio of binding pairs but also on unspecific binding, was obtained from the donor emission dependent on the concentration. As serum promotes unspecific binding, the overall FRET efficiency of the assay was reduced. We conclude that QDs are good substitutes for acceptors in FRET if combined with slow decay donors like Europium. The investigation of the influence of the serum provides guidance towards improving binding properties of QD assays.
Objective:
Brain-derived neurotrophic factor (BDNF) supports neurogenesis, angiogenesis, and promotes the survival of various cell types in the brain and the coronary system. Moreover, BDNF is associated with both coronary heart disease (CHD) and depression. The current study aims to investigate whether serum BDNF levels are associated with the course of depressive symptoms in CHD patients.
Methods:
At baseline, N = 225 CHD patients were enrolled while hospitalized. Of these, N = 190 (84%) could be followed up 6 months later. Depressive symptoms were assessed both at baseline and at the 6-months follow-up using the Patient Health Questionnaire (PHQ-9). Serum BDNF concentrations were measured using fluorometric Enzyme-linked immunosorbent assays (ELISA).
Results:
Logistic regression models showed that lower BDNF levels were associated with persistent depressive symptoms, even after adjustment for age, sex, smoking and potential medical confounders. The incidence of depressive symptoms was not related to lower BDNF levels. However, somatic comorbidity (as measured by the Charlson Comorbidity Index) was significantly associated with the incidence of depressive symptoms.
Conclusions:
Our findings suggest a role of BDNF in the link between CHD and depressive symptoms. Particularly, low serum BDNF levels could be considered as a valuable biomarker for the persistence of depressive symptoms among depressed CHD patients.