Filtern
Dokumenttyp
- Zeitschriftenartikel (4)
- Buchkapitel (1)
Sprache
- Englisch (5)
Schlagworte
- Dye (2)
- Fluorescence (2)
- Optical imaging (2)
- Cetuximab (1)
- Chemistry (1)
- Contrast agent (1)
- Cyanine (1)
- Dimerization constant (1)
- Extinction coefficient (1)
- Fluorescence quantum yield (1)
Organisationseinheit der BAM
Recent developments of fluorescent probes beyond approved indocyanine green (ICG) – itself increasingly spreading into new imaging applications like lymphatic mapping, arthritis imaging and tumor surgery – exploit various photophysical and biochemical mechanisms to monitor molecular events with higher specificity and accuracy. Emphasizing nanoparticulate formulations, targeted conjugates, activatable probes, probes with a sensor function and multimodality probes, this review discusses advantages and limitations of each type of probe, thereby critically assessing the desired translation into the clinic.
The rational design of bright optical probes and dye–biomolecule conjugates in the NIR-region requires fluorescent labels that retain their high fluorescence quantum yields when bound to a recognition unit or upon interaction with a target. Because hydrophilicity-controlled dye aggregation in conjunction with homo-FRET presents one of the major fluorescence deactivation pathways in dye–protein conjugates, fluorescent labels are required that enable higher labeling degrees with minimum dye aggregation. Aiming at a better understanding of the factors governing dye–dye interactions, we systematically studied the signal-relevant spectroscopic properties, hydrophilicity, and aggregation behavior of the novel xS-IDCC series of symmetric pentamethines equipped with two, four, and six sulfonic acid groups and selected conjugates of these dyes with IgG and the antibody cetuximab (ctx) directed against the cancer-related epidermal growth factor (EGF) receptor in comparison to the gold standard Cy5.5. With 6S-IDCC, which displays a molar absorption coefficient of 190 000 M1 cm1 and a fluorescence quantum yield (Φf) of 0.18 in aqueous media like PBS and nearly no aggregation, we could identify a fluorophore with a similarly good performance as Cy5.5. Bioconjugation of 6S-IDCC and Cy5.5 yielded highly emissive targeted probes with comparable Φf values of 0.29 for a dye-to-protein (D/P) ratio <1 and a reduced number of protein-bound dye aggregates in the case of 6S-IDCC. Binding studies of the ctx conjugates of both dyes performed by fluorescence microscopy and FACS revealed that the binding strength between the targeted probes and the EGF receptor at the cell membrane is independent of D/P ratio. These results underline the importance of an application-specific tuning of dye hydrophilicity for the design of bright fluorescent reporters and efficient optical probes. Moreover, we could demonstrate the potential of fluorescence spectroscopy to predict the size of fluorescence signals resulting for other fluorescence techniques such as FACS.
Organic fluorescent dyes are a fundamental component in biomedical research and diagnostic imaging. The major classes encompass polymethine dyes, xanthene dyes, 4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dyes, phenoxazines, and rare earth metal complexes. These compounds have been synthesized in manifold variations to optimize their photophysical properties and physicochemical behavior in physiological media and to enable conjugation to targeting molecules and nanocarriers. Furthermore, stimuli-responsive structural motifs were designed to apply these fluorophores as sensors for disease-related physiological and molecular conditions. This chapter is devoted to the chemical base of optical imaging agents, covering the relevant properties of fluorophores and the synthetic concepts toward intelligent optical imaging probes.
The synthesis of water-soluble dyes, which absorb and emit in the range between 650 and 950 nm and display high extinction coefficients (ε) as well as high fluorescence quantum yields (Φf), is still a demand for optical imaging. We now present a synthetic route for the preparation of a new group of glycerol-substituted cyanine dyes from dendronized indole precursors that have been functionalized as Nhydroxysuccinimide (NHS) esters. High Φf values of up to 0.15 and extinction coefficients of up to 189 000 L mol−1 cm−1 were obtained for the pure dyes. Furthermore, conjugates of the new dendronized dyes with the antibody cetuximab (ctx) that were directed against the epidermal growth factor receptor (EGFR) of tumor cells could be prepared with dye to protein ratios between 0.3 and 2.2 to assess their potential as imaging probes. For the first time, ctx conjugates could be achieved without showing a decrease in Φf and with an increasing labeling degree that exceeded the value of the pure dye even at a labeling degree above 2. The incorporation of hydrophilically and sterically demanding dendrimers into cyanines prevented dimer formation after covalent conjugation to the antibody. The binding functionality of the resulting ctx conjugates to the EGFR was successfully demonstrated by cell microscopy studies using EGFR expressing cell lines. In summary, the combination of hydrophilic glycerol dendrons with reactive dye labels has been established for the first time and is a promising Approach toward more powerful fluorescent labels with less dimerization.
Lanthanide-based, spectrally shifting, and multi-color luminescent upconverting nanoparticles (UCNPs) have received much attention in the last decades because of their applicability as reporter for bioimaging, super-resolution microscopy, and sensing as well as barcoding and anti-counterfeiting tags. A prerequisite for the broad application of UCNPs in areas such as sensing and encoding are simple, robust, and easily upscalable synthesis protocols that yield large quantities of UCNPs with sizes of 20 nm or more with precisely controlled and tunable physicochemical properties from lowcost reagents with a high reproducibility. In this context, we studied the reproducibility, robustness, and upscalability of the synthesis of β-NaYF4:Yb, Er UCNPs via thermal decomposition. Reaction parameters included solvent, precursor chemical compositions, ratio, and concentration. The resulting UCNPs were then examined regarding their application-relevant physicochemical properties such as size, size distribution, morphology, crystal phase, chemical composition, and photoluminescence.
Based on these screening studies, we propose a small volume and high-concentration synthesis approach that can provide UCNPs with different, yet controlled size, an excellent phase purity and tunable morphology in batch sizes of up to at least 5 g which are well suited for the fabrication of sensors, printable barcodes or authentication and recycling tags.