PAMAM dendrimers images

Wiener and co-workers used folic acid-conjugated Gd(DTPA)-PAMAM dendrimers for visualizing the high-affinity folate receptor, overexpressed in many tumors.201 The contrast agent accumulated in the cells, resulting in a remarkable contrast enhancement on 7)-weighted images. 

Use of sulfo-NHS-LC-SPDP or other heterobifunctional crosslinkers to modify PAMAM dendrimers may be done along with the use of a secondary conjugation reaction to couple a detectable label or another protein to the dendrimer surface. Patri et al. (2004) used the SPDP activation method along with amine-reactive fluorescent labels (FITC or 6-carboxytetramethylrhodamine succinimidyl ester) to create an antibody conjugate, which also was detectable by fluorescent imaging. Thomas et al. (2004) used a similar procedure and the same crosslinker to thiolate dendrimers for conjugation with sulfo-SMCC-activated antibodies. In this case, the dendrimers were labeled with FITC at a level of 5 fluorescent molecules per G-5 PAMAM molecule. 

Figure 11.16 is a cryo-TEM image of G10 PAMAM dendrimers in water. The cryo technique involves flash freezing of the dendrimer solution as a thin film on a grid and is described elsewhere [20]. Individual dendrimers appear to be organized into an array of single dendrimer thickness. While there are complicating factors due to the sample preparation, the picture is consistent with... 

Figure 12.3 Tapping mode AFM images of G4 PAMAM dendrimers on mica surface at different concentrations, (a) 0.1% w/w (b) 0.01% w/w (provided by Jing Li, D. A. Tomalia) [18]...

Figure 12.11 Tapping Mode AFM image of G9 PAMAM dendrimer molecules on mica surface. Sample prepared by placing 6 jA of a dilute aqueous solution, cone. 5x 10-3% (w/w) G9 on a freshly cleaved mica surface and allowing the film to dry slowly at room temperature (provided by Jing Li and D. A. Tomalia)...

Bielinska et al. define DNCs as hybrid nanoparticles formed by the dispersion and immobilization of guest atoms or small clusters in dendritic polymer matrices. These authors describe the synthesis of 5-25 nm DNCs of Au NPs and G5-PAMAM dendrimers through UV decomposition of the PAMAM-HAuCf precursor. These nanoparticles have been imaged by in both in vitro and in vivo conditions [135]. 

Like PAMAM dendrimers, polylysine dendrimers are largely characterised by amide bonds. They attracted interest as potential therapeutic agents for use in boron neutron capture therapy and in magnetic resonance imaging (MRI) (see Chapter 8), since dendritic polylysines apparently have a lower toxicity than their linear counterparts. The polylysine shown in Fig. 4.10 with a total of 80 terminal boron atoms in the carborane units and a dansyl group was designed specifically for boron neutron capture therapy [20]. 

Fig. 8. (a) Schematic illustration of photolithographic formation of poly(propyl-eneimine) (PPI) dendrimer/ -octadecyltrimethyoxysilane (ODS) patterns and AFM images with section analyses at reaction steps, (b) Schematic illustration of adsorption process and AFM images before and after adsorption of NaPGA on PAMAM dendrimer/ODS patterns. Reprinted with permission from Ref. [112], 2005, American Scientific Publishers. 

Fig. 3. Tapping mode AFM 3D images of PAMAM dendrimers from G5 to G10. Dendrimer molecules (0.001 wt%) are deposited on the mica surface by spin coating. Reprinted with permission from [15]. Copyright 2002 American Chemical Society...

The size and shape of dendrimers have been estimated using transmission electron microscopy [14]. Producing better images of dendrimers may supply answers to fundamental questions such as whether dendrimers have truly uniform sizes, spherical shapes, and dense cores. The visualization of dendrimer assemblies would also be helpful to confirm the structure and morphology for many applications of dendrimers. The positively stained PAMAM dendrimers are shown in Fig. 2 for G10 to G5, respectively. The dendrimer molecules appear as dark objects on a light background of the amorphous carbon substrate and they are well separated from each other. The shapes of the stained molecules are spherical to a first approximation for G10 to G7, with some molecules showing... 

Table 2. Size measurements on poly(amidoamine)PAMAM dendrimers (ethylenediamine core) from computer analysis of TEM images...

Figure 5.29. PAMAM dendrimer multifunctional conjugates for cancer treatment. The FA group is a folic acid cancer cell target, and FITC is fluorescein isothiocyanate, used as an imaging agent. Also shown (bottom) is the molecular structure for the anticancer drug, taxol, denoting the -OH group that covalently attaches to the dendrimer. Reproduced with permission from Majoros, I. J. Myc, A. Thomas, T Mehta, C. Baker, J. R. Biomacromolecules, 2006, 7, 572. Copyright 2006 American Chemical Society.

A novel PAMAM dendrimer-based nanoprobe, G6-(Cy5.5)(1.25)(lB4M-Gd)(145), has been synthesized for dual magnetic resonance and fluorescence imaging modalities [23]. The potential of this nanoprobe was demonstrated in vivo by the efficient visualization of sentinel lymph nodes in mice by both MRI and fluorescence imaging modalities. 

The micropatterning of PAMAM dendrimers relies on (xCP with a hy-drophilized stamp. An UV/ozone treatment increases the surface energy of the PDMS [159,160] and thus provides the necessary homogeneous loading of the stamp (Fig. 16). Contact mode AFM height and friction images recorded on micropatterned dendrimer surfaces show that elevated areas... 

The patterning strategy (high molecular mass adsorbate and robust covalent attachment) can be extended to sub-lOOnm sized patterns by exploiting AFM-tip assisted transfer of PAMAM dendrimers. By scanning smfaces with an AFM tip, which has been previously coated with the dendrimers, molecules can be deposited onto, say, sihcon, mica or SAMs of NHS - CIO. In the case of mica and oxidized sihcon substrates, the originally deposited patterns were detectable, but the AFM friction images showed that dendrimer molecules may have diffused over the substrates. Based on the cmrently available data, spontaneous diffusion or tip-induced effects cannot be differentiated. It is, however, clear that the patterns produced do not possess sufficient stability and definition to be of any use. 

By contrast, when a NHS - CIO SAM on gold was used as a substrate in DPN experiments, stable patterns were deposited, as observed in AFM friction images. By scanning an AFM tip inked with G4 PAMAM dendrimers (5.6 X 10 M methanolic solution) over a NHS-CIO SAM, patterns with sub-100 nm line widths could be fabricated via DPN. hi Fig. 17a, a friction force AFM image of lines 2 xm long and 50 20 nm wide is shown in Fig. 17b the fines are 1 (xm long and 70 10 nm wide. 

Fig. 17 Top Schematic of DPN process bottom Sequence of LFM force images (acquired in air friction forces (a.u.) increase from dark to bright contrast) of arrays of lines with mean widths ( standard deviation) of 50 20 nm and 70 10 nm produced by DPN of G4 PAMAM dendrimers on NHS-CIO SAMs on granular gold. The contrast in the LFM scans is reversed compared to the microcontact-printed patterns, which were scanned with a clean Si3N4 tip. As also observed in an independent study [92], the remaining ink on the AFM tip used for DPN alters the relative magnitude of the friction forces in this situation. (Reprinted with permission from [77], copyright (2004), American Chemical Society)...

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