Advances in Fingerprint Technology.pdf

CdS/Dendrimer Nanocomposites 26,27
Dendrimers — polymers of tree-like structure — have lately begun to command
intense attention 28 in many areas of science, especially in connection
with their incorporation with nanoparticles of various kinds for purposes of
applications that include cancer drug delivery, catalysis, waste clean-up, optical
devices, etc. Of particular interest here is a photoluminescent nanocomposite
of CdS with Starburst ® (PAMAM) dendrimer that was first (outside
the forensic science arena) described by Sooklal, Hanus, Ploehn, and Murphy.
29 The nanocomposite contains nanoparticle-size clusters of CdS that are
incorporated into aggregates of dendrimer molecules. The Starburst ® dendrimers
are of particular interest from our perspective because they are
commercially available (Aldrich), a must for any practical utilization in fingerprint
laboratories. These dendrimers come with either amino or carboxylate
terminal functional groups, which are useful for chemical fingerprint
processing. Depending on size, amino-functionalized Starburst ® (PAMAM)
dendrimers are referred to as generation 0, 1, 2, 3, 4, … They have, respectively,
4, 8, 16, 32, 64, … terminal amino groups. Similarly, generation –0.5,
0.5, 1.5, 2.5, 3.5, … have, respectively, 4, 8, 16, 32, 64, … terminal carboxylate
(sodium salt) groups. The first three generations of each type are shown in
Figures 6.12 and 6.13.
The initial CdS/dendrimer nanocomposite study involved generation 0,
1, and 4 dendrimer (4, 8, 64 amino terminal groups, respectively). As purchased,
the dendrimers come in methanol solution. The preparation in methanol
of the CdS/dendrimer nanocomposite simply involves diluting the
dendrimer solution and adding to it small quantities (aliquots) of equimolar
methanol solutions, in equal volumes, of cadmium nitrate and of sodium
sulfide. In the absence of dendrimer, the reaction of the cadmium nitrate
and sodium sulfide would produce the cadmium sulfide as a precipitate in
large clumps. In the presence of dendrimer, however, an aggregate of CdS of
nanoparticle size with the dendrimer is formed, as is depicted in Figure 6.14.
The aliquots of cadmium nitrate and sodium sulfide may be added to the
dendrimer solution simultaneously or sequentially in either order. In our
experiments, either five or ten aliquots of each reagent were used to produce
the desired nanocomposite, with concentrations as described shortly. In addition
to the methanol formulation of the CdS/dendrimer nanocomposite, a
10% methanol: 90% water formulation was also investigated. The nanocomposite
preparation utilized 1:9 methanol:water solutions of the dendrimer,
cadmium nitrate, and sodium sulfide instead of pure methanol solutions,
but was otherwise conducted the same way. The rationale for the 1:9 methanol:water
solvent system was simply the general desirability of water-based
chemistry. The methanol served for initial dissolution of reagents and was
then added to the water.