4. Nanomaterial-based detection of pork
adulteration in meat products
More recently, the GNPs have been successfully demonstrated
as a potential sensor for detection of pork adulteration in beef
and chicken meatball preparations [11e14]. On the basis of an
interesting noncross-linking method [54,55], Ali et al [13]
developed an analytical method using 20-nm citrate-coated
GNPs to determine pork adulteration in beef and chicken
meatball preparations. The basic principle for analysis
involved measurement of change in color of GNPs from red to
purple grey in vials containing swine DNA, with red remaining
unchanged in nonpork samples (chicken or beef). More elaborately,
the GNPs were well dispersed in deionized water
without incubation and also dispersed in 3mM PBS after a 3-
minute incubation of GNPs with 3nM single-stranded DNA
probe at 50C. In contrast, the GNPs aggregated in 3mM PBS
without incubation and also aggregated in 3mM PBS after a 3-
minute incubation of GNPs with 3nM double-stranded DNA
probe at 25C, resulting in a change in color of GNPs from red
to purple grey (Fig. 1A and 1B) [13]. In general, the negative
coatings of citrate ions on the GNP surface electrostatically
repel each other providing good dispersion of GNPs in deionized
water. Likewise, the single-stranded DNA adsorbed on
GNPs by van der Waals interactions provides more phosphatenegative
charges on GNP surfaces further stabilizing the GNPs.
However, the aggregation of GNPs in PBS can be attributed to
the reduction of repulsive negative charges between individual
GNPs. In addition, unlike single-stranded DNA, the doublestranded
DNA could not protect the GNPs from salt-induced
aggregation because of the highly stable and uncoiled nature
of the latter (Fig. 1B). This phenomenon could be clearly
visualized in transmission electron microscopy (TEM) images
and in the absorption spectra as shown in Fig. 1A [13].