Biocompatibility and Functionalization - Nanomaterials for Medical Applications - page 102

(3) Incubate the cells under manufacturer's recommended conditions (usually
at 37 °C with 5% CO 2 in an incubator oven).
(4) When the growth reaches 70-80% confluence, remove the growth medium.
(5) Add 500 µL of 1× Dulbecco phosphate buffered saline (DPBS).
(6) Add 10 µL of 1-50 nM QDs-Ab and aspirate gently to mix.
(7) Incubate at 37 °C with 5% CO 2 in an incubator oven for 3-10 min.
(8) Wash three or more times with 1× DPBS with 0.02% Tween 20 and 1%
BSA to remove excess QDs-Ab.
(9) Observe under a fluorescence microscope.
The SK-BR3 cells in Figure 3.6 under a fluorescent microscope show the QDs-
Ab as dots along the cell surface. This is the result of the QDs-Ab targeting and
attaching to specific proteins on the surface of the cell membrane. Specific tar-
geting with NMs attached to Abs is a very useful application of NMs for sensor
development as well as for targeted drug delivery. 42,44,140,141,159,192
3.3.3 Physical Adsorption
Surface functionalization of NMs is carried out with the use of molecules that
serve as stabilizers, which may be added during or after the synthesis process (in
situ functionalization). These molecules are attached to the surface of the NMs
by physisorption or by ligand-like interactions as in the case of sulfur containing
molecules as discussed in various review articles. 193,194,109 In addition, the surface
groups on NMs such as the carboxyl, amine or hydroxyl groups can lead to inter-
action with similarly modified biomolecules allowing physical adsorption (PA).
Thus, cell tracking with water-soluble NMs dispersed in DI water very easily cling
on the surfaces of proteins, DNA, lipids, carbohydrates, and cells. Although this
is useful for some studies such as the easy visualization of cells under the micro-
scope, this leads to problems of nonspecific adsorption especially during biosensor
or diagnostic tool development. Some ways to minimize PA had been the subject of
studies. 195 Aguilar and coworkers 195 developed buffers that minimize background
signal from QDs that physically adsorb to cell surfaces. The protocol below has
been designed for PA of QDs on cells followed by a process to minimize it.
3.3.3.1 Protocol for PA of QDs on Cells
The following protocol is used in the nonspecific adsorption of QDs and other
NMs on human cell lines such as SK-BR3, MDA MB231, etc.
Cell cultures of human breast cancer cells (SK-BR3) that were originally
obtained from ATCC (Manassas, VA).
(1) Grow the cells in a flask containing RPMI-1640 medium supplemented
with 10% fetal bovine serum (FBS) and 1% of streptomycin/penicillin
antibiotics.
(2) Place the flask in a cell culture incubator at a humidified atmosphere with
5% CO 2 at 37 °C.