Biomedical Engineering Reference
In-Depth Information
surface in a controllable way. Figure 11.36b shows positively charged
avidin assembled onto nega-
tively charged lines using the same technique. Figure 11.36c shows albumin FITC bovine that was
assembled onto negatively
charged squares.
11.2.8.3.2
Biochip Manufacturing
Techniques for manufacturing biological materials in microarrays have attracted great interest, as
microarrays are indispensable for genetics, medical diagnostics, and pharmaceutical analyses to enable
the parallel tests of many compounds [87-90]. Therefore, there is a demand for the biochip manufac-
turing technologies with which a variety of proteins in infi nitesimal amounts can be prepared in small
spots to enhance the screening throughput without losing their biological activity. Electrospraying has
been developed as a method to prepare biochips of biological materials to meet the requirements. It
is a method of generating very fi ne droplets from a solution by means of electrostatic charging and
is an effective technique for immobilizing biological materials with a very small amount of samples.
During the electrospraying process, the dehydration process for biological materials is extremely
quick, and thus the activity loss of bioactive materials is low. Moreover, the electrospraying can allow
a spontaneous deposition of many identical arrays with a remarkable spatial resolution.
Morozov and Morozova applied electrospraying technique as a method for mass fabrication of
mono- and multicomponent microarrays of biological and biologically active substances on certain
areas of a substrate [91]. Microarrays of protein and DNA can be deposited simultaneously through an
array of holes in a dielectric mask covering a slightly conductive substrate. Multicomponent microar-
rays can be manufactured by shifting the mask with respect to the substrate and then depositing a
new substance on a desired area. A schematic illustration is shown in Figures 11.37a and 11.37b. The
basic setup included a glass capillary connected to a power supply, a dielectric mask with an array of
holes, a ground electrode, a conducting substrate, and a chamber. The microarrays on a biochip can
be produced by attracting electrosprayed substances onto the specifi ed substrate areas under the con-
trol of a local electrostatic fi eld. One way to form such a fi eld was to cover a conducting substrate with
a dielectric mask containing an array of holes, as shown in Figure 11.37a. Another way was to locally
increase conductivity of a photoconductive substrate by illuminating it through an appropriate photo-
mask to attract charged substances onto the illuminated areas, as illustrated in Figure 11.37b.
Proteins (bovine intestinal AP, horseradish peroxidase, HHb, HSA, BSA, OA, the IgG fraction
of a goat anti-HSA antiserum and mouse monoclonal antibiotin AP conjugate) were deposited from
water solutions with concentrations of 0.1-1.0 mg/mL. The processing parameters for depositing
the proteins were as follows: a voltage of 3.0-4.0 kV, a current of 5-50 nA, a humidity of 30-70%,
and a fl ow rate of 0.1-0.2 µL/min. The precursor solutions were dialyzed for 12-24 h before elec-
trospraying in order to reduce their electrical conductivity. The results demonstrated that dots in a
micrometer range were fabricated using this electrospraying technique. Importantly, the proteins
and DNA biochip retained their ability to specifi cally bind antibodies and match DNA probes,
which enabled the fabrication of matrices in dot immunobinding (DIB) and in DNA hybridization
assays. The results also provided additional evidence for the preservation of functional properties
of the electrosprayed biological molecules, such as antigenic and enzyme catalytic properties of
proteins and the hybridization ability of DNA molecules. By using the electrospraying technique,
enzymes can be deposited on the surface of redox or pH electrodes to design multicomponent
enzyme biosensors. Different antibodies or DNA molecules can also be deposited onto an array of
quartz resonators used in a plasmon resonance detector.
Lee et al. used electrospraying to prepare protein microarrays for immunoassay [92]. In the
work, an antibody-based protein microarray for high-throughput immunoassay was fabricated by an
electrospraying method using a quartz mask with holes. The protein was deposited under the control
of a local electrostatic fi eld, which was formed by masking a conducting substrate using a dielectric
mask with holes. Therefore, the electrosprayed protein was attracted and deposited onto specifi ed
substrate areas through the holes in the mask. An anti-immunoglobulin (IgG) antibody solution was
electrosprayed onto a glass substrate using parameters of 3.0-4.0 kV and humidity 20-30%. After the
