Nanobiosensors - Nanomaterials for Medical Applications - page 127

called nanobiosensors have been developed to detect and measure biomolecules
and cells with high sensitivity. Such biosensors use nanoparticles for transduction.
A nanobiosensor can be homogeneous or heterogeneous. A homogeneous
nanobiosensor occurs in solution and does not have a phase separation. A het-
erogeneous nanobiosensor involves a solid platform that serves to anchor the
analyte being detected. The heterogeneous nanobiosensor will be the main
focus of the discussions in this chapter.
Just like the biosensors in bulk, the heterogeneous nanobiosensor that will be
referred to as nanobiosensor from hereon involves a solid surface called the capture
platform ( Figure 4.1 ) which is coated with a specific receptor that specifically rec-
ognizes and captures the analyte. The receptor can be a protein (antigen) when the
analyte is an antibody ( Figure 4.1 A) or an antibody, when the analyte is a protein
( Figure 4.1 B). The protein analyte may be found in a cell, in which case, the whole
cell will be captured on the solid surface ( Figure 4.2 ). To detect the presence of the
antigen or the antibody, a second receptor that specifically recognizes the analyte
is added. This receptor may be tagged with a nanomaterial (NM) or another recep-
tor recognizing the second receptor that is tagged with a NM is added to complete
the assay. Because NMs can be detected at very low concentrations, the sensitivity
of nanobiosensors is expected to be in the low picogram to attogram levels. Thus,
nanobiosensors hold promise for early disease detection that can provide valuable
insights into the medical biology at the systems level.
NMs exhibit unique size-tunable as well as shape-dependent physicochemi-
cal properties that do not resemble those of bulk materials. Recent advances in
FIGURE 4.1 Schematic diagrams of QD-based nanobiosensors for analyte that is an (A) antigen and
(B) antibody. (For color version of this figure, the reader is referred to the online version of this topic)
FIGURE 4.2 Schematic diagrams of a QD-based nanobiosensor for a whole cell such as breast
cancer cell SK-BR3. (For color version of this figure, the reader is referred to the online version
of this topic)