Biomedical Engineering Reference
In-Depth Information
uncorrected errors, the genetic composition of the viruses changes as they replicate in
humans and animals, and the existing strain is replaced with a new antigenic variant.
These constant, permanent and usually small changes in the antigenic composition of
IAVs are known as antigenic “drift.”
The tendency of influenza viruses to undergo frequent and permanent antigenic
changes necessitates constant monitoring of the global influenza situation and annual
adjustments in the composition of influenza vaccines.
Influenza viruses have a second characteristic of great public health concern: IAVs,
including subtypes from different species, can swap or “reassort” genetic materials and
merge. This reassortment process, known as antigenic “shift,” results in a novel subtype
different from both parent viruses. As populations will have no immunity to the new sub-
type, and as no existing vaccines can confer protection, antigenic shift has historically
resulted in highly lethal pandemics. For this to happen, the novel subtype needs to have
genes from human influenza viruses that make it readily transmissible from person to
person for a sustainable period.
Conditions favorable for the emergence of antigenic shift have long been thought to
involve humans living in close proximity to domestic poultry and pigs. Because pigs are
susceptible to infection with both avian and mammalian viruses, including human strains,
they can serve as a “mixing vessel” for the scrambling of genetic material from human and
avian viruses, resulting in the emergence of a novel subtype. Recent events, however, have
identified a second possible mechanism. Evidence is mounting that, for at least some of
the 15 AI virus subtypes circulating in bird populations, humans themselves can serve as
the “mixing vessel” [7,8].
22.2
Sensor Design and Immunoassay System
22.2.1
Detection of Hanta Virus
The immunosensor design concept, previously described [9], has been modified and
adapted into the immunoassay prototype system. The immunocolumn, which is the dis-
posable sensing element, consists of a plastic column with a filter membrane at the bot-
tom. The immunosorbent is deposited on the filter membrane (by centrifugation) resulting
in highly dispersed immunosorbent forming the measuring (working) electrode or immu-
noelectrode. The immunocolumn was prepared by adding 100 µL of 0.5 mg/mL
immunosorbent to the microcentrifuge filters. The immunosorbent consist of carbon par-
ticles that are coated with a predetermined optimum quantity of recombinant nucleocap-
sid protein (RNP), usually 10
g/0.5 mg of carbon particles. The immobilization of RNP
of SN virus on carbon microdispersed powder was performed using Woodward's reagent
[10]. A plastic column holder comprised of a supporting electrode assembly: a platinum
counter electrode and Ag/AgCl reference electrode that are exposed into a channel, which
serve as an outlet for the flow-through immunosensor. The flow-through immunoassay
system is described in detail [9,11]. The immunocolumn adaptor contains a capillary tube
that is inserted and fixed into a hollow carbon rod. The capillary tube serves as the inlet to
the immunosensor while the carbon rod serves as a current collector for the working
electrode (immunoelectrode). When assembled, the current collector rests on top of the
immunoelectrode to collect the amperometric output. This flow cell serves as an
immunoreactor as well as an electrochemical cell. The optimization of disposable
immunosensing elements of the amperometric transducer is based on the principle of
close attachment of the components of the ligand
receptor system to the electrode surface
