Biomedical Engineering Reference
In-Depth Information
5.4.3
Sample Handling
While liquid handling in volumes >5µl is reliable, procedures like sample
storage and retrieval,weighing,dissolving,and distributing are more sophisti-
cated.In principal,sample storage is performed following two different strate-
gies: in diluted form [e.g. in dimethylsulfoxide (DMSO)], or as pure samples
either in tubes or in deep-well plates.Besides defined storage conditions which
should minimize stability problems, a reliable and fast retrieval of samples is
required.Automated systems should be able to handle hundreds ofthousands of
different compounds [storage, multiplication, sample (back-) tracking, move-
ment, etc.] with efficient logistics. Due to the different needs the automated
storage and retrieval concepts installed in pharmaceutical companies are more
or less customer designed.
Automated sample preparation suitable for the assays starting with solid or
oily material is rather complicated and causes problems. This highly labour
intensive procedure caused problems when it was done manally due to the
nature of the material to be handled.Thus,only certain percentages of the com-
pounds delivered in solid form can be handled by robotics.For this procedure
in screening companies, only a low rate of automation is observable so far.
Nevertheless,first automated filling stations exist in which a defined amount of
a powder can be transferred from standardized vessels to test tubes for sub-
sequent dilution.
Due to the fact that in most companies the sample storage and retrieval
facilities are centralized,the test samples have to be transferred to the screening
groups at various locations.Therefore,logistics such as bar-coding,data trans-
fer,and delivery are crucial points.Delivery of the samples is performed usually
in 96-well format after sealing with removable films in solution (e.g.on dry ice
in DMSO), or as neat-films. Workstations able to seal microplates, label with
bar-codes,and remove organic solvents in order to prepare neat-films are com-
mercially available.
5.4.4
Screening Systems
Automation of assays based on nearly every biochemical effect like enzymatic
reactions,cell-surface receptor-,and intracellular receptor binding,protein-pro-
tein-,and protein-nucleic acid interaction,cell adhesion,etc.has been reported.
Robotic systems used in biological screening can be devided into workstation-
type systems [354] and integrated systems [355].Integrated systems are custom-
made and allow one to integrate nearly every peripheral module necessary for
screening courses.
As a recently developed technology, a novel automation concept has been
presented which is based on a mover,a stacking device,and a reader or washer
(Twister,Zymark).In comparison to the above mentioned systems,assays based
on the Twister concept are only semi-automated.The outstanding benefit is the
simplification of feeding,handling,set-up,as well as the small laboratory space
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