![]() Sunghou Lee first developed an additional vacuum filtration system integrated with a conventional plate washer to speed up the wash process for applications involving filter plates ( Lee 2006). A third component is the vacuum/pump assembly, which supplies the necessary pressure differential to drive efficient aspiration. This manifold (or a separate manifold depending on the design) aspirates the liquid from the wells after an optional soaking period, leaving a pre-defined residual volume in the wells. The two most critical components of a plate washer are a plate carrier and a manifold containing a number of fixed stainless steel needle probes for solution dispensing ( Fig.1A). The development of automated plate washers has decreased the time required for laborious washing steps involved in many screening assays and improved reproducibility through standardized plate handling across multiple wash cycles (defined as a single dispense and aspirate step per cycle). Over the years, fully programmable plate washers have been developed with numerous features. In 1990, Stobbs developed the first multiple plate washer using readily available materials as a low cost alternative to the commercially available plate washers of the era (Stobbs 1990). They play an important role in areas such as high-content screening and enzyme-linked immunosorbent assays (ELISA). Microplate washers are laboratory instruments designed to automate and expedite assay applications, where a washing step is essential. Droplet volume depends on several factors, including bore diameter, solution viscosity and the voltage pulse amplitude and frequency ( James and Papen 1998 Kong et al. Several thousand drops can be dispensed per second, with attainable drop sizes spanning the picoliter and nanoliter range ( Schober et al. The ejection is at high acceleration with minimal wetting of the nozzle ( Schober et al. Upon voltage application, the piezoelectric element contracts causing pressure on the capillary to generate fine drops. A piezoelectric crystal collar is bound to the capillary, which is filled with solution. The system is composed of a capillary tube made of quartz or steel, with one end connected to the reagent reservoir and the other end ending in an orifice from which droplets are ejected ( Niles and Coassin 2005). Various biochemical solutions (DNA, RNA, proteins) and bacterial suspensions have been tested with no negative effects ( Schober et al. This technology has been utilized in contemporary inject printers and refined to be implemented in the biological sciences. The piezoelectric dispenser is a non-contact technology, where solutions are delivered as multiple tiny drops of defined size ( Niles and Coassin 2005). The process is faster than using permanent tips or pins ( Fig.1), because there is no washing step between delivery, while reducing cross-contamination and evaporation ( Dunn and Feygin 2000). Non-contact devices utilize additional force other than gravity to eject liquids, as minute volumes cannot be dispensed efficiently with gravity alone ( Kong et al. Contact-based devices allow the fluid to be transferred to touch the surface of the destination container or solution, offering a simple and dependable alternative to sub-microliter fluid handling. In terms of application, they are broadly classified as bulk liquid dispensers, transfer devices and plate washers ( Rudnicki and Johnston 2009).īased on the way the reagent is being transferred, these instruments can follow two dispensing modes: contact or non-contact ( Kong et al. These instruments encompass different technologies for distinct purposes. A whole array of liquid handlers has been developed for every aspect of drug discovery.
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