The microplate is a standard tool in analytical research and clinical diagnostic testing laboratories. A clear trend that is emerging in microplate instrumentation lies in the use of smaller well sizes which (i) increases the number of assays that can be conducted per plate thereby increasing throughput, and (ii) reduces sample volume needed per assay which is crucial when the test samples/reagents are scarce or expensive. A more far reaching objective is to develop microplates that are cost effective enough to be available for use in resource-limited laboratories . The Whitesides laboratory has been pioneering in this aspect via the development of paper-based alternatives. It turns out that in addition to low cost, these plates have benefits of low space, weight, as well as ease of production and disposal.

• Microplates made with transparencies (NEW)

  

  Apart from good retention features for small liquid volumes, the ability for effective diagnosis is crucial in microplate instrumentation. Paper based microplates have been proven to work well for electrochemical analysis; however, its limitations in optical based diagnostics have been highlighted. This is unfortunate as optical approaches, in particular with the use of fluorescence, provide arguably the highest sensitivity measurements with greatest versatility. For this reason they are used extensively in protein formulation and characterization studies; and are the method of choice in high throughput screening due to high sensitivity and speed. We have demonstrated an approach of using a silicone sheet with holes, conveniently cut out precisely using an inexpensive cutting plotter to correspond with regions where liquid is to be dispensed, and attaching it to a transparency to create very thin well arrays. With this, the contact angle hysteresis behavior of liquid could be harnessed to produce taller drop shapes so that the fiber probe used could read in the emitted light more effectively. Experimentation conducted revealed fluorescence measurements that were significantly more sensitive than standard microplates; notwithstanding that favorably smaller volumes of liquid were needed. This was achieved using both the fiber optic or imaging evaluation modes. The two methods investigated, one with a lid placed and one without, showed the latter to produce marginally more sensitive readings as opposed to improved immunity from the environment with the former. These favorable measurement characteristics were found to be achievable with an estimated production cost of AU$0.40 and fabrication times of 3.5 (96 well) and 6.5 minutes (384 well) per plate.

  B.H.-P. Cheong, V. Diep, T.W. Ng, O.W. Liew, Transparency based microplates for fluorescence quantification. Analytical Biochemistry. Accepted 23/12/2011.