We use the Spectra microplate reader in our lab to measure absorbance for both MTT and p24 ELISA assays. The Spectra microplate reader is fully-automated and microprocessor-controlled, measuring the light absorbance (or optical density) of samples in a 96-well format (for our needs). Components of the reader include a halogen lamp for the light source, a 2x16 digit LCD display and a 20-key membrane keyboard. The reader is very compact, measuring 28.5 cm x 32 cm x 17 cm, weighs only 8 kg and can easily be connected to a printer. The support for the microplate is located in the front of the reader and opens to obtain readings. The instrument consists of the following modules: A CPU, an optical unit, a carriage transport system, a keyboard, a display, a power supply and interfaces. It is operated and controlled by a menu-driven system, with the main screen presenting standby and setup/service menus. The standby menu is the user level menu and is used to set parameters for sample measurement. The setup/service menu is used to set the parameters for instrument control and enter the service menu for instrument troubleshooting.
The reader offers three measurement procedures: normal, manual, and quick. Conveniently, one can also recall or print stored data from a previously measured microplate and re-evaluate it using any of the available test procedures (can store up to 20 user programs). The evaluation modes for obtained data include measurements for raw data, screening (qualitative), curve fit (quantitative), agglutination and kinetics. The instrument can be used with any type of microplate but it is recommended that a minimum of 200 microliters per well is used to minimize error. In addition, one should try to avoid the formation of a meniscus in the solution, which can also lead to error.
Microplate measurement options include single/dual wavelength measurements, automatic blanking and shaking. The instrument has a wavelength range from 340-750nm, a resolution of 0.001 Abs, and up to four filters can be mounted per carriage (uses up to 8 different carriages). Dual wavelength measurement mode eliminates any non-specific influence on absorbance readings such as from the sample preparation, the microplate itself or mechanical blemishes like finger prints, etc. In the dual wavelength mode, 12 wells can be read simultaneously enabling the entire plate to be processed in about 8 sec. In contrast, the single wavelength mode takes approximately 6 seconds to read a plate, hence, one can obtain accurate readings very quickly. Blanking involves the absorbance of an empty well or a well only filled with reagent. To insure accurate measurements, the instrument provides options for pre-measurement microplate shaking (high, normal, low and wide). In addition, up to 12 individual blank positions can be selected and the instrument will calculate average absorbance to serve as the blank value.
An advantage of this instrument that I found particularly useful is the self-check calibration procedure that ensures the instrument is working correctly and calibrates the optical system. I use this instrument on a daily basis and have encountered no problems with it. I would recommend this instrument to others without any hesitation.
Hee Chul Lee
Post-Doctoral Fellow
Department of Biochemistry
NYU School of Medicine