I have used Molecular Devices’ Vmax 96-well microplate readers since about the time of their inception in the mid to late-1980s. These instruments are all elegant and simple in their form and function. The Vmax Kinetic Microplate Reader is designed to measure any of the visual wavelengths so that you can use your substrate of choice. A sampling of the reagents that can be used includes ABTS, CPRG, BCIP, TMB, NBT, Pierce’s protein assay reagents, Bio-Rad’s assay reagents, Lowry and Coomassie. Also, the plate reader can also be used for cytotoxic cell assays. If you need to use temperature control for enzyme analysis, Tmax is available. The temperature controller feature, for instance, is for elucidation of the kinetics of the turnover of your enzyme-labeled conjugate. I have used this instrument in numerous applications including enzyme turnover, protein estimation, and variety of different ELISAs. Additionally, I have used it to estimate the amount of protein attached to particles, the number of biotin binding sites per mole of protein, as well as other assays.
To use the instrument, one simply places the microtiter plate in the holder, turns on the instrument, selects the wavelength of the chromagen, selects the optical density mode: absorbance or mOD/min (with or without plate mixing). If you need to utilize the temperature function, you’ll need to turn it on in enough time for the temperature to stabilize. However, if you need just an OD reading, the electronics of the system are very efficient so no appreciable warm up is needed. However, I generally give the instrument approximately five minutes to warm up. If one uses the SOFTmax® Pro software, which can be interfaced with Windows or Mac OS, you have the flexibility to place the plate layout for your standard curve on the system. You can then add single, duplicate or multiple wells and have the software determine the concentration of the sample. It can also store your previous data for spreadsheet analysis across days and assays. It calculates all the necessary information, including the correlation coefficient, slope, intercept and mOD/min. My only negative comment is the software is not as fast as I would like and the user interface is not as intuitive as it could be. I rarely comment about the system is not functioning fast enough with respect to the software because I am fairly understanding of the nuances and intricacies of the software. But the software interface is slow with SOFTmax® Pro software and not as easy to move around in the various areas of the software. Additionally, it is not as intuitive as many of today’s software packages, which are often rather easy to use with minimal time to learn and utilize.
I have previously validated the instrument and have found it to be extremely accurate. When I validated the instrument, I looked at a variety of parameters: i) comparison of readings with multiple observations, ii) stability of the readings at different discrete times without turning on/off the instrument, iii) stability of the readings between turning on and off the instrument. The values studied were from a standard curve, blank and substrate for each point as well as for the mOD/min for enzyme turnover. I further compared the mean, standard deviation and did error analysis looking at the p values for statistical analysis for the above indicated subsets. Molecular Device has designed an effective and efficient instrument.