A few months ago, our Shimadzu (Kyoto, Japan) spectrophotometer finally failed after 12 years of nearly daily use. It was an incredibly reliable instrument, needing only bulb changes from time to time to keep it running. This dependability motivated us to see what spectrophotometers were currently in the Shimadzu lineup. After comparing instruments from several companies, our choice was, once again, a Shimadzu. This time around, we opted for the BioSpec-mini, a UV-visible bench-top spectrophotometer. For the price (less than $5,000), the array of features that are standard on the BioSpec-mini is unsurpassed. Other spectrophotometers in this price range either offered far fewer features or were seen as somewhat unreliable by fellow researchers at my institution who had had first-hand experience with these other models.
Upon turning the BioSpec-mini on, the instrument performs a check of several parameters and then, if all parameters pass, the Mode Menu screen is displayed. This screen lists all of the various measurement modes as well as a choice for the Optional Program Pack and a Utilities folder. The normal measurement modes consist of DNA/RNA Analysis, Protein Analysis, Spectrum, Cell Count, and Tm Prediction. So far, we have used the nucleic acid quantification, protein assays, and cell counting. All have worked perfectly and each includes some very useful features.
In the DNA/RNA Analysis mode, options include ds and ssDNA, RNA, long DNA oligo, long RNA oligo, short DNA oligo, short RNA oligo, and a few others. In the short oligo mode, you can enter the base sequence of the oligo and the instrument software calculates the extinction coefficient; it will then use this value to estimate the oligo concentration from its absorbance and the user-defined dilution information. It also measures absorbance at 3 wavelengths simultaneously and reports pertinent absorbance ratios. The long oligo mode works similarly except the instrument only needs the base composition (i.e. how many As, Gs, Cs, and Ts) to calculate the extinction coefficient. I used the short oligo mode to calculate the concentration of a PCR primer and the value given by the instrument was within 10% of what I had expected based on the oligo quantity information supplied by the company that synthesized the primer. Overall, the DNA/RNA Analysis mode is quite flexible and the interface is straightforward.
Without going into too much detail, the other measurement modes are set up similarly to the DNA/RNA Analysis mode, with features geared towards procedures commonly used in biological, biochemical, and biomedical research. Some key features of a few of the other measurement modes:
Spectrum: The BioSpec-mini is capable of performing scans between 190 nm and 1100 nm. Scan speeds from very slow to very fast are possible. The spectrum is displayed on the screen and is printable or downloadable, as is any graphical or numerical information that is displayed on the screen.
Protein Analysis: Algorithms for protein estimation by all the common methods (Lowry, BCA, Bradford, Biuret, and A280) are standard. Calibration curves are shown and can be printed out or downloaded.
Tm Prediction: Just what it sounds like but with plenty of user-definable parameters to increase the accuracy of the prediction.
For those situations that require only a quick reading, the current wavelength and photometric value are displayed at all times. The wavelength can be selected directly from the input pad and the blank solution can be auto zeroed with the press of a button. When you insert the cuvette containing your sample and close the lid, the absorbance reading is displayed. This direct measurement option is available from the start-up screen and from within any of the measurement mode screens.
Although we have had the BioSpec mini for only a few months, we have no complaints. It is convenient, easy to use, accurate, and doesn’t take up much space (approx. 38 x 38 cm footprint).