Micro-volume spectroscopy of DNA samples
23 October 2019
Measuring DNA concentrations of plasmid DNA and genomic DNA samples is a very frequent occurance in our lab. Initially we used a Nanodrop spectrophotometer that was available in our Division. However, with increasing sample numbers and measurement requirements it made sense to buy our own machine, which is now very frequently used. The idea for this particular machine came at the time from SLS. The BioDrop was a new machine they were telling and I was immediately taken by the idea that this particular spectrophotometer has no movable parts. SLS was very quick to organise a demo and for our particular puposes the BioDrop μLite+ performed very well. The old model we have has a relatively large footprint for what it does and by now there are smaller devices on the market. However, for a strange reason I immediately developed a personal affinity to the Biodrop and to the present day it remains my favourite piece of equipment. My students tease me, as every time I am measuring DNA concentrations with them I have to do the measuring.
At the time one of the unique features of the machine was that it does not have any moving parts. The light path is horizontal, which means essentially as long as therer is enough liquid in the sample holder to cover the light path the machine will give accurate measurements. The ends of both sides of the light path in the sample holder are reinforced by metal and we have not noticed any bending. The recommended sample volume is 2 μl and in our hands this indeed yields very reliable results. 1.5 μl work pretty well and 1 μl works most of the time, but with samller volume there is the danger that the probes are not fully covered, which can lead to variability.
The machine comes with a big touchscreen that offers a variety of measurements and settings. Dilutions can be set and other variables adjusted. The machine comes with some pre-defined measurement options, such as dsDNA, ssDNA, protein etc. In theory it can also be used to measure the OD600, but at least in our hands this was never as reliable than using a conventional spectrophotometer. Given that we routinely use a completely different setup for measuring the optical density of our cultures this is no loss whatsoever.
I find this machine simply a pleasure to work with – it just works and it has done so reliable and without any problems for the past 5 years. After calibration with the relevant elution buffer or water 2 μl of the sample are put in the sample holder and seconds later the machine gives a spectrum and the concentration of the sample, allowing judgment of quality, concentation and all the other parameters required. There are various ways to transfer data or even connect a computer, but we rarely use this functionality.
Overall I would highly recommend this machine. For us it does exactly what it needs to do, and has done so for years without any problems. It came at quite a substantial price, but I would happily spend this amount again.
The Biodrop was purchased via SLS