The NanoDrop ND-1000 is a full-spectrum spectrophotometer (UV and visible spectrum, 220-750 nm) for measuring the absorbance of DNA, RNA, proteins and dyes. The newly developed sample retention system allows for measurement of small samples volumes: the sample droplet is held in place by surface tension when it is slightly compressed between the pedestal and the sample arm; this generates the defined pathway of 1 mm. The spectrum measurement is then performed with two optical fibers installed in the pedestal (emitting light of a Xenon lamp) and the sample arm (spectrometer with linear CCD array). Quantification is performed based on the spectrum measurement at the defined pathway of 1 mm. DNA, RNA, protein or dye in 1 µl can be measured without using a cuvette or capillaries.
The NanoDrop ND-1000 is a small apparatus (20 cm x 14 cm). A measurement only takes 10 sec. Sample measurements are possible over a wide range of concentrations, e.g. double-stranded (ds) DNA: 2-3700 ng/µl, single-stranded (ss) DNA: ≤ 2400 ng/µl, RNA: ≤3000 ng/µl, and protein: 0.10-100 mg/ml BSA (at 280 nm); this is 50x higher than ranges of normally used spectrophotometers. Multiple types of readings can be performed. For example, DNA and RNA sample absorbance are measured at 230 nm, 260 nm and 280 nm; the absorbance values, concentrations and the ratios at 230/260 nm and 260/280 nm (to evaluate purity of DNA) are calculated by the NanoDrop ND-1000 software and displayed on the attached computer (PC with Microsoft Windows 2000). All measurements are automatically stored in a table. For pre-selection of labeled DNA hybridization probes for gene expression arrays, it is possible to analyze the DNA concentration at 260 nm together with 2 different fluorescent dyes (e.g. Cy3, Cy5, different Alexa dyes) in the same sample simultaneously. Protein can be measured at 280 nm, in combination with fluorescent dye labels (see above for DNA), and after performing standard protein assays, e.g. BCA, Lowry and Bradford assays. Protein values of up to 7 standards can be used to set up a standard curve necessary for the calculation of protein concentrations when performing protein assays. For calculations of protein concentration measured at 280 nm, users can choose between different protein references (e.g. BSA, IgG, Lysozyme or a user entered reference) to obtain the molar extinction coefficient.
NanoDrop Technologies provides proof for the lack of carry-over between samples, as well as for the instrument’s reproducibility and linearity; this information is available on their website.
When I measured several genomic or plasmid DNA samples isolated from mice tails or minipreps, I liked to use the NanoDrop ND-1000 for DNA concentration measurements. It is easy to use and fast in measuring and calculating all data; in addition, cleaning up is easy as the pedestal just needs to be wiped with a fresh dry Kleenex tissue. There was never a contamination between 2 samples of DNA. I only needed 1 µl or 2 µl (when I measured the sample twice, to test the data and also to check if the DNA was completely dissolved) of the sample to measure DNA concentration and purity. Thus, I saved enough of the purified DNA for my downstream applications, e.g. enzymatic digestion and further determination of the flanking region of a transgene. Care has to be taken that the DNA is completely dissolved since partially or un-dissolved DNA can easily obscure the accuracy of the absorbance measurement due to the small sample volume. (This is also indicated in the companies test for ‘Homogenity,’ available on the website). I also used the NanoDrop ND-1000 to measure protein concentration at 280 nm from sciatic nerve preparations and had enough sample left to perform several Western blots.
For fast and easy measurements of DNA and protein, I highly recommend the NanoDrop ND-1000, especially when measuring multiple samples or limited sample volumes. It also limits cost, because no cuvettes are needed. Nano Drop Technologies’ website provides information about the ND-1000, including specifications and accessories, an extended user manual with troubleshooting section, articles, applications and FAQ. The NanoDrop ND-1000 is provided with a one year warranty, which can be extended and includes the preventive maintenance plans for e.g. calibration, cleaning, alignment of pedestals (the plan can be also purchased separately). For high throughput, NanoDrop Technologies recently developed a new apparatus, The NanoDrop® ND-8000 8-Sample Spectrophotometer, where 8 samples in a microtiter plate can be measured at once.