While I worked at Boehringer Mannheim in the Biochemical Division as a Product Development Scientist II (1987-1994), I had an opportunity to use, review and analyze the DNA Dipstick Kit™ from Invitrogen. As part of my work in the product development area, I tested and evaluated products. The DNA Dipstick™ was evaluated because they were to be used on a regular basis in the product development cycle. They were rated with respect to sensitivity and specificity as well as other aspects such as ease-of-use, hands-on time, the level of complexity of results interpretation and the required skill level of the user.
I found the DNA Dipstick Kit™ instructions to be clear, concise and detailed enough so that anyone skilled in the sciences could perform the assay. Additionally, the color chart was a surprisingly good match to the color and intensity of the reaction. If one desired, I believe that the assay could be read with a densitometer to generate an absolute number. However, with the use of a densitometer, the time-savings would be lost. After analysis, the strips can be glued into your lab book as a permenent record of your analysis (i.e. after the strips dried the color intensity (quantification) was essentially the same).
The drawbacks of the DNA Dipstick™ are that i) there is a higher cost involved than the spectrophotometer (if you already have a spectrophotometer) and ii) your sample cannot be recovered. If you are using precious sample(s) then the Invitrogen DNA Dipstick™ would not necessarily be a prudent choice.
The chemistry utilized in the Invitrogen DNA Dipstick™ is the ferricynide and ferrocynide oxidation/reduction which is well characterized and utilized in the glucose monitoring assays for diabetic individuals. The assay was reliably consistent and really an excellent kit. It did a very nice job with double and single stranded DNA. The linear range was only 10X and it is necessary to have 2 dilutions within the linear range of your standards (color chart is supplied also) for complete confidence of the result. For this reason, you may need to run a few more dilutions than expected if you did not have any idea on the concentration of your sample. Since the strips were generously wide, with care, multiple spots (6 or 7 spots) could be added to each strip (by spotting the samples in a zig zag pattern). From a touchie / feelie prospective, the colors were rather nice and intense. While there was excellent strip-to-strip matching of colors, obtaining this matching required consistent technique with respect to the dotting of the sample: Variability in dot size can lead to inconsistent color intensity and thus, to poor estimation of concentration.
Additionally, due to the direct correlation of the ferrocynide reactivity with the DNA/RNA and the number of base pairs, the color of the reaction proceeds proportionally to concentration (concentration per unit surface area). The assay specifically interacts with the negative charge on the oxygen which binds the chemical moiety quantitatively; as a result, the oxidative/reductive chemical reaction (thus production of color) changes on a quantitative basis.
In my opinion, it is critical to run a standard curve run with a standard which contains the same number of base pairs of your sample. If the standards and sample(s) are identical, the intensities of the spots should correlate very well. The instructions do not address this particular issue. There is a standard which is supplied and utilized. I will say with the samples I ran, some of them left some room for interpretation (but very little). However, in reality, the more samples I ran, the more confidence I had with the assay and its results.
Although, I tried the assay with only one single-stranded DNA and two double-stranded DNA samples, they all were within the manufactures stated levels. Honesty, I really tried to find some negative comments or perspectives of the assay and its technology. In reality, I found very little to say which is negative or very critical. The big plus of the DNA/RNA quantification assay with respect to the other assays’ is its ability to work with single and double stranded DNA and it ability to be used with samples which as small as 6 nucleotides in length. All other assays had limitations with respect to length of DNA and if the samples were double or single stranded nucleic acid (except of course the gold standard UV/Vis spectrophotometer). I would be interested to see the product tested with nucleotides. I attempted to fool it with more than 2 types of samples (at various concentrations) and could not find fault/flaw. As with most scientific assays, the directions have to executed precisely, however the degree of detail is highly necessary with this assay.
I recommend the Invitrogen DNA Dipstick™ for its technology, reproducibility and sensitivity/specificity. The instructions were clear, precise and accurate. In addition, there was very little clean up and preparation time.