poster-style print of user endorsements for the Qubit Fluorometer  

Trusted when accuracy matters

Qubit® instruments and assays have a proven track record, with over 3,000 citations and hundreds of testimonials. With high sensitivity for DNA, high specificity for RNA, and a broad range of available assays, the Qubit® Fluorometer is the instrument of choice when accuracy matters most


Qubit® Fluorometer vs. Quantus™ Fluorometer

The Qubit® Fluorometer is an analytical instrument for DNA, RNA, and protein quantification with a small benchtop footprint and an intuitive user interface. The instrument works with Qubit® assay kits to enable greater sensitivity and accuracy than UV absorbance measurements, and is ideal for applications including cloning, sequencing, transfection, qPCR, and protein assays. Here we compare accuracy and specificity data for the Qubit® Fluorometer and assays with the Quantus™ Fluorometer and QuantiFluor® assays from Promega.

DNA assay sensitivity

Promega claims that dsDNA assays on the Quantus™ Fluorometer are 10 times more sensitive than Qubit® Fluorometer dsDNA assays,* but assay precision is compromised for both instruments at concentrations below 0.5 ng/mL (Figure 1). The Qubit® Fluorometer gives an out-of-range message when the calculated value exceeds a CV of 20%, providing you with confidence in the results. Table 1 summarizes these results along with other attributes of each instrument.

  bar graph showing Qubit assay performance compared to QuantFluor assays on the Quantus Fluorometer for low-concentration DNA samples  

Figure 1. Assay sensitivity.
Comparable results are achieved at 0.5 ng/mL for both the Qubit® dsDNA HS assay and the QuantiFluor® dsDNA assay, but the coefficient of variation (CV) for the QuantiFluor® assay is 112% at 0.1 ng/mL. The Qubit® fluorometer reports an out-of-range message at levels >20% CV; the Quantus™ Fluorometer does not.

Table 1. Comparison of dsDNA quantification data and other instrument features.

  Qubit® Fluorometer and assays Quantus™ Fluorometer and QuantiFluor® assays
Sensitivity (dsDNA) 0.5 ng/mL (10% CV) 0.1 ng/mL (112% CV)
Dynamic range† (dsDNA) 0.5 ng/mL to 5 µg/mL 0.1 ng/mL to 1 µg/mL
Detection limit Yes—out-of-range message at low and high ends of assays No—gives concentration values for any sample with fluorescence signal above background
Display Large, intuitive touch screen Push-button navigation
Data storage 1,000 samples 20 samples
Data transfer USB thumb drive or cable Indirect—need to download software onto computer
† Combined range of Qubit® Broad Range and High Sensitivity assays.

RNA quantification accuracy in the presence of DNA

Qubit® RNA assays are designed to be specific and accurate for RNA even in the presence of a 1:1 mixture of RNA and DNA, whereas the QuantiFluor® RNA assay on the Quantus™ Fluorometer cannot distinguish RNA from DNA below 3 µg/mL (Figure 2). This is critical for limited, low-concentration samples that may also contain DNA.

  bar graph showing Qubit assay performance compared to QuantFluor assays on the Quantus Fluorometer for DNA-contaminated RNA samples  

Figure 2. Accuracy in the presence of DNA.
The Qubit® RNA BR (broad range) assay demonstrates high specificity, even at low concentrations and in the presence of DNA. A significant amount of DNA is detected as RNA with the QuantiFluor® assay.

The Qubit® Fluorometer has more compatible assays

The Qubit® Fluorometer supports assays for high-sensitivity or broad-range dsDNA and RNA quantitation (Table 2). Assays for oligos, ssDNA, protein, and microRNA quantification are also available.

Table 2. Assays available for each fluorometer.

Assay‡  Qubit® assays for the Qubit® Fluorometer QuantiFluor® assays for the Quantus™ Fluorometer
dsDNA  Yes Yes
RNA  Yes Yes§ 
microRNA  Yes No 
Protein  Yes No 
ssDNA or oligos Yes Yes
‡New assays including those for cholesterol and glucose can be added to the Qubit® 2.0 and 3.0 Fluorometers.  
§QuantiFluor® RNA assay for the Quantus™ Fluorometer also detects DNA. 

Qubit® Fluorometer vs. NanoDrop® Spectrophotometer

Detection and quantification of nucleic acids are vital to many biological studies. Historically, DNA and RNA have been quantified using spectrophotometry to measure absorbance at 260 nm. Although this method is very common, in some applications it can be inaccurate [1–4].

The Qubit® and NanoDrop® instruments may be used together to determine RNA or DNA concentration—the Qubit® Fluorometer for accurate quantification of the target molecule and the NanoDrop® spectrophotometer to indicate contaminants. We have compared the Qubit® Fluorometer to the NanoDrop® ND-1000 spectrophotometer. The major differences are listed in Table 3, illustrated in Figures 3–5, and demonstrated in this video.

See how fluorescence quantitation works compared to UV-absorbance quantitation

Table 3. Quantification method comparison.

  Qubit® Fluorometer NanoDrop® ND-1000
Quantification method Fluorescence-based dyes that bind specifically to DNA, RNA, or protein UV absorbance measurements (measures absorbance at 260 nm and 260 nm/280 nm ratio)
Selectivity for DNA or RNA (Figure 3) Accurately measure both DNA and RNA in the same sample Results for samples containing both DNA and RNA are nondiscriminatory—you cannot distinguish one from the other
Accuracy and precision at low concentrations (Figure 4) Accurately quantifies DNA in samples with concentrations as low as 10 pg/μL Not recommended for concentrations under 2 ng/μL; variation for sample concentrations <10 ng/μL is often high
Sensitivity and range (Figure 5) The effective range covers a sample concentration range of  10 pg/μL to 1 μg/μL DNA Covers a sample concentration range of 2 ng/μL to 15 μg/μL; uses 0.5–2 μL of sample
Can indicate contamination No Gives peaks revealing the presence of contaminants

bar graph showing Qubit assay performance compared to NanoDrop Spectrophotometer performance for DNA samples, RNA samples, and RNA-contaminated DNA samples
  Figure 3. Selectivity of the Qubit® assays compared to UV spectroscopy. Triplicate samples containing lambda DNA (10 ng/μL) and varying amounts of ribosomal E. coli RNA (0–100 ng/μL) were assayed using Qubit® DNA BR and Qubit® RNA BR assays on the Qubit® Fluorometer according to kit protocols. The same samples were subsequently measured in triplicate using a NanoDrop® ND-1000 Spectrophotometer, and single measurements were made using a Perkin Elmer Lambda 35 Spectrophotometer. The concentrations indicated are the concentrations of DNA and RNA in the starting samples, before dilution in the Qubit® assay tubes. The red and orange trendlines indicate the actual concentrations of DNA and RNA, respectively, in the starting samples. The actual concentration of nucleic acid was set by diluting pure, concentrated solutions of DNA and RNA to an optical density of 1.0 at 260 nm using a Perkin Elmer Lambda 35 Spectrophotometer. The concentrations of the stock solutions were then calculated and used for all subsequent dilutions. With UV analysis, results for samples containing both DNA and RNA are nondiscriminatory—you cannot distinguish one from the other..
bar graph showing Qubit assay performance compared to NanoDrop Spectrophotometer performance for low-concentration DNA samples
Figure 4. Accuracy and precision of Qubit® fluorometric quantification. Ten replicates of lambda DNA at concentrations from 0.01 to 10 ng/μL were assayed using the Quant-iT® DNA HS Assay on the Qubit® Fluorometer according to the standard kit protocol. The same concentrations of DNA were measured in 10 replicates using a NanoDrop® ND-1000 Spectrophotometer, and results were compared for both accuracy (A) and precision (B). Accuracy was defined as the average deviation from the known concentration. The concentrations indicated are the concentrations of DNA in the starting samples, before dilution in the Qubit® assay tubes.
Comparison of sample concentration ranges for Qubit® assays and for the NanoDrop Spectrophtometer  

Figure 5. Comparison of sample concentration ranges for the Qubit® assays using the Qubit® Fluorometer and UV absorbance measurements using the NanoDrop® spectrophotometer.