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Short answer: A Qubit fluorometer is a benchtop instrument from Thermo Fisher Scientific that measures how much DNA, RNA or protein is in a sample by reading the fluorescence of a dye that binds the target molecule. It reports quantity, not purity, and each assay kit has its own stated concentration range.
This page is general instrument information for lab staff and core-facility users. The Qubit 1X dsDNA assay kits are labelled for research use only, not for diagnostic procedures. Always follow the current manual for your instrument and kit.
Definition and scope
The Thermo Fisher Qubit product page describes the Qubit fluorometers as instruments that detect fluorescent dyes which bind specifically to the target molecule, with separate assays for DNA, RNA and protein. Two current models are described there: the Qubit 4, which reads one sample at a time, and the Qubit Flex, which reads up to eight samples at a time. The general fluorescence principle is covered in fluorescence spectroscopy.
How does a Qubit fluorometer work?
The kit manuals describe a dilution-and-read workflow. A small sample (1 to 20 µL) is mixed into a working solution containing the dye, the tubes incubate for 2 minutes, and the instrument reads the fluorescence. The reading is converted to concentration using a calibration against two standards supplied with the kit (0 and 10 ng/µL for the 1X dsDNA HS kit). The dye is selective: the 1X dsDNA assays are described as highly selective for double-stranded DNA over RNA, and common contaminants such as salts, solvents, detergents and protein are described as well tolerated.
Because the signal comes from dye bound to the target rather than from absorbance of everything that absorbs near 260 nm, the result is specific to the assay chosen. That is the main reason labs use a fluorometer next to, or instead of, a microvolume spectrophotometer; the two approaches are set side by side in Qubit vs NanoDrop, and the spectrophotometric route is described in spectrophotometer for DNA concentration.
What is the high sensitivity range of the Qubit dsDNA assay kit?
For the Qubit 1X dsDNA HS assay, the manual (MAN0017455, Rev. C.0) recommends initial sample concentrations of 10 pg/µL to 100 ng/µL, giving a core detection range of 0.2 ng to 100 ng of DNA. The broad range (BR) kit covers higher concentrations. The table compares the two 1X kits as stated in their manuals.
| Item | 1X dsDNA HS | 1X dsDNA BR |
|---|---|---|
| Manual | MAN0017455 Rev. C.0 | MAN0019617 |
| Recommended initial sample concentration | 10 pg/µL to 100 ng/µL | 200 pg/µL to 4 µg/µL |
| Sample volume | 1 to 20 µL | 1 to 20 µL |
| Final volume per tube | 200 µL | 200 µL |
| Incubation, then signal stability | 2 minutes; stable 3 hours at room temperature, protected from light | 2 minutes; stable 3 hours at room temperature, protected from light |
| Instruments named in the manual | Qubit 4 and Qubit Flex | Qubit 4 and Qubit Flex |
| Tubes | Qubit assay tubes (Q32856) for Qubit 4; Flex tube strips (Q33252) for Flex | Same |
The ranges above apply to the 1X kits only. Other Qubit kit generations list different ranges, so read the manual that ships with the kit you use.
Does Qubit measure DNA quality?
Not in the sense of purity ratios. The Thermo Fisher product page says Qubit assays can distinguish dsDNA from ssDNA, or intact from degraded RNA, because the dye used is selective for a particular form of the molecule. Those are properties of the assay chosen, not a general quality score for any sample. Integrity of RNA is assessed with other metrics as well; see RNA integrity number (RIN). Upstream extraction quality is covered in DNA extraction protocol basics.
Checklist: parameters the manuals identify as critical
- Temperature: optimal performance when all solutions are at room temperature (18 to 28 °C); temperature fluctuations can influence accuracy.
- Handling: do not hold assay tubes in your hand, and do not label the side of the tube, which can interfere with the read.
- Incubation: 2 minutes after mixing sample or standard with the working solution.
- Time window: signal stable for 3 hours at room temperature when protected from light; tubes containing standards and samples are stable for no longer than 3 hours.
- Repeat readings: the temperature inside the instrument can be as much as 3 °C above room temperature after 1 hour, so the manual advises removing a tube and letting it equilibrate for 30 seconds before another reading.
- Calibration: perform a new calibration the first time you use the instrument; the manual lets you reuse a previous calibration, within its stated stability limits.
- Tubes: thin-wall, clear 0.5 mL tubes for Qubit 4; 8 × 200 µL strips for Qubit Flex.
- Dye disposal: the manual says no mutagenicity or toxicity data are available, so treat the dye as a potential mutagen and dispose of it under local regulations.
How much does a Qubit fluorometer cost?
Pricing is set by the supplier and varies by model, region and contract, so no figure is given here; request a current quote. Budgeting should also include the recurring consumables: each measurement uses working solution from an assay kit plus a tube or tube strip.
Common misunderstandings
- “It gives a purity ratio.” The Thermo Fisher page describes target-selective quantification, not a general purity assessment.
- “One kit covers every concentration.” HS and BR kits have different stated ranges.
- “A calibration lasts all day.” The manuals cap signal stability at 3 hours and tell users to consider temperature fluctuations in the lab when reusing a calibration.
- “Any tube will do.” The manuals specify tube types for each instrument.
FAQ
What is the high sensitivity range of the Qubit dsDNA assay kit?
For the 1X dsDNA HS kit, 10 pg/µL to 100 ng/µL initial sample concentration, a core detection range of 0.2 ng to 100 ng DNA (MAN0017455 Rev. C.0).
How much does a Qubit fluorometer cost?
Cost depends on model and supplier, so request a quote and include recurring assay kit and tube costs.
Does Qubit measure DNA quality?
It measures quantity with selective dyes. Assays can distinguish dsDNA from ssDNA or intact from degraded RNA, but it does not return purity ratios.
How does a Qubit fluorometer work?
It reads the fluorescence of a dye that binds the target molecule in a diluted sample and converts it to concentration using two standards.
Sources
- Thermo Fisher Scientific, Qubit fluorometers, read 2026-11-08.
- Thermo Fisher Scientific, Qubit 1X dsDNA HS Assay Kits user guide, MAN0017455 Rev. C.0, read 2026-11-08.
- Thermo Fisher Scientific, Qubit 1X dsDNA BR Assay user guide, MAN0019617, read 2026-11-08.
