Nitric Oxide Measurement in Cell and Tissue Samples: Test Strips vs Assay Kits

Nitric oxide (NO) is a signalling molecule that has been studied extensively in biology. It is involved in the processes of function of blood vessels, immune response, inflammation, nerve signalling and cell death. This is a normal readout in cell culture, tissue and animal studies.

But NO is hard to measure directly. It lasts only a few seconds in biological samples before it turns into nitrite and nitrate. So, most methods measure these stable products instead of NO itself.

This is a guide for researchers and lab teams that require to measure NO in the cells or tissue of interest. It discusses the working of test strips and assay kits, their usage and what to lookout for before purchasing a NO assay kit in India.

Why NO is measured as nitrite and nitrate

Nitric Oxide reacts quickly with oxygen and other molecules. In cell culture media, it mostly turns into nitrite. In blood and tissue, much of it turns into nitrate.

This is why:

• Nitrite alone is a good marker in cell culture supernatants
• Total NOx (nitrite + nitrate) is a better marker in serum, plasma, urine and tissue.

Measuring plasma nitrite only will underestimate the majority of NO formed. Select your technique based on your sample, and not the expense.

Option 1: Nitric oxide test strips

Test strips will turn color if they meet a nitrite sample. The approximate level is determined by comparing the colour with a chart.

Good for:

• Quick checks before running a full assay
• Screening many samples to see which ones need full testing
• Field work, teaching labs and pilot experiments
• Checking samples where you only need low, medium or high

Limits:

• Results are approximate, not exact numbers
• Reading depends on the person and the lighting
• Not suited to data for publications or reports
• Usually measure nitrite only, not nitrate

Strips are useful in saving time and money in screening. The laboratories that conduct routine rapid tests can purchase them from a nitric oxide test strips supplier in India and have assay kits for samples requiring precise readings.

Option 2: Nitric oxide assay kits

Assay kits give exact numbers. There are two main types.

Griess (colorimetric) assay kits

The Griess colour test causes nitrite to appear pink purple. It is measured on a plate reader at about 540 nm and compared to a standard curve.

• Most widely used NO assay
• Simple, low cost and works with a standard plate reader
• Detects nitrite down to the low micromolar range
• For total NOx, nitrate is first converted to nitrite using an enzyme (nitrate reductase) or a chemical step

Fluorometric assay kits

These use a dye that becomes fluorescent when it reacts with nitrite. They are more sensitive than Griess kits and can detect much lower levels.

• Better for samples with very low NO, such as small cell numbers or diluted samples
• Needs a fluorescence plate reader

Other methods researchers use

• Fluorescent probes (such as DAF-FM): show NO inside living cells under a microscope or by flow cytometry. Useful as a supplementary source for indication of the location of NO production, but not for quantitative determinations.
• Chemiluminescence analysers: very sensitive and accurate but need costly equipment. Mostly used in specialised labs.
• Electrochemical NO sensors: measure NO in real time. Used in specialised physiology studies.

Test strips vs assay kits briefly

Sample tips that save experiments

Small mistakes in sample handling are the most common reason NO results don't make sense.

• Use phenol red-free media for cell culture work, as phenol red can interfere with colour readings
• Remove proteins from serum, plasma and tissue samples before Griess testing, usually with a 10 kDa spin filter
• Homogenise tissue in cold buffer, spin it down, and use the clear supernatant
• Check your water and tubes: nitrite contamination from water or glassware can raise background
• Run the standard curve in the same medium or buffer as your samples
• Store samples at −80°C if you can't test them the same day, and avoid repeated freeze-thaw.

What to check before buying an NO assay kit

• What it measures: Some kits read nitrite only, while others also convert nitrate so you get total NOx. Pick the one that suits your sample.
• Sample type: Make sure the kit has been tested on the sample you work with, whether that's cell media, serum, plasma or tissue.
• Detection range: The range should match the levels you expect to see. A quick check with test strips can give you a rough idea first.
• Format: Look at the plate format and the number of tests in the box and make sure the reading wavelength works with your plate reader.
• Storage: Enzymes and standards often need cold storage, so ask how the kit will be shipped to you.
• Documents: Every lot should come with a datasheet, a manual and a certificate of analysis.

Buying from one life science products supplier India for your assay kits, test strips and reagents also makes ordering and documentation simpler.

Sourcing NO assay kits and test strips in India

Imported assay kits can take time to reach Indian labs. Working with a local distributor helps with stock, cold-chain delivery and documents. Most of the labs already receive the reagents and kits from the Thermo Fisher distributors in India and the same questions are applicable to NO assay kits: Ensure genuine stock, lot documents, and correct storage in transit. Biochain Incorporated is an ISO 9001:2015 Certified Distributor of New Delhi. We supply nitric oxide test strips, research assay kit and reagents to various research laboratories, universities and biotechnology firms in India.

Need an NO assay kit or test strips? Tell us your sample type, what you want to measure (nitrite or total NOx) and how many samples you run. We will send you a quote.

FAQs

1. Why is nitric oxide measured as nitrite and nitrate?

NO lasts only seconds in samples. It quickly turns into nitrite and nitrate, which are stable and easy to measure.

2. Are nitric oxide test strips accurate enough for research?

They are good for quick screening. For exact numbers or publication data, use a Griess or fluorometric assay kit.

3. What is a Griess assay kit?

A colorimetric kit that turns nitrite into a coloured product read on a plate reader at around 540 nm.

4. Should I measure nitrite or total NOx?

Nitrite is usually enough for cell culture media. For serum, plasma and tissue, measure total NOx.

5. Does Biochain Incorporated supply NO assay kits outside Delhi?

Yes. Biochain supplies assay kits and test strips to labs across India.