The phrase "assay the level" is correct and usable in written English.
It can be used in contexts where you want to evaluate or measure the extent or concentration of something, often in scientific or technical discussions.
Example: "The researchers aimed to assay the level of contaminants in the water samples collected from the river."
Alternatives: "measure the level" or "evaluate the level".
A survey was designed to assay the level of guideline compliance in Florida.
HPLC was used to assay the level of ergosterol in all transgenic P. pastoris strains containing GuSQS1.
Cells from the same cultures were used to assay the level of expression of the StrepII-tagged integrases by western blots (Table 1).
The miniantibodies were analyzed by Western blotting under reducing and non reducing conditions and after treatment of the purified miniantibodies with glycosidase PNGaseF to assay the level of glycosylation.
We used periodate oxidation followed by polyadenylation, reverse transcription, and quantitative real-time PCR (RT-qPCR) to assay the level of miR-34a in intestinal RNA isolated from the mice.
Results were expressed as levels of reactivity based on the number of standard deviations (SD) above the mean for 10 normal blood donor controls tested in the same assay; the level was considered to be raised when greater than 3 SD above the mean; that is, an antibody level of 3 or more.
In this assay, the levels of ectopically expressed p53 in mammalian cells in the absence or presence of co-expressed E6 protein are evaluated by Western blotting.
Based on the cytokine array assay, the levels of GCP-2, GRO-α, ENA-78, IGFBP-3 and LAP secreted from CAFs were lower than NAFs (Figure 2A).
By ELISA assay, the levels of CCL21 in lung lysates and serum were elevated above baseline in the group vaccinated with LPS+rPorB and then challenged with LVS, as compared with unvaccinated unchallenged mice.
Interestingly, in this assay, the levels of cholesterol which have an inhibitory effect on Kir channels are well below those typically found in plasma membranes of mammalian cells (between 30 50% of total membrane lipids [2], [3]).
We therefore decided to assay the levels of pyridine dinucleotides in the leaves of wild type and transformant plants.
