This study describes a simple, reliable, highly sensitive and quantitative fluorescence microplate-assay of H2O2 from activated leukocytes using a novel horse radish peroxidase (HRP) substrate N-acetyl-3,7-dihydroxyphenoxazine (A6550). Unlike the widely used fluorescent HRP substrate scopoletin, A6550 is non-fluorescent and becomes highly fluorescent upon HRP-catalyzed H2O2 oxidation. Using 50 microM A6550, the change in fluorescence due to H2O2 generated from phorbol 12-myristate 13-acetate-activated human eosinophils and neutrophils is found to have a linear cell dose response up to 1.5 x 10(4) and 5 x 10(4) cells, respectively. The increase in fluorescence from A6550 is specifically due to H2O2 generation since it is inhibitable by catalase. Oxidized A6550 is found to be highly stable and the H2O2 dose response is linear as long as the ratio of A6550:H2O2 in the reaction mixture is higher than five. Unlike scopoletin, A6550 has a very low background, which changes little with time. In addition, the high fluorescent yield of oxidized A6550 results in an increased sensitivity for the detection of H2O2. When the concentrations of A6550 and HRP were 10 microM and 0.2 U/ml, respectively, as low as 2 pmol of H2O2 could be reliably measured. The sensitivity of A6550/H2O2 assay is found to be at least 10-fold higher than with scopoletin as the HRP substrate. The protocol described in this study using A6550 to measure H2O2 release from activated granulocytes can be easily adapted to other cell types which generate H2O2.
This research output has an Altmetric Attention Score of 6. This is our high-level measure of the quality and quantity of online attention that it has received. This Attention Score, as well as the ranking and number of research outputs shown below, was calculated when the research output was last mentioned on 25 August 2026.
All research outputs
#6,780,480
of 31,591,940 outputs
Outputs from Journal of Immunological Methods
#1,258
of 5,555 outputs
Outputs of similar age
#7,135
of 39,242 outputs
Outputs of similar age from Journal of Immunological Methods
#15
of 39 outputs
Altmetric has tracked 31,591,940 research outputs across all sources so far. This one has received more attention than most of these and is in the 74th percentile.
So far Altmetric has tracked 5,555 research outputs from this source. They typically receive a little more attention than average, with a mean Attention Score of 5.6. This one has gotten more attention than average, scoring higher than 56% of its peers.
Older research outputs will score higher simply because they've had more time to accumulate mentions. To account for age we can compare this Altmetric Attention Score to the 39,242 tracked outputs that were published within six weeks on either side of this one in any source. This one has gotten more attention than average, scoring higher than 65% of its contemporaries.
We're also able to compare this research output to 39 others from the same source and published within six weeks on either side of this one. This one is in the 38th percentile – i.e., 38% of its contemporaries scored the same or lower than it.
