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Amplite® Fluorimetric Monoamine Oxidase Assay Kit *Red Fluorescence*

PAO dose response was obtained with Amplite® Fluorimetric Monoamine Oxidase Assay Kit in a 96-well solid black plate using a Gemini fluorescence microplate reader (Molecular Devices).
PAO dose response was obtained with Amplite® Fluorimetric Monoamine Oxidase Assay Kit in a 96-well solid black plate using a Gemini fluorescence microplate reader (Molecular Devices).
PAO dose response was obtained with Amplite® Fluorimetric Monoamine Oxidase Assay Kit in a 96-well solid black plate using a Gemini fluorescence microplate reader (Molecular Devices).
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Spectral properties
Excitation (nm)571
Emission (nm)584
Storage, safety and handling
H-phraseH303, H313, H333
Hazard symbolXN
Intended useResearch Use Only (RUO)
R-phraseR20, R21, R22


Excitation (nm)
Emission (nm)
Monoamine oxidases (MAO) are a family of flavin-containing amine oxidoreductases that catalyze the oxidation of monoamines. They are found bound to the outer membrane of mitochondria in numerous tissues including liver, intestinal mucosa, and nerves. In humans there are two types of MAO: MAO-A and MAO-B. MAO-A is particularly important in the metabolism of monoamines ingested in food. MAOs play a major role in the inactivation of neurotransmitters. MAO dysfunction has been associated with depression, schizophrenia, substance abuse, attention deficit disorder, migraines, and irregular sexual maturation. The Amplite® Monoamine Oxidase Assay Kit provides a quick and sensitive method for the measurement of monoamine oxidase and semicarbazide-sensitive amine oxidase (SSAO) activities in blood samples and other biological samples. The kit uses our Amplite® Red substrate which enables a dual recordable mode. The signal can be easily read by either a fluorescence microplate reader or an absorbance microplate reader. With the Amplite® Monoamine Oxidase Assay Kit, we have detected as little as 1 mU/mL SSAO in a 100 µL reaction volume. It can be performed in a convenient 96-well or 384-well microtiter-plate format and easily adapted to automation.


Fluorescence microplate reader

Recommended plateSolid black


Example protocol


Protocol summary

  1. MAO standards or test samples (50 µL)
  2.  Add MAO working solution (50 µL)
  3. Incubate at room temperature for 30-60 min 
  4. Read fluorescence intensity at Ex/Em = 540/590 nm(cut off 570 nm) 

Important notes
Thaw all the kit components to room temperature before starting the experiment.


Unless otherwise noted, all unused stock solutions should be divided into single-use aliquots and stored at -20 °C after preparation. Avoid repeated freeze-thaw cycles.

1. Amplite™ Red stock solution (250X):
Add 40 µL of DMSO (Component F) into the vial of Amplite™ Red substrate (Component A). The stock solution should be used promptly. Note: The Amplite™ Red substrate is unstable in the presence of thiols such as dithiothreitol (DTT) and 2-mercaptoethanol. The final concentration of DTT or 2-mercaptoethanol in the reaction should be no higher than 10 µM. The Amplite™ Red substrate is also unstable at high pH (>8.5). Therefore, the reaction should be performed at pH 7 – 8. The provided assay buffer, pH 7.4, is recommended.

2. HRP stock solution (200X):
Add 100 µL of Assay Buffer (Component B) into the vial of horseradish peroxidase (Component C).

3. Plasma Amine Oxidase (PAO) standard solution (20 U/mL):
Add 125 µL of Assay Buffer (Component B) into the vial of Plasma Amine Oxidase Standard (Component E).


PAO standard

For convenience, use the Serial Dilution Planner: https://www.aatbio.com/tools/serial-dilution/11303

Add 50 µL of 20 U/mL PAO standard solution into 950 µL of Assay Buffer (Component B) to get 1000 mU/mL PAO standard solution (PAO7). Take 1000 mU/mL PAO standard solution and perform 1:3 serial dilutions to get remaining serially diluted PAO standards (PAO6 - PAO1). Note: Higher concentrations of PAO may cause reduced fluorescence signal due to the over oxidation of Amplite™ red substrate (to a non-fluorescent product).


Add 20 μL of Amplite™ Red stock solution (250X), 25 µL of HRP stock solution (200X) and 25 µL of MAO Substrate (Component D) into 5 mL of Assay Buffer (Component B) to make a total volume of 5.07 mL Monoamine Oxidase (MAO) working solution. Protect from light.


Table 1. Layout of PAO standards and test samples in a solid black 96-well microplate. PAO = plasma amine oxidase standard (PAO1 - PAO7, 1 to 1000 mU/mL); BL = blank control; TS = test sample.


Table 2. Reagent composition for each well

PAO1 - PAO750 µLserial dilution (1 to 1000 mU/mL)
BL50 µLAssay Buffer (Component B)
TS50 µLsample
  1. Prepare plasma amine oxidase standards (PAO), blank controls (BL), and test samples (TS) into a 96-well solid black microplate according the the layout provided in Table 1 and Table 2. For a 384-well plate, use 25 µL of reagent per well instead of 50 µL.

  2. Add 50 µL of MAO working solution into each well of the PAO standard, blank control, and test samples to make the total PAO assay volume of 100 µL/well. For a 384-well plate, add 25 µL of MAO working solution into each well instead, for a total volume of 50 µL/well.

  3. Incubate the reaction for 30 to 60 minutes at room temperature, protected from light.

  4. Monitor the fluorescence intensity with a fluorescence plate reader at Excitation = 530 - 570, Emission = 590 - 600 nm (optimal Ex/Em = 540/590 nm, cutoff = 570 nm). Note: The contents of the plate can also be transferred to a white clear bottom plate and read by an absorbance microplate reader at the wavelength of 576 ± 5 nm. However, the absorption detection will have a lower sensitivity compared to that of the fluorescence reading.


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Spectral properties

Excitation (nm)571
Emission (nm)584



View all 3 citations: Citation Explorer
An Increase in Plasma Homovanillic Acid with Cocoa Extract Consumption Is Associated with the Alleviation of Depressive Symptoms in Overweight or Obese Adults on an Energy Restricted Diet in a Randomized Controlled Trial
Authors: Ibero-Baraibar, Idoia and Perez-Cornago, Aurora and Ramirez, Maria J and Martínez, J Alfredo and Zulet, M Angeles
Journal: The Journal of nutrition (2016): 897S--904S
An increase in plasma homovanillic acid with cocoa extract consumption is associated with the alleviation of depressive symptoms in overweight or obese adults on an energy restricted diet in a randomized controlled trial
Authors: Ibero-Baraibar, Idoia and Perez-Cornago, Aurora and Ramirez, Maria J and Mart{\'\i}nez, J Alfredo and Zulet, M Angeles
Journal: The Journal of nutrition (2015): 897S--904S


View all 58 references: Citation Explorer
Monoamine oxidase-B activity is not involved in the neuroinflammatory response elicited by a focal freeze brain injury
Authors: Sanz E, Quintana A, Valente T, Manso Y, Hidalgo J, Unzeta M.
Journal: J Neurosci Res (2009): 784
Decreased monoamine oxidase (MAO) activity and MAO-A expression as diagnostic indicators of human esophageal cancers
Authors: Yang B, Jiang J, Du H, Geng G, Jiang Z, Yao C, Zhang Q, Jin L.
Journal: Biomarkers (2009): 624
Mutagenic probes of the role of Ser209 on the cavity shaping loop of human monoamine oxidase A
Authors: Wang J, Harris J, Mousseau DD, Edmondson DE.
Journal: Febs J (2009): 4569
Monoamine oxidase A and childhood adversity as risk factors for conduct disorder in females
Authors: Prom-Wormley EC, Eaves LJ, Foley DL, Gardner CO, Archer KJ, Wormley BK, Maes HH, Riley BP, Silberg JL.
Journal: Psychol Med (2009): 579
Inhibitory effect of dehydroepiandrosterone on brain monoamine oxidase activity: in vivo and in vitro studies
Authors: Perez-Neri I, Montes S, Rios C.
Journal: Life Sci (2009): 652
Monoamine oxidase B inhibitors versus other dopaminergic agents in early Parkinson's disease
Authors: Caslake R, Macleod A, Ives N, Stowe R, Counsell C.
Journal: Cochrane Database Syst Rev (2009)
Lipopolysaccharide-induced epithelial monoamine oxidase mediates alveolar bone loss in a rat chronic wound model
Authors: Ekuni D, Firth JD, Nayer T, Tomofuji T, Sanbe T, Irie K, Yamamoto T, Oka T, Liu Z, Vielkind J, Putnins EE.
Journal: Am J Pathol (2009): 1398
Anti-oncogenic and pro-differentiation effects of clorgyline, a monoamine oxidase A inhibitor, on high grade prostate cancer cells
Authors: Zhao H, Flam and V, Peehl DM.
Journal: BMC Med Genomics (2009): 55
Association of dopamine transporter and monoamine oxidase molecular polymorphisms with sudden infant death syndrome and stillbirth: new insights into the serotonin hypothesis
Authors: Filonzi L, Magnani C, Lavezzi AM, Rindi G, Parmigiani S, Bevilacqua G, Matturri L, Marzano FN.
Journal: Neurogenetics (2009): 65
Monoamine oxidase inhibitory activities of indolylalkaloid toxins from the venom of the colonial spider Parawixia bistriata: functional characterization of PwTX-I
Authors: Saidemberg DM, Ferreira MA, Takahashi TN, Gomes PC, Cesar-Tognoli LM, da Silva-Filho LC, Tormena CF, da Silva GV, Palma MS.
Journal: Toxicon (2009): 717