TR-FRET Bridge-It® L-Tryptophan Fluorescence Assay Kit for Plasma and Serum Samples, 384-well format

L-Met 1-1-1006B

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TR-FRET Bridge-It® L-Tryptophan Fluorescence Assay Kit for Plasma and Serum Samples, 384-well 



  • Quantification of Tryptophan levels in plasma and serum samples

  • Measurement of total tryptophan in plasma and serum samples

  • High throughput screening for drug discovery (please contact us for bulk discount pricing)

  • Diet and nutrition, mental health, and immunology studies



  • Easy: Treat samples to extract tryptophan, incubate, and mix test sample or standard with the Assay solution and incubate at ~25°C. No wash steps!

  • Fast: Read fluorescent signal after 30 minutes of incubation (can be read after 8 minutes)

  • Sensitive: Assay measures tryptophan at a lower limit of sensitivity of 0.1 µM

  • (i.e. 10 pmol / well in a 96-well or 2 pmol in a 384-well black microplate)

  • Flexible: Assay is adaptable to both low- and high-throughput screening formats

  • Reproducible: Inter- and Intra-assay values are 10% or less

  • High Signal to Background Ratio: TR-FRET option of the Bridge-It Assay kit gives high signal to background ratio (8+ fold) which is useful for high throughput screening and drug discovery



Comparison to ELISA: 

Bridge-It® Assay for Plasma and Serum Samples: 4 reagents, 1 hour

ELISA for Plasma and Serum Samples: 19 reagents, 18+ hours work with overnight incubation


TRF vs ELISA timeline


Background Information on Tryptophan


L-tryptophan (tryptophan) is one of eight essential amino acids that must be obtained from the diet. Tryptophan serves as a key building block for synthesis of proteins and as a precursor for various brain neurotransmitters including serotonin. Tryptophan is the only recognized precursor that can be converted into serotonin by the body. Serotonin promotes feelings of well being and calm and thereby helps to counterbalance the physiological effects of brain dopamine and the nor-adrenaline circuits which encourage fear, anger, tension, aggression, obsessive-compulsive actions, over-eating (especially of carbohydrates), migraine headache, depression, and sleep disturbances. Melatonin, a metabolite of serotonin, is a sleep promoting natural hormone made by the pineal gland. In addition, tryptophan is a key precursor for niacin (vitamin B3), a vitamin that is essential for normal respiration, metabolism, and synthesis of sex hormones. Because tryptophan plays such a critical role in the proper balancing of metabolism, mood and sleep patterns, insufficient dietary availability of this essential amino acid can lead to serious adverse consequences.


Bridge-It® L-Tryptophan Fluorescence Assay

The Bridge-It® tryptophan fluorescence assay is based on the activity of tryptophan repressor protein (TrpR), a bacterial DNA-binding protein. TrpR protein binds to its DNA-binding site in tryptophan-dependent fashion.

The central feature of this assay design is the TrpR-dependent association of two fluorochrome-labeled DNA half-fragments (one labeled with fluorescein and the other labeled with Oyster® 645 fluophore. Each fragment contains about one-half of the TrpR protein DNA-binding site. In the presence of L-tryptophan an increase in fluorescence signal can be detected as a result of the tryptophan-dependent association of the labeled DNA half-fragments. Tryptophan is readily detectable using the Bridge-It® tryptophan fluorescence assay in various types of test samples including bacterial growth medium, brain extract, yeast extract, as well as in human serum and urine. The linear range of the assay is 0.4 µM-10 µM and the minimum tryptophan detection level is ~0.1 µM. The assay is highly specific for measuring tryptophan. No significant TrpR protein binding activity was observed using the assay when L-tryptophan was replaced with each of nineteen (19) other L-amino acids (up to 100 µM) or D-tryptophan, serotonin, and the tryptophan precursor 5’HTP (up to 20 µM).

TRF Trp Standard Curve Pic


The TR-FRET Bridge-It® L-tryptophan fluorescence assay for plasma and serum samples is performed using the 96-well or 384-well microplate format and is, therefore, ideally suited for the rapid, simultaneous measurement of tryptophan in large numbers of test samples.


Pricing: The 100-well kit is a one-time trial purchase. For bulk pricing options, please contact us. For any other questions or comments, please do not hesitate to contact us. We are always happy to help!


To learn more about the TR-FRET Bridge-It technology, please visit our technology page. This product is protected patents and pending patents.


References Using Mediomics’ Bridge-It L-Tryptophan Fluorescence Assay Kit

  1. The Effect of Branched-Chain Amino Acids, Citrulline, and Arginine on High-Intensity Interval Performance in Young Swimmers. Hsueh CF, Wu HJ, Tsai TS, Wu CL, Chang CK. Nutrients. 2018 Dec 14;10(12). pii: E1979.

  2. Profiling targetable immune checkpoints in osteosarcoma. McEachron TA, Triche TJ, Sorenson L, Parham DM, Carpten JD. Oncoimmunology. 2018 Sep 11;7(12):e1475873.

  3. Branched-chain amino acids and arginine improve physical but not skill performance in two consecutive days of exercise. Lin YT, Chiu MS, Chang CK. Sci Sport. 2017 Dec; 32(6):e221-e228.

  4. Involvement of Host Defense Mechanisms against Toxoplasma gondii Infection in Anhedonic and Despair-Like Behaviors in Mice. Mahmoud ME, Fereig R, Nishikawa Y. Infect Immun. 2017 Mar 23;85(4). pii: e00007-17.

  5. Quantitative Protein Profiling of Chlamydia trachomatis Growth Forms Reveals Defense Strategies Against Tryptophan Starvation. Østergaard O, Follmann F, Olsen AW, Heegaard NH, Andersen P, Rosenkrands I. Mol Cell Proteomics. 2016 Dec;15(12):3540-3550.

  6. Challenges in the Discovery of Indoleamine 2,3-Dioxygenase 1 (IDO1) Inhibitors. Röhrig UF, Majjigapu SR, Vogel P, Zoete V, Michielin O. J Med Chem. 2015 Dec 24;58(24):9421-37.

  7. Synthetic two-way communication between mammalian cells. Bacchus W, Lang M, El-Baba MD, Weber W, Stelling J, Fussenegger M. Nat Biotechnol. 2012 Oct;30(10):991-6.



  1. Bridge-It® is a registered trademark of Mediomics, LLC, St. Louis, Missouri, U.S.A. Mediomics has a worldwide, exclusive license for this assay platform from Saint Louis University, St. Louis, Missouri.
  2. The TR-FRET Bridge-It® tryptophan fluorescence assay is intended for laboratory research use only. This product is not approved by the U.S. Government or by the government of any other country of the world for use in disease diagnosis or treatment of humans or animals.
  3. Oyster® is a registered trademark of Denovo Biolabels, GmbH, Munster, Germany.
  4. Flownamics® Analytical Instruments, Inc., Madison, Wisconsin, is the authorized U.S. distributor for Oyster® dyes.



Catalog #: TRF-1-1-1002TRP-PS384A (100 measurements-trial kit) , TRF-1-1-1002TRP-PS384B  (384 measurements)

Protocol :