# Highly sensitive and selective detection of L-tryptophan by ECL using boron-doped diamond electrode

Emmanuel Scorsone, Samuel Stewart, Matthieu Hamel

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Emmanuel Scorsone, Samuel Stewart, Matthieu Hamel. Highly sensitive and selective detection of L-tryptophan by ECL using boron-doped diamond electrode. EUROSENSORS XXXV CONFERENCE, Sep 2023, Lecce, Italy. cea-05405534

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Submitted on 8 Dec 2025

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# Highly sensitive and selective detection of L-tryptophan by ECL using boron-doped diamond electrode†

Emmanuel Scorsone <fnref n="1" />*, Samuel Stewart <fnref n="1" /> and Matthieu Hamel <fnref n="1" />,

**Abstract:** We report here on the detection of L-Tryptophan, an essential amino-acid involved in neurological functions, using co-reactant-less electrochemiluminescence on boron doped diamond (BDD) electrode. The detection takes place through the unique production of reactive oxygen species (ROS) at the surface of the BDD electrode, which interacts with the oxidized form of L-Tryptophan to produce a luminescent intermediate species. The results show a linear trend between L-Tryptophan concentration and ECL emission peak height, with a correlation co-efficient of R² = 0.99 in the range from 0-5 µM L-tryptophan. The LOD of this method was found to be 0.77 nM. Comparing to previous work on detecting L-tryptophan these performances are highly promising. Non-ECL techniques such as HPLC (fluorescence detector), or HPLC-MS/MS achieved one level of magnitude higher in sensitivity, in the range of 10-25 nM.

**Keywords:** boron doped diamond; electrochemical sensing; electrochemiluminescence (ECL); L-Tryptophan

## 1. Introduction

L-Tryptophan is an amino acid that is essential to the metabolism of humans. It is involved in the biosynthesis of proteins but it also plays other important roles, along with it metabolites such as serotonin, in neurophysiological functions. L-Tryptophan can only be obtained through food intake and the recommended daily dose for adults is estimated to be between 250 mg and 425 mg. Low levels of the amino acid could be compensated by the consumption of L-tryptophan-based dietary supplements as a possible strategy to help in the treatment of disorders such as depression, insomnia, obesity, or Parkinson disease. Nevertheless, high levels of L-Tryptophan may also be harmful for the central nervous system and has been suggested to accelerate aging and neurodegeneration processes []. Therefore, there is a high interest for the detection of this important amino acid in biological fluids including blood, urine, saliva etc. in medical studies in particular in the area of neuroscience and oncology. A variety of analytical methods has been reported for the determination of L-Tryptophan, which includes for instance high performance liquid chromatography (HPLC), colorimetric and spectrofluorometric methods []. These methods require expensive equipment, trained personnel and are time-consuming. Therefore, there is a need for alternative solutions that are low-cost, rapid, accurate and easy to use. In this context, we have developed an ECL analytical procedure for the detection of L-tryptophan. It takes advantage of some unique properties of boron doped diamond electrodes, which include wide potential window in water, and capability to generate ROS that do not adsorb to the electrode surface and therefore are available for interacting with L-tryptophan to generate a strong ECL signal. This paper reports on the analytical performances of such detection system.

<footnote n="1">¹ Université Paris-Saclay, CEA, List, F-91120 Palaiseau, France</footnote>

<footnote>* Correspondence: emmanuel.scorsone@cea.fr</footnote>

<footnote>† Presented at the Eurosensors XXXIV, Lecce, Italy, 10-13 September 2023.</footnote>
## 2. Materials and Methods

Boron doped diamond electrodes were grown by microwave plasma enhanced chemical vapor deposition in a Seki Diamond AX6500 reactor, following a procedure described elsewhere []. All chemicals were purchased from Sigma-Aldrich (France) and used as received. Measurements were carried out using a dedicated 3D-printed (grey photoreactive resin, Formlabs, France) 3-electrode cell, using two 1 cm² BDD worker and counter electrodes and a platinum wire as pseudo-reference electrode. Electrochemical measurements were performed using an Autolab PGSTAT128N and the photon emission was measured with a PDM03-9107-USB PMT (ET Enterprises, U.K.).

## 3. Results and discussion

Fig.1 (Left) shows the typical electrochemical signal applied to the BDD electrode and resulting ECL emission from a solution of 500 µM L-tryptophan in phosphate buffer saline PBS (EC scan from 0 V to -3 V to +1.5 V vs Pt at 100 mV·s⁻¹). Fig.1 (Centre) shows the resulting calibration in the range 0-5 µM showing linear dependence between concentration and ECL signal. Fig.1 (Right) shows the absence of interference signal recorded in the same conditions in solutions containing a range of analog indolic compounds.

<figure><img src="image_2.png" /><figcaption>Fig.1 (Left). ECL emission from 500 µM L-tryptophan in PBS; (Centre). Calibration curve in PBS; (Right). ECL signal recorded in the same conditions from potential indolic interference compounds</figcaption></figure>

The detection mechanism was suggested to involve the formation of a dioxetane intermediate through the interaction of the oxidized form of L-Tryptophan with hydrogen peroxide produced at the BDD surface during the cathodic sweep. The LOD was found to be remarkably low with no significant interference signal observed from similar indolic compounds. The method holds high promises for the analytical detection of L-Tryptophan e.g. for medical diagnostic applications.

**Author Contributions:** "Conceptualization, E. Scorsone and S. Stewart.; methodology, S. Stewart; validation, S. Stewart; formal analysis, S. Stewart; investigation, S. Stewart; writing—original draft preparation, E. Scorsone; writing—review and editing, S. Stewart, M. Hamel, E. Scorsone.; M. Hamel, E. Scorsone.; All authors have read and agreed to the published version of the manuscript."

**Funding:** "This research received no external funding"

**Conflicts of Interest:** "The authors declare no conflict of interest."

## References

1. Majidi, M.R.; Omidi, Y.; Karami, P; Johari-Ahar, M. Reusable potentiometric screen-printed sensor and label-free aptasensor with pseudo-reference electrode for determination of tryptophan in the presence of tyrosine. *Talanta* 2016, Volume 150, 425-433.

2. Dheepthi GunaVathana, S; Thivya, P; Wilson, J; Cyrac Peter, Sensitive voltammetric sensor based on silver dendrites decorated polythiophene nanocomposite: Selective determination of L-Tryptophan. *Journal of Molecular Structure* 2020, Volume 1205, 127649.

3. Stewart, S; Scorsone, Prunier, A; Hamel, M, Novel ECL method for the determination of skatole in porcine adipose tissue, *Analytical Chemistry* 2022, 94 (16), 6403-6409.

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© 2023 by the authors. Submitted for possible open access publication under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).