Citation: Alam, I.; Lertanantawong,
B.; Sutthibutpong, T.;
Punnakitikashem, P.; Asanithi, P.
Molecularly Imprinted
Polymer-Amyloid Fibril-Based
Electrochemical Biosensor for
Ultrasensitive Detection of
Tryptophan. Biosensors 2022, 12, 291.
https://doi.org/10.3390/
bios12050291
Received: 3 April 2022
Accepted: 29 April 2022
Published: 2 May 2022
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Article
Molecularly Imprinted Polymer-Amyloid Fibril-Based
Electrochemical Biosensor for Ultrasensitive Detection
of Tryptophan
Ibrar Alam
1
, Benchaporn Lertanantawong
2
, Thana Sutthibutpong
3,4,5
, Primana Punnakitikashem
6,7
and Piyapong Asanithi
1,3,4,5,
*
1
Nanoscience and Nanotechnology, Faculty of Science, King Mongkut’s University of Technology Thonburi,
Bangkok 10140, Thailand; ibrar.alam@mail.kmutt.ac.th
2
Department of Biomedical Engineering, Faculty of Engineering, Mahidol University, Salaya 73170, Thailand;
benchaporn.ler@mahidol.ac.th
3
Department of Physics, Faculty of Science, King Mongkut’s University of Technology Thonburi,
Bangkok 10140, Thailand; thana.sut@mail.kmutt.ac.th
4
ThEP Center, Commission of Higher Education, 328 Si Ayuthaya Rdad, Bangkok 10400, Thailand
5
Theoretical and Computational Science Center (TaCS), Science Laboratory Building, Faculty of Science,
King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand
6
Siriraj Center of Research Excellence in Theranostic Nanomedicine, Faculty of Medicine, Siriraj Hospital,
Mahidol University, Bangkok 10700, Thailand; primana.pun@mahidol.ac.th
7
Department of Biochemistry, Faculty of Medicine, Siriraj Hospital, Mahidol University,
Bangkok 10700, Thailand
* Correspondence: piyapong.asa@kmutt.ac.th
Abstract:
A tryptophan (Trp) sensor was investigated based on electrochemical impedance spec-
troscopy (EIS) of a molecularly imprinted polymer on a lysozyme amyloid fibril (MIP-AF). The
MIP-AF was composed of aniline as a monomer chemically polymerized in the presence of a Trp
template molecule onto the AF surface. After extracting the template molecule, the MIP-AF had
cavities with a high affinity for the Trp molecules. The obtained MIP-AF demonstrated rapid Trp
adsorption and substantial binding capacity (50
µ
M mg
−1
). Trp determination was studied using
non-Faradaic EIS by drop drying the MIP-AF on the working electrode of a screen-printed electrode.
The MIP-AF provided a large linear range (10 pM–80
µ
M), a low detection limit (8 pM), and high
selectivity for Trp determination. Furthermore, the proposed method also indicates that the MIP-AF
can be used to determine Trp in real samples such as milk and cancer cell media.
Keywords:
electrochemical impedance spectroscopy; molecularly imprinted polymer; amyloid fibril;
sensor; tryptophan
1. Introduction
Tryptophan (Trp) is an essential amino acid that acts as a precursor for niacin, mela-
tonin, and serotonin. Determining Trp can help us monitor the creation of a toxic substance
in the brain, which can cause schizophrenia, delusions, and hallucinations [
1
,
2
]. Further-
more, the pattern of Trp usage observed in cancer growth media can be utilized as a signal
for monitoring metastasis (aggressiveness) [
3
]. As a matter of fact, devising a simple ap-
proach to make Trp determination easier is important. Several techniques for determining
Trp have been developed, including liquid chromatography with fluorescence detection [
4
],
chemiluminescence [
5
], gas chromatography–mass spectrometry [
6
], high-performance
liquid chromatography [
7
], and infrared spectroscopy [
8
]. These techniques can determine
trace quantities of Trp because of their great sensitivity. The electrochemical technique is an
alternative technique that has been extensively employed because of its high sensitivity,
fast response time, miniaturization capability, low cost, low power consumption, and
Biosensors 2022, 12, 291. https://doi.org/10.3390/bios12050291 https://www.mdpi.com/journal/biosensors
