{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,22]],"date-time":"2026-07-22T23:06:32Z","timestamp":1784761592353,"version":"3.55.0"},"reference-count":46,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2022,1,22]],"date-time":"2022-01-22T00:00:00Z","timestamp":1642809600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>Stress, a state of body tension, sometimes caused by increased levels of tyrosine (Tyr) in the body, can lead to serious illnesses such as depression, irritability, anxiety, damage to the thyroid gland, and insomnia. The body can be provided with an adequate concentration of tyrosine by taking pharmaceutical products or by dietary intake. Therefore, this study presents the development of a new enzyme sensor for the quantification of Tyr in pharmaceuticals. A screen-printed carbon electrode (SPCE) was modified with the conductive polymer (CP) polypyrrole (PPy) doped with hexacyanoferrate (II) anion (FeCN), the polymer having been selected for its excellent properties, namely, permeability, conductivity, and stability. The enzyme laccase (Lacc) was subsequently immobilized in the polymer matrix and cross-linked with glutaraldehyde, as this enzyme is a thermostable catalyst, greatly improving the performance of the biosensor. The electrochemical method of analysis of the new device, Lacc\/PPy\/FeCN\/SPCE, was cyclic voltammetry (CV), and chronoamperometry (CA) contributed to the study of changes in the biosensor with doped PPy. CV measurements confirmed that the Lacc\/PPy\/FeCN\/SPCE biosensor is a sensitive and efficient platform for Tyr detection. Thus, this enzyme sensor showed a very low limit of detection (LOD) of 2.29 \u00d7 10\u22128 M, a limit of quantification (LOQ) of 7.63 \u00d7 10\u22128 M, and a very high sensitivity compared to both devices reported in the literature and the PPy\/FeCN\/SPCE sensor. Quantitative determination in pharmaceuticals was performed in L-Tyr solution of different concentrations ranging from 0.09 to 7 \u00d7 10\u22126 M. Validation of the device was performed by infrared spectrometry (FT-IR) on three pharmaceuticals from different manufacturers and with different Tyr concentrations.<\/jats:p>","DOI":"10.3390\/polym14030441","type":"journal-article","created":{"date-parts":[[2022,1,23]],"date-time":"2022-01-23T20:34:40Z","timestamp":1642970080000},"page":"441","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":19,"title":["Quantification of Tyrosine in Pharmaceuticals with the New Biosensor Based on Laccase-Modified Polypyrrole Polymeric Thin Film"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-6291-1008","authenticated-orcid":false,"given":"Ancu\u021ba","family":"Dinu","sequence":"first","affiliation":[{"name":"Department of Chemistry, Physics and Environment, Faculty of Sciences and Environment, \u201cDun\u0103rea de Jos\u201d University of Galati, 47 Domneasc\u0103 Street, RO-800008 Galati, Romania"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3823-4174","authenticated-orcid":false,"given":"Constantin","family":"Apetrei","sequence":"additional","affiliation":[{"name":"Department of Chemistry, Physics and Environment, Faculty of Sciences and Environment, \u201cDun\u0103rea de Jos\u201d University of Galati, 47 Domneasc\u0103 Street, RO-800008 Galati, Romania"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2022,1,22]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Stoikov, D., Ivanov, A., Shurpik, D., Stoikov, I., and Evtugyn, G. (2021). Flow-Through Electrochemical Biosensor with a Replaceable Enzyme Reactor and Screen-Printed Electrode for the Determination of Uric Acid and Tyrosine. Anal. Lett., 1\u201315.","DOI":"10.1080\/00032719.2021.2000621"},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Dinu, A., and Apetrei, C. (2021). Development of a Novel Sensor Based on Polypyrrole Doped with Potassium Hexacyanoferrate (II) for Detection of L-Tryptophan in Pharmaceutics. Inventions, 6.","DOI":"10.3390\/inventions6030056"},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Singh, A., Sharma, A., Ahmed, A., Sundramoorthy, A.K., Furukawa, H., Arya, S., and Khosla, A. (2021). Recent Advances in Electrochemical Biosensors: Applications, Challenges, and Future Scope. Biosensors, 11.","DOI":"10.3390\/bios11090336"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"549","DOI":"10.14429\/dsj.70.16359","article-title":"Electrochemical Biosensors for Point of Care Applications","volume":"70","author":"Karunakaran","year":"2020","journal-title":"Def. Sci. J."},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Han, A. (2021). Effects of Mindfulness-Based Interventions on Depressive Symptoms, Anxiety, Stress, and Quality of Life in Family Caregivers of Persons Living with Dementia: A Systematic Review and Meta-Analysis. Res. Aging, 016402752110434.","DOI":"10.1177\/01640275211043486"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"1091","DOI":"10.1080\/09658211.2021.1955935","article-title":"The Effects of Acute Stress on Eyewitness Memory: An Integrative Review for Eyewitness Researchers","volume":"29","author":"Marr","year":"2021","journal-title":"Memory"},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Dinu, A., and Apetrei, C. (2020). A Review on Electrochemical Sensors and Biosensors Used in Phenylalanine Electroanalysis. Sensors, 20.","DOI":"10.3390\/s20092496"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"16970","DOI":"10.1021\/ja206324q","article-title":"Oxidative Modification of Native Protein Residues Using Cerium(IV) Ammonium Nitrate","volume":"133","author":"Seim","year":"2011","journal-title":"J. Am. Chem. Soc."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Teke Kisa, P., Eroglu Erkmen, S., Bahceci, H., Arslan Gulten, Z., Aydogan, A., Karalar Pekuz, O.K., Yuce Inel, T., Ozturk, T., Uysal, S., and Arslan, N. (2021). Efficacy of Phenylalanine- and Tyrosine-Restricted Diet in Alkaptonuria Patients on Nitisinone Treatment: Case Series and Review of Literature. Ann. Nutr. Metab., 1\u201313.","DOI":"10.1159\/000519813"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"067517","DOI":"10.1149\/1945-7111\/ac0a22","article-title":"Review\u2014Recent Trends in Supramolecular Recognition of Dopamine, Tyrosine, and Tryptophan, Using Electrochemical Sensors","volume":"168","author":"Negut","year":"2021","journal-title":"J. Electrochem. Soc."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1080\/01652176.2020.1857887","article-title":"Nutritional Significance of Amino Acids, Vitamins and Minerals as Nutraceuticals in Poultry Production and Health\u2014A Comprehensive Review","volume":"41","author":"Alagawany","year":"2021","journal-title":"Vet. Q."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"101","DOI":"10.1134\/S1061934820010189","article-title":"A Chiral Voltammetric Sensor Based on a Paste Electrode Modified by Cyanuric Acid for the Recognition and Determination of Tyrosine Enantiomers","volume":"75","author":"Maistrenko","year":"2020","journal-title":"J. Anal. Chem."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"936","DOI":"10.1016\/S0022-3476(95)70031-5","article-title":"Effect of High-Dose Tyrosine Supplementation on Brain Function in Adults with Phenylketonuria","volume":"127","author":"Pietz","year":"1995","journal-title":"J. Pediatr."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"622","DOI":"10.1176\/ajp.137.5.622","article-title":"Tyrosine for the Treatment of Depression","volume":"137","author":"Gelenberg","year":"1980","journal-title":"Am. J. Psychiatry"},{"key":"ref_15","first-page":"8814236","article-title":"Therapeutic Role of Protein Tyrosine Phosphatase 1B in Parkinson\u2019s Disease via Antineuroinflammation and Neuroprotection In Vitro and In Vivo","volume":"2020","author":"Feng","year":"2020","journal-title":"Parkinson\u2019s Dis."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"131","DOI":"10.1136\/jms.7.3.131","article-title":"Use of the Phenylalanine: Tyrosine Ratio to Test Newborns for Phenylketonuria in a Large Public Health Screening Programme","volume":"7","author":"Eastman","year":"2000","journal-title":"J. Med. Screen."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Dinu, A., and Apetrei, C. (2020). Voltammetric Determination of Phenylalanine Using Chemically Modified Screen-Printed Based Sensors. Chemosensors, 8.","DOI":"10.3390\/chemosensors8040113"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Biland\u017eija, H., Ma, L., Parkhurst, A., and Jeffery, W.R. (2013). A Potential Benefit of Albinism in Astyanax Cavefish: Downregulation of the Oca2 Gene Increases Tyrosine and Catecholamine Levels as an Alternative to Melanin Synthesis. PLoS ONE, 8.","DOI":"10.1371\/journal.pone.0080823"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"259","DOI":"10.1002\/jimd.12172","article-title":"Dietary Restriction of Tyrosine and Phenylalanine Lowers Tyrosinemia Associated with Nitisinone Therapy of Alkaptonuria","volume":"43","author":"Hughes","year":"2020","journal-title":"J. Inherit. Metab. Dis."},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Dinu, A., and Apetrei, C. (2021). Development of Polypyrrole Modified Screen-Printed Carbon Electrode Based Sensors for Determination of L-Tyrosine in Pharmaceutical Products. IJMS, 22.","DOI":"10.3390\/ijms22147528"},{"key":"ref_21","first-page":"467","article-title":"Fabrication of a Novel Phenolic Compound Biosensor Using Laccase Enzyme and Metal-Organic Coordination Polymers","volume":"8","author":"Kashanian","year":"2021","journal-title":"Anal. Bioanal. Chem. Res."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"109694","DOI":"10.1016\/j.enzmictec.2020.109694","article-title":"Laccase-Catalyzed Oxidative Cross-Linking of Tyrosine and Potato Patatin- and Lysozyme-Derived Peptides: Molecular and Kinetic Study","volume":"143","author":"Li","year":"2021","journal-title":"Enzym. Microb. Technol."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"59286","DOI":"10.1039\/C5RA07233F","article-title":"Determination of Tryptophan and Tyrosine by Chemiluminescence Based on a Luminol\u2013N-Bromosuccinimide\u2013ZnS Quantum Dots System","volume":"5","author":"Li","year":"2015","journal-title":"RSC Adv."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"407","DOI":"10.1016\/S1570-0232(02)00632-3","article-title":"Gas Chromatography\u2013Mass Spectrometry Method for Determination of Phenylalanine and Tyrosine in Neonatal Blood Spots","volume":"780","author":"Deng","year":"2002","journal-title":"J. Chromatogr. B"},{"key":"ref_25","doi-asserted-by":"crossref","unstructured":"Rigobello-Masini, M., and Masini, J.C. (2012). Sequential Injection Chromatography for Fluorimetric Determination of Intracellular Amino Acids in Marine Microalgae. Amino Acid Analysis, Springer.","DOI":"10.1007\/978-1-61779-445-2_24"},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Peat, J., and Garg, U. (2016). Determination of Phenylalanine and Tyrosine by High Performance Liquid Chromatography-Tandem Mass Spectrometry. Clinical Applications of Mass Spectrometry in Biomolecular Analysis, Springer.","DOI":"10.1007\/978-1-4939-3182-8_23"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"1074","DOI":"10.1016\/j.clinbiochem.2013.05.047","article-title":"Simultaneous Determination of Phenylalanine and Tyrosine in Peripheral Capillary Blood by HPLC with Ultraviolet Detection","volume":"46","author":"Mo","year":"2013","journal-title":"Clin. Biochem."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"3527","DOI":"10.20964\/2018.04.130","article-title":"Electrochemical Determination of Tyrosine and Nitrite Using CS\/CMWNTs\/GCE-Modified Electrode","volume":"13","author":"Zhang","year":"2018","journal-title":"Int. J. Electrochem. Sci."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"14661","DOI":"10.33263\/BRIAC116.1466114672","article-title":"Rapid Electrochemical Monitoring of Tyrosine by Poly (Riboflavin) Modified Carbon Nanotube Paste Electrode as a Sensitive Sensor and Its Applications in Pharmaceutical Samples","volume":"11","author":"Manjunatha","year":"2021","journal-title":"Biointerface Res. Appl. Chem."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"23","DOI":"10.1016\/j.colsurfb.2014.09.005","article-title":"Simultaneous Determination of Norepinephrine, Acetaminophen and Tyrosine by Differential Pulse Voltammetry Using Au-Nanoparticles\/Poly(2-Amino-2-Hydroxymethyl-Propane-1,3-Diol) Film Modified Glassy Carbon Electrode","volume":"123","author":"Taei","year":"2014","journal-title":"Colloids Surf. B Biointerfaces"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"22871","DOI":"10.1039\/D0RA04015K","article-title":"Low-Cost Electrochemical Detection of l-Tyrosine Using an RGO\u2013Cu Modified Pencil Graphite Electrode and Its Surface Orientation on a Ag Electrode Using an Ex Situ Spectroelectrochemical Method","volume":"10","author":"Kavitha","year":"2020","journal-title":"RSC Adv."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"1484","DOI":"10.1016\/j.bios.2008.10.024","article-title":"Electrochemical Detection of Protein Tyrosine Kinase-Catalysed Phosphorylation Using Gold Nanoparticles","volume":"24","author":"Kerman","year":"2009","journal-title":"Biosens. Bioelectron."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"41","DOI":"10.1134\/S1023193520110063","article-title":"Electrochemical Determination of Tyrosine Using Graphene and Gold Nanoparticle Composite Modified Glassy Carbon Electrode","volume":"57","author":"Liu","year":"2021","journal-title":"Russ. J. Electrochem."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"103708","DOI":"10.1016\/j.jfca.2020.103708","article-title":"New Voltammetric Method for Determination of Tyrosine in Foodstuffs Using an Oxygen-Functionalized Multi-Walled Carbon Nanotubes Modified Acetylene Black Paste Electrode","volume":"96","author":"Feng","year":"2021","journal-title":"J. Food Compos. Anal."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"107990","DOI":"10.1016\/j.measurement.2020.107990","article-title":"Detection of L-Tyrosine by Electrochemical Method Based on Binary Mixed CdO\/SnO2 Nanoparticles","volume":"163","author":"Alam","year":"2020","journal-title":"Measurement"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"321","DOI":"10.1016\/j.cej.2013.02.074","article-title":"Laccase Immobilization on Chitosan\/Poly(Vinyl Alcohol) Composite Nanofibrous Membranes for 2,4-Dichlorophenol Removal","volume":"222","author":"Xu","year":"2013","journal-title":"Chem. Eng. J."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"10989","DOI":"10.1007\/s10854-020-03647-6","article-title":"New and Sensitive Sensor for Voltammetry Determination of Methamphetamine in Biological Samples","volume":"31","author":"Haghighi","year":"2020","journal-title":"J. Mater. Sci. Mater. Electron."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"37774","DOI":"10.1016\/j.ijhydene.2021.09.039","article-title":"The Importance of Identifying the True Catalyst When Using Randles-Sevcik Equation to Calculate Turnover Frequency","volume":"46","author":"Abdi","year":"2021","journal-title":"Int. J. Hydrog. Energy"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"673","DOI":"10.1016\/j.foodres.2012.06.010","article-title":"Novel Method Based on Polypyrrole-modified Sensors and Emulsions for the Evaluation of Bitterness in Extra Virgin Olive Oils","volume":"48","author":"Apetrei","year":"2012","journal-title":"Food Res. Int."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"4802","DOI":"10.1039\/c1an15649g","article-title":"In Situ Encapsulation of Laccase in Nanofibers by Electrospinning for Development of Enzyme Biosensors for Chlorophenol Monitoring","volume":"136","author":"Liu","year":"2011","journal-title":"Analyst"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.talanta.2018.02.053","article-title":"Fabrication of a Novel Enzymatic Electrochemical Biosensor for Determination of Tyrosine in Some Food Samples","volume":"183","author":"Varmira","year":"2018","journal-title":"Talanta"},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"648","DOI":"10.1016\/j.ijbiomac.2018.02.060","article-title":"Development of a New Paper Based Nano-Biosensor Using the Co-Catalytic Effect of Tyrosinase from Banana Peel Tissue (Musa Cavendish) and Functionalized Silica Nanoparticles for Voltammetric Determination of l-Tyrosine","volume":"113","author":"Raoof","year":"2018","journal-title":"Int. J. Biol. Macromol."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"335707","DOI":"10.1088\/0957-4484\/23\/33\/335707","article-title":"A Reduced Graphene Oxide Based Electrochemical Biosensor for Tyrosine Detection","volume":"23","author":"Wei","year":"2012","journal-title":"Nanotechnology"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"5707","DOI":"10.1007\/s11694-021-01099-y","article-title":"Enzymatic Sensing of Tyrosine in Egg and Cheese Samples Using Electrochemical Sensor Amplified with Reduced Graphene Oxide","volume":"15","author":"Moghadam","year":"2021","journal-title":"Food Meas."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"308","DOI":"10.1080\/00032719.2019.1649417","article-title":"Electrochemical Determination of Tyrosine Using a Novel Tyrosinase Multi-Walled Carbon Nanotube (MWCNT) Polysulfone Modified Glassy Carbon Electrode (GCE)","volume":"53","author":"Phelane","year":"2020","journal-title":"Anal. Lett."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"51","DOI":"10.1016\/j.orgel.2016.10.037","article-title":"Enzymatic Sensing with Laccase-Functionalized Textile Organic Biosensors","volume":"40","author":"Battista","year":"2017","journal-title":"Org. Electron."}],"container-title":["Polymers"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-4360\/14\/3\/441\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T22:05:53Z","timestamp":1760133953000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-4360\/14\/3\/441"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2022,1,22]]},"references-count":46,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2022,2]]}},"alternative-id":["polym14030441"],"URL":"https:\/\/doi.org\/10.3390\/polym14030441","relation":{},"ISSN":["2073-4360"],"issn-type":[{"value":"2073-4360","type":"electronic"}],"subject":[],"published":{"date-parts":[[2022,1,22]]}}}