Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Selection, characterization, and electrochemical biosensing application of DNA aptamers for sepiapterin Shimaa Eissa a,1 , Shahad Alkhaldi a,1 , Raja Chinnappan a,1 , Ayesha Siddiqua a , Mai Abduljabbar b , Anas M. Abdel Rahman b,c,d , Majed Dasouki b , Mohammed Zourob a,b,∗ a Department of Chemistry, Alfaisal University, Al Zahrawi Street, Al Maather, AlTakhassusi Rd, Riyadh, 11533, Saudi Arabia b Department of Genetics, King Faisal Specialist Hospital and Research Center, Zahrawi Street, Al Maather, Riyadh, 11211, Saudi Arabia c College of Medicine, Alfaisal University, Riyadh, Saudi Arabia d Department of Chemistry, Memorial University of Newfoundland, St. John's, NL, Canada ARTICLE INFO Keywords: Sepiapterin reductase defciency Aptamers Electrochemical sensor Competitive biosensor Neurotransmitter ABSTRACT Sepiapterin reductase defciency (SR) is a rare inborn disorder of neurotransmitter metabolism. The early di- agnosis of SR disease should be achieved through the determination of the sepiapterin level in body fuids of suspected patients. Here, we report the selection, identifcation, and characterization of DNA aptamers against sepiapterin. The aptamer selection was achieved via the systematic evolution of ligand by the exponential en- richment technique. After ten rounds of selection, high-afnity aptamers were identifed. The binding afnities of the selected aptamers were evaluated using fuorescence binding assays showing dissociation constants ranging from 37.3 to 79.0 nM. The highest afnity aptamer was then integrated into a competitive electro- chemical biosensor. The biosensor achieved outstanding sensitivity with a detection limit of 0.8 pg/ml which was much lower than the reported chromatographic method for sepiapterin quantifcation. The aptasensor has also shown a high degree of selectivity against the closely-related compound. The aptasensor was then chal- lenged by detecting the sepiapterin in spiked serum samples where a good recovery percentage was achieved. 1. Introduction Sepiapterin reductase defciency (SR) is a rare inborn genetic error of neurotransmitter metabolism [1–3]. The SR is usually characterized by motor and cognitive abnormalities, and usually involves a pattern of involuntary and sustained muscle contractions. Unlike some other dis- orders of neurotransmitters metabolism, this disease is not associated with hyperphenylalaninemia [4]. The early diagnosis of neuro- transmitter diseases is very important to avoid the progressive neuro- logic symptoms that can be misdiagnosed as a neurodegenerative dis- order [5]. The diagnosis of SR is usually achieved by measuring the metabolites of the biogenic monoamines, serotonin and dopamine, and various pterins such as (isoxanthopterin, biopterin, neopterin, mon- apterin, primapterin, xanthopterin, sepiapterin, and 7,8-dihy- drobiopterin) in the cerebrospinal fuid [1]. Typically, decreased con- centrations of 5-hydroxyindolacetic acid and homovanillic acid, and elevated levels of 7,8-dihydrobiopterin are found in such patients [1]. However, the signifcant increase in the sepiapterin level in Cere- brospinal fuid (CSF) is the main confrmatory diagnostic test for SR. The detection of sepiapterin is challenging and can only be done in a few specialized laboratories worldwide. A High-performance liquid chromatography (HPLC) method has been reported for the detection of sepiapterin showing elevated levels in CSF of patients with SR def- ciency compared with healthy controls [6]. However, this method is still costly, time-consuming, and cannot be easily applied for high throughput screening of a large numbers of samples in newborn screening programs adopted mainly by hospitals. Therefore, the de- velopment of cost-efective, easy-to-use and rapid biosensor-based methods for the detection of sepiapterin is highly needed. Aptamers have emerged over the past few decades as excellent al- ternatives to antibodies in various biosensing platforms [7] particularly in biomedical diagnosis [8–11]. Aptamers are single-stranded DNA or RNA molecules that can bind to their target analytes with high afnity and specifcity [12,13]. They ofer several advantages over antibodies in terms of stability under various conditions, low synthesis cost, re- producibility, and ease of integration in biosensors. Several aptamers have been successfully selected against various small molecule targets [14] such as toxins [15–17], hormones [18,19], and pesticides [20] https://doi.org/10.1016/j.talanta.2020.120951 Received 27 February 2020; Received in revised form 15 March 2020; Accepted 17 March 2020 ∗ Corresponding author. Department of Chemistry, Alfaisal University, Al Zahrawi Street, Al Maather, AlTakhassusi Rd, Riyadh, 11533, Saudi Arabia. E-mail address: mzourob@alfaisal.edu (M. Zourob). 1 S. E, S. A., R. C contributed equally. Talanta 216 (2020) 120951 Available online 20 March 2020 0039-9140/ © 2020 Elsevier B.V. All rights reserved. T