A fluorescent lateral flow biosensor for the quantitative detection of Vaspin using upconverting nanoparticles Muhsin Ali a , Memoon Sajid a, b , Muhammad Asad Ullah Khalid a , Soo Wan Kim a , Jong Hwan Lim a , Dongeun Huh c , Kyung Hyun Choi a, * a Department of Mechatronics Engineering, Jeju National University, Jeju, South Korea b GIK Institute of Engineering Sciences and Technology Topi, Swabi, KP, Pakistan c Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, 19104, USA article info Article history: Received 9 May 2019 Received in revised form 19 August 2019 Accepted 6 October 2019 Available online 8 October 2019 Keywords: Aptamers Upconverting nanoparticles Bioconjugation Vaspin Lateral flow biosensor abstract Vaspin is a protein present in human serum that can cause type-2 diabetes, obesity, and other cardio- vascular diseases. We report fluorescent upconverting nanoparticles (UCNPs)-based lateral flow biosensor for ultrasensitive detection of Vaspin. A pair (primary and secondary) of cognate aptamers was used that has duo binding with Vaspin. UCNPs with a diameter of around 100 nm were used as a tag to label a detection probe (secondary aptamer). A primary aptamer (capture probe) was immobilized on the test zone. Sandwich type hybridization reactions among the conjugate probe, target Vaspin, and primary aptamer were performed on the lateral flow biosensor. In the presence of target Vaspin, UCNPs were captured on the test zone of the biosensor and the fluorescent intensity of the captured UCNPs was measured through a colorimetric app under NIR. Fluorescence intensity indicates the quantity of Vaspin present in the sample. A range of Vaspin concentration across 0.1e55 ng ml 1 with a Limit of detection (LOD) 39 pg ml 1 was tested through this UCNPs based LFSA with high sensitivity, reproducibility and repeatability, whereas it’s actual range in human blood is from 0.1 to 7 ng ml 1 . Therefore, this research provides a well-suited lateral flow strip with an ultrasensitive and low-cost approach for the early diagnosis of type-2 diabetes and this could be applied to any targets with a duo of aptamers generated. © 2019 Published by Elsevier B.V. 1. Introduction Visceral adipose tissue-derived serpin (Vaspin) is considered one of the newest adipocytokine, incorporated with insulin- sensitizing effect [1], it has been potentially associated with obesity, insulin resistance, metabolic syndrome, and type-2 dia- betes [2]. Type-2 diabetes mellitus (T2DM) is a nexus metabolic disorder which has influenced more than 150 million people globally and is guessed at to become 439 million worldwide in 2030 [3]. Its prevalence is expected to increase exponentially around the world particularly in developing countries [4]. Level of Vaspin is considerably increased in type-2 diabetes patients as related to normal individuals and further increased in patients with both T2DM and coronary artery disease (CAD). Moreover, Vaspin correlates positively with body mass index, fasting plasma glucose, insulin and Homeostatic model assessment and Insulin resistant (HOMA-IR) in all patients with T2DM (P < 0.05) [5,6]. Point-of-care (POC) diagnostic devices are essential in the health safety programs because of identifying the disease bio- markers at the patient site [7 ,8]. To date, major advances have been accomplished in development of miniaturized and portable devices in the field of healthcare system for immune chromatographic strip (ICS)/lateral flow strip assay (LFSA) which became an imperative technology for the speedy analysis due to its low cost, simple handling, and less conclusion time [9e11]. LFSA was firstly intro- duced in 1956, which has later been adopted from a logical extension of technology used in latex agglutination test [12] and it can be used at patient site. Lateral flow technology generally avoids the use of standards, data processing, and usually requires the least number of steps depending on the category of POCT, satisfying the acronym "ASSURED" (Affordable, sensitive, specific, user-friendly, robust, equipment free and deliverable to end) [13]. Based on bio- receptors, two types of LFSA have been reported as immunosensors and aptasensor [14]. Furthermore, aptasensor could be generated including target induced displacement [15] and sandwich-type * Corresponding author. E-mail addresses: memoonsajid@gmail.com (M. Sajid), asadullah967@gmail. com (M.A.U. Khalid), dolage89@naver.com (S.W. Kim), jhlim@jejunu.ac.kr (J.H. Lim), amm@jejunu.ac.kr (K.H. Choi). Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa https://doi.org/10.1016/j.saa.2019.117610 1386-1425/© 2019 Published by Elsevier B.V. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 226 (2020) 117610