key: cord-1011002-khfmeady authors: Karakuş, Erman; Erdemir, Eda; Demirbilek, Nisa; Liv, Lokman title: Colorimetric and Electrochemical Detection of SARS-CoV-2 Spike Antigen with a Gold Nanoparticle-Based Biosensor date: 2021-08-11 journal: Anal Chim Acta DOI: 10.1016/j.aca.2021.338939 sha: 35c5c547e09ac2ce4fb21e943408126ee14dd8cf doc_id: 1011002 cord_uid: khfmeady Since emerging in China in December 2019, COVID-19 has spread globally, wreaked havoc for public health and economies worldwide and, given the high infectivity and unexpectedly rapid spread of the virus responsible—that is, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)—urged the World Health Organization to declare it a pandemic. In response, reducing the virus’s adverse effects requires developing methods of early diagnosis that are reliable, are inexpensive and offer rapid response. As demonstrated in this article, the colorimetric and electrochemical detection of SARS-CoV-2 spike antigens with gold nanoparticle-based biosensors may be one such method. In the presence of the SARS-CoV-2 antigen, gold nanoparticles aggregated rapidly and irreversibly due to antibody–antigen interaction and consequently changed in colour from red to purple, as easily observable with the naked eye or UV-Vis spectrometry by way of spectral redshifting with a detection limit of 48 ng/mL. Moreover, electrochemical detection was achieved by dropping developed probe solution onto the commercially available and disposable screen-printed gold electrode without requiring any electrode preparation and modification. The method identified 1 pg/mL of the SARS-CoV-2 spike antigen and showed a linear response to the SARS-CoV-2 spike antigen ranging from 1 pg/mL to 10 ng/mL. Both methods were highly specific to detecting the SARS-CoV-2 antigen but not other antigens, including influenza A (i.e. H1N1), MERS-CoV and Streptococcus pneumoniae, even at high concentrations. infectivity and rapid spread have posed serious threats across the globe, as evidenced by the 35 steep rise in mortality in the past 16 months, during which time more than 3.2 million people 36 have died worldwide [5, 6] . 37 On 31 January 2020, the World Health Organization listed COVID-19 as a "Public Health 38 Emergency of International Concern" [1] . The disease's well-known symptoms usually begin 39 with a fever and difficulty with breathing, followed by a severe cough and other acute 40 symptoms, and may even result in death [7, 8] . However, asymptomatic cases have also been 41 reported [9,10]. With or without symptoms, the dramatic increase in the number of cases of 42 COVID-19 has driven high demand for diagnostic tests to confirm the virus's presence rapidly, 43 accurately and selectively [11] [12] [13] [14] . To date, the process of developing such tests has confirmed 44 that spike (S), envelope (E), membrane (M) and nucleocapsid (N) are the significant structural 45 proteins for coronavirus particles [15] . Added to that evidence, various studies have indicated 46 that the spike protein plays the most important role in the virus's entry and binding to the human Although those methods afford considerable convenience in detecting SARS-CoV-2 and 54 COVID-19 and its progression, most of them share certain limitations. For example, the most 55 commonly used and arguably most reliable method, reverse transcription RT-PCR, which can 56 detect viral genetic material (i.e. RNA) in samples collected with nasopharyngeal swabs, its 57 administration requires highly trained personnel, which prevents its general application and 58 use. It is also a time-consuming method, one entailing long nucleic acid extraction, and has 59 been prone to giving false negatives [30] . Given such limitations in the most frequently used, 60 reliable method, a much simpler, faster, more sensitive method has been needed to detect 61 SARS-CoV-2, provide timely treatment to patients and prevent the spread of the disease. Therefore there is a continuous demand for selective, rapid, repeatable, cost-effective, ready-63 to-use, and ultrasensitive biosensors. Against that background, the demand for rapid, selective, 64 repeatable, cost-effective, ready-to-use, ultrasensitive biosensors has continually risen. Of the assay is a simple, direct method of visual detection that does not require any complicated 68 equipment. Metal nanoparticle-based colorimetric assays are commonly used to diagnose 69 diseases in humans, and the development of those biosensors has also enabled the development 70 of rapid colorimetric diagnostic tests that can be used even at home. In particular, gold 71 nanoparticles (AuNPs) are often used in colorimetric assays due to their easy synthesis, low In this article, we present the design, synthesis and spectral features of an AuNP-based 84 biosensor platform for detecting the SARS-CoV-2 spike antigen with high selectivity and 85 sensitivity. The detection process relies on two techniques: a voltammetric method and an 86 optical sensing method using the naked eye or UV-Vis spectrophotometry. The SARS-CoV-2 spike antigen was diluted serially at 250, 500, 750, 1000, and 2000 ng mL - Because selectivity is a crucial parameter for detection, the selectivity of our AuNP-mAb 282 probe was tested with different types of spike antigens, including the influenza A antigen (i.e. AuNPs-mAb had few oxidation peaks but two well-defined reduction peaks at 205 mV and -310 50 mV (Fig. 6 ). In particular, the peak at -50 mV decreased with the addition of the SARS- indicate the satisfactory selectivity of the proposed sensing method. As given in Table S1 , 336 AuNPs-mAb exhibited comparative advantages over other published studies previously in 337 terms of diversity of the sensing methods and detection limit (Table S1) . CoV-2 spike antigen, the relative standard deviation and recovery values for both optical and 347 electrochemical methods varied from 2.2% to 4.8% and 94.1% to 102.2%, respectively (Table 348 1). Absorbance spectra and voltammograms for the spiked and non-spiked saliva sample appear 349 in Fig. S5 . The graphs exhibited that our sensing media (AuNPs-mAb) was not affected by the 350 J o u r n a l P r e -p r o o f saliva matrix. The results generally suggest that the method offers good precision and trueness, 351 thus a good accuracy. 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