(C) UVCvis absorption spectra of QBs and QDs, respectively

(C) UVCvis absorption spectra of QBs and QDs, respectively. about one order of magnitude improvement in analytical sensitivity compared to standard platinum nanoparticle-based LFIA. In addition, the developed QB-LFIA performed well in clinical study in dynamic monitoring of serum antibody levels in the whole course of SARS-CoV-2 contamination. In conclusion, we successfully developed a encouraging fluorescent immunological sensing tool for characterizing the host immune response to SARS-CoV-2 contamination and confirming the acquired immunity to COVID-19 by evaluating the SRAS-CoV-2 total antibody level in the masses. 1.?Introduction Since early December of 2019 and up to November 18, 2020, over 54 million cases of coronavirus disease 2019 (COVID-19) caused by novel coronavirus (SARS-CoV-2) contamination, with over 1.9 million deaths have been reported in 223 countries [1]. The timely and accurate diagnosis of SARS-CoV-2 infections is crucial for e? ;ectively managing the infected patients and controlling the epidemic of SARS-CoV-2 in a population [[2], [3], [4]]. Currently, the detection of viral nucleic acid using reverse transcription-polymerase chain reaction (RT-PCR) has been widely regarded as the gold standard for confirming SARS-CoV-2 infection [[5], Hoechst 33258 analog 2 [6], [7]]. However, the accessibility and reliability of this method was largely compromised by the high test cost, the delayed feedback of test results, the need of specialized instrument, high-level biosafety laboratories and skilled technicians, Hoechst 33258 analog 2 as well as the high false negative rates (even up to 30 %30 %) [[8], [9], [10], [11]]. Increasing studies indicated that COVID-19 infection can also be determined indirectly by monitoring the host immune response to EDA SARS-CoV-2 infection [[12], [13], [14], [15]]. Serological diagnosis by measuring the level of specific antibodies against SARS-CoV-2 in the host is becoming another important approach supplemental to assist COVID-19 diagnosis because the antibodies have been reported with nearly 100 % positive rate within 2 weeks after symptom onset [16,17]. It has been reported that IgM could be found to be positive in the blood of patients even as early as the fourth day after symptom onset [8,18,19]. In addition, serological Hoechst 33258 analog 2 detection contributes not only to the better knowledge of the antibody response characteristics to SARS-CoV-2 infection, but also the extent of COVID-19 within the community and the identification of individuals who have immunity and are likely to protect against infection [16,20,21]. The total antibodies against SARS-CoV-2 are considered as the most sensitive and earliest serological marker compared to IgM or IgG, and has been recommended as the diagnosis standard for COVID-19 by the World Health Organization (WHO) [22]. Therefore, developing a rapid, sensitive and specific method for detecting total antibodies is capable of serving as a valuable and promising tool to improve the diagnosis of COVID-19 [[23], [24], [25]]. To Hoechst 33258 analog 2 date, a number of serologic testing strategies, including enzyme linked immunosorbent assay (ELISA) [26], lateral flow immunoassay (LFIA) [27], and chemiluminescent immunoassay (CLIA) [28] have been recently reported for the detection of total antibodies, IgM and IgG to SARS-CoV-2. Among the available immunoassays, LFIA has attracted increasing interest due to its simplicity, convenience, rapidity and low cost [29]. In particular, colloidal gold nanoparticle-based LFIA (AuNP-LFIA) for the detection of SARS-CoV-2 infection has experienced rapid development in a short period and some commercial products approved for serological assays have sprung up in various countries and regions [8,30,31]. However, the widespread use of AuNP-LFIA in aiding the COVID-19 diagnosis is still controversial because of its low sensitivity and high false negative rates [32,33]. Recent studies have suggested that the use of fluorescent materials Hoechst 33258 analog 2 with highly luminescent intensity as alternative LFIA label to AuNPs is beneficial to improving the analytical sensitivity [34,35]. As a novel fluorescent nanomatieral, quantum dot nanobeads (QBs) have been well demonstrated with great potential in enhancing target detection through LFIA based on their high luminescence and resistance to matrix interference [36,37]. Hence, in this work, we design and develop a QB-based LFIA (QB-LFIA) for the detection of total antibodies to SARS-CoV-2 in.

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