Background: SARS-CoV-2 is a threat to humanity. Both the spike (S) protein and its receptor binding domain (sRBD) are extensively used for rapid detection. Although real-time reverse transcription polymerase chain reaction (rRT-PCR) is mostly used method for the molecular detection of SARS-CoV-2, rapid assays for antigenic detection are always needed. Lateral flow assays (LFAs) are the most commonly used tests for this purpose, and aptamers having stability and long shelf life are used as capture reagents. Objective: This study aimed to develop the LFAs based on the aptamer pairs for the antigenic detection of SARS-CoV-2 with the naked eye. Method: Gold nanoparticles (AuNPs) were used as labels, and six sandwich models by three different aptamers were prepared using 4 μM and 8 μM probes and two kinds of membranes for developing the LFAs. Results: The 8 μM probe concentration and M2 membrane showed the best recognition of both the synthetic sRBD and SARS-CoV-2 coming from the naso/oropharingeal swabs by designed LFAs as 100% sensitivity and 93.3% specificity compared to the antibody-detecting LFAs. Conclusions: Our developed strip assays based on aptamer pairs recognized the target directly in 5–6 min with the naked eye. It was also concluded that aptamer pairs, membrane types, assay buffers, and probe concentrations have a significant role in the detection of SARS-CoV-2 by LFAs. Highlights: The detection of SARS-CoV-2 in clinical samples was demonstrated with the best aptamer pairs, sensitively and selectively among the designed six aptamer pairs for LFAs. Developed LFAs can be an alternative method to the conventional antibody-based LFAs for SARS-CoV-2 detection.

Salmonella is among the very important pathogens threating human and animal health. It is a common food pathogen transmitted from animals to humans via contaminated food, drinking water, and air. It invades the intestinal tract of hosts and causes salmonellosis leading to death. S. enteritidis was the most common species accounted for all salmonellosis cases. S. typhimurium is also another significant species causing the serious cases worldwide. To ensure public health, early detection of pathogens is crucial. Lateral flow assay (LFA), immunochromatographic assay, is a simple and rapid diagnostic test kits used in various fields and can be developed by, aptamers, antibodies (Abs), and nucleic acids. They are also being continued to develop different capture reagents coming from the recombinant technology. It has many advantages such as having mature technology, market presence, low cost, easy to use for end users without education, and stable shelf life. Gold nanoparticles (GNPs) are the most commonly used labels in the LFAs for the naked-eye analysis. Therefore, Salmonella detection by LFA based on GNPs in a rapid and simple way is always open to be developed by new reagents and methods.

SARS-CoV-2, the causative agent of the COVID-19 pandemic, remains a significant threat to global public health. Therefore, rapid and accurate detection of the virus continues to be of critical importance. Among the specific gene regions of SARS-CoV-2, the Nucleocapsid (N) protein gene is one of the most frequently targeted for viral identification, with NIID_2019-nCOV_N being a notable example. While reverse transcriptase polymerase chain reaction (RT-PCR) remains the gold standard for diagnosis, alternative molecular detection methods are still limited. In this study, a lateral flow assay (LFA) was developed for the detection of a conserved gene region within NIID_2019-nCOV_N. Gold nanoparticles (AuNPs) were employed to enable visual detection, and the assay was designed based on nucleic acid hybridization principles. Two different membrane types (M17 and M12), three oligonucleotide probe concentrations (2, 4, and 8 µM) conjugated to AuNPs, and the assay's limit of detection (LOD) were evaluated. The target sequence from NIID_2019-nCOV_N was successfully detected by the naked eye within 5-6 min. No significant differences in performance were observed between the two membrane types across all probe concentrations, and the LOD was determined to be 1 pM. Consequently, the nucleic acid-based lateral flow assay (NABLFA) designed in this study, which targets a specific conserved base sequence, demonstrated high potential for rapid and sensitive molecular detection of SARS-CoV-2. Furthermore, this approach may be adapted for the identification of emerging viral variants or future outbreaks.