DNA Aptamer Gold Nanoparticle Colorimetric Diagnostic Test Kit of Saliva Samples for SARS_Cov2 Virus Linked to Mobile Phone Application (Aptamex™)

The development of the use of DNA aptamers for clinical applications to detect human diseases is at the forefront of research. Synthetic DNA aptamers are easy to generate, inexpensive, highly specific and have been postulated to replace antibodies for research and clinical use. Despite the considerable amount of published work on the use of DNA aptamers for research use, to date they have not been exploited for clinical diagnostics. SARS-CoV-2 virus is a pandemic causing a global disruptive event preventing people from travel, work and leisure activities resulting in a major health crisis, hospital overloads and a high death rate. The detection of SARS-CoV-2 virus in communities is therefore very important, especially for returning normality of life. The current gold standard for detection of SARS-CoV-2 virus is RT-PCR, a technique that is relatively expensive and most importantly with a slow turnaround time between sample procurement and result. This paper describes the development of a rapid, accurate, low-cost, facile to use assay for the detection of the SARS-CoV-2 spike protein in saliva. The assay exploits a simple system based on the use of a gold nanoparticle-aptamer complex, that can be easily produced and distributed, facilitating its deployment to the point-of-need, potentially reaching millions of individuals in resource-limited settings. The proposed colorimetric diagnostic test kit uses a SARS-CoV-2 DNA aptamer adsorbed on gold nanoparticles and salt-induced aggregation to detect the presence of SARS-CoV-2 Spike protein in saliva samples indicated by a color change of the gold absorbance spectrum that can be quantified by a spectrophotometer, linked to a mobile phone for data processing and analysis. The assay parameters were optimized and then tested in a field calibration clinical test in Indonesia. At a research level, a limit of detection of ca. 1.25 nM to synthetic spike protein (S1) was observed and a method to test human saliva samples developed. The DNA aptamer was specific to SARS-CoV-2, with minor cross-reactivity observed with MERS and SARS-CoV-1, but negligible cross-reactivity seen with common cold coronaviruses. A calibration clinical test of patients in Indonesia demonstrated a classification resulting in a > 97% sensitivity and a > 97% specificity compared with saliva RT-PCR test for SARS-CoV-2. Furthermore, the data indicates that anatomical location and sample type (swab vs saliva) can affect RT-PCR results. In conclusion, we have developed the use of a robust and reproducible aptamer-gold nanoparticle assay for clinical diagnostic use based on a colorimetric system that is cheap, simple, rapid, sensitive and can be employed for large scale testing of human populations for SARS-CoV-2 virus.