There is an urgent need for accurate measurement tools to test for the presence of the novel coronavirus SARS-CoV-2 in samples, so that this information may be used for diagnosing the novel coronavirus infectious disease 2019 (COVID-19). Obtaining test results on the timeline of minutes is essential to limiting spread of the virus and helping individuals and communities make appropriate decisions. Alarmingly high rates of missed virus presence (false negatives) have been found using some of the current fast testing routes. Those routes typically rely on sample amplification that is time-consuming and resource-intensive, and due to their complicated multi-step sample treatments, those routes are more likely to generate false negatives. The immediate goal of this project, led by Dr. Gangli Wang and colleagues at Georgia State University, is to design and develop electrochemical sensors whose "switched-on" response to SARS-CoV-2 presence results from target interactions with specific chemical species in the nucleic acids of the virus. The response is rapidly intensified to allow for trace-level detection of virus, potentially within minutes. The design principle provides several benefits, such as drastically simplified sample pretreatment, fast turn-around time, and simplified one-step detection with greatly decreased false negative outcomes. These essential qualities pave the way for future point-of-use applications that go beyond SARS-CoV-2. The project provides a rare opportunity for fundamental measurement science to address an ongoing societal and global crisis through cutting-edge research. In addition, the project provides a rich and diverse educational experience for students and postdoctoral fellows at Georgia State University, an institution with large numbers of minority students and students from low-income backgrounds. Scientific concepts and results are disseminated through classroom teaching, local events, attendance at scientific meetings, and publications. Additional educational and outreach activities provide opportunities to many in the Atlanta Metro Area and beyond through an on-going NSF undergraduate research program and the Atlanta Science Festival, as well as several other recently established mentor programs at Georgia State University.
The enabling intellectual merit is the in-situ signal amplification mechanism in signal-on electrochemical sensors via redox cycling. The novel design drastically improves the lower limit of detection (LoD) to be competitive with and possibly surpass that of existing methods and eliminates the need for error-prone, multi-step sample treatments, such as enrichment, labeling, or amplification. The concept, employed in single-entity electrochemistry, is fundamentally different from the sample amplification strategy adopted in most nucleic acid analysis tools being used. In principle, the LoD is anticipated to approach utmost levels, i.e., single copies of ribonucleic acid (RNA) where the response time is correlated through statistical analysis. The sensor specificity to the SARS-CoV-2 specific RNA sequence(s) is based on their recognition by electrode-immobilized probes. With key components pre-assembled as integral parts of the sensor, near-zero background may be established, which is the prerequisite to improve the LoD and resolve binding of single nucleic acids. Binding with the target sequence turns on the designed electron-transfer pathway: the redox molecule on the recognition probe is then abled to repeatedly mediate electron transfers between the sensor electrode and the co-reactants in solution. The signal-on mechanism further mitigates nonspecific adsorption concerns. Individual sensors are assembled into arrays to simultaneously detect multiple target RNAs. The multiplex signal readout design represents another intellectual merit for enhanced sensor performance. The mechanistic insights from cyclic voltammetry and low LoD achieved with pulse voltammetry are envisioned as critical for the formulation of optimal and generalizable measurement methods and protocols. Synthetic samples, common biomatrices, viral RNA extractions, and virus-infected cell lysates are selected to establish calibration profiles and detection strategies. Comparison of the results with those from laboratory analysis techniques, such as reverse-transcription polymerase chain reaction, provides further validation of the sensor efficacy. In addition to offering qualitative Yes/No answers for fast testing, the sensor approach may provide quantitative information in absolute concentrations over a wide dynamic range, an outcome of great value to the COVID-19 pandemic, as well as to other on-going and future needs in the biological sensing community.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.