Using aptamers and SERS in an antigen-targeting assay to directly detect the OspA protein
Lyme disease is an infection spread by the bite of infected blacklegged ticks and is the fastest growing vector borne disease in the US according to the CDC, with greater than 450,000 new cases annually. If caught and treated early, the infection most often clears quickly. The person infected may have many signs and symptoms such as fever, headaches, exhaustion, and an erythema migrans-like skin rash (circular red area that sometimes clears in the middle, forming a bull’s-eye pattern). However, if not found until the later stages of infection, as is often the case, people with Lyme disease are more likely to have a lifetime of chronic symptoms including arthritis, carditis and meningitis.
While two established methods, PCR and EIA, are appropriate to address many diseases, there is a significant number of diseases that are not well served by these established techniques. One particularly important example of this is Lyme disease. The Surface-enhanced Raman scattering (SERS)-based approach described by Ionica Sciences is well adapted to direct detection of biomarkers associated with disease state without the need for other reagents or purification procedures; this makes it an emergent technology that has the potential to address the gap in testing capabilities left by PCR and EIA-based approaches.
SERS is among the most promising methods in detecting trace amounts of molecules owing to its high molecular specificity and sensitivity. SERS can produce spectral enhancement up to 1014 times. Owing to these benefits, numerous biosamples like DNA, RNA, cancer markers, bacteria, viruses, and genes have been examined using the SERS spectroscopy.
Due to the high concentrations of proteins irrelevant to the target disease, it is difficult to identify specific proteins in biological matrices. Human serum normally contains 60 to 80 g/L of total protein, although cancer biomarkers and other disease-specific proteins are frequently present at concentrations below 10 ng/L. This requires the use of recognition elements to identify the target protein within the larger, complex matrix found in many biological samples, such as aptamers. Without utilizing aptamers specific to the target protein, Outer Surface Protein A (OspA), it is extremely challenging to identify the target protein, as all proteins are made up of combinations of the same 20 amino acids, resulting in overlapping spectral contributions from all blood proteins.
To address this limitation, Dr. Joel Tabb, Dr. Eli Rapoport, Dr. Il Han, Professor John Lombardi and Dr. Omar Green from Ionica Sciences and The City College of New York developed a new diagnostic method to detect OspA, a biomarker specific to Lyme disease, which can be identified in clinical serum samples using a diagnostic platform that combines SERS and aptamers. The new research is now published in the journal Nanomedicine: Nanotechnology, Biology, and Medicine.
Two key advancements were achieved by the Ionica Sciences; first the efficiency of merging SERS and DNA aptamers for disease detection, and secondly the application of this strategy to a disease where there is a prominent need for better clinical diagnostic assay. In their studies orthogonal projections to latent structures discriminant analyses (OPLS-DA) and leave-one-out cross validation (LOOCV) statistical analyses enabled differentiation of serum from Lyme-infected individuals and from Lyme-uninfected control individuals with greater (91%) sensitivity and (96%) specificity, representing a nearly 50% increase in the sensitivity as compared to the current Lyme diagnostic assay without reduction in specificity. The authors demonstrated their new method is capable of detecting OspA at concentrations 104–105 times lower than those found in early Lyme cases, indicating that it could detect Lyme illness at the time when therapy is most effective.
In conclusion, the new ultrasensitive platform which is considered a breakthrough addresses the first evidence of a SERS and aptamer-based analytical approach that offers a significant need in the clinical laboratory setting. It is possible from the authors’ findings that adapting this novel technique to detect diseases other than Lyme disease requires only replacing the aptamer. The combination of aptamers and SERS in a diagnostic system could serve as the foundation of a diagnostic platform capable of addressing numerous clinical needs in the future beyond Lyme disease. In addition to overcoming the shortcomings of the existing Lyme assays, this novel method for the detection of biological targets may also make it easier to diagnose a number of infectious diseases that are currently underserved by PCR- or EIA-based methods.
Tabb JS, Rapoport E, Han I, Lombardi J, Green O. An antigen-targeting assay for Lyme disease: Combining aptamers and SERS to detect the OspA protein. Nanomedicine: Nanotechnology, Biology and Medicine. 2022 Apr 1;41:102528.