I’d like to think that in your typical romantic comedy Elisa is the dreadful girl the leading actor dates before he meets the girl of his dreams. However in this biochemical tale of epitope and antibody ELISA (enzyme-linked immunosorbent assay) isn’t dreadful at all. On the contrary, it serves as a very useful diagnostic tool.
The problem with most infectious diseases lies in the time lapse between accurate diagnosis and onset of treatment. The development of Point-of-Care blood and urine diagnostic kits (based on ELISA) have been crucial in the management of diseases today. Alere Inc is a major service provider for point of care solutions for diseases such as TB, Syphillis and HIV. Introducing *drumroll* Enzymatically enhanced collisions on ultramicroelectrodes (for specific and rapid detection of individual viruses).
We report the specific collision of a single murine cytomegalovirus (MCMV) on a platinum ultramicroelectrode (UME, radius of 1 μm). Antibody directed against the viral surface protein glycoprotein B functionalized with glucose oxidase (GOx) allowed for specific detection of the virus in solution and a biological sample (urine). The oxidation of ferrocene methanol to ferrocenium methanol was carried out at the electrode surface, and the ferrocenium methanol acted as the cosubstrate to GOx to catalyze the oxidation of glucose to gluconolactone. In the presence of glucose, the incident collision of a GOx-covered virus onto the UME while ferrocene methanol was being oxidized produced stepwise increases in current as observed by amperometry. These current increases were observed due to the feedback loop of ferrocene methanol to the surface of the electrode after GOx reduces ferrocenium methanol back to ferrocene. Negative controls (i) without glucose, (ii) with an irrelevant virus (murine gammaherpesvirus 68), and (iii) without either virus do not display these current increases. Stepwise current decreases were observed for the prior two negative controls and no discrete events were observed for the latter. We further apply this method to the detection of MCMV in urine of infected mice. The method provides for a selective, rapid, and sensitive detection technique based on electrochemical collisions.
Read more here: PNAS
How the concept works is simple: An antibody specific to MCMV surface protein glycoprotein B (gB) is bound to glucose oxidase (GOx). The enzyme is responsible for the oxidation of glucose to gluconolactone. It is also responsible for the reduction of ferrocenium methanol (FeMeOH+) to ferrocene methanol (FeMeOH). The oxidation of ferrocene back to ferrocenium occurs at the electrode, and this loop results in an increase in the current response. Naturally, one enzyme is not enough to result in a large enough current response to be detected. The structure of the virus (and its many surface antigens) allows the specific antibody to bind to epitopes across the viral surface, therefore amplifying the signal.
The virus generally blocks oxidation of ferrocene by non-specifically binding to the electrode surface, therefore causing a decrease in the current response. In the presence of the GOx bound anti-gB antibody the virus pre-concentrates the enzyme on its surface and when it binds to the electrode feedback is generated resulting in the positive (increase) current response.
The experiment was also performed with Murine Gammaherpesvirus 68 (MHV68), however the virus was unable to pre-concentrate GOx at its surface and no feedback loop was detected, proving the specificity of detection.
Interestingly the study also discussed the ionic strength of urine and how this contributes positively to the number of collisions at the electrode. Plus its less invasive than drawing blood (win-win!)
The researchers believe that this tool can be developed for the rapid diagnosis (as early as five days post-infection) of other viral infections such as Ebola, Zika, HIV and influenza (It’s winter – atishoo anyone?). At this stage factors such as the size of the virus and the accumulative clumping of virus-antibody complexes need to be taken into account, but further research is underway.
Sourced from Popular Science.