Antibodies, proteins produced by the immune system, bind to foreign particles in the body such as viruses or bacteria, called antigens. They are crucial diagnostic biomarkers that can inform a quick diagnosis of a medical condition in an individual. Yet measuring specific antibodies (in contrast to simply detecting their presence) remains difficult.
Researchers at UC Santa Barbara are addressing this challenge by developing technology that can provide fast, easy-to-use antibody quantification for medical testing.
E-DNA scaffold sensors, developed several years ago in chemistry professor Kevin Plaxco’s lab, have previously shown the ability to detect antibodies in small volume samples rapidly and in a single step.
“More recently we have worked hard to demonstrate they can actually have a major impact on the way we detect antibodies,” Claudio Parolo, a former Beatriu de Pinós postdoctoral fellow in Plaxco’s lab and recipient of the 2016 Lindros Award for Translating Research to Medical Practice, said in an email.
To further assess the clinical potential of E-DNA sensors, the group tested them on authentic human samples of antibodies diagnostic for HIV. The researchers then compared the performance of the E-DNA scaffold sensors against those of two current gold standard techniques for antibody quantification. Their results are published in Microsystems & Nanoengineering.
a. When the targeted antibody is absent, the DNA scaffold transfers electrons to the gold electrode. Upon antibody binding to the epitope (antigen), electron transfer is reduced. b The resultant change in electron transfer rate is detected using square wave voltammetry. Addition of the target antibody produces a decrease in the signaling current. Courtesy of Microsystems & Nanoengineering
One common method of serological testing, which measures the amount of antibodies in the blood, is the enzyme-linked immunosorbent assay (ELISA). While it delivers accurate results and can test numerous assays simultaneously, an ELISA takes up to 20 steps to carry out, hours to complete and must be performed by trained personnel using specialized equipment. Another leading technique, the lateral flow assay (LFA) — which is used in home pregnancy tests — is inexpensive, quick and simple to perform in just two steps. Still, LFAs are limited in their ability to measure multiple analytes at once, are qualitative (mostly used for “yes/no” responses) and time-sensitive, as the test must be read in a narrow time window.
Finding a way to combine the advantages offered by each immunoassay platform could enhance serological testing and enable “improved diagnosis within the timeframe of a single visit to the clinic,” according to the paper.
Parolo, the lead author of the study, and the other scientists first established a baseline analytical standard. Using real patient serum samples, some of which were HIV-positive and some HIV-negative, they determined the clinical sensitivity and specificity of ELISAs and LFAs.
The investigators aimed to match the sensitivity and specificity of these techniques in E-DNA scaffold sensors — and in two or fewer steps, in 12 minutes or fewer, in quantitative detail and without a fixed read-out time window.
The performance of the E-DNA scaffold sensors paralleled the performances of ELISAs and LFAs, the study reports. “[The E-DNA sensors] discriminated HIV-positive and HIV-negative as [well as] the other two techniques,” Parolo said.
In fact, the clinical sensitivity of E-DNA sensors exceeded that of LFAs. E-DNA scaffold sensors could also provide quantitative information about antibody levels. Although ELISAs showed better analytical sensitivity limits of antibody detection, the E-DNA sensors delivered similar results for this serum test set — but in minutes and with one step.
The researchers demonstrated the applicability of E-DNA scaffold sensors by detecting HIV-diagnostic antibodies due to a “clinical need” as well as the potential to “give a real contribution to the field of HIV-diagnosis,” according to Parolo. Nonetheless, the platform can be adapted to detect any type of antibody as long as there is a well-defined bioreceptor on the antigen to which it can bind.
“For example we could use it for the detection of anti-SARS-CoV-2 antibodies, or for the detection of antibodies produced in response to an allergic reaction, and even for validating the efficiency of a new vaccine,” Parolo said.
He continued, “We are very satisfied with the behavior of our sensors and we believe that they can represent an alternative to current serological tests … Although replacing technologies that have been out there for almost 50 years is not an easy challenge, we will do everything we can to convince people of the huge potential E-DNA scaffold sensors can have on serological studies and diagnostics.”
Now a Marie Skłodowska-Curie fellow at the Catalan Institute of Nanoscience and Nanotechnology, Parolo is continuing his work with E-DNA scaffold sensors. His current project intends to consolidate E-DNA sensors in a paper-based microchip.
“I am now trying to combine the E-DNA scaffold sensors into a cheap, environmentally friendly and safe platform made of paper,” he said.
With this, Parolo seeks to help diagnose HIV and syphilis in pregnant women. A precise diagnosis can initiate treatment to prevent mother-to-child transmission.
“I hope that during the next months I will be able to go into low income countries to test the final platform in the field.”
