A DNA-based nanostructure inspired by antibodies as the core of a programmable sensing platform for rapid, single-step diagnostics

by Virginia Greco

A team consisting of current and former members of the ICN2 Nanobioelectronics and Biosensors Group has developed an electrochemical sensor based on a modified DNA scaffold nanostructure able to detect antibodies and proteins in unprocessed biological fluids. It has a Y-shaped architecture that mimics the one of natural Immunoglobulin antibodies. According to the results published in an article in ‘Advanced Functional Materials’, it is selective, specific, and adaptable to the detection of different biomarkers.

The need to simplify and shorten the response time of diagnostic techniques –for conditions ranging from viral infections to cancer, to autoimmune diseases, and more— is driving the development of new biosensing platforms able to quickly and reliably detect the presence of relevant biomarkers (such as specific antibodies and proteins) directly in untreated body fluids. Current laboratory-based techniques are slow, multi-step, and require specialised personnel, while self-tests and point-of-care devices often fall short of the necessary accuracy in identifying only specific targets in low concentrations.

Among the many alternative approaches explored is the use of DNA strands as structural elements, which thanks to their complementarity can be conveniently assembled and modified to include specific recognition elements that bind to the selected target. A study recently published in Advanced Functional Materials and led by current and former members of the ICN2 Nanobioelectronics and Biosensors Group –headed by ICREA Prof. Arben Merkoçi— adopts this strategy to develop a novel DNA-based sensor for the detection of antibodies and proteins. Specifically, the authors propose a new architecture inspired by the structure of natural Immunoglobulins G (IgGs) themselves. In addition to be minimalistic and easy to assemble, it makes the most of the property of antibodies of establishing multiple simultaneous bonds.

Three segments of DNA single strands are modified at their extremities and assembled into a Y-shaped structure. This DNA ‘scaffold’ nanostructure is anchored at one end to the gold electrode of the sensing device, while the other two arms are free and devoted to binding the target antibody and to producing a measurable signal, which is made possible by the introduction at both edges of a functional group and an electroactive tag molecule, respectively.

This scaffold structure, which mimics the shape and flexibility of antibodies, is nano-engineered so as to facilitate the attachment of the target to both its free arms. It results in a bivalent binding that reduces the mobility of the DNA scaffold and, consequently, the electrochemical signal produced by the interaction of the free arms with the gold electrode. The researchers were able to measure the relative change in signal in absence or presence of the target antibody, even at low nanomolar concentrations, in untreated serum and artificial saliva. Further studies are needed to characterise and optimise the sensor in order to work with real biological saliva.

The authors of this work successfully applied the same approach to the detection of different target molecules (which required modifying the recognition functional groups) and could also prove the superior analytical performance due to the design of their structure by performing a set of tests on a few similar architectures. Thanks to the sensitivity and specificity shown, as well as its adaptable Y-shaped structure, the proposed electrochemical DNA-based biosensor could be used as a programmable sensing platform for fast (i.e., less than 15 minutes), single-step detection of antibodies and proteins in untreated biological fluids.

This work was carried out by Dr Andrea Idili, former senior researcher in the Nanobioelectronics and Biosensors Group and currently tenure-track assistant professor at the University of Rome Tor Vergata (Italy), and Dr Andrea Bonini, who worked in the same ICN2 group as a visiting PhD student and is now a postdoctoral researcher at the University of Pisa (Italy). Contributed to the study Dr Claudio Parolo and Dr Ruslán Álvarez-Diduk (from Prof. Arben Merkoçi’s group), as well as Prof. Fabio Di Francesco (from the University of Pisa).

Image credit: Dr Ruslán Álvarez/ICN2

Reference article:

Andrea Idili, Andrea Bonini, Claudio Parolo, Ruslán Alvarez-Diduk, Fabio Di Francesco, Arben Merkoçi, A Programmable Electrochemical Y-Shaped DNA Scaffold Sensor for the Single-Step Detection of Antibodies and Proteins in Untreated Biological Fluids. Adv. Funct. Mater. 2022, 2201881. DOI: 10.1002/adfm.202201881