The challenges posed by the COVID-19 pandemic have spurred innovation on multiple fronts. One is the development of low-cost clinical diagnostic methods. Genosensors are a case in point. Based on nucleic acids that detect simple complementary sequences of DNA or RNA, genosensors are biosensors that make mass testing possible for immediate and sensitive testing of genetic material.
A device of this type, already proven effective in detecting SARS-CoV-2, has just been produced in Brazil by a multidisciplinary team of researchers affiliated to various institutions and led by physicist Osvaldo Novais de Oliveira Junior, professor at the University of the Institute. of Physics São Carlos of São Paulo (IFSC-USP).
The analysis result can be ready in 30 minutes, for a laboratory-scale cost of less than US $ 1
per genosensor. Impedance analyzer components, a durable part of the device, cost less than $ 200. The device already exists on a laboratory scale and the technology can be transferred to any company with the means to mass produce it.
“Our genosensor can immobilize a simple DNA strip used as a capture probe. Under appropriate conditions, the immobilized strip binds to a complementary DNA strip contained in the liquid sample to be analyzed. This process, called hybridization, demonstrates the presence of SARS-CoV-2 in the sample, which can be saliva or another body fluid, “said chemist Juliana Coatrini Soares.
Soares is the first author of an article describing the research and published in Materials Chemistry Frontiers.
How does it work
The device consists of a self-assembled monolayer of 11-mercaptoundecanoic acid (11-MUA) chemically bonded to glass electrodes containing micrometric gold conductors or surfaces containing gold nanoparticles. This environment is capable of immobilizing the simple DNA or RNA strip used as a capture probe. Hybridization with the complementary strip, if present in the sample, is shown by variations in physical parameters detected by electrical or electrochemical impedance spectroscopy and localized surface plasmon resonance.
“After hybridization, there is an increase in electrical resistance on the sensor surface, which can be monitored by a low-cost impedance analyzer costing approximately $ 100, and developed in our laboratory by engineer Lorenzo Buscaglia, member of the group. Another effect of hybridization between the capture sequence and the complementary SARS-CoV-2 sequence is a shift in the absorbance peak in the transmitted spectrum, which can be monitored by localized surface plasmon resonance using a spectrophotometer, “said the chemist. Paulo Augusto Raymundo – Pereira, researcher at IFSC-USP who took part in the research.
The maximum sensitivity achieved in the study was 0.3 copies per microliter, sufficient to detect the DNA sequence in saliva or other body fluids. SARS-CoV-2 complementary sequences were also diagnosed using machine learning techniques applied to scanning electron microscope images obtained from genosensors exposed to different concentrations of complementary DNA sequences.
“By applying machine learning algorithms to image processing, we were able to achieve a high degree of accuracy in distinguishing between different concentrations of complementary SARS-CoV-2 DNA sequences,” said Raymundo-Pereira.
In the detection experiments, the sensitivity of the genosensors was verified in control samples, including a negative sequence for SARS-CoV-2 and other non-virus related DNA biomarkers. Analysis of data obtained with a multidimensional projection technique called interactive document mapping (IDMAP) showed a clear separation between complementary DNA sequences at various concentrations and samples containing a non-complementary sequence or other non-SARS-related DNA biomarkers. CoV-2.
“The advantage of using multiple detection methodologies is the versatile operating mode so that the diagnostic method can be implemented in accordance with the reality of each country, or the different regions of continental-sized countries such as Brazil. Our genosensor is also promising as a detector of genetic material from new variants of SARS-CoV-2. To do this, if the genetic sequence of the variant is known, it is sufficient to replace the simple DNA strip used as a capture probe, “explained Oliveira Junior.
The multidisciplinary team that developed the device included researchers from the São Carlos Institute of Physics of the University of São Paulo (IFSC-USP), the São Carlos Institute of Chemistry (IQSC-USP), the Institute of Mathematical Sciences and Computer Science (ICMC-USP), the Instrumentation Unit of the Brazilian Agricultural Research Society (EMBRAPA) and the Pelé Pequeno Príncipe Research Institute in Curitiba, in the state of Paraná.
The study was supported by the São Paulo Research Foundation – FAPESP through ten projects: 16 / 01919-6, 19 / 13514-9, 18 / 18953-8, 19 / 00101-8, 20 / 02938-0, 16 / 23763- 8, 19 / 07811-0, 18 / 19750-3, 14 / 50867-3 and 18 / 22214-6.
/ Public release. This material comes from the original organization and can be point in nature, modified for clarity, style and length. View in full here.