November 17, 2021 -- Researchers have constructed a portable, virus-imprinted chip that detects low concentrations of SARS-CoV-2 particles in clinical samples. The chip proved to be almost 27 times more sensitive than polymerase chain reaction (PCR) tests, positioning the technology as a rapid, point-of-care test, according to research published in ACS Sensors on November 11.
"The sensor provided a rapid and sensitive detection platform with a detection limit of 57 pg/mL (3.7 copy/mL), 27-fold more sensitive than RT-PCR," wrote the authors, led by Heba Hussein, PhD, of the Animal Health Research Institute at the Agricultural Research Center in Giza, Egypt.
Biosensors such as this virus-imprinted chip have become increasingly popular for detecting pathogens in recent years due to their speed and ability to detect virus concentrations at lower levels than other diagnostic methods such as PCR.
The biosensor engineered by Hussein et al has another benefit touted by the authors: It is small enough to be portable, making it suitable for instantaneous and simple point-of-care use wherever clinical samples are collected.
"Dealing directly with clinical samples on the chip could be provided as a portable device for instantaneous and simple point of care in hospitals, airports, and hotspots," they wrote.
The new sensor is a type of impedimetric biosensor, which is a kind of electrochemical biosensor that measures changes in charge conductance and capacitance as measured by electrochemical impedance spectroscopy at the sensor surface as the selective binding of the target occurs.
The sensing platform is built on a printed electrode made of carbon nanotubes and tungsten oxide. A matrix of polymerized meta-aminophenol is layered on top and imprinted with SARS-CoV-2 particles to create the viral complementary binding sites.
In a process called "SARS-CoV-2 knock-out," the whole virus particles are removed from the imprinted matrix by an acid-washing step to create the complementary binding sites for SARS-CoV-2 detection.
The design allows the samples to be processed directly at the collection site without sample preparation and without the need for a laboratory, the authors noted.
"Patients could be diagnosed quickly within 5 [minutes] and accurately using the provided sensor by the direct application of a nasopharyngeal swab on the VIP [virus-imprinted] chip with no need of a well-equipped laboratory," the authors wrote.
To test the sensing platform, the researchers collected 23 clinical specimens from nasopharyngeal swabs obtained from suspected SARS-CoV-2 cases. Of the 23 samples, the sensor judged 20 as positive and three as negative.
The sensor results were then compared to reverse transcription PCR (RT-PCR) results. The results were the same except for one sample (S20), which came back negative on the RT-PCR test but had a positive result on the sensor.
The researchers also demonstrated that the sensor could selectively target SARS-CoV-2 by testing the sensor against a large range of other viruses, including the respiratory adenovirus; orthomyxoviruses; influenza A (H1N1, H3N2, and H5N1); influenza B; human coronaviruses (hCoVs) QC43, NL63, and 229E; and MERS-CoV.
The results showed high selectivity for SARS-CoV-2 with no obvious cross-reactivity except for the human coronaviruses, which triggered a positive cross-reactivity of 36%, and MERS-CoV, which triggered a positive cross-reactivity of 20%, the authors noted.
"A wide range of interferent viruses were used for testing the competence of the designed sensors to discriminate between the target virus from the other interference respiratory viruses," the authors wrote. "Hence, the sensor was successfully applied in the diagnosis of clinical specimens."
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