Researchers at the University of South Africa’s Institute for Nanotechnology and Water Sustainability have engineered an electrochemical aptasensor that can detect vanishingly small quantities of the SARS-CoV-2 spike glycoprotein in real wastewater samples. The device, described in the journal Discover Electrochemistry, combines the conducting polymer polyaniline with gadolinium telluride selenide quantum dots capped with 3-mercaptopropionic acid, creating a nanocomposite platform on which a thiolated aptamer specific to the spike protein is immobilised. The team reports a limit of detection of 0.04 femtomolar, a figure that places the sensor among the most sensitive electrochemical approaches for this target published to date.
The rationale behind the design rests on the complementary strengths of its two nanomaterials. Polyaniline is prized among conducting polymers for its mechanical robustness, low cost, electrical conductivity and chemically active conjugated backbone of alternating diamine and diimine units. However, its conductivity drops markedly at neutral pH, precisely the condition under which environmental water samples are typically analysed. Quantum dots, by contrast, offer quantum confinement effects, abundant edge sites and favourable electronic properties. By marrying the two, the researchers aimed to create a synergistic nanocomposite in which the quantum dots act as electron mediators, reducing charge transfer resistance and compensating for polyaniline’s weakness at neutral pH.
Fabrication began with the aqueous synthesis of the quantum dots themselves. Gadolinium chloride was combined with 3-mercaptopropionic acid in an alkaline solution, where the deprotonated thiol groups coordinated to the rare-earth metal, a transition signalled by the solution turning from clear to white. Separate sodium borohydride reductions of tellurium and selenium powders generated the chalcogenide precursors, which were injected sequentially into the gadolinium solution, the more reactive tellurium first. After refluxing at 100 degrees Celsius for an hour under anaerobic conditions, the reaction was quenched in an ice bath and the product washed and centrifuged. The result was a water-soluble, thiol-capped quantum dot suitable for biological interfacing.
The polyaniline layer was grown directly on a glassy carbon electrode by electropolymerising aniline in hydrochloric acid over thirty cyclic voltammetry cycles, producing the thin green deposit characteristic of the emeraldine salt form. This form matters: of polyaniline’s three redox states, only the emeraldine salt is both electrically conductive and stable in air and moisture, unlike the fully oxidised pernigraniline or the fully reduced leucoemeraldine. The nanocomposite was then co-deposited from a solution containing aniline, the quantum dots and acid, with the carboxylic acid termini of the capping ligand activated by EDC and NHS chemistry to form stable amide bonds with the amine groups of the polymer.
Spectroscopic characterisation confirmed the chemistry. Fourier transform infrared spectra of the nanocomposite showed a new band at 881 wavenumbers assigned to the gadolinium-sulfur stretching vibration, alongside shifts at 2977 and 1639 wavenumbers consistent with conversion of the carboxylic acid group into an amide linkage. Raman spectroscopy of the modified electrode revealed the characteristic D and G bands of graphitic carbon, with a decreasing defect-to-graphitic ratio indicating that the polymer coating dominated over disordered carbon sites. X-ray diffraction confirmed a cubic crystal structure for the quantum dots with crystallite sizes between 10 and 32 nanometres, averaging 17 nanometres.
Imaging and scattering analyses added further detail. Scanning electron microscopy showed quantum dot nanocrystals bound along the polymer nanofibres in a well-defined distribution, and energy-dispersive X-ray spectroscopy detected carbon, oxygen, sulfur, nitrogen, tellurium and selenium, with gadolinium present only in trace amounts, a limitation the authors attribute to the detection threshold of the EDS system. Small-angle X-ray scattering revealed that the quantum dots adopt core-shell shapes while the composite takes on a dumbbell geometry, and that introducing the dots onto polyaniline actually reduced particle size, improving dispersion and preventing the agglomeration that could otherwise impair conductivity and sensing performance.
The sensing element itself is a thiolated aptamer, a short single-stranded DNA sequence that folds into a defined three-dimensional structure upon binding its target. The team compared thiolated and non-thiolated versions of the CoV-RBD-4C aptamer and found the thiolated variant superior, reaching optimal electrocatalytic performance after just seven minutes of incubation in the presence of 10 nanomolar spike glycoprotein, compared with eleven minutes for the non-thiolated version. The rapid response reflects the strong covalent attachment achieved through thiol-ene chemistry between the aptamer’s thiol group and alkene functionalities on the nanocomposite surface, which produces a well-oriented monolayer with improved accessibility and stability. Bovine serum albumin was then applied to block any remaining non-specific binding sites.
When the finished sensor was exposed to increasing concentrations of spike glycoprotein, the anodic current decreased in proportion to concentration, an inverse relationship the authors explain through the aptamer’s conformational switch. Upon binding the spike protein, the aptamer folds into its three-dimensional recognition structure, and the resulting electrostatic repulsion hinders electron transfer through the film. Using square wave voltammetry across a concentration range of 0 to 0.95 femtomolar in phosphate-buffered saline, the team obtained a linear response between 0.45 and 0.80 femtomolar, with a limit of detection of 0.04 femtomolar and a limit of quantification of 0.4 femtomolar, alongside a sensitivity of 7.55 times ten to the minus four microamperes per femtomolar.
The critical test came with real environmental samples. Effluents from two South African wastewater treatment plants, Darville and Goudkoppies, were spiked with spike glycoprotein at three concentrations spanning 0.40 to 0.80 femtomolar. The sensor achieved recoveries of 98.6 to 101.4 percent with relative standard deviations below 1.4 percent in the Darville samples, and 91.5 to 103.1 percent with deviations up to 2.5 percent at Goudkoppies, performance figures that demonstrate the device can function in the chemically complex matrix of treated wastewater rather than only in idealised buffer solutions.
The implications extend beyond the current pandemic. Wastewater-based epidemiology has relied largely on reverse transcription polymerase chain reaction, the gold standard, but that approach requires laboratory infrastructure that many low-income and rural regions lack. Because the aptasensor is portable, inexpensive and amenable to miniaturisation, the authors suggest it could serve as an alternative environmental or clinical diagnostic tool during future disease outbreaks, and potentially be adapted to other biomarkers. They note that further work should optimise the number of electropolymerisation cycles to probe stability, and test the sensor against structurally similar proteins to fully establish its selectivity and durability in the field.
Subject of Research: An electrochemical aptasensor combining polyaniline and gadolinium telluride selenide quantum dots for ultrasensitive detection of SARS-CoV-2 spike glycoprotein in wastewater
Article Title: Polyaniline metal dichalcogenide-based amplified aptasensor for SARS-CoV-2 spike glycoprotein detection in wastewater
Article References: Gazu, N. T., Fuku, X., Cabunda, Z. N., Mamba, B. B., & Feleni, U. (2026). Polyaniline metal dichalcogenide-based amplified aptasensor for SARS-CoV-2 spike glycoprotein detection in wastewater. Discover Electrochemistry, 3(1), Article 59. https://doi.org/10.1007/s44373-026-00146-x
Image Credits: AI Generated
DOI: 10.1007/s44373-026-00146-x
Keywords: aptasensor, SARS-CoV-2, spike glycoprotein, wastewater surveillance, polyaniline, quantum dots, electrochemical biosensor, nanocomposite, thiolated aptamer, gadolinium telluride selenide, femtomolar detection, waterborne epidemiology
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Kristina Jarvis. (September 30, 2026). Conducting Polymer and Quantum Dot Sensor Detects Traces of SARS-CoV-2 in Wastewater. Scienmag. https://scienmag.com/conducting-polymer-and-quantum-dot-sensor-detects-traces-of-sars-cov-2-in-wastewater/
Kristina Jarvis. “Conducting Polymer and Quantum Dot Sensor Detects Traces of SARS-CoV-2 in Wastewater.” Scienmag, 30 September 2026, https://scienmag.com/conducting-polymer-and-quantum-dot-sensor-detects-traces-of-sars-cov-2-in-wastewater/. Accessed 30 September 2026.
Kristina Jarvis. “Conducting Polymer and Quantum Dot Sensor Detects Traces of SARS-CoV-2 in Wastewater.” Scienmag. September 30, 2026. https://scienmag.com/conducting-polymer-and-quantum-dot-sensor-detects-traces-of-sars-cov-2-in-wastewater/
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Tags: advanced nanomaterials for environmental pathogen detectionaptamer-based biosensors for SARS-CoV-2aptasensorconducting polymer sensors for environmental monitoringelectrochemical aptasensor for virus detectionelectrochemical biosensorfemtomolar detectiongadolinium telluride selenidelow detection limit virus sensorsnanocompositenanocomposite sensors in water quality testingnanotechnology for pandemic surveillancepolyanilinepolyaniline and gadolinium telluride quantum dotsquantum dot-based virus sensorsquantum dotsreal-time wastewater viral monitoringSARS-CoV-2SARS-CoV-2 wastewater detectionspike glycoproteinthiolated aptamerultra-sensitive viral protein detection in wastewaterWastewater surveillancewaterborne epidemiology
