# A smartphone-integrated aptasensor for SARS-CoV-2 S1 protein using multi-walled carbon nanotube–ionic liquid modified electrodes

## TL;DR

A portable biosensor using smartphone technology and carbon nanotubes can detect SARS-CoV-2 with high sensitivity and specificity, suitable for point-of-care testing.

## Contribution

A smartphone-integrated, low-cost aptasensor using MWCNT–IL electrodes for highly sensitive SARS-CoV-2 S1 protein detection is developed.

## Key findings

- The biosensor detected SARS-CoV-2 S1 protein in buffer with a limit of detection of 0.11 fg/mL.
- The sensor maintained high specificity and accuracy in artificial saliva with a recovery range of 108% to 120%.
- A smartphone-connected system enabled detection with a limit of 0.83 fg/mL in a portable setup.

## Abstract

An aptamer-based electrochemical biosensor was developed for the highly sensitive detection of SARS-CoV-2 S1 protein using electrodes modified with a multi-walled carbon nanotube–ionic liquid (MWCNT–IL) composite. Comprehensive electrochemical and microscopic characterizations of the MWCNT–IL material were conducted, followed by the optimization of experimental parameters including ionic liquid concentration and surface modification time. Critical parameters for aptasensor construction, aptamer concentration, immobilization time, and aptamer-protein interaction time, were also optimized. Under optimal conditions, the biosensor exhibited a wide linear response from 1 fg/mL to 1 ng/mL in buffer, with a remarkably low limit of detection (LOD) of 0.11 fg/mL. Selectivity evaluations against hemagglutinin antigen (HA) and MERS-CoV-S1 (MERS) protein confirmed the sensor’s high specificity for SARS-CoV-2 S1 protein. The sensor’s applicability in artificial saliva was also successfully demonstrated, yielding accurate quantification and low detection limits (LOD: 0.16 fg/mL). Recovery studies in artificial saliva demonstrated satisfactory accuracy, with recoveries ranging from 108% to 120% and high reproducibility. Notably, the aptasensor maintained strong selectivity even in the presence of matrix interferents. Furthermore, the potential for point-of-care use was assessed via a smartphone-connected portable potentiostat. This handheld system enabled a linear detection range of 1 fg/mL to 1 ng/mL with a LOD of 0.83 fg/mL. Collectively, these results highlight the MWCNT–IL-based aptasensor as a robust, low-cost, and portable platform for rapid COVID-19 diagnostics, offering considerable promise for deployment in point-of-care and resource-constrained environments.

The online version contains supplementary material available at 10.1007/s00604-026-07918-7.