Traditional DNA detection techniques, such as polymerase chain reaction (PCR), are sensitive but expensive and time-consuming, making them ill-suited for applications outside the lab. Biosensors, which integrate biological recognition with physical transducers, provide a faster and more practical alternative.
The new device is an absorbance-based optical biosensor, which provides a simple and affordable route to measuring DNA concentrations.
The Reduced Graphene Oxide Biosensor
Reduced graphene oxide (rGO) enhances biosensor performance thanks to its large surface area, conductivity, and ability to interact with biomolecules. Compared with alternatives such as gold nanoparticles, graphene oxide (GO), or carbon nanotubes, rGO combines high sensitivity with cost-effectiveness and biocompatibility.
The team hypothesized that rGO’s superior optical and structural properties would allow their sensor to overcome the limitations of conventional DNA biosensors, which often struggle with the complexity of biological samples.
The researchers synthesized rGO using a modified Hummers’ method followed by hydrothermal reduction at 175 °C, a process that restored graphene-like structures while preserving the functional groups necessary for dispersibility and bioconjugation.
This method produced layered nanosheets, the structure of which was confirmed by SEM imaging and XRD analysis. The nanosheets provided a high surface area with numerous active sites for DNA interactions.
Functionalization was achieved by linking rGO nanosheets with amino-modified probe DNA specific to E. coli. Structural and chemical characterization using FTIR, XRD, and electron microscopy verified the successful reduction of GO and the stability of the resulting material.
DNA was extracted from multiple bacterial strains to test specificity: E. coli, Bacillus subtilis, Enterococcus, Staphylococcus, and Vibrio proteolyticus. Ultraviolet-visible (UV-Vis) spectroscopy measured the changes to DNA absorbance, serving as the detection signal.
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Key Results: Sensitivity and Selectivity
The biosensor demonstrated highly sensitive detection of E. coli DNA across a concentration range of 0-476.19 fM, with a linear response and a detection limit of 80.28 fM. Increasing DNA concentrations produced rising absorbance signals at 273 nm, confirming successful hybridization of the target DNA with the probe.
Importantly, the sensor showed excellent selectivity. Non-target bacterial DNA samples produced negligible responses, with only the E. coli BL21-mediated probe generating clear signals.
The rGO sensor also exhibited superior performance compared to GO-based biosensors. While rGO produced increasing absorbance with rising DNA concentrations, GO displayed the opposite trend, a decrease in absorbance, indicating rGO’s stronger reliability and sensitivity.
Implications and Applications
By combining rGO’s optical properties with DNA probe specificity, the biosensor demonstrated a powerful platform for rapid and low-cost DNA detection. Its high sensitivity and selectivity highlight its potential for real-world applications.
Such sensors could transform how clinicians, food safety professionals, and environmental monitors detect E. coli, moving beyond costly lab-based methods to portable, efficient, and accessible systems. Tailoring probe sequences may also extend the approach to other pathogens, offering a versatile strategy for tackling microbial detection challenges.
Journal Reference
Hoang, C. N., Nguyen, S. H., Tran, M. T. (2025). Reduced graphene oxide-based absorbance biosensors for detecting Escherichia coli DNA. Scientific Reports, 15(1), 1-13. DOI: 10.1038/s41598-025-14189-4, https://www.nature.com/articles/s41598-025-14189-4
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