In recent years, the detection of proteins by using bare graphene oxide (GO) to quench the fluorescence of fluorescein-labeled aptamers has been reported. However, the proteins can be adsorbed on the surface of bare GO to prevent the sensitivity from further being improved. In order to solve this problem, polyethylene glycol (PEG)-protected GO was used to prevent the proteins using thrombin as an example from nonspecific binding. The detection limit was improved compared to bare GO under the optimized ratio of GO to PEG concentration. The results show that our method is a promising technique for the detection of proteins.

Molybdenum disulfide (MoS₂) has shown highly attractive superiority as a platform for sensing. However, DNA physisorption on the surface of MoS₂ was susceptible to nonspecific probe displacement and false-positive signals. To solve these problems, we have developed a novel MoS₂–aptamer nanosheet biosensor for detecting thrombin using a covalently linked aptamer to the MoS₂ nanosheet. Ten percent Tween 80 was used to prevent thrombin from nonspecific binding and to rapidly form thiol-DNA/gold nanoparticle (AuNP) conjugates. Furthermore, an MoS₂ and exonuclease coassisted signal amplification strategy was developed to improve the detection limit for thrombin. We used the hybridization of the aptamer molecules and the matched strand with a 5' terminal thiol to immobilize the aptamer molecules on the surface of AuNPs in [email protected]₂ nanocomposites. Exonuclease digested the single-strand aptamer and released the thrombin, which was then detected in the next recycle. With the coassisted amplification strategy, a 6 fM detection limit was achieved, showing that this method has higher sensitivity than most reported methods for thrombin detection. The results presented in this work show that this method of covalently attaching the aptamer and using the coassisted amplification is a promising technique for the detection of protein in medical diagnostics.

The mercury ion (Hg²⁺) is one of the heavy metal ions, and its presence in trace amounts can cause physiological damage to an organism. Traditional methods of Hg²⁺ detection have been useful but have also had numerous limitations and challenges, and as a result, it is important to design new and sophisticated methods that can aid in the detection of Hg²⁺. In this paper, two fluorescent dyes, carboxyfluorescein (FAM) and SYBR Green I, were used to label and intercalate DNA probes immobilized on the surface of graphene oxide (GO) for sensors to detect Hg²⁺. FAM and SYBR Green I dye share close excitation and emission wavelength spectra, which can promote and amplify the detection of signals, and also increase the limit of detection (LOD). The results showed that the limit of detection in this method was 0.53 nM. Moreover, when the sensors with double amino groups on the surface of GO were carried out to detect Hg²⁺, a limit of detection was improved to 0.43 nM. The sensors were then applied in the real sample. The results show that this method has a promising potential in Hg²⁺ detection.

Graphene oxide (GO) is widely used in sensors. The detection of proteins based on bare GO has been developed; however, the detection sensitivity needs to be improved. In this paper, a novel GO-DNA sensor for thrombin detection was developed using an aptamer linked to the surface of GO. Polyethylene glycol (PEG) was further used to prevent thrombin from nonspecific adsorption and to improve the sensitivity of the sensor for detection of thrombin. In order to improve the limit of detection for thrombin, we developed a GO and RecJf exonuclease co-assisted signal amplification strategy, and a detection limit of 24.35 fM for thrombin was achieved using this strategy. The results show that it is a promising method in analytical applications.