# Role of Forster Resonance Energy Transfer in Graphene-Based Nanomaterials for Sensing
## 3 Application of Graphene-Based Nanomaterials in Sensing
### Biomolecule, Bacteria, and Virus Sensor  
In 2019, the FRET-based GO/aptamer complex (**G12**) was fabricated using the DNase I-assisted cyclic enzymatic signal amplification (CESA) method, and thus could be further utilized to detect specific antibiotics reported by [PERSON] et al. [69]. The synthesized aptasensor was selective to sulfadimethoxine (SD), kanamycin (KM), and ampicillin (AMP), which were linked to cyanine 3 (Cy3), 6-Carboxyfluorescein (FAM), and Cyanin 5 (Cy5), respectively (Figure 14). The fluorescence intensities of three different fluorophores, Cy3, Cy5, and FAM, were quenched through the influence of GO. The LODs of the **G12** modified aptasensor with different antibiotics were calculated to be 1.997 (SD), 2.664 (KM), and 2.337 (AMP) ng/mL, respectively. The results from the **G12** aptasensor indicated that it could detect multiple antibiotics at the same time, and its sensing approach was further evaluated in milk samples. In this work, [PERSON] and [PERSON] et al. [70] proposed a new way of synthesizing probe **G13** with the bioconjugation of antibodies with GQDs. The synthesized **G13** used for the specific detection of _Campylobacter jejuni_, which made a new distance between GO and GQDs, was fluorescent ON and FRET OFF (Figure 15). In the absence of _Campylobacter jejuni_, the distance between GO and GQD was low via \(\pi\)-\(\pi\) stacking and caused fluorescence OFF and FRET ON. The LODs were calculated to be 10 CFU/mL and 100 CFU/mL in the PBS buffer and poultry liver, respectively. Figure 13: Schematic diagrams of the FRET sensing mechanism between gGQDs and rGQDs (**G11**) with the HE4 antibody. Reprinted from [68] with permission from Elsevier. [PERSON] and [PERSON] et al. [71] synthesized a fluorescent apta-nanobiosenesor **G14** with the help of rGQDs in connection with a biological fluid. Here, rGQDs were used as an optical probe, and a biological fluid digoxin (DX) aptamer was used as a sensing element. The synthesized **G14** probe was allowed to interact with free biological aptamers, and caused fluorescence enhancement. Later, upon the addition of the targeted biological fluid DX molecule, **G14** was bound with DX and resulted in a decreased fluorescence intensity (Figure 16). Reversibility was carried out using oxidized carbon nanotubes with **G14**-DX complexation aptamers through FRET. Upon the addition of DX into the aptamer, there was a notable interconnection between CNTs and rGQDs, and thus recovery of the rGQDs. The LOD was calculated to be 29.87 \(\pm\) 1.01 \(\times\) 10\({}^{-12}\) mol L\({}^{-1}\). Alternatively, the **G14** probe with CNT and rGQDs showed a high selectivity and reproducibility towards the detection of DX, with an ultra-low detection limit of 7.95 \(\pm\) 0.22 \(\times\) 10\({}^{-12}\) mol L\({}^{-1}\). Both aptabiosensors were successfully applied in human urine and serum samples for the detection of DX biological fluid. Figure 14: Schematic representation of the GO-based aptasensor (**G12**) for antibiotics via CESA. Reprinted from [69] with permission from Nature Scientific reports. Figure 15: Schematic diagram of _Campylobacter jejuni_ detection using the antibody GQDs/GO (**G13**). Reprinted from [70] with permission from Elsevier. GURE:S6.F16][ENDFIGURE]  
[PERSON] and co-workers [72] synthesized a GQD-based fluorescent probe **G15** for the selective detection of Vi antigens. The probe iron porphyrin bio-mimicking Fe-N-GQDs were prepared using a solvothermal approach through mechanochemical mixing of Fe, N, and C sources. The prepared **G15** could act as an energy donor because of \(\pi\)-\(\pi\) stacking, and GO could act as a quencher (Figure 17). As a result of the specific antibody-antigen interaction in **G15** in the presence of the Vi antigen, the distance between the probe and GO was increased, which hindered the FRET process. When an antibody was introduced to **G15**, the fluorescence response of Fe-N-GQD/Ab was quenched because of the FRET assay.