## 4 Graphene/Graphene Oxide-Based RF Biosensing Platforms  
### Graphene Oxide-Based Passive RF Biosensors  
Table 3 summarizes the passive RF biosensors combined with GO or rGO for detecting biomolecules, such as glucose, biotin, streptavidin, and DNA, in the past decade. These sensing schemes based on a wafer substrate mainly focused on validation as RF biosensors via diverse RF sensing parameters, e.g., resonant frequency, reflection or transmission coefficient, transmission line (TL) parameters, and impedance.  
The tabulated RF biosensors are based on three kinds of passive RF devices and circuits--transmission line [66], capacitor [67], and resonator [68]. First, the rGO-ground-signal-ground (GSG) electrode-based RF sensing scheme was validated with TL parameters, i.e., resistance (R), inductance (L), conductance (G), and capacitance (C), as sensing parameters with different glucose concentrations (Figure 5a) using the measured scattering-parameter (S-parameter). Here, rGO was functionalized with a phenylbutyric acid (PBA) linker to detect glucose molecules (Figure 5b). [PERSON] et al. showed that the resistance was the most critical parameter for monitoring the glucose level with stable linearity and small fluctuation.  
The other sensing schemes focused on validating RF biosensors through the resonant frequency shift with different analyte concentrations. Furthermore, the coplanar waveguide (CPW)-resonator-based sensing scheme examined the RF characteristics of impedance and permittivity for DNA sensing in the broad frequency region, i.e., 0.5 GHz to 26 GHz.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sensing** & **Target Gas** & **Sensitivity** & **LOD** & **Response Time** & **Ref.** \\ \hline Graphene (\({}^{1}\) MPCVD) & NO\({}_{2}\) & 1141\% & 785 ppt & 2 s & [58] \\ Graphene (CVD) & NH\({}_{3}\) & 9.3 \(\times\) 10\({}^{-5}\) ppm\({}^{-1}\) & 17 ppm & 10 min & [59] \\ rGO & \({}^{2}\) DMMP & \(\Delta\)R/R0 \(>\) 10\% & 50 ppm & 150 s & [60] \\ Pd-3 PANI-rGO & H\({}_{2}\) & \(\Delta\)R/R0 \(=\) 25\% & 1 vol\% & 20 s & [61] \\ AgNPs+rGO & NH\({}_{3}\) & \(\Delta\)R/R\({}_{0}\) = 6.52\% & 1 ppm & 70 s & [62] \\ ZnO+rGO & Chloroform vapor & \(\Delta\)R/R\({}_{0}\) = 1.75\% & 20 ppm & 10 s & [63] \\ Ni-doped SnO\({}_{2}\)/GO & Acetone & \(\Delta\)G/C\({}_{0}\) = 27.5\% & 200 ppm & 5.4 s & [64] \\ GO- SnO2 & Ethanol & R\({}_{a}\)/R\({}_{b}\) = 160 & 200 ppm & - & [65] \\ \hline \hline \end{tabular}  
* MPCVD, \({}^{2}\) DMMP, and \({}^{3}\) PANI represent the microwave plasma chemical vapor deposition, dimethyl methylphosphonate, and polyaniline, respectively.  
\end{table}
Table 2: Performance between graphene and graphene derivatives in gas sensors.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sensing Materials** & **Analytes** & **Operating** & **LOD/** & **RF Devices** & **System** (Forms)** & **Ref** \\
**(Agents)** & & **Frequency** & **Sensitivity** & **Rf** & **Devices** & **Systems** \\ \hline rGO & Glucose & 0.5–4.5 GHz & 3 \(\times\) 10\({}^{-5}\) mol/L & \({}^{1}\) GSG electrode & TL & (\({}^{3}\) HR-Si) & [66] \\ (2 rBA) & Glucose & 0.5–4.5 GHz & 3 \(\times\) 10\({}^{-5}\) mol/L & \({}^{1}\) GSG electrode & & Resonator \\ GO & & & & & (Hof-Si) & [67] \\ (Biotin-5 PEG-NH\({}_{2}\)) & & & & & (Hof-Si) & [68] \\ GO & \({}^{6}\) DNA & 0.5–26 GHz & 1 \(\mu\)g/mL & \({}^{7}\) CPW—resonator & Resonator & [68] \\ (Chitosan) & & & & & (Glass) & [68] \\ \hline \hline \end{tabular}  
* GSG, \({}^{2}\) PBA, \({}^{3}\) HR, \({}^{4}\) IDEs, \({}^{5}\) PEG, \({}^{6}\) DNA, and \({}^{7}\) CPW represent the ground-signal-ground, pyrene butyric acid, high-resistivity, interdigital capacitor electrodes, polyethylene glycol, deoxyribonucle acid, and coplanar waveguide, respectively.  
\end{table}
Table 3: GO/rGO-based passive RF biosensors for wireless biosensing platform.