Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Graphene and Its Derivatives <s> We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in concentrations up to 10(13) per square centimeter and with room-temperature mobilities of approximately 10,000 square centimeters per volt-second can be induced by applying gate voltage. <s> BIB001 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Graphene and Its Derivatives <s> Graphene has been used to explore the fascinating electronic properties of ideal two-dimensional carbon, and shows great promise for quantum device architectures. The primary method for isolating graphene, micromechanical cleavage of graphite, is di cult to scale up for applications. Epitaxial growth is an attractive alternative, but achieving large graphene domains with uniform thickness remains a challenge, and substrate bonding may strongly a ect the electronic properties of epitaxial graphene layers. Here, we show that epitaxy on Ru(0001) produces arrays of macroscopic single-crystalline graphene domains in a controlled, layer-by-layer fashion. Whereas the first graphene layer indeed interacts strongly with the metal substrate, the second layer is almost completely detached, shows weak electronic coupling to the metal, and hence retains the inherent electronic structure of graphene. Our findings demonstrate a route towards rational graphene synthesis on transition-metal templates for applications in electronics, sensing or catalysis. <s> BIB002 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Graphene and Its Derivatives <s> High-performance, transparent and stretchable electrodes are in demand for the development of flexible electronic and optoelectronic applications. Graphene is a candidate as the basis material, because of its excellent optical, electrical and mechanical properties. This paper describes a technique to grow centimetre-scale films using chemical vapour deposition on nickel films and a method to pattern and transfer the films to arbitrary substrates. The electrical conductance and optical transparency are as high as those for microscale graphene films. <s> BIB003 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Graphene and Its Derivatives <s> In this work we present a low cost and scalable technique, via ambient pressure chemical vapor deposition (CVD) on polycrystalline Ni films, to fabricate large area (∼cm2) films of single- to few-layer graphene and to transfer the films to nonspecific substrates. These films consist of regions of 1 to ∼12 graphene layers. Single- or bilayer regions can be up to 20 μm in lateral size. The films are continuous over the entire area and can be patterned lithographically or by prepatterning the underlying Ni film. The transparency, conductivity, and ambipolar transfer characteristics of the films suggest their potential as another materials candidate for electronics and opto-electronic applications. <s> BIB004 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Graphene and Its Derivatives <s> An improved method for the preparation of graphene oxide (GO) is described. Currently, Hummers’ method (KMnO4, NaNO3, H2SO4) is the most common method used for preparing graphene oxide. We have found that excluding the NaNO3, increasing the amount of KMnO4, and performing the reaction in a 9:1 mixture of H2SO4/H3PO4 improves the efficiency of the oxidation process. This improved method provides a greater amount of hydrophilic oxidized graphene material as compared to Hummers’ method or Hummers’ method with additional KMnO4. Moreover, even though the GO produced by our method is more oxidized than that prepared by Hummers’ method, when both are reduced in the same chamber with hydrazine, chemically converted graphene (CCG) produced from this new method is equivalent in its electrical conductivity. In contrast to Hummers’ method, the new method does not generate toxic gas and the temperature is easily controlled. This improved synthesis of GO may be important for large-scale production of GO as well as the ... <s> BIB005 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Graphene and Its Derivatives <s> The synergism of excellent properties of carbon nanotubes and gold nanoparticles is used in this work for bio-sensing of recombinant bovine growth hormones (rbST) by making Multi Wall Carbon Nanotubes (MWCNT) locally optically responsive by augmenting it optical properties through Localized Surface Plasmon Resonance (LSPR). To this purpose, locally gold nano particles decorated gold–MWCNT composite was synthesized from a suspension of MWCNT bundles and hydrogen chloroauric acid in an aqueous solution, activated ultrasonically and, then, drop-casted on a glass substrate. The slow drying of the drop produces a “coffee ring” pattern that is found to contain gold–MWCNT nanocomposites, accumulated mostly along the perimeter of the ring. The reaction is studied also at low-temperature, in the vacuum chamber of the Scanning Electron Microscope and is accounted for by the local melting processes that facilitate the contact between the bundle of tubes and the gold ions. Biosensing applications of the gold–MWCNT nanocomposite using their LSPR properties are demonstrated for the plasmonic detection of traces of bovine growth hormone. The sensitivity of the hybrid platform which is found to be 1 ng/ml is much better than that measuring with gold nanoparticles alone which is only 25 ng/ml. <s> BIB006 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Graphene and Its Derivatives <s> Abstract In this study an approach for the fabrication and characterization of a surface plasmon resonance (SPR) based fiber optic sensor for the detection of ethanol in 0–10 mM concentration range has been reported. The sensing probe has been prepared by coating films of silver and silicon over the unclad portion of an optical fiber followed by immobilization of enzyme (ADH) and coenzyme (NAD) entrapped hydrogel layer. The sensor works on spectral interrogation mode of operation. The resonance wavelength has been found to decrease with the increase in ethanol concentration. For the concentration range 0–10 mM, a 30 nm shift in resonance wavelength has been observed. The maximum sensitivity of the sensor has been found to be 21.70 nm/mM near zero concentration of ethanol solution. The calculated values of limit of detection (LOD) and limit of quantification (LOQ) of the sensor are 15.34 μM and 29.63 μM respectively. In addition, the sensor has high selectivity, repeatability and stability. Further, the sensor has various other advantages such as ease of operation, low cost, and fast response. Since the probe has been fabricated on optical fiber, it can work for online monitoring and remote sensing of analyte without any interference of electromagnetic fields. <s> BIB007 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Graphene and Its Derivatives <s> Abstract Reduced graphene oxide-polyaniline (rGO-Pani) nanocomposite based highly sensitive fiber optic pH sensor utilizing SPR technique is fabricated and characterized. The rGO-Pani nanocomposite is successfully synthesized using in-situ method. The sensing probe is fabricated by coating a thin film of silver over the unclad core of the optical fiber which is further coated by a film of rGO-Pani nanocomposite. The preparation of rGO, Pani and rGO-Pani nanocomposite are confirmed using different characterization tools such as X-ray diffraction (XRD), Raman and Fourier-transform infrared spectroscopy (FTIR). The morphology of the rGO-Pani nanocomposite is characterized by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The operating pH sensing range of the present sensor is checked by performing experiments on samples of pH lying from 2.4 to 11.35. The sensor's performance is excellent for low and high pH and it possesses the maximum sensitivity of 75.09 nm/pH at pH 11.35. The high sensitivity of the sensor is because of the change in the optical band gap of the rGO-Pani nanocomposite at the low and high pH values of the samples which is confirmed by using Tau plot. The sensor has many advantages such as compact size, low cost, high sensitivity, stability, repeatability and capability of remote sensing. <s> BIB008
Although few-layer graphite was synthesized around 1958, the first graphene monolayer film was prepared by Novoselov, Geim, and co-workers in 2004 by mechanical exfoliation of the highly oriented pyrolytic graphite. In this technique, graphite crystal is repeatedly peeled with adhesive tape until the monolayer is found BIB001 . Now, many techniques and methods, like chemical vapor deposition (CVD), thermal reduction, and chemical, have been developed for this. The most popular method for the preparation of the graphene oxide (GO) and reduced graphene oxide (rGO) was reported in 1958 by Hummers, in which graphite was oxidized by KMnO BIB007 and NaNO 3 in the presence of concentrated H 2 SO 4 . Later, various modifications were made by the researchers of the Hummers method, and now it is known as the modified Hummers method. GO nanosheets are the oxidized form of graphene and can be reduced by various methods  BIB005 . In the CVD method, the substrate is exposed to one or more precursors, with certain conditions, such as temperature and pressure, and the precursor reacts with the substrate and deposits the desired film over the substrate. Various transition-metal substrates, like Ni, Cu, Pd, and Ru, have been used for the preparation of graphene by the CVD process  BIB003 BIB004 BIB002 . In most of the CVD growth of graphene, Ni and Cu substrates have been used. Methane gas at 900 • C exposed over Ni forms thin graphite  . In 2006, the first experiment to prepare graphene via the CVD method was performed, in which the precursor camphor was used on Ni foil  . Nowadays, various hydrocarbons, such as methane, benzene, ethylene, and acetylene, are decomposed on various transition metals substrates, such as Ni, Cu, Au, Co, and Ru, for the preparation of graphene BIB004 . In recent years graphene, GO, reduced graphene oxide (rGO), and their nanocomposites have been extensively exploited for various biosensors, gas sensors, and chemical sensors. Graphene and its nanocomposites act as a sensing layer in various sensors, including plasmonic sensors. Since the plasmonic sensors are very sensitive to the change in the refractive index of the surrounding medium, if there is a possibility of an interaction between graphene and analyte there will be a possibility of its sensing. In such a case, one can develop a sensor using graphene and its nanocomposites. Based on this approach, a pH sensor was reported utilizing rGO and polyaniline (PANI) as sensing layers BIB008 . As is known, pH is a very important parameter and it plays a vital role in biological processes, drinking water, environment, food quality control, biochemistry, and chemical reactions. The study has utilized surface plasmon resonance on optical fibers. The rGO-Pani nanocomposite was prepared by an in situ method. Figure 15a shows the scanning electron microscope (SEM) image of Pani, in which the chain-like porous structure of Pani can be seen. Figure 15b represents the transmission electron microscope (TEM) image of rGO which depicts a very thin sheet of rGO. Figure 15c shows the SEM image of the rGO-Pani nanocomposite and Figure 15d shows the TEM image of the rGO-Pani nanocomposite. In this figure, the lighter portion in the image represents the rGO nanosheets and the darker part represents Pani. A gold nanoparticle-decorated CNTs platform was developed recently for the LSPR based sensing of bovine growth hormone BIB006 . Due to the high surface to volume ratio and favorable electron transfer reactions, CNTs were augmented with Au nanoparticles to provide synergistic effects to LSPR sensing. The properties of the unique nanocomposite were explored to absorb and sense the biomolecular interaction with increased sensitivity, as compared to individual material. A concentration as low as 1 ng/mL of rbST was detected with the composite based LSPR platform, providing a new window for ultrasensitive plasmonic detection of polypeptides and proteins. In recent years graphene, GO, reduced graphene oxide (rGO), and their nanocomposites have been extensively exploited for various biosensors, gas sensors, and chemical sensors. Graphene and its nanocomposites act as a sensing layer in various sensors, including plasmonic sensors. Since the plasmonic sensors are very sensitive to the change in the refractive index of the surrounding medium, if there is a possibility of an interaction between graphene and analyte there will be a possibility of its sensing. In such a case, one can develop a sensor using graphene and its nanocomposites. Based on this approach, a pH sensor was reported utilizing rGO and polyaniline (PANI) as sensing layers BIB008 . As is known, pH is a very important parameter and it plays a vital role in biological processes, drinking water, environment, food quality control, biochemistry, and chemical reactions. The study has utilized surface plasmon resonance on optical fibers. The rGO-Pani nanocomposite was prepared by an in situ method. Figure 15a shows the scanning electron microscope (SEM) image of Pani, in which the chain-like porous structure of Pani can be seen. Figure 15b represents the transmission electron microscope (TEM) image of rGO which depicts a very thin sheet of rGO. Figure 15c shows the SEM image of the rGO-Pani nanocomposite and Figure 15d shows the TEM image of the rGO-Pani nanocomposite. In this figure, the lighter portion in the image represents the rGO nanosheets and the darker part represents Pani. The design of the sensor probe is shown in Figure 16 . The unclad core of an optical fiber, in the middle, was coated with a thin silver film by the thermal evaporation method, over which another coating of rGO-Pani was done by the dip coating method. Figure 17a shows the SPR spectra for the acidic region from pH 7 to pH 2.4. As one moves towards the acidic region from pH 7, a red shift is observed in resonance wavelength. The reason behind the red shift is the chemical interaction between the rGO-Pani nanocomposite with the acidic pH samples. When an acidic sample comes into contact with polyaniline, the emeraldine form of Pani changes to pernigraniline base through an oxidation process, which changes the refractive index of Pani. Since an acidic sample has an excess of H + ions, when it comes in contact with rGO nanosheets, the rGO nanosheets get converted to the n-doped material, which alters the band gap of the rGO nanosheets. Thus, both the materials in the nanocomposite are sensitive to the acidic sample and, therefore, the change in the effective refractive index of the nanocomposite is the result of change in both the materials, and hence one obtains a cumulative effect on the red shift in resonance wavelength. The sensitivity of the sensor is defined as the change in resonance wavelength per unit of change in the pH of the sample. For the acidic range, the maximum sensitivity of the sensor was found to be 24.93 nm/pH, which means the resonance wavelength shifts around 24.93 nm, when the The design of the sensor probe is shown in Figure 16 . The unclad core of an optical fiber, in the middle, was coated with a thin silver film by the thermal evaporation method, over which another coating of rGO-Pani was done by the dip coating method. The design of the sensor probe is shown in Figure 16 . The unclad core of an optical fiber, in the middle, was coated with a thin silver film by the thermal evaporation method, over which another coating of rGO-Pani was done by the dip coating method. Figure 17a shows the SPR spectra for the acidic region from pH 7 to pH 2.4. As one moves towards the acidic region from pH 7, a red shift is observed in resonance wavelength. The reason behind the red shift is the chemical interaction between the rGO-Pani nanocomposite with the acidic pH samples. When an acidic sample comes into contact with polyaniline, the emeraldine form of Pani changes to pernigraniline base through an oxidation process, which changes the refractive index of Pani. Since an acidic sample has an excess of H + ions, when it comes in contact with rGO nanosheets, the rGO nanosheets get converted to the n-doped material, which alters the band gap of the rGO nanosheets. Thus, both the materials in the nanocomposite are sensitive to the acidic sample and, therefore, the change in the effective refractive index of the nanocomposite is the result of change in both the materials, and hence one obtains a cumulative effect on the red shift in resonance wavelength. The sensitivity of the sensor is defined as the change in resonance wavelength per unit of change in the pH of the sample. For the acidic range, the maximum sensitivity of the sensor was found to be 24.93 nm/pH, which means the resonance wavelength shifts around 24.93 nm, when the Figure 17a shows the SPR spectra for the acidic region from pH 7 to pH 2.4. As one moves towards the acidic region from pH 7, a red shift is observed in resonance wavelength. The reason behind the red shift is the chemical interaction between the rGO-Pani nanocomposite with the acidic pH samples. When an acidic sample comes into contact with polyaniline, the emeraldine form of Pani changes to pernigraniline base through an oxidation process, which changes the refractive index of Pani. Since an acidic sample has an excess of H + ions, when it comes in contact with rGO nanosheets, the rGO nanosheets get converted to the n-doped material, which alters the band gap of the rGO nanosheets. Thus, both the materials in the nanocomposite are sensitive to the acidic sample and, therefore, the change in the effective refractive index of the nanocomposite is the result of change in both the materials, and hence one obtains a cumulative effect on the red shift in resonance wavelength. The sensitivity of the sensor is defined as the change in resonance wavelength per unit of change in the pH of the sample. For the acidic range, the maximum sensitivity of the sensor was found to be 24.93 nm/pH, which means the resonance wavelength shifts around 24.93 nm, when the pH of the sample is changed by unity. As reported, the exponential nature of the sensitivity plot is due to the H + ions, which increase exponentially with the decrease in pH of the sample. pH of the sample is changed by unity. As reported, the exponential nature of the sensitivity plot is due to the H + ions, which increase exponentially with the decrease in pH of the sample. Figure 17b shows the SPR curves corresponding to the basic region from 7 pH to 11.35, and in this case also a red shift in the resonance wavelength was observed with the increase in pH of the sample (increase in alkanity). Again, the reason for the red shift is the interaction between the pH sample and rGO-Pani nanocompoite. The emeraldine form of Pani changes to a leucoemeraldine base after the interaction with the basic sample through the reduction process. The samples with pH from 7 to 11 have an excess of OH − ions. The rGO nanosheets get converted to p-doped material via OH − ions. Therefore, the overall band gap of the nanocomposite changes, which results in a change in the effective refractive index of the sensing layer. The maximum sensitivity was found to be around 75.09 nm/pH at the pH value 11.35. In this study, the behavior of rGO nanosheets changed when they came in contact with acidic/basic samples, resulting in a change in the effective refractive index. Thus, rGO nanosheets act as a sensing matrix for the measurement of the pH.