Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <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> Kretschmann-Reather Configuration in Optical Fiber <s> Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrödinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment. <s> BIB002 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> Since the introduction of optical fiber technology in the field of sensor based on the technique of surface plasmon resonance (SPR), fiber-optic SPR sensors have witnessed a lot of advancements. This paper reports on the past, present, and future scope of fiber-optic SPR sensors in the field of sensing of different chemical, physical, and biochemical parameters. A detailed mechanism of the SPR technique for sensing purposes has been discussed. Different new techniques and models in this area that have been introduced are discussed in quite a detail. We have tried to put the different advancements in the order of their chronological evolution. The content of the review article may be of great importance for the research community who are to take the field of fiber-optic SPR sensors as its research endeavors. <s> BIB003 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> With advances in nanotechnology enabling us to structure new materials at the nanoscale, the opportunity exists for developing novel material systems and devices capable of self-sensing and active response. Intrinsic coupling of electrical properties and mechanical deformation in carbon nanotubes makes them ideal candidates for future multi-functional material systems that combine adaptive and sensory capabilities. For development of these material systems with multi-functional constituents for sensing and actuation a fundamental knowledge of their structure/property relations is necessary. In this article, we review some of the recent advances in nanotube and nanotube-based composite sensors and actuators, with a particular emphasis on their electromechanical behavior. The fundamentals of carbon nanotube electromechanical behavior and its application towards the development of nanoscale sensor and actuator systems are first introduced. Then, research on the electrical percolation behavior of carbon nanotube-based composites is reviewed. Finally, the development of carbon nanotube-based composites and their potential use as macroscopic actuators and sensors is highlighted. <s> BIB004 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> The richness of optical and electronic properties of graphene attracts enormous interest. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental stability. So far, the main focus has been on fundamental physics and electronic devices. However, we believe its true potential to be in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, even in the absence of a bandgap, and the linear dispersion of the Dirac electrons enables ultra-wide-band tunability. The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light emitting devices, to touch screens, photodetectors and ultrafast lasers. Here we review the state of the art in this emerging field. <s> BIB005 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> Graphene plasmons provide a suitable alternative to noble-metal plasmons because they exhibit much larger confinement and relatively long propagation distances, with the advantage of being highly tunable via electrostatic gating. We report strong light- matter interaction assisted by graphene plasmons, and in particular, we predict unprecedented high decay rates of quantum emitters in the proximity of a carbon sheet, large vacuum Rabi splitting and Purcell factors, and extinction cross sections exceeding the geometrical area in graphene ribbons and nanometer-sized disks. Our results provide the basis for the emerging and potentially far-reaching field of graphene plasmonics, offering an ideal platform for cavity quantum electrodynamics and supporting the possibility of single-molecule, single-plasmon devices. <s> BIB006 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> Current discoveries of different forms of carbon nanostructures have motivated research on their applications in various fields. They hold promise for applications in medicine, gene, and drug delivery areas. Many different production methods for carbon nanotubes (CNTs) have been introduced; functionalization, filling, doping, and chemical modification have been achieved, and characterization, separation, and manipulation of individual CNTs are now possible. Parameters such as structure, surface area, surface charge, size distribution, surface chemistry, and agglomeration state as well as purity of the samples have considerable impact on the reactivity of carbon nanotubes. Otherwise, the strength and flexibility of carbon nanotubes make them of potential use in controlling other nanoscale structures, which suggests they will have a significant role in nanotechnology engineering. <s> BIB007 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> Infrared spectroscopy is the technique of choice for chemical identification of biomolecules through their vibrational fingerprints. However, infrared light interacts poorly with nanometric size molecules. Here, we exploit the unique electro-optical properties of graphene to demonstrate a high-sensitivity tunable plasmonic biosensor for chemically-specific label-free detection of protein monolayers. The plasmon resonance of nanostructured graphene is dynamically tuned to selectively probe the protein at different frequencies and extract its complex refractive index. Additionally, the extreme spatial light confinement in graphene, up to two orders of magnitude higher than in metals, produces an unprecedentedly high overlap with nanometric biomolecules, enabling superior sensitivity in the detection of their refractive index and vibrational fingerprints. The combination of tunable spectral selectivity and enhanced sensitivity of graphene opens exciting prospects for biosensing. <s> BIB008 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> The facile assembly of three-dimensional (3D) plasmonic substrates has been demonstrated. The assembly is based on the homogeneous decoration of multi-walled carbon nanotube/gold nanoparticle (CNT/AuNP) hybrid nanocomposites on a commercial polyvinylidene difluoride (PVDF) membrane, which is achieved via simple filtration. The CNT/AuNP hybrids with a unique 1D/0D structure remarkably improve the coverage and uniformity of plasmonic nanostructures on the membrane. The effective inter-particle and inter-tube coupling creates a multitude of hot spots within the probe area, and can produce a strong SERS effect. Moreover, the flexible membrane-based scaffold can efficiently collect and concentrate trace targets from large-volume sample solutions at milliliter-scale. The membrane-based SERS sensor shows high sensitivity and good reproducibility. The SERS sensor is employed to detect various molecular contaminants in aqueous samples, demonstrating its excellent field-testing capabilities for applications ranging from food safety to environmental monitoring. <s> BIB009 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> Abstract A three-dimensional (3D) surface-enhanced Raman scattering (SERS) substrate is fabricated by decorating multi-walled carbon nanotubes (MWNTs) arrays with silver nanoparticles (AgNPs) on silicon, via magnetron sputtering and annealing method. The MWNTs-AgNPs hybrids with 3D structure increase the coverage of plasmonic nanostructures. The effect of inter-particle and inter-tube coupling creates a multitude of hot spots, with a strong SERS effect. The structure of MWNTs-AgNPs hybrid material is confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Furthermore, Raman scattering from MWNTs, which is significantly enhanced in such hybrids, is systematically investigated in all samples. Surface-enhanced Raman scattering property is proved using 4-mercaptobenzoic acid (4-MBA) as standard analyte and the detection concentration level is down to 10−10 M. Additionally, the stability and recyclability of MWNTs-AgNPs substrates have been studied, positioning SERS mapping within an area of 10 × 10 μm2 is carried out to investigate the uniformity; time-course SERS mapping is performed to study the influence induced by molecule solution evaporation process. Finally, finite-difference time-domain (FDTD) method is utilized to simulate E-field distribution of the hybrid structures with multilayer AgNPs decorated on MWNTs. The results show a Raman scattering enhancement factor (EF) of 107. <s> BIB010 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> The increasing pollution of aquatic environments by antibiotics makes it necessary to develop efficient enrichment and sensitive detection methods for environmental antibiotics monitoring. In this work, silver nanoparticles and carbon nanotube-intercalated graphene oxide laminar membranes (Ag NPs/CNT-GO membranes) were successfully prepared for enrichment and surface-enhanced Raman scattering (SERS) detection of antibiotics. The prepared Ag NPs/CNT-GO membranes exhibited a high enrichment ability because of the π-π stacking and electrostatic interactions of GO toward antibiotic molecules, which enhanced the sensitivity of SERS measurements and enabled the antibiotics to be determined at sub-nM concentrations. In addition, the nanochannels created by the intercalation of CNTs into GO layers resulted in an 8-fold enhancement in the water permeance of Ag NPs/CNT-GO membranes compared to that of pure GO membranes. More importantly, the Ag NPs/CNT-GO membranes exhibited high reproducibility and long-term stability. The spot-to-spot variation in SERS intensity was less than 15%, and the SERS performance was maintained for at least 70 days. The Ag NPs/CNT-GO membranes were also used for SERS detection of antibiotics in real samples; the results showed that the characteristic peaks of antibiotics were obviously recognizable. Thus, the sensitive SERS detection of antibiotics based on Ag NPs/CNT-GO offers great potential for practical applications in environmental analysis. <s> BIB011 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> Abstract In this work, a functional nanocomposite consisting of silver nanoparticles and multiwalled carbon nanotubes (MWCNTs-Ag) was successfully synthesized using a two-step chemical process. The MWCNTs-Ag nanocomposite has been studied as a surface-enhanced Raman scattering (SERS) sensing platform for detection of methylene blue (MB) dye in an aqueous medium. The obtained results reveal that the MWCNTs-Ag nanocomposite exhibits higher SERS detection activity than that of pure Ag-nanoparticles (Ag-NPs). The calculated enhancement factors are 1.51 × 106 for pure Ag-NPs and 4.68 × 106 for the MWCNTs-Ag nanocomposite. MB detection has been achieved as low as 1 ppm. The SERS enhancement of the MWCNTs-Ag nanocomposite can be attributed to the combination of both an electromagnetic (EM) effect and a chemical effect (CE). With exhibited properties, the MWCNTs-Ag nanocomposite can be effectively used for detection of various organic dyes in water solution. <s> BIB012 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> We synthesized a carbon nanotube (CNT) loaded with silver nanoparticles (AgNPs) composite as an effective surface enhanced Raman scattering (SERS) substrate via a low-cost, simple citrate reduction method. The hybrid materials were confirmed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectrophotometer and Raman spectroscopy. Rhodamine 6G (R6G) was used as the probe analyte. The experimental results indicated that the detection concentration level was down to 10(-14) M. Additionally, we discussed the uniformity by conducting SERS position mapping within an area of 5 μm × 5 μm; meanwhile, we performed time-course SERS mapping experiments to study the evaporation process of probe molecules of the prepared samples. Finally, we simulated the electromagnetic field distribution based on SEM images (obtained the ratio of surface area to the area of silver particles) by the finite difference time domain (FDTD) method. <s> BIB013 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> The carbon nanotube (CNT) has been proved to be a promising material in infrared detection, due to its many advantages of high mobility, strong infrared light absorption, and carrier collection efficiency. However, the absorption restriction from the single layer limits its effective utilization of incident light. In this paper, we introduce a plasmonic electrode structure in a CNT thin-film photodetector based on random deposited high-purity semiconducting CNTs, which can collect photoinduced carriers effectively and enhance light absorption at the same time. The largest enhancement of photocurrents can be achieved at 1650 nm wavelength with suitable plasmonic structure size. Especially, we further discuss the influence of plasmonic structures on the performance of devices. We demonstrate that the best performance improvement of the carbon nanotube detector with plasmonic structure can be enhanced by 13.7 times for photocurrent mode and 5.62 times for photovoltage mode compared to those devices without s... <s> BIB014 </s> Carbon-Based Nanomaterials for Plasmonic Sensors: A Review <s> Kretschmann-Reather Configuration in Optical Fiber <s> The photoluminescence properties of carbon nanotubes (CNTs), including the large Stokes shift and the absence of fluorescent photobleaching, can be used as a fluorescent label in biological measurements. In this study, the performance of CNTs as a fluorescent label for surface plasmon resonance (SPR)-assisted fluoroimmunoassay is evaluated. The fluorescence of (8, 3) CNTs with an excitation wavelength of 670 nm and an emission wavelength of 970 nm is observed using a sensor chip equipped with a prism-integrated microfluidic channel to excite the SPR. The minimum detectable concentration of a CNT dispersed in water using a visible camera is 0.25 μg/mL, which is equivalent to 2 × 1010 tubes/mL. The target analyte detection using the CNT fluorescent labels is theoretically investigated by evaluating the detectable number of CNTs in a detection volume. Assuming detection of virus particles which are bound with 100 CNT labels, the minimum number of detectable virus particles is calculated to be 900. The result indicates that CNTs are effective fluorescent labels for SPR-assisted fluoroimmunoassay. <s> BIB015
The prism-based Kretschmann configuration requires some sophisticated instrumentation and is also bulky in size. For the compact design, the prism is replaced by the core of an optical fiber. The light inside the optical fiber is guided through the total internal reflection and the field of the evanescent wave generated decays exponentially in the cladding region. The principle for the excitation of surface plasmons is the same as in the prism-based configuration. In the case of optical fiber, cladding is removed from a small part of the fiber and the unclad core is coated with a thin metal layer. The incident light from the polychromatic source is launched from one end of the fiber and the transmitted spectrum is recorded at the other end of the fiber. A sharp dip in the spectrum is obtained at a particular wavelength, called the resonance wavelength, depending on the refractive index of the dielectric medium in contact of the metal layer BIB003 . The prism-based Kretschmann configuration requires some sophisticated instrumentation and is also bulky in size. For the compact design, the prism is replaced by the core of an optical fiber. The light inside the optical fiber is guided through the total internal reflection and the field of the evanescent wave generated decays exponentially in the cladding region. The principle for the excitation of surface plasmons is the same as in the prism-based configuration. In the case of optical fiber, cladding is removed from a small part of the fiber and the unclad core is coated with a thin metal layer. The incident light from the polychromatic source is launched from one end of the fiber and the transmitted spectrum is recorded at the other end of the fiber. A sharp dip in the spectrum is obtained at a particular wavelength, called the resonance wavelength, depending on the refractive index of the dielectric medium in contact of the metal layer BIB003 . it shows extraordinary properties, such as ultra-high-mobility carriers, gate-tunable carrier densities, fine structure constant defined optical transmission, long mean free path, and quantum Hall effect BIB002 . The confinement of the surface plasmons in the graphene is much stronger than in conventional noble metals  . Therefore, graphene plasmons have been used in biosensor, terahertz detector, terahertz emitter, plasmonic metamaterial, and terahertz optoelectronics. The advantages of graphene plasmons over conventional noble metals plasmons are that they have relatively low loss, high confinement, and tunability. All these advantages make graphene plasmons promising materials for the future BIB001 BIB005 BIB006 BIB008 . Another interesting carbon nanomaterial is the 1D form of rolled graphene sheets, i.e., carbon nanotubes. Carbon nanotubes (CNTs) were discovered by Iijima in 1991, and since then they have emerged as the most extensively utilized nanomaterials in various research areas due to their unique properties. CNTs are graphene sheets rolled into a cylindrical structure, which are classified as single walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), depending on the number of rolled graphene sheets. Their properties are highly influenced by their atomic structure (chirality), size, and morphological arrangement. They have remarkable mechanical strength, extremely high electrical and thermal conductivity, exceptional physical and chemical properties, ultrafast charge transfer properties, and distinct optical response in the whole EM spectrum BIB007 . The intrinsic relationship between their electrical, mechanical, and optical properties make them ideal for future nanoscale sensors BIB004 . The ultrafast charge transfer reactions and the possibility of their surface functionalization in numerous ways have made CNTs an ideal candidate for the designing of specific sensors for a plethora of applications, along with the plasmonic properties endowed by the graphitic structure    BIB014 . There are numerous reports on the study of optical and plasmonic properties of carbon nanotubes, but their direct use as plasmonic material for sensing is limited due to the excitation regime in the UV or IR region. In plasmonic sensors, either the surface plasmon phenomenon itself is employed for sensing, or it contributes towards the enhancement of other spectroscopic methods, like surface enhanced Raman spectroscopy (SERS) and surface plasmon enhanced fluorescence BIB005 BIB010 BIB011 BIB009 BIB015 BIB012 BIB013 . Carbon nanomaterials have long been known for the enhancement of surface plasmons in several of these phenomena, however, in this review the attention is on SPR-based sensors. The role played by CBNs is basically divided in three categories for SPR sensors-plasmonic materials, sensitivity enhancement material of plasmonic sensors, and as a sensing matrix for such sensors. They are used as plasmonic materials because they are a superior substitute for noble metals, which suffer from some shortcomings, such as high ohmic losses, less tunability, and chemical instability in harsh environments. CBNs fulfill these limitations of noble metals, along with their high refractive index, which renders them with highly sensitive plasmonic properties. Due to their high refractive index, conductivity, and high surface to volume ratio, they are also utilised with noble metals for sensitivity enhancement tags in plasmonic sensors. Furthermore, their ability of numerous surface functionalization with various biomolecules, polymers, and other nanomaterials make them ideal candidates for sensing matrix in plasmonic sensors.