Graphene-based Optical Sensor Research Articles

Localized Surface Plasmon Resonance-Modulated Graphene-Based Optical Sensor for Ultrasensitive Immunoassays

Quantitative detection of disease markers at ultralow concentrations has rigorous requirements on the performance of graphene-based optical sensors (GOSs). In this work, a localized surface plasmon resonance-modulated GOS was developed by uniformly dispersing gold nanorods (AuNRs) on the graphene surface. As an optical sensor based on refractive index sensing, the refractive index resolution and sensitivity of the optical sensor reached 2.34 × 10–9 and 2.14 × 107 mV/RIU, respectively. The sensitivity of the optical sensor toward IgG immunoassay reached 6.5 mV (μg mL–1)−1, a value 7-fold that without the AuNRs. A limit of detection of 1.22 ng/mL toward IgG immunoassay was obtained, a value one-tenth that without the AuNRs. Most critically, it has been demonstrated that the improved performance of the optical sensor was attributed to the enhanced evanescent field on graphene caused by the coupling of the evanescent field and LSRR of AuNRs. The proposed optical sensor in this study has the characteristics of high sensitivity, being label-free, and a simple preparation process. The successful application of the proposed sensor will also greatly promote the development of quantitative detection of disease markers at ultralow concentrations.

Graphene and its Derivatives-Based Optical Sensors.

Being the first successfully prepared two-dimensional material, graphene has attracted extensive attention from researchers due to its excellent properties and extremely wide range of applications. In particular, graphene and its derivatives have displayed several ideal properties, including broadband light absorption, ability to quench fluorescence, excellent biocompatibility, and strong polarization-dependent effects, thus emerging as one of the most popular platforms for optical sensors. Graphene and its derivatives-based optical sensors have numerous advantages, such as high sensitivity, low-cost, fast response time, and small dimensions. In this review, recent developments in graphene and its derivatives-based optical sensors are summarized, covering aspects related to fluorescence, graphene-based substrates for surface-enhanced Raman scattering (SERS), optical fiber biological sensors, and other kinds of graphene-based optical sensors. Various sensing applications, such as single-cell detection, cancer diagnosis, protein, and DNA sensing, are introduced and discussed systematically. Finally, a summary and roadmap of current and future trends are presented in order to provide a prospect for the development of graphene and its derivatives-based optical sensors.

Graphene Optical Biosensors.

Graphene shows great potential in biosensing owing to its extraordinary optical, electrical and physical properties. In particular, graphene possesses unique optical properties, such as broadband and tunable absorption, and strong polarization-dependent effects. This lays a foundation for building graphene-based optical sensors. This paper selectively reviews recent advances in graphene-based optical sensors and biosensors. Graphene-based optical biosensors can be used for single cell detection, cell line, and anticancer drug detection, protein and antigen–antibody detection. These new high-performance graphene-based optical sensors are able to detect surface structural changes and biomolecular interactions. In all these cases, the optical biosensors perform well with ultra-fast detection, high sensitivities, unmarked, and are able to respond in real time. The future of the field of graphene applications is also discussed.

Research of detection depth for graphene-based optical sensor

Graphene-based optical sensors have been developed for research into the biological intercellular refractive index (RI) because they offer greater detection depths than those provided by the surface plasmon resonance technique. In this Letter, we propose an experimental approach for measurement of the detection depth in a graphene-based optical sensor system that uses transparent polydimethylsiloxane layers with different thicknesses. The experimental results show that detection depths of 2.5 μm and 3 μm can be achieved at wavelengths of 532 nm and 633 nm, respectively. These results prove that graphene-based optical sensors can realize long-range RI detection and are thus promising for use as tools in the biological cell detection field. Additionally, we analyze the factors that influence the detection depth and provide a feasible approach for detection depth control based on adjustment of the wavelength and the angle of incidence. We believe that this approach will be useful in RI tomography applications.

Refractive index mapping of single cells with a graphene-based optical sensor

Graphene-based optical sensors exhibit good performance in cell refractive index (RI) measurements, with high resolution and large detection depths. In this manuscript, we report an RI mapping method based on the polarization-sensitive light absorption of graphene, in focused scanning mode. Several RI mapping images of normal and cancerous human colonic cells have been obtained. A high-numerical-aperture microscope objective is used to minimize the focusing spot size. Under optimized conditions, the experimental spatial resolution reaches 2.34μm. A ring-shaped perfect optical vortex beam with a tunable diameter is generated to control the incident angles, and the experimental RI resolution is 9.3×10−4 refractive index units. The large longitudinal penetration depth of the graphene evanescent field allows the recognition of RI difference between two individual cancer cells. The RI distribution and morphology of the cells can be determined, and different carcinogenesis stages can also be concluded from the image. This method has potential in biomedical sciences, especially in cell imaging, differentiation, and sorting.

An ultra-high sensitivity surface plasmon resonance sensor based on graphene-aluminum-graphene sandwich-like structure

An ultra-high sensitivity graphene optical sensor based on the surface plasmon resonance (SPR) is proposed using the graphene-aluminum (Al)-graphene sandwich-like structure. Here, the graphene sheets are introduced for enhancing the SPR and preventing the oxidation. It is found that our proposed graphene optical sensor is 3.4 times more sensitive than the Al-based sensor without the graphene layers. We demonstrate that a higher sensitivity can be obtained at the short wavelength due to the increases of the sensitivity with the decreases of wavelength. Especially, the sensitivity can be enhanced marked by increasing the number of graphene layers, which is totally different from the previous graphene-based optical sensor where the sensitivity is often decreased with the increases of the number of graphene layers.

Reduced graphene oxide for fiber-optic humidity sensing.

Graphene-based electrical chemical vapor sensors can achieve extremely high sensitivity, whereas the comparatively slow sensing response and recovery, the research focused on only low concentration detection, have been known as drawbacks for many applications requiring rapid and high concentration detection. Here we report a novel graphene-based fiber-optic relative humidity (RH) sensor relying on fundamentally different sensing mechanism. The sensor can achieve power variation of up to 6.9 dB in high relative humidity range (70-95%), and display linear response with correlation coefficient of 98.2%, sensitivity of 0.31 dB/%RH, response speed of faster than 0.13%RH/s, and good repeatability in 75-95%RH. Theoretical analysis of sensing mechanism can explain the experimental result, and reveal the broad applying prospect of the sensor for other kinds of chemical vapor detection. This novel graphene-based optical sensor provides a beneficial complement to the existing electrical ones, and will promote the employment of graphene in chemical sensing techniques.

Ultrasensitive flow sensing of a single cell using graphene-based optical sensors.

On the basis of the polarization-dependent absorption of graphene under total internal reflection, we designed a graphene-based optical refractive index sensor with high resolution of 1.7 × 10(-8) and sensitivity of 4.3 × 10(7) mV/RIU, as well as an extensive dynamic range. This highly sensitive graphene optical sensor enables label-free, live-cell, and highly accurate detection of a small quantity of cancer cells among normal cells at the single-cell level and the simultaneous detection and distinction of two cell lines without separation. It provides an accurate statistical distribution of normal and cancer cells with fewer cells. This facile and highly sensitive sensing refractive index may expand the practical applications of the biosensor.