Kehan Yu

Specific Protein Detection Using Thermally Reduced Graphene Oxide Sheet Decorated with Gold Nanoparticle‐Antibody Conjugates

Novel nanomaterials, such as nanowires and carbon nanotubes (CNTs), have attracted considerable attention in electrical detection of chemical and biological species for clinical diagnosis and practical pharmaceutical applications during the past decade. [ 1–3 ] Electrical detection of biomolecules using nanomaterials can often achieve high sensitivity because nanomaterials are extremely sensitive to electronic perturbations in the surrounding environment. By using CNTs and CNT-based fi eldeffect transistors (FETs), biosensors have been demonstrated for the detection of protein binding [ 4–7 ] and DNA hybridization events. [ 8 , 9 ] The detection limit of reported CNT protein sensors is normally at 0.1–10 nM level, [ 2 , 5 , 10 ] and an improved detection limit could reach 1 ng/ml through cleaving the protein using an enzyme. [ 7 ] Although CNT devices are promising candidates for biosensors with high sensitivity, the variation in the device characteristics is an obstacle to the device reliability and the device sensitivity is still limited by surface area and electrical properties of CNTs. Graphene, a single layer of carbon atoms in a two-dimensional honeycomb lattice, has potential applications in the electrical detection of biological species due to their unique physical properties. [ 11–13 ] Intrinsic graphene is a zero-gap semiconductor that has remarkably high electron mobility ( ∼ 15 000 cm 2 ⋅ V − 1 ⋅ s − 1 ) at room temperature, [ 12 ] which is even higher than that of CNTs. [ 14 ] Although graphene has been explored for various applications, [ 15–26 ] there are only limited reports on graphenebased biosensors until recently. [ 27–33 ] For instance, large-sized graphene fi lm FETs were fabricated for the electrical detection of DNA hybridization; [ 27 ] graphene oxide (GO) was used in single-bacterium and label-free DNA sensors. [ 29 ] In addition, electrolyte-gated graphene FETs for electrical detection of pH and protein adsorption were reported. [ 30 ] Despite the sparse demonstration of graphene for biosensing applications, graphene-based FETs have not been reported for detection of protein binding (antibody to antigen) events. Because the carrier

Toward practical gas sensing with highly reduced graphene oxide: a new signal processing method to circumvent run-to-run and device-to-device variations

Graphene is worth evaluating for chemical sensing and biosensing due to its outstanding physical and chemical properties. We first report on the fabrication and characterization of gas sensors using a back-gated field-effect transistor platform with chemically reduced graphene oxide (R-GO) as the conducting channel. These sensors exhibited a 360% increase in response when exposed to 100 ppm NO(2) in air, compared with thermally reduced graphene oxide sensors we reported earlier. We then present a new method of signal processing/data interpretation that addresses (i) sensing devices with long recovery periods (such as required for sensing gases with these R-GO sensors) as well as (ii) device-to-device variations. A theoretical analysis is used to illuminate the importance of using the new signal processing method when the sensing device suffers from slow recovery and non-negligible contact resistance. We suggest that the work reported here (including the sensor signal processing method and the inherent simplicity of device fabrication) is a significant step toward the real-world application of graphene-based chemical sensors.

Enhancing Solar Cell Efficiencies through 1-D Nanostructures

The current global energy problem can be attributed to insufficient fossil fuel supplies and excessive greenhouse gas emissions resulting from increasing fossil fuel consumption. The huge demand for clean energy potentially can be met by solar-to-electricity conversions. The large-scale use of solar energy is not occurring due to the high cost and inadequate efficiencies of existing solar cells. Nanostructured materials have offered new opportunities to design more efficient solar cells, particularly one-dimensional (1-D) nanomaterials for enhancing solar cell efficiencies. These 1-D nanostructures, including nanotubes, nanowires, and nanorods, offer significant opportunities to improve efficiencies of solar cells by facilitating photon absorption, electron transport, and electron collection; however, tremendous challenges must be conquered before the large-scale commercialization of such cells. This review specifically focuses on the use of 1-D nanostructures for enhancing solar cell efficiencies. Other nanostructured solar cells or solar cells based on bulk materials are not covered in this review. Major topics addressed include dye-sensitized solar cells, quantum-dot-sensitized solar cells, and p-n junction solar cells.

Metal Nitride/Graphene Nanohybrids: General Synthesis and Multifunctional Titanium Nitride/Graphene Electrocatalyst

A facile, efficient, and general strategy is developed for the fabrication of a new class of nanohybrids consisting of nitrogen-doped graphene functionalized with metal nitride nanoparticles. The graphene decorated with titanium nitride nanoparticles is explored for multifunctional electrocatalytic applications, i.e., as a low-cost counter electrode for I(3)(-) reduction in dye-sensitized solar cells and for nicotinamide adenine dinucleotide (NADH) oxidation in dehydrogenase enzyme-based biosensors.

Tuning gas-sensing properties of reduced graphene oxide using tin oxide nanocrystals

We report a novel and selective gas-sensing platform with reduced graphene oxide (RGO) decorated with tin oxide (SnO2) nanocrystals (NCs). This hybrid SnO2 NC–RGO platform showed enhanced NO2 but weakened NH3 sensing compared with bare RGO, showing promise in tuning the sensitivity and selectivity of RGO-based gas sensors.

Hg(II) Ion Detection Using Thermally Reduced Graphene Oxide Decorated with Functionalized Gold Nanoparticles

Fast and accurate detection of aqueous contaminants is of significant importance as these contaminants raise serious risks for human health and the environment. Mercury and its compounds are highly toxic and can cause various illnesses; however, current mercury detectors suffer from several disadvantages, such as slow response, high cost, and lack of portability. Here, we report field-effect transistor (FET) sensors based on thermally reduced graphene oxide (rGO) with thioglycolic acid (TGA) functionalized gold nanoparticles (Au NPs) (or rGO/TGA-AuNP hybrid structures) for detecting mercury(II) ions in aqueous solutions. The lowest mercury(II) ion concentration detected by the sensor is 2.5 × 10(-8) M. The drain current shows rapid response within less than 10 s after the solution containing Hg(2+) ions was added to the active area of the rGO/TGA-AuNP hybrid sensors. Our work suggests that rGO/TGA-AuNP hybrid structures are promising for low-cost, portable, real-time, heavy metal ion detectors.

Direct growth of vertically-oriented graphene for field-effect transistor biosensor.

A sensitive and selective field-effect transistor (FET) biosensor is demonstrated using vertically-oriented graphene (VG) sheets labeled with gold nanoparticle (NP)-antibody conjugates. VG sheets are directly grown on the sensor electrode using a plasma-enhanced chemical vapor deposition (PECVD) method and function as the sensing channel. The protein detection is accomplished through measuring changes in the electrical signal from the FET sensor upon the antibody-antigen binding. The novel biosensor with unique graphene morphology shows high sensitivity (down to ~2 ng/ml or 13 pM) and selectivity towards specific proteins. The PECVD growth of VG presents a one-step and reliable approach to prepare graphene-based electronic biosensors.

Binding Sn-based nanoparticles on graphene as the anode of rechargeable lithium-ion batteries

A facile method has been developed to synthesize Sn-based nanoparticle-decorated graphene through simultaneous growth of SnO2 nanoparticles and a carbonaceous polymer film on graphene oxide sheets followed by heat treatment at various temperatures (250, 550, 750, and 900 °C). Detailed characterization of the resulting composite material using transmission electron microscopy and field emission scanning electron microscopy suggests that Sn-based nanoparticles were reliably bound to the graphene surface through a carbon film. Cyclic voltammograms and galvanostatic technique were used to investigate electrochemical properties of the Sn-based composite material as the anode of lithium-ion batteries (LIBs). Samples obtained with 550 °C heat treatment, which contained mixed Sn-based components (Sn, SnO, SnO2), exhibit the best electrochemical performance among the series of nanocomposites in terms of specific capacity and cycling stability.

Modulating Gas Sensing Properties of CuO Nanowires through Creation of Discrete Nanosized p−n Junctions on Their Surfaces

We report significant enhancement of CuO nanowire (NW) sensing performance at room temperature through the surface functionalization with SnO(2) nanocrystals (NCs). The sensitivity enhancement can be as high as ∼300% for detecting 1% NH(3) diluted in air. The improved sensitivity could be attributed to the electronic interaction between p-type CuO NWs and n-type SnO(2) NCs due to the formation of nanosized p-n junctions, which are highly sensitive to the surrounding gaseous environment and could effectively manipulate local charge carrier concentration. Our results suggest that the NC-NW structure is an attractive candidate for practical sensing applications, in view of its outstanding room-temperature sensitivity, excellent dynamic properties (rapid response and quick recovery), and flexibility in modulating the sensing performance (e.g., by adjusting the coverage of SnO(2) NCs on CuO NWs and doping of SnO(2) NCs).

Hierarchical vertically oriented graphene as a catalytic counter electrode in dye-sensitized solar cells

Vertically oriented graphene (VG) nanosheets are synthesized for counter electrodes (CEs) of dye-sensitized solar cells (DSSCs). The VG electrode exhibits charge transfer resistance about 1% of the Pt electrode and improves power conversion efficiency of DSSCs from 4.68% (for Pt CEs) to 5.36%.