Graphene Oxide Functionalized Biosensor for Detection of Stress-Related Biomarkers

A graphene oxide (GO)-based cortisol biosensor was developed to accurately detect corti-sol concentrations from sweat samples at point-of-care (POC) sites. A reference electrode, counter electrode, and working electrode make up the biosensor, and the working electrode was functional-ized using multiple layers consisting of GO and antibodies, including Protein A, IgG, and anti-Cab. Sweat samples contact the anti-Cab antibodies to transport electrons to the electrode, resulting in an electrochemical current response. The sensor was tested at each additional functionalization layer and at cortisol concentrations between 0.1 and 150 ng/mL to determine how the current response differed. A potentiostat galvanostat device was used to measure and quantify the electrochemical response in the GO-based biosensor. In both tests, the electrochemical responses were reduced in magnitude with the addition of antibody layers and with increased cortisol concentrations. The proposed cortisol biosensor has increased accuracy with each additional functionalization layer, and the proposed device has the capability to accurately measure cortisol concentrations for diagnostic purposes

Room-Temperature High On/Off Ratio in Suspended Graphene Nanoribbon Field Effect Transistors

We have fabricated suspended few layer (1-3 layers) graphene nanoribbon field effect transistors from unzipped multiwall carbon nanotubes. Electrical transport measurements show that current-annealing effectively removes the impurities on the suspended graphene nanoribbons, uncovering the intrinsic ambipolar transfer characteristic of graphene. Further increasing the annealing current creates a narrow constriction in the ribbon, leading to the formation of a large band-gap and subsequent high on/off ratio (which can exceed 104). Such fabricated devices are thermally and mechanically stable: repeated thermal cycling has little effect on their electrical properties. This work shows for the first time that ambipolar field effect characteristics and high on/off ratios at room temperature can be achieved in relatively wide graphene nanoribbon (15 nm ~50 nm) by controlled current annealing.Comment: 19 pages, 6 figures, accepted for publication in Nanotechnology (2011

Electrical Transport Properties of Graphene Nanoribbons Produced from Sonicating Graphite in Solution

A simple one-stage solution-based method was developed to produce graphene nanoribbons by sonicating graphite powder in organic solutions with polymer surfactant. The graphene nanoribbons were deposited on silicon substrate, and characterized by Raman spectroscopy and atomic force microscopy. Single-layer and few-layer graphene nanoribbons with a width ranging from sub-10 nm to tens of nm and length ranging from hundreds of nm to 1 {\mu}m were routinely observed. Electrical transport properties of individual graphene nanoribbons were measured in both the back-gate and polymer-electrolyte top-gate configurations. The mobility of the graphene nanoribbons was found to be over an order of magnitude higher when measured in the latter than in the former configuration (without the polymer electrolyte), which can be attributed to the screening of the charged impurities by the counter-ions in the polymer electrolyte. This finding suggests that the charge transport in these solution-produced graphene nanoribbons is largely limited by charged impurity scattering.Comment: 19 pages, 5 figures, accepted for publication in Nanotechnology 201

Graphene Oxide Functionalized Biosensor for Detection of Stress-Related Biomarkers

A graphene oxide (GO)-based cortisol biosensor was developed to accurately detect cortisol concentrations from sweat samples at point-of-care (POC) sites. A reference electrode, counter electrode, and working electrode make up the biosensor, and the working electrode was functionalized using multiple layers consisting of GO and antibodies, including Protein A, IgG, and anti-Cab. Sweat samples contact the anti-Cab antibodies to transport electrons to the electrode, resulting in an electrochemical current response. The sensor was tested at each additional functionalization layer and at cortisol concentrations between 0.1 and 150 ng/mL to determine how the current response differed. A potentiostat galvanostat device was used to measure and quantify the electrochemical response in the GO-based biosensor. In both tests, the electrochemical responses were reduced in magnitude with the addition of antibody layers and with increased cortisol concentrations. The proposed cortisol biosensor has increased accuracy with each additional functionalization layer, and the proposed device has the capability to accurately measure cortisol concentrations for diagnostic purposes

Multifunctional Cellular Targeting, Molecular Delivery, and Imaging by Integrated Mesoporous-Silica with Optical Nanocrescent Antenna: MONA

Multifunctional nanoprobes have attracted significant attention in a wide range of disciplines such as nanomedicine, precision medicine, and cancer diagnosis and treatment. However, integrating multifunctional ability in a nanoscale structure to precisely target, image, and deliver with cellular spatial/temporal resolution is still challenging applications. This is because the development of such high-precision resolution needs to be carried out without labeling, photobleaching, and structurally segregating live cells. In this study, we present an integrated nanostructure of a mesoporous-silica nanosphere with an optical nanocrescent antenna (MONA) for multifunctional cellular targeting, drug delivery, and molecular imaging with spatiotemporal resolution. MONA comprises a systematically constructed Au nanocrescent (AuNC) antenna as a nanosensor and optical switch on a mesoporous-silica nanosphere as a cargo to molecular delivery. MONA made of antiepithelial cell adhesion molecules (anti-EpCAM)-conjugated AuNC facilitates the specific targeting of breast cancer cells, resulting in a highly focused photothermal gradient that functions as a molecular emitter. This light-driven molecular, doxorubicin (DOX) delivery function allows rapid apoptosis of breast cancer cells. Since MONA permits the tracking of quantum biological electron-transfer processes, in addition to its role as an on-demand optical switch, it enables the monitoring of the dynamic behavior of cellular cytochrome pivoting cell apoptosis in response to the DOX delivery. Owing to the integrated functions of molecular actuation and direct sensing at the precisely targeted spot afforded by MONA, we anticipate that this multifunctional optical nanoantenna structure will have an impact in the fields of nanomedicine, cancer theranostics, and basic life sciences

Highly Sensitive Detection of Biological Substances using Microfluidic Enhanced Fabry-Perot Etalon-Based Optical Biosensors

A microfluidic based optical biosensor is introduced to detect concentrations of biochemical substances in solution using refractive index measurement with high sensitivity and accuracy. The sensor consists of a liquid channel forming a Fabry-Perot cavity between two semitransparent Ag/SiO_2 reflective surfaces. Light is transmitted through the cavity to construct interference peaks in the transmission spectra which depend on the refractive index of the test samples in the channel. The refractive index of glucose, potassium chloride, and sodium chloride solutions is measured in different concentrations. Continuous change in refractive index is resolved by observing the peak wavelength shift in the transmitted spectrum. The sensor is characterized using the contact angle measurer, surface profilometer, and spectrophotometer. The proposed Fabry-Perot etalon biosensor shows real time linear responses as well as high accuracy and sensitivity of 10^(-3) refractive index per percent of glucose, 1.4 × 10^(-3) and 1.8 × 10^(-3) refractive index per percent of KCl and NaCl solution, respectively

Highly Sensitive Detection of Biological Substances using Microfluidic Enhanced Fabry-Perot Etalon-Based Optical Biosensors

A microfluidic based optical biosensor is introduced to detect concentrations of biochemical substances in solution using refractive index measurement with high sensitivity and accuracy. The sensor consists of a liquid channel forming a Fabry-Perot cavity between two semitransparent Ag/SiO_2 reflective surfaces. Light is transmitted through the cavity to construct interference peaks in the transmission spectra which depend on the refractive index of the test samples in the channel. The refractive index of glucose, potassium chloride, and sodium chloride solutions is measured in different concentrations. Continuous change in refractive index is resolved by observing the peak wavelength shift in the transmitted spectrum. The sensor is characterized using the contact angle measurer, surface profilometer, and spectrophotometer. The proposed Fabry-Perot etalon biosensor shows real time linear responses as well as high accuracy and sensitivity of 10^(-3) refractive index per percent of glucose, 1.4 × 10^(-3) and 1.8 × 10^(-3) refractive index per percent of KCl and NaCl solution, respectively