Chemical and biological sensors based on van der Waals heterostructures of graphene and carbon nanomembrane

In this thesis, single-layer graphene (SLG)-based field-effect devices were built to realize two different sensors: a pH sensor and a sensor measuring the concentration of the chemokine CXCL8 in clinical samples. CXCL8 is a signal protein that has various promising new applications in the field of disease diagnostics.20 For building these devices, a recently proposed new functionalization approach for graphene was employed.78 The approach is based on the assembly of an all-carbon van der Waals (vdW) heterostructure of carbon nanomembrane (CNM) and SLG. The effect of different substrates including SiO2, poly(ethylene 2,6-naphthalate) (PEN) and SiC and different types of SLG including graphene grown by chemical vapor deposition (CVD), epitaxial graphene, and nanoporous graphene (NPSLG) on the sensor response was investigated. Devices of increasing complexity were designed and investigated. At first, devices for measurements in vacuum. As a next step, devices for measurements of the pH value, and as final step the devices for biosensing. The fabrication of devices included their successive optimization based on transport measurements, electrical impedance spectroscopy (EIS) measurements, and surface sensitive characterization techniques. The device concept was the solution-gated field-effect transistor (SGFET),33 which has promising applications for point-of-care devices247 and lab-onchip technology

Hot-carrier luminescence in graphene

In this thesis, the effect of the sample properties on the characteristics of the hot carrier luminescence in graphene is investigated. The present work focuses on the two main issues described below. The first issue is the modification effects of near-infrared pulsed laser excitation on graphene. For excitation fluences several orders of magnitude lower than the optical damage threshold, the interaction with ultrafast laser pulses is found to cause a stable change in the properties of graphene. This photomodification also results in a decrease of the hot photoluminescence intensity. The detailed analysis shows that ultrafast photoexcitation leads to an increase in the local level of hole doping, as well as a change in the mechanical strain. The variation of doping and strain are linked with the enhanced adsorption of atmospheric oxygen caused by the distortion of the graphene surface. These findings demonstrate that ultrashort pulsed excitation can be invasive even if a relatively low laser power is used. Secondly, the variation of the hot photoluminescence intensity with the increasing charge carrier density in graphene is investigated. The electro-optical measurements performed using graphene field-effect transistors show a strong dependence of the photoluminescence intensity on the intrinsic carrier concentration. The emission intensity has a maximum value in undoped graphene and decreases with the increasing doping level. The theoretical calculations performed using a refined two-temperature model suggest that the reduction of the photoluminescence intensity is caused by an increase in the hot carrier relaxation rate. The modification of the carrier relaxation dynamics caused by photoinduced doping is probed directly using the two-pulse correlation measurements. The discovered sensitivity of the hot photoluminescence to the intrinsic carrier concentration can be utilised for spatially-resolved measurements of the Fermi level position in graphene samples, offering an advantage in resolution and speed

A Sub-30 mpH Resolution Thin Film Transistor-Based Nanoribbon Biosensing Platform

We present a complete biosensing system that comprises a Thin Film Transistor (TFT)-based nanoribbon biosensor and a low noise, high-performance bioinstrumentation platform, capable of detecting sub-30 mpH unit changes, validated by an enzymatic biochemical reaction. The nanoribbon biosensor was fabricated top-down with an ultra-thin (15 nm) polysilicon semiconducting channel that offers excellent sensitivity to surface potential changes. The sensor is coupled to an integrated circuit (IC), which combines dual switched-capacitor integrators with high precision analog-to-digital converters (ADCs). Throughout this work, we employed both conventional pH buffer measurements as well as urea-urease enzymatic reactions for benchmarking the overall performance of the system. The measured results from the urea-urease reaction demonstrate that the system can detect urea in concentrations as low as 25 μM, which translates to a change of 27 mpH, according to our initial pH characterisation measurements. The attained accuracy and resolution of our system as well as its low-cost manufacturability, high processing speed and portability make it a competitive solution for applications requiring rapid and accurate results at remote locations; a necessity for Point-of-Care (POC) diagnostic platforms

A Sub-30 mpH Resolution Thin Film Transistor-Based Nanoribbon Biosensing Platform

We present a complete biosensing system that comprises a Thin Film Transistor (TFT)-based nanoribbon biosensor and a low noise, high-performance bioinstrumentation platform, capable of detecting sub-30 mpH unit changes, validated by an enzymatic biochemical reaction. The nanoribbon biosensor was fabricated top-down with an ultra-thin (15 nm) polysilicon semiconducting channel that offers excellent sensitivity to surface potential changes. The sensor is coupled to an integrated circuit (IC), which combines dual switched-capacitor integrators with high precision analog-to-digital converters (ADCs). Throughout this work, we employed both conventional pH buffer measurements as well as urea-urease enzymatic reactions for benchmarking the overall performance of the system. The measured results from the urea-urease reaction demonstrate that the system can detect urea in concentrations as low as 25 μM, which translates to a change of 27 mpH, according to our initial pH characterisation measurements. The attained accuracy and resolution of our system as well as its low-cost manufacturability, high processing speed and portability make it a competitive solution for applications requiring rapid and accurate results at remote locations; a necessity for Point-of-Care (POC) diagnostic platforms

A sub-30 mpH resolution thin film transistor-based nanoribbon biosensing platform

We present a complete biosensing system that comprises a Thin Film Transistor (TFT)-based nanoribbon biosensor and a low noise, high-performance bioinstrumentation platform, capable of detecting sub-30 mpH unit changes, validated by an enzymatic biochemical reaction. The nanoribbon biosensor was fabricated top-down with an ultra-thin (15 nm) polysilicon semiconducting channel that offers excellent sensitivity to surface potential changes. The sensor is coupled to an integrated circuit (IC), which combines dual switched-capacitor integrators with high precision analog-to-digital converters (ADCs). Throughout this work, we employed both conventional pH buffer measurements as well as urea-urease enzymatic reactions for benchmarking the overall performance of the system. The measured results from the urea-urease reaction demonstrate that the system can detect urea in concentrations as low as 25 µM, which translates to a change of 27 mpH, according to our initial pH characterisation measurements. The attained accuracy and resolution of our system as well as its low-cost manufacturability, high processing speed and portability make it a competitive solution for applications requiring rapid and accurate results at remote locations; a necessity for Point-of-Care (POC) diagnostic platforms

Preparation, Physico-Chemical Properties and Biomedical Applications of Nanoparticles

Nowadays, the impact of nanotechnology on applications in medicine and biomedical sciences has broader societal and economic effects, enhancing awareness of the business, regulatory, and administrative aspects of medical applications. The selected papers included in the present Special Issue gives readers a critical, balanced and realistic evaluation of existing nanomedicine developments and future prospects, allowing practitioners to plan and make decisions.The topics of this book covers the use of nanoparticles and nanotechnology in medical applications including biomaterials for tissue regeneration, diagnosis and monitoring, surgery, prosthetics, drug delivery systems, nanocarriers, and wound dressing. I would like to express my gratitude to all contributors to this issue, who have given so much of their time and effort to help create this collection of high quality papers