Nikos A. Chaniotakis

Semiconductor quantum dots in chemical sensors and biosensors

Quantum dots are nanometre-scale semiconductor crystals with unique optical properties that are advantageous for the development of novel chemical sensors and biosensors. The surface chemistry of luminescent quantum dots has encouraged the development of multiple probes based on linked recognition molecules such as peptides, nucleic acids or small-molecule ligands. This review overviews the design of sensitive and selective nanoprobes, ranging from the type of target molecules to the optical transduction scheme. Representative examples of quantum dot-based optical sensors from this fast-moving field have been selected and are discussed towards the most promising directions for future research.

Bioconjugated quantum dots as fluorescent probes for bioanalytical applications.

AbstractQuantum dots (QDs) are inorganic semiconductor nanocrystals that have unique optoelectronic properties responsible for bringing together multidisciplinary research to impel their potential bioanalytical applications. In recent years, the many remarkable optical properties of QDs have been combined with the ability to make them increasingly biocompatible and specific to the target. With this great development, QDs hold particular promise as the next generation of fluorescent probes. This review describes the developments in functionalizing QDs making use of different bioconjugation and capping approaches. The progress offered by QDs is evidenced by examples on QD-based biosensing, biolabeling, and delivery of therapeutic agents. In the near future, QD technology still faces some challenges towards the envisioned broad bioanalytical purposes. FigureBioanalytical applications of luminescent quantum dot-bioconjugates

Novel semiconductor materials for the development of chemical sensors and biosensors: A review

The aim of this manuscript is to provide a condensed overview of the contribution of certain relatively new semiconductor substrates in the development of chemical and biochemical field effect transistors. The silicon era is initially reviewed providing the background onto which the deployment of the new semiconductor materials for the development of bio-chem-FETs is based on. Subsequently emphasis is given to the selective interaction of novel semiconductor surfaces, including doped conductive diamond, gallium nitride, and indium nitride, with the analyte, and how this interaction can be properly transduced using semiconductor technology. The main advantages and drawbacks of these materials, as well as their future prospects for their applications in the sensor area are also described.

SMARTDIAB: A Communication and Information Technology Approach for the Intelligent Monitoring, Management and Follow-up of Type 1 Diabetes Patients

SMARTDIAB is a platform designed to support the monitoring, management, and treatment of patients with type 1 diabetes mellitus (T1DM), by combining state-of-the-art approaches in the fields of database (DB) technologies, communications, simulation algorithms, and data mining. SMARTDIAB consists mainly of two units: 1) the patient unit (PU); and 2) the patient management unit (PMU), which communicate with each other for data exchange. The PMU can be accessed by the PU through the internet using devices, such as PCs/laptops with direct internet access or mobile phones via a Wi-Fi/General Packet Radio Service access network. The PU consists of an insulin pump for subcutaneous insulin infusion to the patient and a continuous glucose measurement system. The aforementioned devices running a user-friendly application gather patients related information and transmit it to the PMU. The PMU consists of a diabetes data management system (DDMS), a decision support system (DSS) that provides risk assessment for long-term diabetes complications, and an insulin infusion advisory system (IIAS), which reside on a Web server. The DDMS can be accessed from both medical personnel and patients, with appropriate security access rights and front-end interfaces. The DDMS, apart from being used for data storage/retrieval, provides also advanced tools for the intelligent processing of the patients data, supporting the physician in decision making, regarding the patients treatment. The IIAS is used to close the loop between the insulin pump and the continuous glucose monitoring system, by providing the pump with the appropriate insulin infusion rate in order to keep the patients glucose levels within predefined limits. The pilot version of the SMARTDIAB has already been implemented, while the platforms evaluation in clinical environment is being in progress.

Biomimetically synthesized silica-carbon nanofiber architectures for the development of highly stable electrochemical biosensor systems.

Biomimetically synthesized silica and conductive activated carbon nanofibers (CNFs) are used in a synergistic manner for the development of a novel electrochemical biosensor system. Poly(L-lysine) templated silica grows and encapsulates the CNF-immobilized enzyme generating a highly stabilizing nanostructured environment for the underlying protein. Concurrently, CNFs provide both the required surface area for the high-capacity enzyme immobilization required in biosensors as well as direct electron transfer to the inner platinum transducer. As a result, this silica/nanofiber superstructure is an ideal architecture for the development of electrochemical biosensor systems that can withstand exposure to extreme operational conditions, such as high temperatures or the presence of proteases. Acetylcholine esterase is used as the model catalyst and with the aid of spectroscopic data it is shown that the observed high operational stability of the biosensor is due to the direct interaction of the protein with the silica backbone, as well as due to the nanostructured enzyme confinement.

GaN-based anion selective sensor: Probing the origin of the induced electrochemical potential

The gallium nitride (GaN) semiconductor has been used as the sensing element in a chemical sensor for the measurement of charged species in solution. The sensor shows remarkable selectivity for anions, such as sulphate (SO42−) and hydroxide (OH−). It is shown that the GaN surface interacts selectively with Lewis bases as shown by impedance spectra. In addition, both the impedance spectra and the surface induced potential of the sensor element correlate very well with the activity of both the negatively charged hydroxide and the sulphate anions used. These results indicate that there is a direct interaction of the electron deficient gallium in the GaN surface with the Lewis base anionic ligands. A band model for the investigated GaN∕KOH-solution system has been deduced.

Electrochemical Biosensing Systems Based on Carbon Nanotubes and Carbon Nanofibers

Abstract Carbon nanomaterials are in the forefront of research in a variety of chemical and physical disciplines. Of these, certain nanostructures seem to be suitable for the development of electrochemical biosensors. In particular carbon nanotubes, and carbon nanofibers have specific chemical and physical characteristics that lent them ideal for the development of biosensors with unique analytical characteristics. In particular, their conductivity, surface area, inherent and induced chemical functionalities, and biocompatibility provide the grounds for the development of a new era of electrochemical biosensors. In this review, we will examine the recent developments of biosensor design based on these new nanostructures.

Comparison of protein immobilisation methods onto oxidised and native carbon nanofibres for optimum biosensor development

AbstractThe properties of native and oxidised graphene layered carbon nanofibres are compared, and their utilisation in enzyme biosensor systems using different immobilisation methods are evaluated. The efficient oxidation of carbon nanofibres with concentrated H2SO4/HNO3 is confirmed by Raman spectroscopy while the introduction of carboxylic acid groups on the surface of the fibres by titration studies. The oxidised fibres show enhanced oxidation efficiency to hydrogen peroxide, while at the same time they exhibit a more efficient and selective interaction with enzymes. The analytical characteristics of biosensor systems based on the adsorption or covalent immobilisation of the enzyme glucose oxidase on carbon nanofibres are compared. The study reveals that carbon nanofibres are excellent substrates for enzyme immobilisation allowing the development of highly stable biosensor systems. FigureImmobilization of proteins on carbon nanofibres

Spectro-electrochemical studies of acetylcholinesterase in carbon nanofiber-bioinspired silica nanocomposites for biosensor development

Poly(L-lysine) templated silica and silica/carbon nanofiber nanocomposites are prepared in the presence of acetylcholinesterase from Drosophila melanogaster (Dm. AChE), leading to the formation of a biocompatible electrochemically active nanocomposite structure with high enzyme loading level. Detailed conformational analysis of poly(L-lysine), Dm. AChE and their interactions with the silica and carbon nanofibers is conducted using micro-Raman spectroscopy, while electrochemical impedance spectroscopy is used to probe the rotational mobility of the protein within the poly(L-lysine) templated silica nanocomposites. It is concluded that the enzyme is highly mobile in its active form, while the carbon nanofibers are very efficient electron transfer nanochannels. Based on these results, biosensors with poly(L-lysine) templated silica/nanofiber nanocomposites were developed, utilizing Dm. AChE as the biocatalyst, poly(L-lysine) templated silica nanostructure as the enzyme stabilizing environment and carbon nanofibers as the direct electron transfer channel to the transducer.

The stabilization of Au NP–AChE nanocomposites by biosilica encapsulation for the development of a thiocholine biosensor

We report on the construction of an amperometric biosensor based on the immobilization of the enzyme acetylcholinesterase (AChE) onto gold nanoparticles (Au NPs). The active enzyme is covalently bound directly onto the surface of the Au NPs via a thiol bond. This immobilization provides increased stability and high electron-transfer between the colloidal Au NPs, the catalyst and the transducer surface. To further increase the biosensor stability by protecting the enzyme from denaturation and protease attack, a layer of biosilica was grown around the Au NP enzyme nanocomposite. All steps, i.e., the conjugation of the enzyme to the gold nanoparticles and the encapsulation into biosilica, are monitored and confirmed by ATR-FT-IR spectroscopy. The stabilizing effect of the entrapment was evaluated amperometrically, while the operation of the biosensor was monitored over a period of 4 months. The initial sensitivity of the biosensor was calculated to be 27.58 nA mM(-1) with a linear response to the concentration of the substrate in the range from 0.04 to 0.4 mM. It is thus shown that the biosilica nanocomposites doped with Au NPs-AChE conjugates create a system that provides both signal mediation and significant enzyme stabilization over the existing AChE biosensor. The biosensor had retained all its activity at the end of the 4 months, compared with the normal AChE biosensor whose activity reached 50% after only 42 days of operation.