Controlling carbon nanodot fluorescence for optical biosensing.

In this work we report on the optical properties of specific synthetic carbon nano-dots (CDs) and their suitability for the development of optical biosensors. We examine the photoluminescence behavior of these CDs under different conditions, in their native form, as well as when conjugated to the catalytic protein glucose oxidase (GOx) for the construction of optical glucose biosensors. The effect of pH and hydrogen peroxide on the observed spectra is examined as the basis for the biosensor development.

Dendrimers as tunable vectors of drug delivery systems and biomedical and ocular applications.

Dendrimers are large polymeric structures with nanosize dimensions (1-10 nm) and unique physicochemical properties. The major advantage of dendrimers compared with linear polymers is their spherical-shaped structure. During synthesis, the size and shape of the dendrimer can be customized and controlled, so the finished macromolecule will have a specific "architecture" and terminal groups.

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.

Carbon-nanofiber-based nanocomposite membrane as a highly stable solid-state junction for reference electrodes.

There is currently a need for a reliable solid-state reference electrode, especially in applications such as autonomous sensing or long-term environmental monitoring. We present here for the first time a novel solid-state nanofiber junction reference electrode (NFJRE) incorporating a junction consisting of poly(methyl methacrylate) and carbon graphene stacked nanofibers. The NFJRE operates by using the membrane polymer junction, which has a very high glass transition temperature (T(g)) and small diffusion coefficient, to control the diffusion of ions, and the carbon nanofibers lower the junction resistance and act as ion-to-electron transducers.

Biosilicated CdSe/ZnS quantum dots as photoluminescent transducers for acetylcholinesterase-based biosensors.

CdSe/ZnS core/shell quantum dots (QDs) are functionalized with mercaptoundecanoic acid (MUA) and subsequently covered with poly-L-lysine (PLL) as the template for the formation of the silica outer shell. This nanocomposite is used as a transduction and stabilization system for optical biosensor development. The covalent immobilization of the enzyme acetylcholinesterase from Drosophila melanogaster (AChE) during the formation of the biomimetically synthesized silica is used here as a model, relatively unstable enzyme, as a proof of principle.

Pesticide detection with a liposome-based nano-biosensor.

Monitoring of the organophosphorus pesticides dichlorvos and paraoxon at very low levels has been achieved with liposome-based nano-biosensors. The enzyme acetylcholinesterase was effectively stabilized within the internal nano-environment of the liposomes. Within the liposomes, the pH sensitive fluorescent indicator pyranine was also immobilized for the optical transduction of the enzymatic activity.

Immobilization of enzymes into nanocavities for the improvement of biosensor stability.

Nanoporous materials with different pore sizes are evaluated as immobilization and stabilization matrices of proteins for the development of highly stable biosensors. It has been proven experimentally that confinement of proteins in cages with a diameter that is 2-6 times larger than their size increases considerably the stability of the biomolecules, as has been shown earlier by theoretical calculations. Porous silica beads with pore sizes of 10nm were utilized for the immobilization of the enzymes HRP and GOx with diameters in the order of 5 and 7 nm, respectively.

Fluorescence detection of enzymatic activity within a liposome based nano-biosensor.

The encapsulation of enzymes in microenvironments and especially in liposomes, has proven to greatly improve enzyme stabilization against unfolding, denaturation and dilution effects. Combining this stabilization effect, with the fact that liposomes are optically translucent, we have designed nano-sized spherical biosensors. In this work liposome-based biosensors are prepared by encapsulating the enzyme acetylcholinesterase (AChE) in L-a phosphatidylcholine liposomes resulting in spherical optical biosensors with an average diameter of 300+/-4 nm.

Tuning the sol-gel microenvironment for acetylcholinesterase encapsulation.

The effect of the sol-gel microenvironment on the activity of acetylcholinesterase, an enzyme of high bio-analytical interest, is presented and is correlated to the overall analytical performance of corresponding biosensors. The sol-gel membranes are initially optimized with respect to the catalyst and the TEOS:H2O ratio (r), for mechanical stability, porosity, and hydrophobicity as well as in terms of enzymatic activity. FT-IR and electrochemical impedance spectroscopy (EIS) are used to probe the configuration and rotational mobility of the enzyme within the sol-gel matrices.

Genetically engineered acetylcholinesterase-based biosensor for attomolar detection of dichlorvos.

The design of a biosensor for the detection of dichlorvos at attomolar levels is described based on a highly sensitive double mutant (E69Y Y71D) of the Drosophila melanogaster acetylcholinesterase (Dm. AChE). This enzyme has a k(i) for dichlorvos equal to 487 microM(-1)min(-1), which is 300 and 20,000 times higher than that of the wild type Dm.

Stabilization of enzymes in nanoporous materials for biosensor applications.

In this study we present the results obtained from efforts to stabilize the inherently unstable m-AChE in nanoporous materials, for the development of biosensors with increased operational stability. Based on existing theoretical models, the entrapment of proteins into relatively small rigid cages drastically increases the stability of these proteins, as this is manifested by their decreased tendency to unfold. The use of two different meso/nanomaterials for the immobilization of the m-AChE shows that there is both a decrease in the leaching of the protein from the biosensor membrane to the test solution, as well as a drastic increase in the operational stability of the resulting biosensor.

Gallium nitride-based potentiometric anion sensor.

The gallium nitride (GaN) semiconductor is used as the sensing element for the development of a potentiometric anion sensor. The anion recognition mechanism is based on the selective interaction of anions in solution with the epitaxial Ga-face polarity GaN (0001) wurtzite crystal film grown on sapphire. The native GaN crystal is used for the development of an ion blocked sensor.