Nanotechnology and biosensors

Oops they did it again! Carbon nanotubes hoax scientists in viability assays

New materials of emerging technological importance are single-walled carbon nanotubes (SWCNTs). Because SWCNTs will be used in commercial products in huge amounts, their effects on human health and the environment have been addressed in several studies. Inhalation studies in vivo and submerse applications in vitro have been described with diverging results. Why some indicate a strong cytotoxicity and some do not is what we report on here. Data from A549 cells incubated with carbon nanotubes fake a strong cytotoxic effect within the MTT assay after 24 h that reaches roughly 50%, whereas the same treatment with SWCNTs, but detection with WST-1, reveals no cytotoxicity. LDH, FACS-assisted mitochondrial membrane potential determination, and Annexin-V/PI staining also reveal no cytotocicity. SWCNTs appear to interact with some tetrazolium salts such as MTT but not with others (such as WST-1, INT, XTT). This interference does not seem to affect the enzymatic reaction but lies rather in the insoluble nature of MTT-formazan. Our findings strongly suggest verifying cytotoxicity data with at least two or more independent test systems for this new class of materials (nanomaterials). Moreover, we intensely recommend standardizing nanotoxicological assays with regard to the material used: there is a clear need for reference materials. MTT-formazan crystals formed in the MTT reaction are lumped with nanotubes and offer a potential mechanism to guide bioremediation and clearance for SWCNTs from "contaminated" tissue. SWCNTs are good supporting materials for tissue growth, as attachment of focal adhesions and connections to the cytoskeleton suggest.

Fast In Vivo Microextraction: A New Tool for Clinical Analysis

Background: We sought to develop a technique with the potential to partly replace current methods of analysis based on blood draws. To achieve this goal, we developed an in vivo microextraction technique that is faster than conventional methods, interferes minimally with the investigated system, minimizes errors associated with sample preparation, and limits exposure to hazardous biological samples.

Methods: Solid-phase microextraction devices based on hydrophilic polypyrrole and polyethylene glycol coatings were used for direct extraction of drugs from the flowing blood of beagle dogs, over a period of 8 h. The drugs extracted on the probes were subsequently quantified by liquid chromatography coupled to tandem mass spectrometry. Two calibration strategies—external and standard on the fiber—were used to correlate the amount extracted with the in vivo concentration.

Results: Diazepam and its metabolites were successfully monitored over the course of a pharmacokinetic study, repeated 3 times on 3 beagles. The fast microextraction technique was validated by comparison with conventional plasma analysis, and a correlation factor of 0.99 was obtained. In addition to total concentrations, the method was useful for determining free drug concentrations.

Conclusions: The proposed technique has several advantages and is suitable for fast clinical analyses. This approach could be used not only for drugs, but for any other endogenous or exogenous compounds.

Bioconjugation of Ln3+-doped LaF3 nanoparticles to avidin

The binding of Eu3+-doped LaF3 nanoparticles with biotin moieties at the surface of the stabilizing ligand layer to avidin, immobilized on cross-linked aragose beads, is described. The biotin moieties were attached to the nanoparticles by reaction of an activated ester with the amino groups on the surface of the nanoparticles resulting from the 2-aminoethyl phosphate ligands that were coordinated to the surface through the phosphate end. This strategy of employing the reactions of amines with activated esters provides a general platform to modify the surface of the 2-aminophosphate stabilized Ln3+-doped LaF3 nanoparticles with biologically relevant groups. Significant suppression of nonspecific binding to the avidin modified aragose beads has been realized by the incorporation of poly(ethylene glycol) units via the same reaction of a primary amine with an activated ester. The particle size distribution of the functionalized nanoparticles was within 10-50 nm, with a quantum yield of 19% in H2O for the LaF3 nanoparticles codoped with Ce3+ and Tb3+. A discreet, 4 unit poly(ethylene glycol) spaced heterobifunctional cross-linker, functionalized with biotin and N-hydroxysuccinimide at opposite termini, was covalently linked to the 2-aminoethyl phosphate ligand via the N-hydroxysuccinimide activated ester, making an amide bond, imparting biological activity to the particle. Modification of the remaining unreacted amino groups of the stabilizing ligands was done with Me(OCH2CH2)3CH2CH2(C=O)-NHS (NHS = N-hydroxysuccinimide).

Enzymatic microreactors in chemical analysis and kinetic studies

The fields of application of microreactors are becoming wider every year. A considerable number of papers have been published recently reporting successful application of enzymatic microreactors in chemistry and biochemistry. Most are devices with enzymes immobilized on beads or walls of microfluidic channels, whilst some use dissolved enzymes to run a reaction in the microfluidic system. Apart from model systems, mostly with glucose oxidase, horseradish peroxidase and alkaline phosphatase, the principal fields of application of microreactors are tryptic digestion of proteins and polymerase chain reaction in automated analyses of proteomic and genetic material, respectively. Enzymatic microreactors also facilitate characterization of enzyme activity as a function of substrate concentration, and enable fast screening of new biocatalysts and their substrates. They may constitute key parts of lab-on-a-chip and muTAS, assisting the analysis of biomolecules. This review provides systematic coverage of examples of reports on enzymatic microreactors published recently, as well as relevant older papers.

On-chip micro-biosensor for the detection of human CD4+ cells based on AC impedance and optical analysis

The current study was undertaken to fabricate a small micro-electrode on-chip to rapidly detect and quantify human CD4(+) cells in a minimal volume of blood through impedance measurements made with simple electronics that could be battery operated implemented in a hand held device. The micro-electrode surface was non-covalently modified sequentially by incubation with solutions of protein G', human albumin, monoclonal mouse anti-human CD4, and mouse IgG. The anti-human CD4 antibody served as the recognition and capture molecule for CD4(+) cells present in human blood. The binding of these biomolecules to the micro-electrodes was verified by impedance and cyclic voltammetry measurements. An increase in impedance was detected for each layer of protein adsorbed onto the micro-electrode surface. This process was shown to be highly repeatable. Increased impedance was measured when CD4(+) cells were captured on the micro-electrode, and the impedance also increased as the number of captured cells increased. Fluorescence microscopy of captured cells immunolabeled with anti-human CD4, CD8, and CD19 antibodies, and the nuclear label DAPI, confirmed that only CD4(+) cells were captured. The results were highly dependent on the specimen preparation method used. We conclude that the on-chip capture system can efficiently quantify the number of CD4(+) cells.

The Chemistry of Organic Nanomaterials

The development of nanotechnology using organic materials is one of the most intellectually and commercially exciting stories of our times. Advances in synthetic chemistry and in methods for the investigation and manipulation of individual molecules and small ensembles of molecules have produced major advances in the field of organic nanomaterials. The new insights into the optical and electronic properties of molecules obtained by means of single-molecule spectroscopy and scanning probe microscopy have spurred chemists to conceive and make novel molecular and supramolecular designs. Methods have also been sought to exploit the properties of these materials in optoelectronic devices, and prototypes and models for new nanoscale devices have been demonstrated. This Review aims to show how the interaction between synthetic chemistry and spectroscopy has driven the field of organic nanomaterials forward towards the ultimate goal of new technology.

Point-of-care immunotesting: Approaching the analytical performance of central laboratory methods

The use of point-of-care (POC) immunoassays has increased significantly and the menu of analytes continues to expand. Most of the rapid immunoassays are currently based on simple manual assay devices such as the immunochromatographic, agglutination, and immunofiltration assays. Although automated readers have recently been introduced at an increasing pace, the major benefit of these genuinely hand-portable assay devices is that they do not usually necessitate instrumentation but can be performed anywhere. Significant advances in assay and detection technologies have, however, recently facilitated the introduction of truly quantitative, sophisticated immunoassay methods to POC settings as well, with the analytical performance characteristics approaching those of conventional laboratory assays. Furthermore, innovative assay technologies such as those based on immunosensors have been introduced to POC testing (POCT) without ever being employed in clinical laboratories. However, further simplification of the assay procedures and analyzers is still feasible, and strong efforts are directed towards the development of miniaturized and simple, yet sensitive and quantitative, novel assay technologies to keep up with the increasing expectations set on future POC immunotesting.

Personalized exposure assessment: promising approaches for human environmental health research

New technologies and methods for assessing human exposure to chemicals, dietary and lifestyle factors, infectious agents, and other stressors provide an opportunity to extend the range of human health investigations and advance our understanding of the relationship between environmental exposure and disease. An ad hoc Committee on Environmental Exposure Technology Development was convened to identify new technologies and methods for deriving personalized exposure measurements for application to environmental health studies. The committee identified a "toolbox" of methods for measuring external (environmental) and internal (biologic) exposure and assessing human behaviors that influence the likelihood of exposure to environmental agents. The methods use environmental sensors, geographic information systems, biologic sensors, toxicogenomics, and body burden (biologic) measurements. We discuss each of the methods in relation to current use in human health research; specific gaps in the development, validation, and application of the methods are highlighted. We also present a conceptual framework for moving these technologies into use and acceptance by the scientific community. The framework focuses on understanding complex human diseases using an integrated approach to exposure assessment to define particular exposure-disease relationships and the interaction of genetic and environmental factors in disease occurrence. Improved methods for exposure assessment will result in better means of monitoring and targeting intervention and prevention programs.

Direct electron transfer between copper-containing proteins and electrodes

The electrochemistry of some copper-containing proteins and enzymes, viz. azurin, galactose oxidase, tyrosinase (catechol oxidase), and the "blue" multicopper oxidases (ascorbate oxidase, bilirubin oxidase, ceruloplasmin, laccase) is reviewed and discussed in conjunction with their basic biochemical and structural characteristics. It is shown that long-range electron transfer between these enzymes and electrodes can be established, and the mechanistic schemes of the DET processes are proposed.

Sensing the sea

The development of the 'ecosystem approach' to the management of marine systems is leading to a requirement for data to be collected with greater frequency and spatial resolution than has been necessary in the past. This is being met both by the analysis of more samples (to better describe variability and temporal change) and by the deployment of instrumented platforms that gather data over long time periods. To meet these requirements in the hostile conditions at sea, a range of sensors based on physical, chemical and biological responses is being developed. These sensors have applications in laboratory analysis of collected samples, during field studies and directly in situ at remote sites for real-time observations of environmental trends. Here, we consider the role that biosensors could have in future marine monitoring programmes.

Optical glucose detection across the visible spectrum using anionic fluorescent dyes and a viologen quencher in a two-component saccharide sensing system

A very general system is described in which anionic fluorescent dyes possessing a wide range of absorbance and emission wavelengths are used in combination with a boronic acid-modified viologen quencher to sense glucose at pH 7.4 in buffered aqueous solution. The present study demonstrates this capability with the use of eleven anionic fluorescent dyes of various structural types. Signal modulation occurs as the monosaccharide binds to the viologen quencher and alters its efficiency in quenching the fluorescence of the anionic dyes. The degree of quenching and the magnitude of the glucose signal were found to correlate roughly with the number of anionic groups on the dye. Optimal quencher : dye ratios were determined for each dye to provide a fairly linear signal in response to changes in glucose concentration across the physiological range.