Independently-addressable micron-sized biosensor elements

With the continuing development of micro-total analysis systems and sensitive biosensing technologies, it is often desirable to immobilize biomolecules onto a surface in a small well-defined area. A novel method was developed to electrochemically attach DNA probes to micron-sized regions of a gold surface using biotin-LC-hydrazide (BH). Previously, we have found that the radical produced during the oxidation of BH will attach to a wide variety of electroactive surfaces. An array of micron-sized gold band electrodes (75 microm wide) was fabricated onto glass microscope slides and BH was deposited onto each electrode through the application of an oxidizing potential. Subsequent attachment of avidin to the biotinylated surface created the 'molecular sandwich' architecture necessary for further immobilization of biotinylated biomolecules to the surface. In this work, we utilized biotinylated DNA probes of varying sequence to illustrate the specificity of the attachment scheme. The immobilization of avidin, DNA probe, and hybridization of DNA target is visualized with fluorescence tags and the spatially selective attachment and hybridization of unique DNA sequences is demonstrated.     

Directed immobilization of recognizing elements of biosensor transducers

Data about the directed immobilisation of recognising structures on metal and silicon surfaces of biosensor transducers are analyzed in the review. Attention is paid to such approaches as pretreatment of surface by silanes, thiol compounds as well as to formation of polyelectrolyte-based layers.     

Novel carbon materials in biosensor systems

In this work, novel carbon materials are evaluated as transducers, stabilizers and mediators for the construction of amperometric biosensors. It is shown that materials such as fullerenes and carbon nanotubes are promising materials as electrochemical mediators and enzyme stabilizers. Additionally porous carbon and porous glassy carbon are excellent transducers for amperometric measurements, while they provide cavities adequate for enzyme immobilization. At the same time, the sensitivity to peroxide is shown to depend on the activation procedures. Treatment that introduces oxygen groups increases the sensitivity of the carbon-based sensor to hydrogen peroxide considerably. These materials are used for the construction, mediation and stabilization of glucose biosensor.     

Detection of DNA via an ion channel switch biosensor

Detection of DNA by an ion channel switch biosensor has been demonstrated in a model system, using single-stranded oligonucleotide sequences of 52-84 bases in length. Two different biotinylated probes are bound, via streptavidin, either to the outer region of a gramicidin ion channel dimer or to an immobilized membrane component. The ion channels are switched off upon detection of DNA containing complementary epitopes to these probes, separated by a nonbinding region, at nanomolar levels. The DNA cross-links the ion channel to the immobilized species, preventing ions passing through the channel. Addition of DNase I after the target DNA has been added switches the ion channels on. The DNA response is dependent on the rate of hybridization of the individual probes to their complementary epitopes, as shown by using a single probe against DNA containing a repeat of the complementary epitope. These results were correlated with hybridization rates determined using surface plasmon resonance (BIAcore 2000), and with free energies of dimer formation for the probes.     

Point-of-care biosensor systems for cancer diagnostics/prognostics

With the growing number of fatalities resulting from the 100 or so cancer-related diseases, new enabling tools are required to provide extensive molecular profiles of patients to guide the clinician in making viable diagnosis and prognosis. Unfortunately with cancer-related diseases, there is not one molecular marker that can provide sufficient information to assist the clinician in making effective prognoses or even diagnoses. Indeed, large panels of markers must typically be evaluated that cut across several different classes (mutations in certain gene fragments--DNA; over/under-expression of gene activity as monitored by messenger RNAs; the amount of proteins present in serum or circulating tumor cells). The classical biosensor format (dipstick approach for monitoring the presence of a single element) is viewed as a valuable tool in many bioassays, but possesses numerous limitations in cancer due primarily to the single element nature of these sensing platforms. As such, if biosensors are to become valuable tools in the arsenal of the clinician to manage cancer patients, new formats are required. This review seeks to provide an overview of the current thinking on molecular profiling for diagnosis and prognosis of cancers and also, provide insight into the current state-of-the-art in the biosensor field and new strategies that must be considered to bring this important technology into the cancer field.     

DNA liquid-crystalline dispersion particles as a basis for sensitive biosensor elements

The data on the morphology, structural parameters, and abnormal optical properties of particles of cholesteric liquid-crystalline dispersions of double-stranded DNA are reviewed. The general principles of the creation and operation of biosensing units based on particles of these suspensions, including dispersed particles immobilized in hydrogels, are described. Examples demonstrating the analytical potentialities of liquid-crystalline biosensing units are given. A method for constructing "sandwich"-type biosensing units based on the particles of liquid-crystalline dispersion formed from molecules of DNA-polycation complexes is described.     

Development of low-cost microfluidic systems for lab-on-a-chip biosensor applications

In this work, we develop low-cost microfluidic systems based on polydimethylsiloxane (PDMS) for lab-on-a-chip applications. PDMS microfluidic structures have been fabricated by micromolding, PDMS casting, and plasma bonding processes. The micromolding technique is used to fabricate PDMS slabs with micro-sized grooves, and the complete microchannel is formed by bonding PDMS slab with glass or PDMS substrate. The molding procedure using SU-8 photoresist patterning on silicon wafer, PDMS microchannel fabrication, and PDMS surface treatment using oxygen plasma and TiO₂ coating, are discussed. The various parameters for oxygen plasma treatment including RF power and treatment time are studied in order to obtain conditions for good bonding with the glass substrate. The best condition for plasma treatment is found to be the low RF power (8 W) with 5 min treatment time. In addition, TiO₂ coating with oxygen plasma treatment has been applied to make PDMS surface more hydrophilic to improve aqueous solution compatilbility. The microfluidic channels for various applications, including sample injection cross channel, micropump channel, T and Y sample mixers, PCR thermocyling chamber and channel, capillary electrophoresis flow channel, and conductimetric systems have been fabricated. Finally, a typical application of the PDMS chip in a flow injection conductimetric system for sodium chloride detection has been demonstrated.     

Functional viromic screens uncover regulatory RNA elements

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A piezoelectric biosensor as an olfactory receptor for odour detection: electronic nose

Humans can detect and differentiate the presence of different odours even at trace levels of these odorous compounds. The odour quantification of any particular samples is normally based on conventional panel decisions. Other analytical instruments could be used to detect trace levels of odorous molecules. This study presents the results of a biological sensor system subject to different odorants. The system consists of a sensor in which the isolated olfactory receptor proteins (ORPs) from bullfrogs (Rana spp.) were coated onto the surface of a piezoelectric (PZ) electrode, similar to the mechanism of human olfaction. The PZ crystal served as a signal transducer. The results indicate rapid (about 400 s), reversible, and longterm (up to 3 months) stable responses to different volatile compounds such as n-caproic acid, isoamyl acetate, n-decyl alcohol, beta-ionone, linalool, and ethyl caporate. The sensitivity of the sensor ranges from 10(-6)-10(-7) g, fully correlated with the olfactory threshold values of human noses. An array of six sensors consisting of five fractionated ORPs and one referenced phospholipid probe is able to respond to different odorants and form a typical fingerprint for each odorant.     

A biosensor generated via high-throughput screening quantifies cell edge Src dynamics

Fluorescent biosensors for living cells currently require laborious optimization and a unique design for each target. They are limited by the availability of naturally occurring ligands with appropriate target specificity. Here we describe a biosensor based on an engineered fibronectin monobody scaffold that can be tailored to bind different targets via high-throughput screening. We made this Src-family kinase (SFK) biosensor by derivatizing a monobody specific for activated SFKs with a bright dye whose fluorescence increases upon target binding. We identified sites for dye attachment and changes to eliminate vesiculation in living cells, providing a generalizable scaffold for biosensor production. This approach minimizes cell perturbation because it senses endogenous, unmodified target, and because sensitivity is enhanced by direct dye excitation. Automated correlation of cell velocities and SFK activity revealed that SFKs are activated specifically during protrusion. Activity correlates with velocity, and peaks 1-2 μm from the leading edge.     

Synchronous and asynchronous systems of threshold elements

The role of synchronism in systems of threshold elements (such as neural networks) is examined. Some important differences between synchronous and asynchronous systems are outlined. In particular, important restrictions on limit cycles are found in asynchronous systems along with multi-frequency oscillations which do not appear in synchronous systems. The possible role of deterministic chaos in these systems is discussed.     

Biomaterials integrated with electronic elements: en route to bioelectronics

Bioelectronics is a progressing interdisciplinary research field that involves the integration of biomaterials with electronic transducers, such as electrodes, field-effect-transistors or piezoelectric crystals. Surface engineering of biomaterials, such as enzymes, antigen-antibodies or DNA on the electronic supports, controls the electrical properties of the biomaterial-transducer interface and enables the electronic transduction of biorecognition events, or biocatalyzed transformation, on the transducers. Bioelectronic sensing devices, biosensors of tailored sensitivities and specificities, are being developed.     

Statistical distribution of impedance elements in biological systems

Electric impedance measurements on systems consisting of nonuniform elements (e.g. nerve bundles, cell suspensions, imperfect dielectrics)_can be interpreted if the impedance characteristics of the individuals and their impedance distribution are known. Conversely, given the observed overall impedance,z(p), the impedance distribution of the individuals is not uniquely determined in both phase angle and static capacitance. If all individual phase angles are equal, the distribution,D(τ), is the solution of Stieltjes' integral equation

$$F[z(p)] = \int_0^\infty {\frac{{D(\tau )d\tau }}{{1 + p\tau }}} ,$$