Development of biosensor for phenolic compounds containing PPO in ß-cyclodextrin modified support and iridium nanoparticles.

A biosensor based on the iridium nanoparticles dispersed in ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (Ir-BMI·PF6) and a celery (Apium graveolens) extract as a source of polyphenol oxidase (PPO) was constructed. A modified support based on ß-cyclodextrin (ß-CDEP) was used for enzyme immobilization. The behavior of phenolic compounds was investigated by square-wave voltammetry and rutin was selected by presenting the greatest signal. The best performance was obtained with a composition of 70:10:10:10% (w/w/w/w) of the graphite powder:ß-CDEP:Nujol:Ir-BMI·PF6 composition, a PPO concentration of 500unitsmL(-1), in 0.1M phosphate buffer solution (pH 6.0) with frequency, pulse amplitude and scan increment at 100Hz, 60mV, and 3.0mV, respectively. Under optimized conditions, the cathodic currents increased linearly for the rutin concentration range of 1.3×10(-7)-2.0×10(-6)M with a detection limit of 7.9×10(-8)M. This sensor demonstrated acceptable repeatability and reproducibility and the results for the rutin recovery ranged from 92.8 to 103.4%. A relative error of 0.7% was obtained in the rutin determination in simulated samples.

Real-time measurement of glucose using chrono-impedance technique on a second generation biosensor.

Chrono-impedance technique (CIT) was implemented as a new transduction method for real time measurement of glucose in a biosensor system based in carbon paste (CP)/Ferrocene (FC)/glucose oxidase (GOx). The system presents high selectivity because the optimal stimulation signal composed by a 165mV DC potential and 50mV(RMS) AC signal at 0.4Hz was used. The low DC potential used decreased the interfering species effect and the biosensor showed a linear impedance response toward glucose detection at concentrations from 0mM to 20mM,with 0.9853 and 0.9945 correlation coefficient for impedance module (|Z|) and phase (Φ), respectively. The results of quadruplicate sets reveal the high repeatability and reproducibility of the measurements with a relative standard deviation (RSD) less than 10%. CIT presented good accuracy (within 10% of the actual value) and precision did not exceed 15% of RSD for high concentration values and 20% for the low concentration ones. In addition, a high correlation coefficient (R(2)=0.9954) between chrono-impedance and colorimetric methods was obtained. On the other hand, when two samples prepared at the same conditions were measured in parallel with both methods (the measurement was repeated four times), it should be noticed that student's t-test produced no difference between the two mentioned methods (p=1). The biosensor system hereby presented is highly specific to glucose detection and shows a better linear range than the one reported on the previous article.

Electrochemical DNA hybridization sensors applied to real and complex biological samples.

DNA hybridization biosensors, also known as genosensors, are analytical devices for the detection of specific DNA "target" sequences in solution, upon hybridization of the targets with complementary "probes" immobilized on a solid substrate. Electrochemical genosensors hold great promise to serve as devices suitable for point-of-care diagnostics and multiplexed platforms for fast, simple and inexpensive nucleic acids analysis. Although a lot of progress has been made in the past few years, the performance of genosensors in complex biological samples has been assayed in only a small fraction of published research articles. This review covers such a group of reports, from the year 2000 onwards. Special attention is played in the nature and complexity of the samples and in the way matrix effects were treated and specificity controls were performed.

Disposable immunosensor for human cardiac troponin T based on streptavidin-microsphere modified screen-printed electrode.

Screen-printed electrodes (SPE) have been widely used in the design of disposable sensors bringing advances in the use of electrochemical immunosensors for in field-clinical analysis. In this work, streptavidin polystyrene microspheres were incorporated to the electrode surface of SPEs in order to increase the analytical response of the cardiac troponin T (cTnT), a specific biomarker for the acute myocardial infarction diagnosis. The precise calculation of the stoichiometric streptavidin-biotin ratio [1:4] allowed the increase of sensitivity and stability of the immunosensor response to the cTnT analyte. The surface of the immunosensor was characterized by scanning electron microscopy and cyclic voltammetry. It was observed that the use of streptavidin microspheres significantly increased the analytical sensitivity of the electrode in 8.5 times, showing a curve with a linear response range between 0.1 and 10 ngmL(-1) of cTnT and a detection limit of 0.2 ngmL(-1). The proposed SPE showed ease preparation and high sensitivity allowing the detection of cTnT in the range of clinical levels. The new device coupled with a portable electrochemical analyzer shows great promise for point-of-care quantitative testing of necrosis cardiac proteins.

Evaluation of chrono-impedance technique as transduction method for a carbon paste/glucose oxidase (CP/GOx) based glucose biosensor.

The chrono-impedance technique (CIT) for real time determination of glucose concentration in a first generation glucose oxidase/carbon paste electrode was implemented. The biosensor was polarized with a signal composed of 900 mV DC potential and 50 mV(RMS) AC signal at 0.4 Hz. A frequency response analyzer was used to measure the complex impedance (magnitude |Z| and phase (Φ)) of the biosensor-bulk interface. Real time measurements were performed while glucose was added to the bulk within a concentration range of 0-40 mM. The cumulative impedance dose-response curves were used to construct calibration curves, both for magnitude and phase. The best fitting was obtained with a hyperbolic equation. Four biosensors were built obtaining five calibration curves for each of them. A single test measurement (unknown glucose concentration) was also obtained after each calibration procedure. Glucose concentrations were estimated with the calibration curves and also measured by colorimetry, the latter being the reference method. Besides, one-way ANOVA test evaluated repeatability. Difference between means was not statistically significant (p>0.01) for both magnitudes (|Z| and Φ). The Student's t-test assessed the differences significance, which produced in all cases p levels lower or equal than 0.44. Thus, CIT was proved to be a reliable method to measure glucose concentration in real time. Moreover, it showed high repeatability and compared well against colorimetry (r(2)=0.98).

Immobilization of pneumococcal polysaccharide vaccine on silicon oxide wafer for an acoustical biosensor.

One the most important aspects of a biosensor is related to immobilization and maintenance of specific reference compounds on sensing surfaces. A method for the immobilization of polysaccharides to a silicon oxide surface intended for Surface Acoustical Waves (SAW) sensors is described. Silicon oxide is a hydrophobic inorganic support used for the fabrication of many electronic devices. The pneumococcal polysaccharide (PPS) vaccine is immobilized via Protein A after pre-treatment of the surface with hydrochloric acid. The effects of non-specific binding are discussed. The results indicate that the immobilization of PPS via Protein A increases the sensitivity of detecting Streptococcus pneumoniae antibodies in human sera and offers greater reproducibility of response compared with ELISA methods. The principles of this technique are simple and are applicable to the immobilization of many capsular polysaccharides.

Miniaturized real-time monitoring system for L-lactate and glucose using microfabricated multi-enzyme sensors.

A miniaturized on-line monitoring system for the detection of L-lactate and glucose is presented. The system is based on a microfabricated multi-enzyme silicon sensor chip with flow channels integrated on the chip. The sensors were fabricated in containment technology. They were characterized in test solutions. The cross-talking behaviour was investigated and was found to be practically negligible. The linear measurement ranges of both glucose and lactate sensors were large enough for most practical applications. As a result of the miniaturization the analyte consumption could be reduced to a few nmol min(-1). The system was equipped with a microdialysis probe whose recovery was 45% for lactate and 37% for glucose in test solutions using a flow rate of 3 microl min(-1). Lower flow rates of 0.5 microl min(-1) resulted in recoveries of over 90%. The long-term stability of the system was acceptable. Initial measurements have also been performed in vitro using human blood serum.