Carmelo J. Felice

Impedance microbiology: quantification of bacterial content in milk by means of capacitance growth curves.

The impedancimetric method is a technique for the rapid evaluation of milk bacterial content and also of its subproducts. Several authors have made use of culture conductance changes during bacterial growth for quantitative and qualitative assessments of microbial growth. However, interface capacitance curves, Ci, have not been used. In this paper, we quantify bacteria in cow raw milk by following their growth as the above-mentioned capacitance change time course event. With it, bigger growth variations, shorter detection times and a better coefficient of correlation with the plate count method were obtained than those yielded by conductance curves. Calibration was performed by plotting initial known concentrations, IC (CFU/ml), as a function of the time detection theshold (TDT).

Evaluation of EMG processing techniques using Information Theory

BackgroundElectromyographic signals can be used in biomedical engineering and/or rehabilitation field, as potential sources of control for prosthetics and orthotics. In such applications, digital processing techniques are necessary to follow efficient and effectively the changes in the physiological characteristics produced by a muscular contraction. In this paper, two methods based on information theory are proposed to evaluate the processing techniques.MethodsThese methods determine the amount of information that a processing technique is able to extract from EMG signals. The processing techniques evaluated with these methods were: absolute mean value (AMV), RMS values, variance values (VAR) and difference absolute mean value (DAMV). EMG signals from the middle deltoid during abduction and adduction movement of the arm in the scapular plane was registered, for static and dynamic contractions. The optimal window length (segmentation), abduction and adduction movements and inter-electrode distance were also analyzed.ResultsUsing the optimal segmentation (200 ms and 300 ms in static and dynamic contractions, respectively) the best processing techniques were: RMS, AMV and VAR in static contractions, and only the RMS in dynamic contractions. Using the RMS of EMG signal, variations in the amount of information between the abduction and adduction movements were observed.ConclusionsAlthough the evaluation methods proposed here were applied to standard processing techniques, these methods can also be considered as alternatives tools to evaluate new processing techniques in different areas of electrophysiology.

Hematocrit measurement by dielectric spectroscopy

Based on permittivity changes, a new method to measure hematocrit (HCT) in extracorporeal blood systems is presented. Human blood samples were tested at different HCT levels pairing the values of permittivity change, obtained by means of a commercial impedance analyzer, with traditional centrifugation measurements. Data were correlated using both linear and nonlinear regression. When using the lineal model, the comparison yielded a high correlation coefficient (r=0.99). Theoretical simplifications suggest that the method is independent of changes in the conductivities of the intracellular and extracellular compartments. The influence of osmolarity and conductivity of the extracellular compartment was analyzed. It is shown that HCT can be predicted within an error lower than 5% when those parameters changed as much as 1 mS/cm and 50 mOsm/kg, respectively. Thus, the method appears as valid and viable showing good possibilities in applications such as renal dialysis.

Impedance bacteriometry: medium and interface contributions during bacterial growth

Impedance was measured in a cell containing culture broth inoculated with E. coli, before and during bacterial growth. The electrode interface impedance components (R/sub i/, X/sub i/) and the culture medium component R/sub m/ were separated by making use of the Warburgs model frequency dependent properties. Measurements were carried out from 18 Hz to 18 kHz with a constant current impedance bridge as growth proceeded. Growth curves for R/sub i/ and X/sub i/ showed a similar temporal pattern within the frequency range of 18-100 Hz. Dispersion was not observed in R/sub m/, meaning that the same growth response was obtained within the 18-18000-Hz range. At low frequency, the resistive and capacitive reactive components, or R/sub i/ and X/sub b/, respectively, were directly measured, where R/sub b/=(2*R/sub i/+R/sub m/) and X/sub b/=2*X/sub i/ and, above 5 kHz, R/sub m/ was obtained (for Z/sub i/ is negligible). Thus, R/sub i/ was easily discriminated from R/sub m/ by simple arithmetic. In four experiments, the maximum spread of X/sub i/, R/sub i/, and R/sub m/ was smaller than 5% indicating good repeatability. There is potential new information in dissecting out the growth curve in three separate component curves.<<ETX>>

A pH Sensor Based on a Stainless Steel Electrode Electrodeposited With Iridium Oxide

A simple procedure to make an iridium oxide (IrO2) electrodeposited pH sensor, that can be used in a chemical, biomedical, or materials laboratory, is presented here. Some exercises, based on this sensor, that can be used to teach important concepts in the field of biomedical, biochemical, tissue, or materials engineering, are also presented. This novel procedure is based on the electrodeposition of IrO2 on a stainless steel electrode, which uses a similar mechanism to an ion selective electrode (ISE) and senses changes in pH. The simplicity and cost effectiveness of this method facilitates the teaching of the concept of half-cell potential and the basics of sensors. This novel sensor has also been shown to outperform the classical glass pH-sensor. In this new methodology, students learn to build the electrode, to calibrate it, and to measure its sensitivity, repeatability, and time-response.

Comparative analysis of hematocrit measurements by dielectric and impedance techniques

In a previous paper, a new dielectric technique was used to estimate hematocrit (HTC) in extracorporeal blood circulation systems, independently of plasma conductivity or osmolarity. Although many impedance techniques have been formerly proposed in the literature, none has been evaluated against plasma conductivity and osmolarity. Herein, we estimate HTC based on permittivity changes and also with other four techniques found in the literature. Besides, the error incurred in each is also studied when plasma conductivity and osmolarity changed as much as 1 mS/cm and 50 mOsm/kg, respectively. The dielectric (permittivity) technique has an error close to 5.4%, while the others showed both tendencies, i.e., lower error (2.5%, two of them) and higher error (8.6% and 16.3%, the other two). The dielectric technique, even though did not produce the lowest error, provides a well-described physical model along with simple instrumentation.

Electrophysiological characterization of texture information slip-resistance dependent in the rat vibrissal nerve

BackgroundStudies in tactile discrimination agree that rats are able to learn a rough-smooth discrimination task by actively touching (whisking) objects with their vibrissae. In particular, we focus on recent evidence of how neurons at different levels of the sensory pathway carry information about tactile stimuli. Here, we analyzed the multifiber afferent discharge of one vibrissal nerve during active whisking. Vibrissae movements were induced by electrical stimulation of motor branches of the facial nerve. We used sandpapers of different grain size as roughness discrimination surfaces and we also consider the change of vibrissal slip-resistance as a way to improve tactile information acquisition. The amplitude of afferent activity was analyzed according to its Root Mean Square value (RMS). The comparisons among experimental situation were quantified by using the information theory.ResultsWe found that the change of the vibrissal slip-resistance is a way to improve the roughness discrimination of surfaces. As roughness increased, the RMS values also increased in almost all cases. In addition, we observed a better discrimination performance in the retraction phase (maximum amount of information).ConclusionsThe evidence of amplitude changes due to roughness surfaces and slip-resistance levels allows to speculate that texture information is slip-resistance dependent at peripheral level.

Non-linear dielectric spectroscopy of microbiological suspensions

BackgroundNon-linear dielectric spectroscopy (NLDS) of microorganism was characterized by the generation of harmonics in the polarization current when a microorganism suspension was exposed to a sinusoidal electric field. The biological nonlinear response initially described was not well verified by other authors and the results were susceptible to ambiguous interpretation. In this paper NLDS was performed to yeast suspension in tripolar and tetrapolar configuration with a recently developed analyzer.MethodsTripolar analysis was carried out by applying sinusoidal voltages up to 1 V at the electrode interface. Tetrapolar analysis was carried on with sinusoidal field strengths from 0.1 V cm-1 to 70 V cm-1. Both analyses were performed within a frequency range from 1 Hz through 100 Hz. The harmonic amplitudes were Fourier-analyzed and expressed in dB. The third harmonic, as reported previously, was investigated. Statistical analysis (ANOVA) was used to test the effect of inhibitor an activator of the plasma membrane enzyme in the measured response.ResultsNo significant non-linearities were observed in tetrapolar analysis, and no observable changes occurred when inhibitor and activator were added to the suspension. Statistical analysis confirmed these results.When a pure sinus voltage was applied to an electrode-yeast suspension interface, variations higher than 25 dB for the 3rd harmonic were observed. Variation higher than 20 dB in the 3rd harmonics has also been found when adding an inhibitor or activator of the membrane-bounded enzymes. These variations did not occur when the suspension was boiled.DiscussionThe lack of result in tetrapolar cells suggest that there is no, if any, harmonic generation in microbiological bulk suspension. The non-linear response observed was originated in the electrode-electrolyte interface. The frequency and voltage windows observed in previous tetrapolar analysis were repeated in the tripolar measurements, but maximum were not observed at the same values.ConclusionContrary to previous assertions, no repeatable dielectric non-linearity was exhibited in the bulk suspensions tested under the field and frequency condition reported with this recently designed analyzer. Indeed, interface related harmonics were observed and monitored during biochemical stimuli. The changes were coherent with the expected biological response.

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 students 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.

Design and construction of a photoresistive sensor for monitoring the rat vibrissal displacement.

Rats sweep their vibrissae in a rhythmic and coordinated fashion in order to acquire tactile information from their environment. Measuring vibrissae movement has become a matter of increased attention, from several labs, over the last few years. We describe the design and construction of an inexpensive photoresistive sensor that registers horizontal vibrissae movement. The device consists of an LED array and a light-dependent resistor (LDR) covered by a coating with varying transparency along its axis. When a vibrissa is located in the sensor, it generates a shadowy line over the photosensitive material, thus changing the LDR resistance. These changes are transduced into voltage changes. Our measurements on vibrissa show that this simple and inexpensive sensor effectively monitors the movement of a single vibrissa.