Design, Construction and Validation of an Electrical Impedance Probe with Contact Force and Temperature Sensors Suitable for in-vivo Measurements

Bioimpedance spectroscopy measurements can be used for tissue characterization. These measurements can be performed in soft tissues by direct contact of a non-invasive probe consisting of two or four electrodes. The amount of force applied by users can be quite different, and the measurements can vary as a result. To compensate for this, we have built an electrical impedance probe (diameter 3.2 mm) with fibre optic contact-force and temperature sensors built in it. The different sensors of the probe were tested individually. The errors in magnitude and phase angle of the probe are <0.9% and <4°, respectively, for a 0.9% NaCl solution. The linear dynamic range of the force sensor was from 0 to 100 grams. An ex-vivo experiment on a section of proximal colon from a guinea-pig was performed. Twenty bioimpedance measurements were taken in a frequency range of 5 kHz to 1 MHz, while simultaneously recording the force applied. For an increase in contact pressure applied to tissue from 0 to 15.4 kPa, the maximum change in resistivity was 33% at 5 kHz and the minimum was 6.6% at 142 kHz. The probe is small enough to be introduced via the instrument port of an endoscope.

Bioimpedance analysis vs. DEXA as a screening tool for osteosarcopenia in lean, overweight and obese Caucasian postmenopausal females

BACKGROUND-OBJECTIVES

We aimed at evaluating the efficiency of a newly developed, advanced Bioimpedance Analysis (BIA-ACC®) device as a screening tool for determining the degree of obesity and osteosarcopenia in postmenopausal women with normal or decreased bone density determined by Dual-Energy X-Ray absorptiometry (DEXA) in a representative sample of Greek postmenopausal women.

METHODS

This is a single-gate cross-sectional study of body composition measured by BIA-ACC® and DEXA. Postmenopausal females with BMI ranging from 18.5 to 40 kg/m2 were subjected to two consecutive measurements of DEXA and BIA-ACC® within 5-10 minutes of each other. We used Pearson's co-efficient to examine linear correlations, the intraclass correlation co-efficient (ICC) to test reliability, Bland-Atman plots to assess bias and Deming regressions to establish the agreement in parameters measured by BIA-ACC® and DEXA. Last, we used ANOVA, with Bonferroni correction and Dunnett T3 post hoc tests, for assessing the differences between quantitative and Pearson's x2 between qualitative variables.

SAMPLE AND RESULTS

Our sample consisted of 84 overweight/obese postmenopausal women, aged 39-83 years, of whom 22 had normal bone density, 38 had osteopenia and 24 had osteoporosis based on DEXA measurements, using quota sampling. ICCs and Deming regressions showed strong agreement between BIA-ACC® and DEXA and demonstrated minimal proportional differences of no apparent clinical significance. Bland-Altman plots indicated minimal biases. Fat, skeletal and bone mass measured by BIA-ACC® and DEXA were increased in the non-osteopenic/non-osteoporotic women compared with those of the osteopenic and osteoporotic groups.

CONCLUSIONS

BIA-ACC® is a rapid, bloodless and useful screening tool for determining body composition adiposity and presence of osteo-sarcopenic features in postmenopausal women. Women with osteopenia and osteoporosis evaluated by DEXA had decreased fat, skeletal and bone mass compared with normal bone density women, suggesting concordance in the change of these three organ masses in postmenopausal women.

Modeling the microscopic electrical properties of thrombin binding aptamer (TBA) for label-free biosensors

Aptamers are chemically produced oligonucleotides, able to bind a variety of targets such as drugs, proteins and pathogens with high sensitivity and selectivity. Therefore, aptamers are largely employed for producing label-free biosensors (aptasensors), with significant applications in diagnostics and drug delivery. In particular, the anti-thrombin aptamers are biomolecules of high interest for clinical use, because of their ability to recognize and bind the thrombin enzyme. Among them, the DNA 15-mer aptamer (TBA), has been widely explored around the possibility of using it in aptasensors. This paper proposes a microscopic model of the electrical properties of TBA and of the aptamer-thrombin complex, combining information from both structure and function, following the issues addressed in an emerging branch of electronics known as proteotronics. The theoretical results are compared and validated with measurements reported in the literature. Finally, the model suggests resistance measurements as a novel tool for testing aptamer-target affinity.

A critical evaluation of bioimpedance spectroscopy analysis in estimating body composition during GH treatment: comparison with bromide dilution and dual X-ray absorptiometry

OBJECTIVE

To compare estimates by bioimpedance spectroscopy analysis (BIS) of extracellular water (ECW), fat mass (FM), and fat-free mass (FFM) against standard techniques of bromide dilution and dual energy X-ray absorptiometry (DXA) during intervention that causes significant changes in water compartments and body composition.

METHODS

Body composition analysis using BIS, bromide dilution, and DXA was performed in 71 healthy recreational athletes (43 men, 28 women; aged 18-40 years; BMI 24 ± 0.4 kg/m(2)) who participated in a double-blinded, randomized, placebo-controlled study of GH and testosterone treatment. The comparison of BIS with bromide dilution and DXA was analyzed using linear regression and the Bland-Altman method.

RESULTS

At baseline, there was a significant correlation between BIS and bromide dilution-derived estimates for ECW, and DXA for FM and FFM (P<0.001). ECW by BIS was 3.5 ± 8.1% lower compared with bromide dilution, while FM was 22.4 ± 26.8% lower and FFM 13.7 ± 7.5% higher compared with DXA (P<0.01). During treatment, the change in ECW was similar between BIS and bromide dilution, whereas BIS gave a significantly greater reduction in FM (19.4 ± 44.8%) and a greater increase in FFM (5.6 ± 3.0%) compared with DXA (P<0.01). Significant differences in body composition estimates between the BIS and DXA were observed only in men, particularly during the treatment that caused greatest change in water compartments and body composition.

CONCLUSION

In healthy adults, bioimpedance spectroscopy is an acceptable tool for measuring ECW; however, BIS overestimates FFM and substantially underestimates FM compared with DXA.

Effects of the electrode size and modification protocol on a label-free electrochemical biosensor

In the present work, the effect of a surface modification protocol along with the electrode size has been investigated for developing an efficient, label-free electrochemical biosensing method for diagnosis of traumatic brain injury (TBI) biomarkers. A microdisk electrode array (MDEA) and a macroelectrode with a comb structure (MECS) were modified with an anti-GFAP (GFAP = glial fibrillary acidic protein) antibody using two protocols for optimum and label-free detection of GFAP, a promising acute-phase TBI biomarker. For the MDEA, an array of six microdisks with a 100 μm diameter and, for the MECS, a 3.2 mm × 5.5 mm electrode 5 μm wide with 10 μm spaced comb fingers were modified using an optimized protocol for dithiobis(succinimidyl propionate) (DSP) self-assembled monolayer formation. Anti-GFAP was covalently bound, and the remaining free DSP groups were blocked using ethanolamine (Ea). Sensors were exposed to solutions with different GFAP concentrations, and a label-free electrochemical impedance spectroscopy (EIS) technique was used to determine the concentration. EIS results confirmed that both types of Ea/anti-GFAP/DSP/Au electrodes modified with an optimized DSP-based protocol can accurately detect GFAP in the range of 1 pg mL(-1) to 100 ng mL(-1) with a detection limit of 1 pg mL(-1). However, the cross-use of the MDEA protocol on the MECS and vice versa resulted in very low sensitivity or poor signal resolution, underscoring the importance of proper matching of the electrode size and type and the surface modification protocol.