Point-of-Need bioanalytics based on planar optical interferometry.

This review brings about a comprehensive presentation of the research on interferometric transducers, which have emerged as extremely promising candidates for viable, truly-marketable solutions for PoN applications due to the attested performance that has reached down to 10(-8) in term of effective refractive index changes. The review explores the operation of the various interferometric architectures along with their design, fabrication, and analytical performance aspects. The issues of biosensor functionalization and immobilization of receptors are also addressed. As a conclusion, the comparison among them is attempted in order to delve into and acknowledge their current limitations, and define the future trends.

Monolithically integrated broad-band Mach-Zehnder interferometers for highly sensitive label-free detection of biomolecules through dual polarization optics.

Protein detection and characterization based on Broad-band Mach-Zehnder Interferometry is analytically outlined and demonstrated through a monolithic silicon microphotonic transducer. Arrays of silicon light emitting diodes and monomodal silicon nitride waveguides forming Mach-Zehnder interferometers were integrated on a silicon chip. Broad-band light enters the interferometers and exits sinusoidally modulated with two distinct spectral frequencies characteristic of the two polarizations. Deconvolution in the Fourier transform domain makes possible the separation of the two polarizations and the simultaneous monitoring of the TE and the TM signals. The dual polarization analysis over a broad spectral band makes possible the refractive index calculation of the binding adlayers as well as the distinction of effective medium changes into cover medium or adlayer ones. At the same time, multi-analyte detection at concentrations in the pM range is demonstrated.

All-silicon monolithic Mach-Zehnder interferometer as a refractive index and bio-chemical sensor.

A complete Mach-Zehnder interferometer monolithically integrated on silicon is presented and employed as a refractive index and bio-chemical sensor. The device consists of broad-band light sources optically coupled to photodetectors through monomodal waveguides forming arrays of Mach-Zehnder interferometers, all components being monolithically integrated on silicon through mainstream silicon technology. The interferometer is photonically engineered in a way that the phase difference of light travelling through the sensing and reference arms is approximately wavelength independent. Consequently, upon effective medium changes, it becomes feasible even with a broad-band source to induce sinusoidal-type of detector photocurrents similar to the classical monochromatic counterparts. The device is completed with its fluidic and interconnect components so that on chip interferometric measurements can be performed. Examples of refractive index and protein sensing are presented to establish the potential of the proposed device for real-time in situ monitoring applications. This is the only silicon device that has achieved complete on-chip interferometry.

Broad-band Mach-Zehnder interferometers as high performance refractive index sensors: theory and monolithic implementation.

Broad-band Mach-Zehnder interferometry is analytically described and experimentally demonstrated as an analytical tool capable of high accuracy refractive index measurements over a wide spectral range. Suitable photonic engineering of the interferometer sensing and reference waveguides result in sinusoidal TE and TM spectra with substantially different eigen-frequencies. This allows for the instantaneous deconvolution of multiplexed polarizations and enables large spectral shifts and noise reduction through filtering in the Fourier Transform domain. Due to enhanced sensitivity, optical systems can be designed that employ portable spectrum analyzers with nm range resolution without compromising the sensor analytical capability. Practical detection limits in the 10(-6)-10(-7) RIU range are achievable, including temperature effects. Finally, a proof of concept device is realized on a silicon microphotonic chip that monolithically integrates broad-band light sources and single mode silicon nitride waveguides. Refractive index detection limits rivaling that of ring resonators with externally coupled laser sources are demonstrated. Sensitivities of 20 µm/RIU and spectral shifts in the tens of a pm are obtained.

Protein adsorption and covalent bonding to silicon nitride surfaces modified with organo-silanes: comparison using AFM, angle-resolved XPS and multivariate ToF-SIMS analysis.

Organo-silanes provide a suitable interface between the silicon-based transducers of various biosensing devices and the sensing proteins, immobilized through physical adsorption, as for (3-aminopropyl)triethoxysilane (APTES), or covalent binding, e.g. via protein amine groups to (3-glycidoxypropyl)trimethoxysilane (GOPS) modified surface. Immobilization of rabbit gamma globulins (RgG) to silicon nitride surfaces, modified either with APTES or GOPS, was examined as a function of incubation time using atomic force microscopy (AFM), angle-resolved X-ray photoelectron spectroscopy (ARXPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). Multivariate technique of principal component analysis was applied to ToF-SIMS spectra in order to enhance sensitivity of immobilized RgG detection. Principal component regression shows a linear relationship with surface density determined rigorously from ARXPS following an organic bilayer approach, allowing for protein coverage quantification by ToF-SIMS. Taking it overall the surface immobilized amount of RgG is higher and develops faster on the surfaces silanized with APTES rather than with GOPS. Similar, although less distinct, difference is observed between the two surface types concerning the temporal evolution of average AFM height. The average height of protein overlayer correlates well with ARXPS and ToF-SIMS data expressed in terms of protein surface density. However, determined linear regression coefficients are distinctively higher for the surfaces modified with epoxy- rather than amino-silane, suggesting different surface density and conformation of the proteins immobilized through to covalent binding and physical adsorption.

Model immunoassay on silicon surfaces: vertical and lateral nanostructure vs. protein coverage.

To provide complete characterization of immunoassay on silicon biosensor surfaces, atomic force microscopy, (angle-resolved) X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry were applied to examine Si(3)N(4) surfaces modified with (3-aminopropyl)triethoxysilane, coated with gamma globulins (IgG), blocked with bovine serum albumin and then reacted with anti-IgG antibody for two complementary pairs (rabbit and mouse IgG) at various concentrations (from 0.3 nM to 330 nM). Protein coverage, as reflected in (amine to total N1s) XPS signal ratio and determined from ARXPS, decreases slightly due to blocking and then increases monotonically for anti-IgG antibody concentrations higher than 1 nM. AFM images reveal hardly any change of lateral nanostructure due to blocking but response to antibody solutions, based on both the mean size (from autocorrelation) and dominant spacing (from Fourier analysis) of surface features, similar to that given by ARXPS. AFM height histograms provided information about the vertical nanostructure and the parameters of height distribution (average height, spread - roughness and skewness) were distinctly influenced by coating, blocking and immunoreaction. Average protein layer thickness values determined based on protein structure (molecular weight, dimensions) and surface coverage provided from ARXPS were in accord with average height of protein layer determined from AFM. TOF-SIMS analysis indicated that BSA blocks free surface sites and in addition replaces some already adsorbed IgGs.

Spectroscopic and microscopic characterization of biosensor surfaces with protein/amino-organosilane/silicon structure.

Composition and structure of biorecognition protein layers created on silicon substrates modified with amino-organosilanes determine the sensitivity and specificity of silicon based biosensing devices. In the present work, diverse spectroscopic and microscopic methods were applied to characterize model biosensor surfaces, formed on Si(3)N(4) or SiO(2) by modification with (3-aminopropyl)triethoxysilane, coating with rabbit gamma-globulins (IgGs) through physical adsorption, blocking with bovine serum albumin (BSA) and specific binding of an anti-rabbit IgG antibody. In addition, silanized substrates with directly adsorbed BSA or anti-rabbit IgG antibody were examined as reference surfaces. The protein/amino-organosilane/silicon structure of all surfaces was confirmed by X-ray photoelectron spectroscopy. Homogeneity of protein coverage was verified with near-field scanning optical microscope, working in reflection and fluorescence mode. Surface coverage with proteins was determined with angle-resolved XPS using a previously established bilayer approach. Inner structure of protein layers was examined with atomic force microscopy. Vertical arrangement of carbon functional groups was revealed by high resolution ARXPS. Combined spectroscopic and microscopic data reveal the complex character of interactions with the immobilized IgG molecules during blocking with BSA and immunoreaction with anti-IgG antibody. Within experimental error, neither surface coverage nor lateral structural scales of protein layer (provided by Fourier and auto-correlation analysis of topographic and phase images) increase during blocking procedure. On the other hand, coverage and all structural measures rise considerably after immunoreaction. In addition, it was found that polar functional groups orient towards substrate for all protein layers, independently of coverage, prior to and after both blocking and specific binding.

Low-dimensional sagittal plane model of normal human walking.

This paper applies a robotics-inspired approach to derive a low-dimensional forward-dynamic hybrid model of human walking in the sagittal plane. The low-dimensional model is derived as a subdynamic of a higher-dimensional anthropomorphic hybrid model. The hybrid model is composed of models for single support (SS) and double support (DS), with the transition from SS to DS modeled by a rigid impact to account for the impact at heel-contact. The transition from DS to SS occurs in a continuous manner. Existing gait data are used to specify, via parametrization, the low-dimensional model that is developed. The primary result is a one-degree-of-freedom model that is an exact subdynamic of the higher-dimensional anthropomorphic model and describes the dynamics of walking. The stability properties of the model are evaluated using the method of Poincare. The low-dimensional model is validated using the measured human gait data. The validation demonstrates the observed stability of the measured gait.

Changing relative roles of hepatitis B and C viruses in the aetiology of hepatocellular carcinoma in Greece. Epidemiological and clinical observations.

Chronic infection with hepatitis B virus (HBV) has been reported in two-thirds of cases of hepatocellular carcinoma (HCC) in Greece from 1973 to 1995, while chronic hepatitis C virus (HCV) infection in 10% of them. We studied the roles of HBV and HCV in HCC in Greece between 1996 and 2000 compared with the past, and possible differences in clinical and laboratory characteristics of HBV- and HCV-related HCC. Complete clinical and laboratory data from 306 patients with HCC, diagnosed from January 1996 to December 2000, were analyzed. Chronic HBV and HCV infection were detected in 52.3 and 21.6% of the patients, respectively. The ratio of HBV- to HCV-related HCC was 2.42. Compared with the data prior to 1996, there was a 101.8% increase in the relative frequency of HCV (P < 0.0001) and an 11.8% decrease in that of HBV (P = 0.033), with a -56.3% change in the ratio of HBV- to HCV-related HCC cases. Statistically significant differences in the male/female ratio, median age and frequency of multifocal lesions were found in HBV- vs HCV-related HCC. Although HBV still represents the major aetiological factor of HCC in Greece, its role has significantly decreased in the last 5 years, while a more significant increase has occurred in HCV-related HCC. The two aetiological types of HCC differ in Greece in demographic, epidemiological and other features.

Systemic AL amyloidosis in Gaucher disease. A case report and review of the literature.

Chronic Gaucher disease [GD] in association with systemic AL amyloidosis is extremely rare. We describe a 46-year-old Greek male with chronic GD confirmed by low glucocerebroside activity in fibroblasts and N370S/L444P mutations at the cerebrosidase gene, who also had systemic AL amyloidosis diagnosed by bone marrow diffuse plasmacytosis, serum monoclonal IgA-lambda, severe total proteinuria with monoclonal IgA-lambda, Bence-Jones-lambda and amyloid deposits in bone marrow, liver, spleen and kidney biopsy specimens. Treatment with melphalan and prednizolon has dramatically decreased both levels of serum M-IgA and proteinuria and also improved the clinical symptoms of amyloidosis. He died from restrictive cardiac disease 30 months after the diagnosis of amyloidosis. Previously reported cases of GD in association with AL amyloidosis are reviewed.

Overlapping syndrome of autoimmune hepatitis and primary sclerosing cholangitis associated with pyoderma gangrenosum and ulcerative colitis.

We describe the case of a 18-year-old male patient who first presented with decompensated cirrhosis, fever and generalized lymphadenopathy. He had abnormal results for liver biochemical tests, with a hepatitic-like picture and high titre of antinuclear antibodies. According to the scoring system proposed by the International Autoimmune Hepatitis Group he had 'definite' autoimmune hepatitis and responded well to immunosuppressive treatment. One year later he developed pyoderma gangrenosum which was successfully treated with cyclosporine. Two years later he experienced bloody diarrhoea as a first presentation of ulcerative colitis. At that time both the cholestatic biochemical picture and the cholangiographic appearances of the biliary tree were consistent with primary sclerosing cholangitis. Despite the addition of azathioprine and ursodeoxycholic acid to his treatment regime he developed recurrent episodes of cholangitis and intractable pruritus for which he underwent successful liver transplantation.