F. Cosi

Long-term ambulatory enterogastric reflux monitoring. Validation of a new fiberoptic technique.

A new technique for the long-term ambulatory detection of enterogastric and nonacid gastroesophageal reflux has been conceived, developed, and validated. It is based on the use of a fiberoptic sensor that utilizes the optical properties of bile.In vitro studies have shown good precision, good stability, sensitivity of 2.5 μmol/liter bilirubin concentration, as well as a useful working range of 2.5–100 μmol/liter bilirubin concentration.In vivo studies have been performed in 29 subjects. Simultaneous gastric aspirations have allowed a comparison of fiberoptic system measurements both with spectrophotometric analysis and bile acid concentrations of corresponding gastric juice samples. Linear correlations were shown between fiberoptic assessment and both spectrophotometric and bile acid concentration findings (P<0.01). Simultaneous assessment of reflux with the fiberoptic system and cholescintigraphy has shown a 92.9% concordance as regards the presence or absence of reflux. Present results imply that the fiberoptic system is an important tool for the understanding of the clinical relevance of enterogastric and nonacid gastroesophageal reflux.

Optical Microspherical Resonators for Biomedical Sensing

Optical resonators play an ubiquitous role in modern optics. A particular class of optical resonators is constituted by spherical dielectric structures, where optical rays are total internal reflected. Due to minimal reflection losses and to potentially very low material absorption, these guided modes, known as whispering gallery modes, can confer the resonator an exceptionally high quality factor Q, leading to high energy density, narrow resonant-wavelength lines and a lengthy cavity ringdown. These attractive characteristics make these miniaturized optical resonators especially suited as laser cavities and resonant filters, but also as very sensitive sensors. First, a brief analysis is presented of the characteristics of microspherical resonators, of their fabrication methods, and of the light coupling techniques. Then, we attempt to overview some of the recent advances in the development of microspherical biosensors, underlining a number of important applications in the biomedical field.

In vivo optical-fibre pH sensor for gastro-oesophageal measurements

Abstract The present work is concerned with the development of an optical-fibre sensor for monitoring pH in the foregut in the extended range 1.0–8.0. Controlled pore glasses (CPGs), with covalently bound chromophore, are fixed at the end of plastic optical fibres using a proprietary process. A good sensitivity, fast response time, the small dimensions of the probe and the biocompatibility of the materials utilized make the sensor suitable for in vivo measurements.

Controlled-Pore Glasses Embedded in Plastic Optical Fibers for Gastric pH Sensing Purposes

The present work is concerned with the development of an optical-fiber pH sensor for gastric monitoring. Bromophenol blue is used as a chromophore, which is immobilized on controlled-pore glasses (CPGs) by means of a silylation process. As far as the optoelectronic unit is concerned, light-emitting diodes as sources and an appropriate electronic circuit as detection system are utilized. Treated CPGs are fixed at the end of two plastic optical fibers (core diameter = 500 μm) by means of a proprietary process; a reflector made of Teflon®, anchored to the distal end of the fibers, ensures good fibers/probe coupling efficiency. The behavior of the realized probe is carefully investigated, with particular attention devoted to the presence of hysteresis, to ionic strength and temperature effect, and to its lifetime. The fast response time, thanks to the absence of a mechanical envelope, the small dimensions of the probe, and the biocompatibility of the utilized materials make this sensor suitable for in vivo measurements.

New fiber optic sensor for ambulatory entero-gastric reflux detection

The problem of entero-gastric reflux is clinically relevant and none of the presently available techniques for its detection is satisfactory. Therefore, a portable fiber optic system for ambulatory reflux assessment has been conceived and developed. Two light emitting diodes (for signal and reference) and a suitable electronic circuit for signal processing are associated with a plastic fiber optic bundle. The working principle of the system is based on the characteristic absorption of bilirubin and bile around 450 nm. In-vitro results have shown good accuracy, linearity, and stability in the measurements of the fiber optic system. In-vivo results are promising.

Absorption-based optical-fibre oxygen sensor

Abstract A model of an optical-fibre sensor for the detection of oxygen is described. Its working principle is based on the absorbance change of a bis(histidinato)cobalt(II) solution at λ = 408 nm as a function of the molecular oxygen concentration in the surrounding environment. The sensor is able to detect very low oxygen concentrations and it is potentially suitable for the detection of oxygen in hostile environments or during production processes in which oxygen must be completely absent.

An extended-range fibre-optic pH sensor

Abstract The present work is concerned with the development of an optical-fibre pH sensor, realized with acid-base indicators immobilized on controlled-pore glasses, that is able to measure gastric pH. Several acid-base indicators have been covalently bound on controlled-pore glasses by a silylation process. A shift of the absorption peak, broadening of the absorption bands and in some cases a noticeable broadening of the pH range are observed. This last characteristic must not be undervalued, because it allows pH detection with optical fibres in an extended range (at least four pH units) compared with the typical pH range of an indicator in solution (1.5–2.OpH units). Particular care is also devoted to the presence of hysteresis and the ionic-strength effect, which can greatly decrease the lifetime of the probe and often prevents the use of the sensor for biomedical applications. A very compact and easy transportable sensor has been developed, equipped with an internal microprocessor that processes the signals and gives the results on a liquid-crystal display. The optical-fibre probe is constituted by a stainless-steel capillary drilled on the lateral surface with 7Oμm holes and filled with treated controlled-pore glasses. A sensitivity of 0.007 pH units in the range 2.00–4.00 and of 0.015 in the extended range 1.2–5.2 is reached.

Performance of Eudragit coated whispering gallery mode resonator-based immunosensors.

Whispering gallery mode resonators (WGMR) are an efficient tool for the realization of optical biosensors. A high Q factor preservation is a crucial requirement for good biosensor performances. In this work we present an Eudragit®L100 coated microspherical WGMR as an efficient immunosensor. The developed resonator was morphologically characterized using fluorescence microscopy. The functionalization process was tuned to preserve the high Q factor of the resonator. The protein binding assay was optically characterized in terms of specificity in buffer solution.

A Compact Optical Fibre Device For The Detection Of PH

The study and the development on an optical fibre sensor for the detection of pH is described. Phenol red, immobilized on XAD-2 microspheres, was used as pH indicator. Particular care was devoted in the planning and construction of the probe in order to obtain high sensitivity and good signal levels. The measuring apparatus is described as well as experimental results are reported.

Optical Fiber Nanotips Coated with Molecular Beacons for DNA Detection

Optical fiber sensors, thanks to their compactness, fast response and real-time measurements, have a large impact in the fields of life science research, drug discovery and medical diagnostics. In recent years, advances in nanotechnology have resulted in the development of nanotools, capable of entering the single cell, resulting in new nanobiosensors useful for the detection of biomolecules inside living cells. In this paper, we provide an application of a nanotip coupled with molecular beacons (MBs) for the detection of DNA. The MBs were characterized by hybridization studies with a complementary target to prove their functionality both free in solution and immobilized onto a solid support. The solid support chosen as substrate for the immobilization of the MBs was a 30 nm tapered tip of an optical fiber, fabricated by chemical etching. With this set-up promising results were obtained and a limit of detection (LOD) of 0.57 nM was reached, opening up the possibility of using the proposed nanotip to detect mRNAs inside the cytoplasm of living cells.