Susanna Bracci

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.

Spectroscopic behavior of acid-base indicators after immobilization on glass supports

This paper describes an extensive spectrophotometric study on several acid-base indicators immobilized, by means of a silylation process, on quartz powder and on controlled pore glass. The spectrophotometric properties of the immobilized indicators are at variance with those of the free indicators with respect to pH dependence and ranges. The different behavior of both types of indicators in the liquid and immobilized phases may be explained by both a modification in the electronic structure of the indicators and a distribution of the molecules on different sites. The differences among the spectrophotometric properties of the indicators, when these are immobilized on different solid supports, can be justified by taking into account the steric hindrance and the reactivity of the indicators. Particular attention was paid to the pH-sensitive bands and their position, keeping in mind that the investigated material could possibly be used as a transducer for pH fiber-optic sensors.

Cross-section and staining-based techniques for investigating organic materials in painted and polychrome works of art: a review.

The article presents a review of the use of cross-section and staining techniques for investigating natural organic materials (mainly proteinaceous and oil-based binders/varnishes) in painted and polychrome artworks, considering the requirements of conservation practice and routine diagnostics. The reviewed literature calls attention to the importance of using cross sections to prepare samples for optical microscopy and to different properties of embedding resins; the most appropriate instrumental conditions for optical microscopy; and the advantages and disadvantages of the most common staining techniques. A few case studies were selected to illustrate the use of autofluorescence (intrinsic fluorescence) and induced fluorescence (using specific staining tests and fluorophore-labeled antibodies) for mapping and identifying organic paint materials in cross sections. New directions of research in cross-section analyses and fluorescence-based techniques for the identification and mapping of artistic materials are presented. The complementary use of different stains on the same cross section, further exploration of intrinsic and induced fluorescence of aged versus fresh materials, and applicability of cross-section observation and staining as complementary methods for assessing the effectiveness of restoration treatments, such as cleaning and consolidation, are discussed in the last section of the article.

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.

Library of UV-Vis-NIR reflectance spectra of modern organic dyes from historic pattern-card coloured papers.

An accurate characterisation of the organic dyes used in artworks, especially those made of paper, is an important factor in designing safe conservation treatments. In the case of synthetic organic dyes used in modern works of art, for example, one frequently encountered difficulty is that some of these dyes are not still commercially available. Recognizing this problem, the authors of this paper present the results of an analysis of UV-Vis-NIR fibre optic reflectance spectra of 82 samples of dyed paper prepared with 41 dyes. The samples come from a historic book, The Dyeing of Paper in the Pulp, which was published by Interessen-Gemeinschaft (I.G.) Farbenindustrie in 1925. The dyes used in the paper pulp belong to the azo compounds, acridine, anthraquinone, azine, diphenylmethane, indigoid, methine, nitro, quinoline, thiazine, triphenylmethane, sulphur and xanthene classes.

Lidar remote sensing of stone cultural heritage: detection of protective treatments

Treatments utilizing different chemical compositions are employed to preserve the surface of historical stone building. The uniform distribution of the protective treatment and the conservation of its integrity over the years are crucial factors for an efficient protection of monuments. A technique that enables a remote mapping of the treatment and its characteristics is therefore very attractive. We describe the first experiments devoted to the investigation of the potential of fluorescence lidar in monitoring protective treatments on stone surfaces. Dolomitic marble samples are treated with different protective substances, and are then analyzed by a laboratory setup that simulates a lidar measurement. Although further investigations will be necessary, these laboratory results indicate an interesting potential for lidar in the nondestructive, remote monitoring of protective treatments.

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.

Optical-fibre sensors by silylation techniques☆

Abstract The detection of chemical parameters by means of optical fibres has had a decisive boost in recent years; the realization of these devices is related to the development of a great number of techniques. The former are characterized by a reagent fixed to an optical fibre, a procedure which is not in itself unique. The silylation technique is one of the most widely used for optrode realization. It generally involves an organosilicon compound that reacts with an external support or directly on the surface of the fibres with one or more functional groups and gives the supports a new functionality. Obviously the activation of the surface must be followed by other appropriate reactions so as to be able to immobilize the optically sensitive reagent. Silylation can be performed either on external glass or quartz supports or directly on the fibre itself. From a chemical point of view, there is not a big difference on where the chemical reaction takes place, but the same cannot be stated from the optical point of view. By changing where the silylation is performed, it is possible to change the optical path and consequently the signal-to-noise ratio, which is strictly related to the performance of the sensor. In fact, if the optical-fibre sensor is to be launched on the market, it must be competitive, in terms of cost and performance, when compared with other instruments that measure the same chemical species. Some of the most significant silylated optrodes are reported here, together with the associated optoelectronic instrumentation. Moreover, the advantages and drawbacks of the different procedures are taken into account.

Analysis of acid-base indicators covalently bound on glass supports

An accurate spectrophotometric study on acid-base indicators immobilized by a silylation process is described. Immobilization modifies the acid-base properties of the indicators: a comparison with their behaviour in solution was made. Particular care was paid to the presence of hysteresis to the sensitivity and also to the peak wavelength. Early measurements performed with optical fibers were also described.

Multidisciplinary approach for the study of an Egyptian coffin (late 22nd/early 25th dynasty): Combining imaging and spectroscopic techniques

This paper demonstrates that an educated methodology based on both non-invasive and micro invasive techniques in a two-step approach is a powerful tool to characterize the materials and stratigraphies of an Egyptian coffin, which was restored several times. This coffin, belonging to a certain Mesiset, is now located at the Museo Civico Archeologico of Bologna (inventory number MCABo EG 1963). Scholars attributed it to the late 22nd/early 25th dynasty by stylistic comparison. The first step of the diagnostic approach applied imaging techniques on the whole surface in order to select measurements spots and to unveil both original and restored areas. Images and close microscopic examination of the polychrome surface allowed selecting representative areas to be investigated in situ by portable spectroscopic techniques: X-ray Fluorescence (XRF), Fiber Optic Reflectance Spectroscopy (FORS) and Fourier Transform Infrared spectroscopy (FTIR). After the analysis of the results coming from the first step, very few selected samples were taken to clarify the stratigraphy of the polychrome layers. The first step, based on the combination of imaging and spectroscopic techniques in a totally non-invasive modality, is quite unique in the literature on Egyptian coffins and enabled us to reveal many differences in the ground layers composition and to identify a remarkable number of pigments in the original and restored areas. This work offered also a chance to check the limitations of the non-invasive approach applied on a complex case, namely the right localization of different materials in the stratigraphy and the identification of binding media. Indeed, to dissolve any remaining doubts on superimposed layers belonging to different interventions, it was necessary to sample few micro-fragments in some selected areas and analyze them prepared as cross-sections. The original ground layer is made of calcite, while the restored areas show the presence of either a mixture of calcite and silicates or a gypsum ground, overlapped by lead white. The original pigments were identified as orpiment, cinnabar and red clay, Egyptian blue and green copper based pigments. Some other pigments, such as white lead, Naples yellow, cerulean blue and azurite were only found in the restored areas.