Paolo Lago

A quasielastic light scattering detector for chromatographic analysis

Very sensitive laser light scattering equipment has been designed to be used in conjunction with chromatographic column separation. The system is prealigned and fully computer controlled. It gives the hydrodynamic radius of the eluting particles on line during separation. With a He‐Ne laser source, the sensitivity is reached with four optical channels and four correlation functions of the scattered light measured in parallel with a special correlator.

AN INTEGRATED INSTRUMENTATION FOR LIGHT-SCATTERING AND TIME-RESOLVED FLUORESCENCE MEASUREMENTS

An integrated instrumentation which combines in the same system static and dynamic laser light scattering and time‐resolved fluorescence spectroscopy is described. The two types of measurements can be performed simultaneously on the same sample contained in a thermostated cuvette. The light scattering allows measurements of molecular weights and hydrodynamic radii in the range of 20 A to a few micrometers. The overall time resolution of fluorescence measurements is around 50 ps. The system provides the simultaneous acquisition of the fluorescence decay curve, of the time integrated emission spectrum, and of two time‐gated spectra. The light‐scattering technique gives information on the global structure of the aggregates, while fluorescence measurements are sensitive to the local interactions of a fluorescence probe with the surroundings. The contemporary use of these two complementary techniques can be quite valuable mostly for biological samples for which stability and reproducibility with time can somet...

Optical interferometer for gas bubble vibration measurements with Angstrom sensitivity

An optical interferometer which measures the radial pulsations of gas bubbles in liquids with Angstrom sensitivity is described. The gas–liquid interfaces act as mirrors. The interferometer, intrinsically differential, is insensitive to the overall movement of the bubble and to vibrations of the optical components. Examples of the resonance behavior of oxygen bubbles in water are given.

Characterization of a vesicle distribution in equilibrium with larger aggregates by accurate static and dynamic laser light scattering measurements

After a brief review of the static and dynamic light scattering theory from large particles, an experimental situation of a vesicle distribution in equilibrium with large aggregates is presented. It is shown that light scattering results in this complicated situation can be properly interpreted only if dynamic data are combined with absolute intensity measurements.

Microcontroller-based digital front-end for near-infrared spectroscopy

Near IR Spectroscopy (NIRS) can be employed to noninvasively and continuously measure in-vivo local changes in haemodynamics and oxygenation of human tissues. Monitoring of these parameters is particularly useful both for basic research and during surgery, when a continuous and real-time measurement can help to avoid permanent damage to the tissues. We present a modular acquisition system in which each subsystem, from the case to the single acquisition front-end is designed to meet all the requirements of a research-grade instrument, dedicated to intraoperatory measurements. Part of the modules of the acquisition system has been dedicated to multipoint NIRS. A module prototype has been developed, which is able to control four LED sources and two detectors. On each front-end a RISC microcontroller performs source and detector multiplexing with a digital correlation technique. A number of such modules can be independently addressed through a bus by a PC-based workstation for data collection, processing and visualization. Preliminary test of the prototype on tourniquet-induced forearm ischemia show adequate detectivity and time response. The operating parameters derived from the prototype will be employed in the design of a high channel count module, which will exploit the capabilities of a digital signal processor, for spatially mapped brain oxygenation monitoring.

Portable microcontroller-based instrument for near-infrared spectroscopy

Near IR Spectroscopy (NIRS) can be employed to noninvasively and continuously measure in-vivo local changes in haemodynamics and oxygenation of human tissues. In particular, the technique can be particularly useful for muscular functional monitoring. We present a portable NIRS research-grade acquisition system prototype, strictly dedicate to low-noise measurements during muscular exercise. The prototype is able to control four LED sources and a detector. Such a number of sources allows for multipoint measurements or for multi-wavelength spectroscopy of tissue constituents other than oxygen, such as cytochrome aa3 oxidation. The LEDs and the detector are mounted on separate probes, which carry also the relevant drivers and preamplifiers. By employing surface-mount technologies, probe size and weight are kept to a minimum. A single-chip mixed-signal RISC microcontroller performs source-to- detector multiplexing with a digital correlation technique. The acquired data are stored on an on-board 64 K EEPROM bank, and can be subsequently uploaded to a personal computer via serial port for further analysis. The resulting instrument is compact and lightweight. Preliminary test of the prototype on oxygen consumption during tourniquet- induced forearm ischaemia show adequate detectivity and time response.

Simple NIR instrument for diagnostic purposes

A noninvasive NIR instrument for diagnostic purposes is presented. It is specifically designed for clinical tests during exercise. The instrument makes use of the most modern optical components and a high performance front-end electronics to enhance the signal to noise ratio and to reject stray light effect. A new signal analysis is proposed. The main features are low noise, high stability and readability.

An optical interferometer for gas bubble measurements

A compact and stable interferometer for the measurement of the radius of a gas bubble in a liquid is described. The system combines a very high sensitivity in radius change measurements (1 A) with a good determination of the absolute value of the radius itself.

Simple instrument for the characterization of diffuse reflectance

An apparatus for the measurement of the radial dependence of the continuous-wave diffuse reflectance of a tissue is described. It consists in a probe, which is applied on the tissue, and a detection unit. By employing an array of incoherent semiconductor light sources (LEDs) and continuous- wave detection, probe structure is considerably simpler than other devices described in literature, allowing moreover an efficient coupling of the emitted light towards the tissue. The high responsivity so obtained permits fast and accurate measurements. Measurement speed, probe compactness and accuracy are potentially sufficient for the in-vivo application of the method to surgically exposed tissue. A preliminary set of data, measured on a scattering phantom and on non-exposed in-vivo tissue, is presented. Even though available models fitted to the measured data give the correct order of magnitude for light transport coefficients, in order to extract reliable absolute values they should be corrected for probe nonidealities. The availability of extensive high- quality in-vivo data is to this regard stimulating for further theoretical investigations.

Simple noninvasive laser diode oxymeter for measurements on human tissues

A compact, light, easy to use, and low cost instrument with technical solutions that make it suitable for wide clinical use is presented. It is specifically designed for rehabilitation of patients after heart failure. The instrument makes use of low power laser diodes, at 750 and 810 nm, and a remote fiber optic probe. Reflectance change at two wavelengths is used to determine variations of the oxygen content of tissues. A time-variant filter enhances signal to noise ratio and rejects stray light. This specific electronic device allows the use of a low-cost, small and reliable photodiode in place of a photomultiplier tube. Time division techniques is used to process both 750 and 810 signals with a single collecting fiber, photodiode, and preamplifier. The instrument output is two analog signals proportional to the reflectance intensities at 750 and 810 nm, so it is possible to acquire these signals by a PC with a standard A/D board to drive directly a chart recorder. Some clinical tests during the exercise are presented.