Luca Lanzanò

Single seed viability checked by delayed luminescence

Time resolved spectral components of delayed luminescence (DL) from single dry soybean seeds were measured using a device with single photon sensitivity. The seeds were aged by a thermal treatment to change their viability. A correlation was observed between the seeds viability and some DL parameters, i.e. the total number of photons emitted and the relative decay probability of excited states. This relevant result confirms the close connection between the state of biological systems and their DL, and it can allow the development of a quick selection technique for single dry seeds, a goal impossible up today.

Delayed luminescence of microalgae as an indicator of metal toxicity

The delayed luminescence (DL) (i.e. the photo-induced photon emission long after the illumination is switched off) of unicellular green algae samples has been measured when different concentrations of heavy metals are added to the standard culture medium, with the aim of assessing the DL as a promising approach for assaying the toxicity of contaminants such as metals. In particular, samples of freshwater green micro-algae Selenastrum capricornutum have been used. Concentrations of cadmium, chromium, lead and copper, ranging from 10−5 to 10−2 M, have been tested. The analysis of the decay trends, in the time interval from tens of microseconds to seconds, of the DL spectral components demonstrates that the DL parameters are sensitive to the presence of such pollutants. More precisely, the performed analysis allowed us to determine phenomenological relationships between the DL parameters and the metal concentration that could be used in view of the possibility of realizing a biosensor for water pollution detection. Attempts to distinguish between different contaminants are also described. Results of this preliminary study show that the DL measure based technique is suitable as a general bioassay of metal contamination and it could also be used to test the efficiency in bioavailability studies.

Single Photon Avalanche Diodes: Towards the Large Bidimensional Arrays

Single photon detection is one of the most challenging goals of photonics. In recent years, the study of ultra-fast and/or low-intensity phenomena has received renewed attention from the academic and industrial communities. Intense research activity has been focused on bio-imaging applications, bio-luminescence, bio-scattering methods, and, more in general, on several applications requiring high speed operation and high timing resolution. In this paper we present design and characterization of bi-dimensional arrays of a next generation of single photon avalanche diodes (SPADs). Single photon sensitivity, dark noise, afterpulsing and timing resolution of the single SPAD have been examined in several experimental conditions. Moreover, the effects arising from their integration and the readout mode have also been deeply investigated.

Time-resolved spectral measurements of delayed luminescence from a single soybean seed: effects of thermal damage and correlation with germination performance

Delayed luminescence from a single dry soybean seed was investigated in both spectral and time domains, under different excitation wavelengths. Emission spectra were collected, under 337 nm laser excitation, from native and artificially deteriorated seeds and the time-dependence of different spectral components was analyzed in detail. The single seed viability was evaluated through observation of germination properties after imbibition and compared with different parameters related to the luminescence kinetics. The significant correlation found between single seed delayed luminescence parameters and germination capability strongly validates the connection of this phenomenon with the functional state of the system and suggests the development of a non-invasive technique for seed quality determination.

A New Generation of SPAD—Single-Photon Avalanche Diodes

Design and characterization of a new generation of single-photon avalanche diodes (SPAD) array, manufactured by ST-Microelectronics in Catania, Italy, are presented. Device performances, investigated in several experimental conditions and here reported, demonstrate their suitability in many applications. SPADs are thin p-n junctions operating above the breakdown condition in Geiger mode at low voltage. In this regime a single charged carrier injected into the depleted layer can trigger a self-sustaining avalanche, originating a detectable signal. Dark counting rate at room temperature is down to 10 s-1 for devices with an active area of 10 mum in diameter, and 103 s-1 for those 50 mum wide. SPAD quantum efficiency, measured in the range 350-1050 nm, can be comparable to that of a typical silicon based detector and reaches the values of about 50% at 550 nm. Finally, the low production costs and the integration possibility are other favorable features in sight of highly dense integrated 1-D or 2-D arrays.

Delayed luminescence: a novel technique to obtain new insights into water structure

Fully understanding the structure of water is a crucial point in biophysics because this liquid is essential in the operation of the engines of life. Many of its amazing anomalies seem to be tailored to support biological processes and, during about a century, several models have been developed to describe the water structuring. In particular, a theory assumes that water is a mixture of domains constituted by two distinct and inter-converting structural species, the low-density water (LDW) and the high-density water (HDW). According to this theory, by using some particular solutes or changing the water temperature, it should be possible to modify the equilibrium between the two species, changing in this way the water behavior in specific biological processes, as in governing the shape and stability of the structures of proteins. In this work, we assess the possibility of obtaining information on the structures induced in water by specific salts or by temperature by measuring the delayed luminescence (DL) of some salt solutions and of water in the super-cooled regime. Previous works have demonstrated that the delayed luminescence of a system is correlated with its dynamic ordered structures. The results show significant DL signals only when the formation of LDW domains is expected. The measurement reveals a similar activation energy for the domains both in aqueous salt solutions and super-cooled water. It is worth noting that the time trend of DL signals suggests the existence of structures unusually long-lasting in time, up to the microsecond range.

Spectral analysis of photo-induced delayed luminescence from human skin in vivo

The UVA induced Delayed Luminescence (DL), has been measured in vivo in the forearm skin of some healthy volunteers of different sex and age during several periods of the year. An innovative instrument able to detect, in single photon counting mode, the spectrum and the time trend of the DL emission has been used. The measured differences in the time trends of the spectral components may be related to the sex and the age. The potential development of a new analysis technique based on this phenomenon is discussed.