Tullio Mariani

Longitudinal patterns similar to G-banding in untreated human chromosomes: evidence from atomic force microscopy

The structure of human metaphase chromosomes, fixed according to standard procedures for optical microscopy but not treated for banding, was exammed by atomic force microscopy (AFM). The images show that chromosomes display a banding pattern very similar to G-banding, detected by the AFM as a variation in the thickness of chromatin. This similarity allows the identification of individual chromosomes.

Laser thermal effects on atomic force microscope cantilevers

Abstract The effects of laser radiation on cantilevers used in atomic force microscopes have investigated. Optical parameters of the cantilevers, deflection due to radiation pressure and thermal effects have been measured on cantilevers freely moving in air. For cantilevers with a gold coating we have found thermal effects at least two orders of magnitude larger than for uncoated cantilevers.

Heterogeneous gene distribution reflects human genome complexity as detected at the cytogenetic level

Human chromosomes are heterogeneous in structure and function and this is the base for the specific banding patterns produced by various chromosome staining techniques. The Human Genome Data Base as of January 2001 was searched for genes mapped to individual chromosomal bands to study the different aspects of human genome organization as they appear at the cytogenetic level of resolution. Genes are unequally distributed both on human chromosomes and chromosome bands. Among more than 5000 genes mapped at individual bands, 81% were located in G-negative bands, which correspond to half of the human genome. The main practical value of having a dense genetic physical map of genes is to accelerate the discovery by positional candidate cloning of human disease genes. Gene content agrees with H3 family isochores and with GC-rich flavors. Interestingly, two G-positive bands, namely 2p chromosome bandings is 12 and 7q35, contain a high number of genes. The finding of heterogeneity in gene content suggests that chromosome banding is not only due to differences in gene content.

Simple, linear, and safe light control for laser diodes

A simple but useful technique for feedback stabilization and modulation of diode lasers is described. The interposition of an optoelectronic coupler between laser diode and feedback amplifier allowed safe circuitry together with good linearity and relatively high speed.

Laser light effects on force sensors in atomic-force microscopes

We discuss recent experiments investigating the effects produced by laser irradiation of cantilevers utilized as force sensors in atomic force microscopy (AFM). Thermal and pressure effects are observed for cantilevers freely moving in air. Mechanical fluctuations of the cantilevers due to thermal noise of the environment have also been measured.

Comment on “The long range voice coil atomic force microscope” [Rev. Sci. Instrum.83, 023705 (2012)]

In a recent article Barnard et al. described the use of voice coil actuators to realize a large range scanner for probe microscopy. The results reported are interesting, but the idea is not new. In two preceding papers [1998, 1991] we had described a large coverage, wide dynamic range scanner based on homemade voice coil actuators, while Garcia Cantu and Huerta Garnica [1986] had already used inductive scanners for tunneling microscopy. Lamentably, none of these articles was cited by Barnard et al.

Characterizing tuning forks as nanomechanics sensors through thermal noise spectra measured by a personal computer sound card

A minimal and convenient experimental set-up is described, which allows an easy characterization of crystal tuning forks, especially after the modifications introduced to exploit them as sensors in nanomechanics and in force microscopy techniques. The system uses the thermal noise of the crystal as test signal, a simple frequency converter for translating the signal itself into the audio-frequency band, and a PC sound card to acquire it and eventually perform a fast Fourier transform spectrum analysis on the noise samples. Our results show that the main decrease of the Q-factor of the tuning fork is caused by its acoustical coupling to the environment, while small masses added to either or both prongs only produce minor variations.

Optical methods in scanning probe microscopy

Scanning Probe Microscopies, particularly AFM (Atomic Force Microscopy), appear to be very useful tools for visualizing biological structures. Their exceptional features are: resolution down to atomic scale, non invasive method, no manipulation of the sample, physiological conditions of operation. But many problems remain to be solved for routine applications in the biomedical field. Here these problems are treated and suitable optical methods for making more reliable the application of Scanning Probe Microscopy to biological preparations are illustrated and discussed.

Normal and lateral force images, sub‐angstrom height resolution, and midlevel lateral resolution with a phonograph cartridge as scanning force sensor

The similarity of the operating principles of the atomic force microscope and the phonograph has suggested testing of a phonograph cartridge as a force sensor for scanning force microscopy (SFM). The results were surprisingly good. A stereophonic piezoelectric cartridge showed a height resolution limit of 0.01 A, and was used, with the original stylus, to take SFM images in both normal and lateral force modes. The device works in constant height mode on a height range of more than 106, from less than 1 A to about 100 μm, but its high capacitance sensors also allow the feedback mode operation. A model of the lateral resolution of an exploring stylus that allows a direct comparison with the resolution of optical instruments is discussed.The similarity of the operating principles of the atomic force microscope and the phonograph has suggested testing of a phonograph cartridge as a force sensor for scanning force microscopy (SFM). The results were surprisingly good. A stereophonic piezoelectric cartridge showed a height resolution limit of 0.01 A, and was used, with the original stylus, to take SFM images in both normal and lateral force modes. The device works in constant height mode on a height range of more than 106, from less than 1 A to about 100 μm, but its high capacitance sensors also allow the feedback mode operation. A model of the lateral resolution of an exploring stylus that allows a direct comparison with the resolution of optical instruments is discussed.

Sub‐Ångstrom resolution with a phonograph cartridge as bidimensional nanodisplacement sensor

A simple and reliable displacement sensor is proposed, which is able to detect axial and transverse displacement with a resolution of the order of 0.01 A. It is based on an inexpensive device borrowed from old‐style audio reproducers.