Project description

1. OBJECTIVES AND EXPECTED ACHIEVEMENTS

1.1. Introduction

The aim of this research project is to investigate the interaction of Terahertz (THz) radiation with biological systems. Present and rapidly increasing future applications of radiation in this spectral range, necessitate preventive rather than reactive research. The project follows a streamline of increasing complexity from bio-molecules to cells, e.g. membranes, chromosomal and DNA integrity. The objectives of the project are to analyse the physical mechanisms of interaction, to assess risk of potential damage to biological activity, both functional and morphological, and to guide and accompany the development of microscopic imaging at THz frequencies for biological and biomedical applications.

The project will bridge the existing gap of knowledge regarding the effects of Terahertz (THz) radiation on biological systems. THz radiation covers the frequency range between 100 GHz and 20 THz (i.e. a wavelength between 3 mm and 15 µm), which spans the spectral interval between the microwave- and the infrared regions of the electromagnetic spectrum.

Fig.1 - Graphical representation of the THz Gap - As it is shown in the figure, research on THz radiation does not include electromagnetic fields of present wireless telecommunication systems, being its frequency about three order of magnitude higher than mobile phone frequencies and two orders of magnitude higher than the most advanced satellite systems.

Recent technological break-through of electromagnetic radiation sources, components and devices, in the THz region, has triggered new applications in the field of material science, biology and biomedicine. Particularly, biological applications are based on the specific spectroscopic fingerprints of biological matter in the far infrared (FIR) and THz spectral regions, due to the high density of electronic, vibrational and rotational states. In addition, the different values of the absorption coefficient and index of refraction of the water and the tissue carbonated proteins at such frequencies, provide a unique contrast mechanism for biomedical imaging applications.

However, very little is known of the effects of THz radiation in biological systems. As it is discussed in detail below, there are indications that THz radiation could induce damages on the molecular scale in certain biological systems due to the mechanism of resonant absorption. Despite the fact that there is not a wide public exposition to THz radiation with the present state of the technology, a timely assessment of potential hazards and health effects at specific occupational sites of research laboratories and industries is required. With the interdisciplinary approach to the microscopic understanding of the interaction of THz radiation with biological matter, the project consortium has been designed to provide spectroscopic databases to the scientific community and will define exposure standards for potential diagnostics application. THz-BRIDGE will be the first research step of European dimension prior to implementing THz technology in biological and biomedical diagnostics.

1.2. Objectives

The general objectives of the research consortium are the following:

To provide a spectroscopic database for selected enzymes, proteins, biological membranes and cells in the frequency range from 100 GHz to 20 THz (the so-called "THz gap") under irradiation conditions that preserve the integrity and functionality of the biological samples.
To identify, from the above data, critical frequencies, which might induce damages on biological systems, and to determine the spectral regions for optimal contrast in imaging applications.
To assess risk of potential damage to biological activity, both functional and morphological, due to the exposure of membranes, cells, and DNA to pulsed and CW THz radiation.

2. INNOVATION ASPECTS

2.1. Origin of the "THz-gap" in sources and devices technology

The region of the spectrum of electromagnetic radiation laying between 100 GHz and 20 THz was usually referred to as the "THz gap", since it was considered a rather poorly explored region at the boundary between the microwave and the infrared regions, which were respectively domain of electronic engineering on one side and optics on the other side. Frequencies in this region were usually considered as too high for electronic devices, due to the technological limits in reducing the size of components as frequency increases, and too low for photonic devices, since the corresponding photon energy is comparable to those of thermal excitations at room temperature. This situation has changed during the past few years with a rapid development of coherent sources, that has been accompanied by a research effort on the realisation of passive components and devices exploiting a number of advanced technologies like deep UV and soft X-ray micro-lithography, and which is now in turn boosting a wide variety of applications from material science to telecommunications, from biology to biomedicine. At European level, the recent technological effort on THz sources and devices has been funded by the IST activity in the 5^th Framework Programme.

2.2. The THz gap still exists in biology and biomedicine

Very little is known about the effects of THz radiation in biological systems. Data available in the literature deal with the study of resonant processes in complex molecules like enzyme and proteins, or with the effects on growth factors in bacteria at specific frequencies. There are indications that the interaction of the electromagnetic radiation with biological systems, in the THz frequency range, could trigger damage at molecular level. The absorption of photons during the interaction of radiation with matter can trigger chemical changes on its molecular structure provided that final or intermediate dissociative electronic excited states are involved. As a result, molecular bonds are broken by the radiation. Taking into consideration that most of the dissociative states of organic molecules or radicals usually occupy the energy range above 4 eV, direct damage at the molecular level occurs when photons of wavelength shorter than 300 nm are absorbed, as it is the case for UltraViolet (UV) and ionising radiation. However, even less energetic electromagnetic radiation, like the one in the THz range (0.001 to 0.1 eV), can induce damage due to the fact that resonant absorption from rotational states may lead to the dissociation of complex molecules.

2.3. Physics, engineering, life sciences and biomedicine link up to generate new knowledge

The potential of joining resources in an interdisciplinary effort is currently being exploited world wide to set up new research institutes in which scientists can work together to solve biological problems [Physics World, February 1999]. This has recently led to the development of new methods to examine the physical and biological properties of complexes of macro-molecules, to understand why cells develop in different ways (the process of gene expression) and to investigate the signalling pathways that links changes in the gene expression within the cell nucleus to molecular interaction at the cell surface [Physics World, September 1999]. Attracting scientists from different fields, this projects will advance the state of the art in the understanding of the interaction of electromagnetic radiation with living matter, by systematically exploring the THz region with a number of sources, from electronic tubes to solid state devices to free electron lasers (FEL), with power and tunability capabilities not previously available.

The interaction of biophysics, biology and biomedical research groups with technology oriented teams in the consortium will also provide the potential for the realisation of new diagnostic devices in the field of THz Near Field Microscopy (TNFM) with unique image contrast. This novel technique, which will be described in detail in the workplan, involves the so-called Terahertz Pulsed Imaging (TPI) which has recently been tested on the macroscopic scale in biomedical field (Fig.2).

Fig.2 - Left: human tooth. Centre: Image of the tooth demonstrating THz absorption reveals cavities in red. Right: time of flight THz data shows enamel and dentine, which have different refraction indices.

TNFM has the potential to be applied to a quantitative analysis of radiation damage in cell cultures. Further drivers for TNFM are:

THz imaging of vascularity: Clinicians and pharmaceutical companies have stressed the importance of new methods of detecting and imaging the degree of vascularity in different types of tissue. TNFM holds great promise as a novel method of the assessment of vascularity, with a view to reducing the time and cost of assessing new drugs before their entry into clinical trials, eliminating the time (5-10 years) and cost (Euros 80 million) of drugs subsequently proven to be ineffective.
THz detection of point mutations in DNA. There is interest in developing TNFM to detect and characterise changes in DNA structure associated with known, defined point mutations by studying the products of the polymerase chain reaction (PCR). The PCR and associated techniques have had a major impact upon: (a) the clinical investigation and detection of DNA mutations associated with inborn errors of metabolism and (b) the large scale screening of populations for gene mutations associated with certain pathologies known to have a genetic component. Almost all current techniques routinely used for mutation screening involve a number of chemical and physical separation processes. TNFM could become a rapid ‘one step’ process for the detection of selected DNA mutations, without the need for further separation of the PCR products, but leaving them intact for further analysis.

2.4. Research results on risk assessment and factors that may affect health are needed prior to implementing new technology.

As mentioned before, the frequency range between 100 GHz and 20 THz has been scarcely explored so far and has not been subjected to a detailed risk analysis. Qualitative risk assessment is currently either done with standards taken from the optical domain (for example from laser safety regulations) or from the microwave technology safety standards and EU recommendations. Also wireless telecommunication systems, which presently extend in frequency up to 30 GHz, are gradually approaching the THz region from the low-frequency side, with an increasing demand of high frequency domains that are often used without previous knowledge and assessment of potential health hazards. At present, a number of laboratory-scale THz sources, like electronic tubes, free-electron lasers, and pulsed solid-state THz sources, are in use at research institutes, raising the issue of potential exposure of specialised personnel and users. The further development of biomedical imaging devices based on such sources, with commercial systems coming into the market, clearly requires adequate measurements to monitor the technical personnel involved and the future patient exposure. These issues will be raised by THz-BRIDGE with the systematic investigation of the effect of THz irradiation on significant biological systems, like membrane model systems, blood cells and other cell cultures, for which comparative data are available in neighbouring spectral regions of non-ionising radiation.

3. PROJECT WORKPLAN

3.1. INTRODUCTION

THz-BRIDGE will use an interdisciplinary approach to study the effects of the interaction of THz radiation with biological systems. To this purpose a consortium formed by the Ente Nazionale per le Nuove tecnologie, l'Energia e l'Ambiente (ENEA), the Forschungszentrum Rossendorf (FZR-DRESDEN), Tel-Aviv University (TAU), Stuttgart University (USTUTT), Frankfurt University (UFRANK:BIOPHYS), the University of Genoa (ICEmB), the National Hellenic Research Foundation (NHRF), the Cambridge Research Laboratory at Toshiba Res. Europe (CRL/TREL), the University of Nottingham (UNOTT) will perform the workplan, which is broken down in three main parts or workpackages (WPs):

WP-1 Spectroscopy of proteins, enzymes, biological membranes, and selected cells
The goal of this workpackage is to understand the interaction of far-infrared (FIR) and THz radiation with biological systems on a molecular level, i.e. on the basis of resonant processes with electronic, vibrational, and rotational states of complex biological molecules in relation to a modulation of their biological activity, which can be stimulation, inhibition, and in the worst case damage. Based on previous experience dealing with the investigation of functionally relevant states of proteins and enzymes by near- and mid-infrared spectroscopy (6000 cm-1 - 500 cm-1), the work in this package shall deliver absorbance and reaction-induced difference spectra of structurally and functionally intact biological samples in the spectral range between 100 GHz and 20 THz.
Techniques such as X-ray crystallography, 2-D NMR spectroscopy, and high-resolution electron microscopy deliver static, frozen pictures of proteins, enzymes, and biological membranes. Information on the function and how it is related to the structure, however, requires spectroscopic techniques which probe structural properties and allow high temporal resolution. Among the variety of spectroscopic techniques, Infrared (IR) spectroscopy has probably the best access to minute structural details, in the order of fractions of a bond dimension. The use of infrared spectroscopy for the study of biological systems has greatly advanced due to the high sensitivity and rapid data acquisition provided by Fourier-Transform infrared (FT-IR) spectrometers. In the mid-IR spectral range, in particular in the region from 2000-1000 cm-1, FT-IR spectroscopy can monitor alterations at individual bonds even in large protein complexes, thus allowing structural and conformational changes in the course of a biological reaction to be monitored in high detail and in real time, and reaction mechanisms to be elucidated. Yet, the presently available frequency range of FT-IR techniques, typically 4000 - 200 cm-1 does by far not cover the full range of functionally relevant modes of enzymes and proteins, which may extend down to 10 cm-1 . Such range will be covered by the research activity in this package.

WP-2 Evaluation of biological effects in vitro after exposure to THz-radiation
The effects of Terahertz radiation on significant biological systems of increasing complexity as a function of incident and absorbed power, wavelength, pulse duration and modulation conditions will be studied in this work-package. This will provide a risk assessment prior the future implementation of THz devices in bio-medical diagnostics. Apart from a limited amount of data in the low-frequency part of the THz region, no information is available on the effect of THz-radiation on biological systems. To study such possible effects, powerful sources of THz radiation, like Free Electron Lasers (FEL), gas lasers, microwave and solid-state sources, with wide and complete control of external parameters, will be available at the partners sites and at collaborating European Facilities over the whole frequency range of interest.

WP-3 Safety issues at specific occupational sites
This package will address safety issues at specific occupational sites, where THz sources are employed or developed. A questionnaire will be distributed to a number of research laboratories involved in THz development to collect information on the main radiation parameters, on the exposure conditions (if any) of technical personnel and on the safety measurements or precautions currently adopted. The results will be analysed and compared with the outcome of WP1 and WP-2. Recommendations on exposure conditions will be provided.

3.2. The projects components

Although the three workpackages use different investigation techniques, each of them provides necessary input to the other ones for the completion of the various tasks with feedback on the research activity, as it is sketched in the following interconnection diagram.

THz-BRIDGE Components

Rectangles represent deliverables (output from- and input to Workpackages)
Rounded blocks are end results of the project
Grey shaded areas are discussed in part C of the proposal

[Back to Home Page]