In situ, real-time identification of biological tissues by ultraviolet and infrared laser desorption ionization mass spectrometry.

Laser desorption ionization-mass spectrometric (LDI-MS) analysis of vital biological tissues and native, ex vivo tissue specimens is described. It was found that LDI-MS analysis yields tissue specific data using lasers both in the ultraviolet and far-infrared wavelength regimes, while visible and near IR lasers did not produce informative MS data. LDI mass spectra feature predominantly phospholipid-type molecular ions both in positive and negative ion modes, similar to other desorption ionization methods. Spectra were practically identical to rapid evaporative ionization MS (REIMS) spectra of corresponding tissues, indicating a similar ion formation mechanism. LDI-MS analysis of intact tissues was characterized in detail. The effect of laser fluence on the spectral characteristics (intensity and pattern) was investigated in the case of both continuous wave and pulsed lasers at various wavelengths. Since lasers are utilized in various fields of surgery, a surgical laser system was combined with a mass spectrometer in order to develop an intraoperative tissue identification device. A surgical CO(2) laser was found to yield sufficiently high ion current during normal use. The principal component analysis-based real-time data analysis method was developed for the quasi real-time identification of mass spectra. Performance of the system was demonstrated in the case of various malignant tumors of the gastrointestinal tract.