Laser produced plasma diagnosis of carcinogenic heavy metals in gallstones
Gall bladder cancer [GBC] is a highly fatal malignancy. Geographically, regions of high prevalence of gallstones [GSs] have shown to have higher rates of GBC, which is now a recognized risk factor for GBC. Heavy metal toxicity has also been reported to be associated with GBC. An effort therefore at recognizing and avoiding potential risk factors for GBC occurrence is therefore paramount. It is also known that over time heavy metals can accumulate in the biliary system and hence in GSs. We hereby measured the levels of heavy metals in GSs via a highly sensitive technique using a laser produced plasma by comparing the levels of heavy metals in a 29 year old man to a 65 year old man. For this direct spectral analysis of GSs, a laser produced plasma was created by focusing a 266 nm pulsed UV laser generated by fourth harmonics of a Nd:YAG laser on GS samples. For the first time to the best of our knowledge, the plasma parameters, electron temperature and electron density for the GS matrix were computed from the Boltzmann distribution of the upper energy levels and Stark broadening of selected spectral lines. The determination of plasma parameters is important to satisfy the optically thin plasma (to avoid self-absorption) and obtain local thermodynamic equilibrium (LTE) conditions, which are critical for the quantitative analysis. The heavy metal concentrations of chromium, lead, cadmium, nickel and mercury were determined in two different GS samples by recording the laser induced breakdown spectra (LIBS) and by drawing the calibration curves of the spectral lines of carcinogenic metals like chromium, lead, cadmium, nickel and mercury. The results obtained from LIBS were crosschecked using a standard inductively coupled plasma-mass spectrometer (ICP-MS) technique. The effect of delay time (time between the laser pulse and the ICCD camera gate opening) and laser energy on the intensity of the spectral lines of lead, chromium and calcium was also investigated. The system developed in this study is highly applicable for the rapid analysis of any biological or human tissue samples.