Electric field assisted LIBS for multi-element analysis of human dental enamel: Signal enhancement and calibration-free quantification

Conventional laser-induced breakdown spectroscopy (LIBS) is a versatile multi-elemental detection technique that offers minimal sample preparation, in situ analysis, and handheld availability. But it inherently suffers from low signal intensity, poor sensitivity, and high detection limit. This research aims to improve analytical performance of standard LIBS by enhancing emission signal intensity, modifying plasma dynamics, and increasing elemental qualitative and quantitative accuracy. With this purpose, thirty enamel tissues are collected to investigate the effect of an applied electric field (E-field) on laser-induced enamel plasma by comparing plasma characteristics with and without E-field. E-field of 120 V/mm increased the signal intensity of several elements, H I (656.28 nm), C I (247.86 nm), and Ca II (370.60 nm), by 96-, 34-, and 25-folds, respectively. It also increased signal-to-noise ratio (SNR), improved signal stability, and allowed the detection of traces (Al, Ag, Cu, Pb, Si, Zn). E-field enhanced the plasma temperature (T), electron number density (N_e), and plasma frequency (ν_p) up to 9500 K, 2.0 × 10¹⁸ cm^-3, and 1.3 × 10¹³ Hz, respectively. Quantitative analysis using calibration-free (CFLIBS) is improved by the use of elevated plasma parameters obtained via electric-field-assisted (EF-LIBS). Upon cross-validation, the relative error between EF-CFLIBS and μ-XRF for Ca and P is measured up to ∼13 %. Presence of toxic trace metals (Pb, Cu, Ag) in healthy enamel tissues is detected only by EF-LIBS and identified as dental health biomarkers. EF-LIBS in conjunction with the CFLIBS formulation, can be implemented as dental screening tool for enamel health monitoring in laser dentistry.