Laser-induced breakdown spectroscopy (LIBS) has the potential to be used as a surgical tool for simultaneous tissue ablation and elemental analysis of the ablated tissue. LIBS may be used to distinguish melanoma lesions from the surrounding dermis based on the quantitative difference of elements within melanoma lesions. Here, we measured the elements in homogenized pellets and real tissues from excised skin samples of melanoma-implanted mice. In addition, statistical analysis of LIBS spectra using principal component analysis and linear discriminant analysis was performed. Our results showed that this method had high detection sensitivity, highlighting the potential of this tool in clinical applications.

Melanoma is acknowledged as the most dangerous form of skin cancer, accounting for 90% of the deaths associated with cutaneous cancers.¹ According to a recent report,¹ the incidence of melanoma is increasing worldwide with the regional incidence rate of up to 10 to 20, 20 to 30, and 50 to 60 per 100,000 populations in Europe, USA, and Australia, respectively. The standard treatment of an operable melanoma involves surgical excision with a safety margin. The safety margin is required in order to completely remove not only the primary cancer but also melanoma cells that might have spread into the surrounding skin.² The determination of a proper safety margin is critical during surgical treatment because a too-large safety margin leaves functionally and cosmetically poor outcome, whereas a too-small safety margin risks incomplete removal of cancer or cancer cells. For the determination of safety margin, Mohs micrographic surgery is widely adopted in dermatology, in which the process of cancer excision and histologic examination is repeated until no cancer cells are found from the excised layer.³ An accurate interpretation of the histologic examination of excised layer during the surgery is critical. One of the shortcomings of the Mohs procedure is the prolonged operation time due to repeated histology test during the surgery, which increases the risk of complications such as wound infection.⁴ Thus an alternative or supporting technique to accurately and rapidly determine the cancer region and appropriate safety margin is highly desired.

Laser induced breakdown spectroscopy (LIBS) measurement of a thin Cu(In,Ga)Se₂ (CIGS) absorber layer was performed under the conditions of open air and argon (Ar) gas jet flow (25 L min⁻¹). A second harmonic Q-switched Nd:YAG laser (λ = 532 nm, τ = 5 ns, top-hat profile) was employed for the ablation of co-evaporated CIGS samples. The use of an Ar gas jet for the LIBS measurement of CIGS thin films leads to two significant differences from the open air measurement results that are important from the precision point of view: (i) the increase of signal intensity and (ii) decrease of relative standard deviation (RSD) of measured intensity or intensity ratios. From calculation of the degree of intensity enhancement, it was shown that the enhancement of signal intensity is primarily due to the increase of plasma temperature and electron density under Ar buffer gas environment. It was also found that in addition to the influence of Ar gas itself the gasdynamic effects of the Ar gas jet contribute significantly to the reduction of RSD.