Contents lists available at ScienceDirect Optics and Laser Technology journal homepage: www.elsevier.com/locate/optlastec Full length article Compositional study of gallbladder stone using photoacoustic spectroscopy Zainab Gazali a , S.N. Thakur b , A.K. Rai a, ⁎ a Photoacoustic Spectroscopy Research Laboratory, Physics Department, University of Allahabad, India b Physics Department, Banaras Hindu University, Varanasi, India HIGHLIGHTS • Study of chemical compounds without any sample preparation is performed using PAS. • Molecular analysis of gallstones using PAS has been done for the first time. • The results of PAS are validated with results of UV–Visible and LIBS. • Presence of Cholesterol, Calcium carbonate and Bile acid are confirmed by PAS. • Elemental profile (C, Ca, Mg etc) of gallstone are confirm using LIBS. ARTICLE INFO OCIS Codes:: Gallbladder stone Photoacoustic Spectroscopy (PAS) UV–Visible absorption Cholesterol Calcium carbonate LIBS ABSTRACT Molecular composition of gallbladder stone has been investigated for the first time by means of photoacoustic spectroscopy (PAS). The presence of cholesterol, calcium carbonate and bile acid, in the photoacoustic spectrum, have been established and compared with the UV–Visible absorption spectrum of acetone solution of powdered gallstone. The results of this investigation show that PAS is better suited to detect the presence of different chemical compounds in gallstones as compared to conventional absorption spectroscopy. Moreover, PAS does not require elaborate biomaterial’s sample preparation. Laser induced breakdown spectroscopy (LIBS) has been applied to reveal presence of atomic species in gallstone, that are involved in the molecular constituents revealed by PAS. 1. Introduction Gallstone formation in gallbladder is a serious health concern as it affects millions of people around the world. Analysis of chemical composition of different kinds of gallstones can provide a significant clue for checking its formation and its treatment [1]. Elemental and molecular composition of gallstone depends upon many factors in which dietary nutrient intake of the patient plays a major role. Con- sumption of abnormally high levels of certain elements, e.g., calcium, magnesium and potassium, are likely to trigger stone formation in the bile inside the gallbladder [2]. Gallstones are classified into many types including cholesterol stones, bile pigment stones, calcium carbonate stones, phosphate stones, calcium stearate stones, protein stones, cy- stine stone, bilirubinate stone and mixed stones. Thus, it is important to know the factors that are responsible for the formation/nucleation of the gallstones. Analysis of molecular composition of different gallstones is likely to provide the clue to the nucleation of the stone in the gallbladder. Various spectroscopic techniques have been widely used to identify and analyze the structural and elemental compositions of gallstones. FTIR Spectroscopy, Scanning Electron Microscopy, Raman spectroscopy, UV–Visible spectroscopy, and Fluorescence spectroscopy are widely used to classify gallstones according to the appearance, profile struc- ture, component content, distribution, microstructure and elemental composition [3–5]. Each of these techniques is time consuming, labor- intensive, and requires elaborate sample preparation. During the past two decades, PAS has emerged as a powerful technique for molecular analysis of any kind of materials, including biomaterials, irrespective of their phases – solid, liquid, gel, powder, vapor etc [6,7]. It is based on Photoacoustic effect where the absorbed optical energy, of the incident electromagnetic radiations, is converted into heat energy via nonradiative transitions and this in turn generates an acoustic signal. PAS becomes particularly advantageous with respect to conventional spectroscopy in the case of optically opaque solid samples because of its dependence on the heat generated in the sample via nonradiative relaxation process [8]. Recently Laser induced https://doi.org/10.1016/j.optlastec.2018.09.003 Received 24 March 2018; Received in revised form 27 July 2018; Accepted 3 September 2018 ⁎ Corresponding author. E-mail address: awadheshkrai@rediffmail.com (A.K. Rai). Optics and Laser Technology xxx (xxxx) xxx–xxx 0030-3992/ © 2018 Published by Elsevier Ltd. Please cite this article as: GAZALI, Z., Optics and Laser Technology, https://doi.org/10.1016/j.optlastec.2018.09.003