ORIGINAL PAPER Target synthesis of biocompatible spherical bismuth sulphide nanoparticles for biological application B. Roy 1 • A. P. Chattopadhyay 1 • A. Samadder 2 • A. R. Khuda-Bukhsh 3 Received: 30 March 2015 / Accepted: 19 September 2015 / Published online: 1 October 2015 Ó Springer Science+Business Media New York 2015 Abstract Bismuth sulphide nanoparticles are prepared by sol–gel method using gelatine as capping agent. Synthe- sized nanoparticles are well dispersed in water and the medium is nearly neutral, both essential for biological application. Triethanolamine is used as a complexing agent for solubilization of Bi 3? in water and sodium sulphide as a sulphur source. Nanoparticles are well characterized by standard methods and show marked cytotoxicity and alter membrane potentials of both mitochondria and HeLa cells. Graphical Abstract Schematic route to synthesize water- soluble Bi 2 S 3 nanoparticles Bi +3 + nTEA Bi(TEA) n Na 2 S Gelatine Bi 2 S 3 +3 Keywords Bismuth sulphide nanoparticles  Sol–gel method  Biocompatibility  Cytotoxicity  HeLa cells 1 Introduction Semiconductor nanomaterials constitute a potent class of material for their inimitable physico-chemical properties due to quantum confinement effect. Decrease in particle size causes increment of band gap of semiconductor and causes a blue shift of absorption edges. By tailoring their shape and size, optoelectronic properties can be tuned for requirement of modern science and technology. Among them, bismuth sulphide (Bi 2 S 3 ) nanoparticles (BNPs) are direct band gap semiconductor with direct band gap of 1.3–1.7 eV and high absorption coefficient [1]. BNPs have application in CT (computed tomography) imaging using X-ray [2], lithium ion battery [3], gas sensor [4], photodi- ode arrays and photovoltaic converters [5], thermoelectric cooling technologies based on Peltier effect [5, 6], etc. Several attempts have been made to synthesize 1D bismuth sulphide nanomaterials such as nanorods [7–11], nanowires [7, 12–15] and nanoribbons [16] using microwave-assisted synthesis [9], protein-assisted synthesis [12], solventless reaction [7, 13] and hydrothermal or solvothermal methods [10, 11, 14–16]. Biomolecule-assisted snowflake-like structures [17], nanorods using colloidal solution process [18] and sonochemical approach [5] were also reported in obtaining more complicated structures of synthesized BNPs. Herein we report a simple sol–gel approach to synthesizing BNPs. For targeted biological application, gelatine as biocompatible capping agent and water as sol- vent are employed. Bismuth salts are generally water insoluble. To overcome this problem, triethanolamine (TEA) is used as complexing agent [19] with bismuth ion. & A. P. Chattopadhyay asoke@klyuniv.ac.in; asoke.chattopadhyay@gmail.com & A. R. Khuda-Bukhsh prof_arkb@yahoo.co.in B. Roy biplabroy31@rediffmail.com; biplabroy09@gmail.com A. Samadder asmita.samadder@gmail.com 1 Department of Chemistry, University of Kalyani, Kalyani 741235, India 2 Department of Zoology, Dumdum Motijheel College, Kolkata 700074, India 3 Departmemt of Zoology, University of Kalyani, Kalyani 741235, India 123 J Sol-Gel Sci Technol (2016) 77:446–452 DOI 10.1007/s10971-015-3873-3