ORIGINAL ARTICLE Cyanobacterial extract-mediated synthesis of silver nanoparticles and their application in ammonia sensing Anuj Kumar Tomer 1 & Tanveer Rahi 1 & Deepesh Kumar Neelam 1 & Pawan K Dadheech 1 Received: 28 April 2018 /Revised: 17 July 2018 /Accepted: 18 July 2018 # Springer Nature Switzerland AG 2018 Abstract Green route for silver nanoparticle synthesis has gained increasing attention. Cyanobacteria are one of the promising organisms to produce a number of secondary metabolites that are capable of reducing silver ions to small-sized silver nanoparticles. In the present study, we employed an aqueous extract of the cyanobacterium Haloleptolyngbya alcalis KR2005/106 isolated from a soda lake for biosynthesis of silver nanoparticles (AgNPs). The extract acted as a reducing agent for AgNPs synthesis and resulted formation of nanoparticles < 50 nm in size. In this study, synthesis of AgNPs obtained only in the sample exposed to photosynthetically active radiation (PAR) while the synthesis of AgNPs was not observed in the samples kept in dark. The biogenic fabrication of AgNPs was carried out by optimizing several governing parameters such as concentration of the silver nitrate solution, pH, temperature, and amount of biomass. Results obtained through different analytical techniques revealed that cyanobacterial taxon H. alcalis isolated from saline-alkaline habitat is a potential candidate for biosynthesis of optimum-sized spherical AgNPs. Surface plasmon resonance (SPR) property of AgNPs was exploited for aqueous ammonia sensing and revealed that AgNPs synthesized using aqueous extract of cyanobacterium H. alcalis could be employed for colorimetric detection of dissolved ammonia for monitoring quality of water. Keywords Cyanobacteria . Haloleptolyngbya . Silver nanoparticle . Biosynthesis . Ammonia sensing Introduction Nanotechnology, a rapidly growing field has become an inte- gral part of modern technology due to nanoparticles applica- tions in pharmaceutical, industrial, and biotechnological pur- poses owing to their unique physical and chemical properties (Chernousova and Epple 2013; Schröfel et al. 2014). Generally, various physical, chemical, and biological methods are deployed for the synthesis of silver nanoparticles (Singh et al. 2015). In the recent years, researches have been focussing more on green synthesis of silver nanoparticles. Biosynthesis of nanoparticles using plants needs large area and relatively long growth periods, which ultimately limits the feasibility of the synthesis process (Rösken et al. 2014). Currently, amongst green chemistry approaches, cyanobacteria, one of the largest, diverse, and most important groups of photoautotrophic bac- teria on earth have attracted special attention for synthesis of nanomaterials due to high growth rate and biomass productiv- ity (Husain et al. 2015; Lengke et al. 2007). A number of cyanobacterial taxa belonging to order Nostocales (Morsy et al. 2014), Oscillatoriales, and Synchococcales (Lengke et al. 2007; Sudha et al. 2013; Roychoudhury et al. 2016) have been used for the synthesis of AgNPs. In case of Nostoc commune, water soluble extracellular polysaccharide was employed for the fabrication of AgNPs without using surfactant and capping agent (Morsy et al. 2014). Dry biomass of a marine cyanobac- terium Phormidium fragile was used to synthesize silver nanoparticles. This approach is apparently cost effective due to reduction in the use of heavy energy and nutrient require- ments for maintaining the algal cells in the bioreactors (Satapathy and Shukla 2017). In another study, the culture supernatant of eight cyanobacterial strains was screened for their ability to synthesize AgNPs in light and dark conditions (Patel et al. 2015). Previous study described the biological synthesis of AgNPs using a proteinaceous pigment phycocy- anin extracted from Nostoc linckia as reducing agent (El- Anuj Kumar Tomer and Tanveer Rahi contributed equally to this work. * Pawan K Dadheech pdadheech@curaj.ac.in 1 Department of Microbiology, School of Life Sciences, Central University of Rajasthan, Bandarsindri, Ajmer, Rajasthan 305817, India International Microbiology https://doi.org/10.1007/s10123-018-0026-x