13. Dresdner Sensor-Symposium 2017 301 DOI 10.5162/13dss2017/P4.08 Detection of metal ions using fluorescent gold nanoclusters M. Vogel 1,2 , S. Matys 1,2 , K. Pollmann 1 , J. Raff 1,2 , 1) Helmholtz-Zentrum Dresden-Rossendorf, Helmholtz Institute Freiberg for Resource Technology, 09599 Freiberg, Germany 2) Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, 01328 Dresden, Germany Contact: s.matys@hzdr.de Abstract S-layer proteins appear to be suitable for wide variety of different technical applications due to their distinctive physico-chemical properties and their multifunctionality. Since several years the focus has been placed especially on their potential use for biosensor applications. There are many approaches under investigation to develop sensors that are highly specific and sensitive as well as robust, reliable and not expensive. Optical methods currently appear an attractive solution. Colloidal gold nanoparticle suspensions as sensory active systems, for instance, have been the subject of intensive investigations for many years. An additional promising approach is the use of proteins as template structures for the production of highly fluorescent, size-controlled gold nanoclusters (Au-NC). These gold nanoclusters can be synthesized directly at the protein by a simple chemical reaction. We present current investigations on different kind of proteins such as bovine serum albumin, calmodulin, and S-layer protein. In combination with the known S-layer or calmodulin mediated selective and specific binding of ionic analytes, e.g. rare earth elements as surrogates/analogues for intrinsic protein bound Ca 2+ , a subsequent analyte-induced change in the fluorescence intensity of the gold nanoclusters might be used as sensory system for the detection of such strategic relevant elements. Keywords S-layer proteins, BSA, gold nanoclusters, bio-sensing, fluorescence Fluorescent gold nanoclusters on bovine serum albumin Part of the joint project BioNEWS was the development of a new sensor concept for the detection of strategically relevant value elements from aqueous streams. For this purpose different approaches were pursued. In addition to the strategy of using sensory active living cells, the use of highly fluorescent and long-term stable gold clusters constitutes a conceivable and promising alternative. We could successfully verify a biological ("green") method of producing fluorescent gold nanoclusters using bovine serum albumin as a template first described by Xie et al. [1] and to transfer this method to other functional proteins such as calmodulin and S-layer proteins. Many proteins have a certain intrinsic reducing potential that can be used to bind ions to produce metallic or ceramic nanoparticles with particular physico-chemical properties under suitable conditions. In a one-pot reaction, fluorescent gold nanoclusters were generated on the proteinaceous support [1]. Depending on the initial pH different sized nanoclusters can be produced, showing different excitation and emission wavelength ranges (see Fig. 1). Blue fluorescent gold clusters are attributed to Fig. 1: BSA-AuNC suspensions with different initial pH under UV irradiation 22 and 118 hours after formation. clusters of eight atoms and red to 25 atoms in size [2]. Suspensions with red-fluorescing gold clusters are stable for a period of more than 22 h 118 h W/O pH pH pH pH BSA 8 9,9 11,7 12,5