Detection of gold nanoparticles with different sizes using absorption and fluorescence based method

Abstract

Growing world demand for gold and decreasing discovery rates of ore deposits necessitates new tech-niques for gold exploration. Current techniques for the detection of ppb level of gold, such as inductivelycoupled plasma mass spectrometry (ICP-MS) are not field-deployable. By contrast, current portable devicesuch as X-ray fluorescence (XRF) based sensors are not sufficiently sensitive. Thus, there is growing inter-est in developing a new, easy-to-use and fast method for detection of low concentrations of gold at thesite of an exploration drilling rig.Two optical methods, absorption and fluorescence, are examined for their suitability for low goldconcentration detection. Absorption study is based on the analysis of localised surface plasmon resonancepeak. For fluorescence analysis, the ability of gold nanoparticles to specifically catalyse the conversionof the non-fluorescent compound (I-BODIPY) to the fluorescent derivative (H-BODIPY) is used. For bothabsorption and fluorescence methods, the limit of quantification (LOQ) of gold nanoparticles (NPs) wasfound to be dependent on the NP size (71 ppb of 5 nm and 24.5 ppb of 50 nm NPs for absorption and 74 ppbof 5 nm and 1200 ppb of 50 nm NPs for fluorescence). The LOQ for fluorescence for 50 nm NPs measuredin a suspended core optical fibre was almost twice lower than in a cuvette. The field deployment potentialof these methods was also determined using a portable set up.