1158 Electrophoresis 2015, 36, 1158–1163 Magdalena Matczuk 1 Svetlana S. Aleksenko 2 Frank-Michael Matysik 3 Maciej Jarosz 1 Andrei R. Timerbaev 2 1 Chair of Analytical Chemistry, Faculty of Chemistry, Warsaw University of Technology, Warsaw, Poland 2 Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russian Federation 3 Institute of Analytical Chemistry, Chemo- and Biosensors, University of Regensburg, Regensburg, Germany Received November 24, 2014 Revised March 2, 2015 Accepted March 2, 2015 Research Paper Comparison of detection techniques for capillary electrophoresis analysis of gold nanoparticles As metallic nanoparticles are growing in importance as analytes in CE, increases an interest in appropriate detection methods for their quantification in various samples. For gold nanoparticles (AuNPs), the most common UV detection poses intricacy of inadequate sensitivity that hinders the applicability of CE. With the objective of resolving this challenge, UV detection was compared with C 4 D and ICP-MS as alternative modes of detection for AuNPs. A C 4 D detector, applied under pressure-driven conditions, exhibited better sensitivity than a UV detector. However, C 4 D turned to be unsatisfactory to differentiate the signal of AuNPs at common CE conditions despite varying the nature of BGE and detection conditions. Due to intrinsic sensitivity and low background levels typical to Au, ICP-MS greatly surpasses UV detection. After optimization trials, CE-ICP-MS gained the LOD of AuNPs as low as 2 × 10 –15 M, as well as an excellent performance in terms of signal stability and linearity. Also importantly, the optimized BGE appears to be well matched to explore the behavior of AuNPs in biologically relevant systems. This was demonstrated by probing the interaction between AuNPs and the main blood-transporting protein, HSA. Keywords: CE / Gold nanoparticles / Inductively coupled plasma MS DOI 10.1002/elps.201400597  Additional supporting information may be found in the online version of this article at the publisher’s web-site 1 Introduction Gold nanoparticles (AuNPs) are a versatile nanoscaffold for an expanding array of applications, including cancer research where AuNPs can discharge both diagnostic and therapeutic functions [1–3]. In view of the exogenous character of AuNPs, there is an urgent need to understand their potential biolog- ical and toxic effects. Although no single analytical platform offers full characterization of any AuNP as a constituent of a biosystem, separation techniques hold considerable promise as an attractive alternative. Indeed, in case of the task to distin- guish various species in which AuNPs would occur in a par- ticular biological environment, only these techniques could be an option to choose. Among separation techniques, our special focus is on CE that has shown a proven record in the Correspondence: Professor Andrei R. Timerbaev, Vernadsky Insti- tute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin Str. 19, 119991 Moscow, Russian Federation E-mail: andrei.timerbaev@univie.ac.at Fax: +7-495-9382054 Abbreviations: AuNP, gold nanoparticle; NP, nanoparticle; PIPES, piperazine-N,N’-bis(2-ethanesulfonic acid) separation, characterization, and quantification of differently protected AuNPs [4–7], as well as their conjugates with biomolecules [8, 9]. The ability to differentiate distinct metal- lic species of interest with minor impact of their distribution during analysis, tolerance to biomatrices, and small-sample volume requirement is the major assets behind an increasing popularity of CE in the bioanalysis of AuNPs. However, insuf- ficient sensitivity remains an obstacle that prevents the recog- nized relevance of CE in the field. Using UV absorbance, as in most of the published accounts, limits the sensitivity to par- ticle concentrations in the milligrams per liter range [10, 11]. Operating at such a threshold is not only inappropriate for many biomedical studies but may also cause complications due to possible particle-to-particle collisions. Therefore, for this research, along with on-capillary UV detector serving for comparative reasons, C 4 D and ICP-MS were chosen, mostly on the score of their commercial accessibility. AuNPs are known to possess a certain conductivity [12, 13] that makes them potentially amenable to C 4 D as a universal detector for charged species. However, it seems that C 4 D has not yet been tried for such CE application. Nor did other electrochemical methods find use in CE of individ- ual AuNPs (but AuNPs utilized as a tag to enhance resolution between other types of analytes [14, 15]). In its turn, ICP-MS C  2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.electrophoresis-journal.com