Nanotech 2010

AuAg-alloy-nanoprobes for specific nucleic acid detection

G. Doria, M. Larguinho, J.T. Dias, E. Pereira, R. Franco, P. Baptista

Keywords: gold, silver, alloy, nanoparticles, diagnostics, nucleic acids


Due to their unique optical properties, noble metal nanoparticles, and in particular gold nanoparticles (AuNPs), have been extensively used for the development of new molecular diagnostic assays[1]. These optical properties derive from the characteristic surface plasmon resonance (SPR) band that can be easily tailored through the synthesis of NPs with different metal composition, either in a alloy or core-shell structure, e.g. different gold:silver ratios[2]. Alloy gold-silver NPs (AuAgNPs), unlike their core-shell counterparts, can be easily synthesized via a simple citrate reduction method[3]. AuAgNPs exhibit interesting properties from both single-metal counterparts: intense SPR bands as in the silver NPs and easiness of thiol functionalization provided by the gold. Here we report the derivatization of alloy AuAgNPs with thiol-ssDNA oligonucleotides (AuAg-alloy-nanoprobes) and their use for nucleic acid detection based on a non-cross-linking method previously developed by our group using AuNPs[4]. This non-cross-linking method consists on the spectrophotometric comparison between solutions before and after salt-induced nanoprobe aggregation. Only the presence of a complementary target stabilizes the nanoprobe, preventing aggregation and colorimetric change (Figure 1). The AuAg-alloy-nanoprobes allowed to specifically detect a sequence derived from the RNA polymerase beta-subunit gene of Mycobacterium tuberculosis, the etiologic agent of human tuberculosis, with a sensitivity of 5 ng/ul total DNA. Additionally, the simultaneous use of AuAg-alloy-nanoprobes with Au-nanoprobes for a dual-color detection strategy was evaluated. References: [1] Baptista P et al., Anal Bioanal Chem, 391 (2008) 943-950; [2] Liz-Marzan LM, Langmuir, 22 (2006) 32-41; [3] Link S et al., J Phys Chem B, 103 (1999) 4212-4217 [4] Baptista P et al., J Biotechnol, 119 (2005) 111-117; Baptista P et al., Clin Chem, 52 (2006) 1433-1434; Doria G et al., IET Nanobiotech, 1 (2007) 53-57; Costa P et al., Clin Microbiol Infect, (2009) Epub. Acknowledgements: Work supported by FCT/MCTES (CIGMH); PTDC/SAU-BEB/66511/2006 and PTDC/QUI/64484/2006; SFRH/BDE/15544/2005 and STAB Vida, Lda. for G. Doria.
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