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. 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. Alloy gold-silver NPs (AuAgNPs), unlike their core-shell counterparts, can be easily synthesized via a simple citrate reduction method. 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. 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:  Baptista P et al., Anal Bioanal Chem, 391 (2008) 943-950;  Liz-Marzan LM, Langmuir, 22 (2006) 32-41;  Link S et al., J Phys Chem B, 103 (1999) 4212-4217  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.
Journal: TechConnect Briefs
Volume: 3, Nanotechnology 2010: Bio Sensors, Instruments, Medical, Environment and Energy
Published: June 21, 2010
Pages: 62 - 65
Industry sectors: Medical & Biotech | Sensors, MEMS, Electronics
Topicss: Chemical, Physical & Bio-Sensors, Diagnostics & Bioimaging