Biosensors and Bioelectronics 32 (2012) 127–132 Contents lists available at SciVerse ScienceDirect Biosensors and Bioelectronics j our na l ho me page: www.elsevier.com/locate/bios Gold-based optical biosensor for single-mismatched DNA detection using salt-induced hybridization Zongrui Zhan a , Xingyi Ma b , Cuong Cao c , Sang Jun Sim b,∗ a Department of Chemical Engineering, Sungkyunkwan University, Suwon 440-746, South Korea b Department of Chemical and biological Engineering, Korea University, Seoul 136-713, South Korea c DTU-Nanotech, Department of Micro and Nanotechnology, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark a r t i c l e i n f o Article history: Received 18 November 2011 Accepted 25 November 2011 Available online 6 December 2011 Keywords: Gold nanoparticles BRCA-1 Single-mismatched detection Salt-induced DNA hybridization a b s t r a c t In this study, a gold nanoparticle (Au-NP)-based detection method for sensitive and specific DNA-based diagnostic applications is described. A sandwich format consisting of Au-NPs/DNA/PMP (Streptavidin- coated MagnetSphere Para-Magnetic Particles) was fabricated. PMPs captured and separated target DNA while Au-NPs modified with oligonucleotide detection sequences played a role in recognition and sig- nal production. Due to the much lower stability of mismatched DNA strands caused by unstable duplex structures in solutions of relatively low salt concentration, hybridization efficiency in the presence of different buffers was well investigated, and thus, the optimized salt concentration allowed for discrim- ination of single-mismatched DNA (MMT) from perfectly matched DNA (PMT). Therefore, quantitative information concerning the target analyte was translated into a colorimetric signal, which could easily and quantitatively measured by low-cost UV–vis spectrophotometric analysis. The results indicated this to be a very simple and economic strategy for detection of single-mismatched DNA strands. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The development of simple and efficient platforms for the rapid detection of nucleic acids for the early diagnosis of various genetic diseases has recently taken precedence (Hacia et al., 1996; Drummond et al., 2003; Cha et al., 2009). Sequence recognition is probably the least understood step in the entire process; small variations in the genome influence biological predisposition to dis- eases, such as cancer and congenital genetic diseases. Identification of these variations has become a major issue in genetics because they are believed to be major determinants of disease onset, pro- gression, and clinical prognosis (Elghanian et al., 1997; Cui et al., 2001; Park et al., 2009). Recently, gold nanoparticles (AuNPs) have come under scrutiny as they offer attractive properties as DNA tags (Han et al., 2006; Katz and Willner, 2004; Zhang et al., 2007). AuNPs labeled with oligonucleotide probes to overcome the problems associated with fluorescent labels have shown their important roles in the devel- opments of multiplexing assays and sensors for genetic analyses (Niemeyer, 2001; Rosi and Mirkin, 2005; Bruchez et al., 1998; Han et al., 2001). Further extensive applications in a variety of electronic and optical biosensing systems have much benefited from sensi- tivity, long lifetime, and multiplexing capability of AuNPs-based ∗ Corresponding author. Tel.: +82 31 3290 4853; fax: +82 2 926 6102. E-mail address: simsj@korea.ac.kr (S.J. Sim). assays (Park et al., 2002; Daniel and Astruc, 2004; Boisselier and Astruc, 2009). Mirkin and co-workers have reported sev- eral optical DNA hybridization detection methods (Nam et al., 2004; Rosi and Mirkin, 2005), in which most of their research focused on the hybridization-induced DNA-Au aggregates based on the unique size-dependent scattering, catalytic, and absorp- tion properties of AuNPs. This was attributable to their discovery that Au particles, heavily functionalized with oligonucleotides, exhibit extraordinarily sharp thermal-denaturation profiles (Jin et al., 2003). Based on this observation, they developed a thermal- stringency wash approach to differentiate target strands from those bearing mismatches and thus achieved the desired analyte selec- tivity (Elghanian et al., 1997; Cao et al., 2002). In addition, Mirkin et al. systematically investigated some of the potential factors affecting the melting properties of these novel materials, and a sub- sequent thermodynamic model was presented to account for the experimental observations (Storhoff et al., 2000). The sharp melt- ing may result from two key factors (Elghanian et al., 1997): the presence of multiple DNA linkers between each pair of nanopar- ticles; a decrease in the melting temperature as the duplex DNA strands melt due to a concomitant reduction in the local dielectric. The interactions (Alexei and Sergey, 1998) between the neighbor- ing DNA molecules play an important role in DNA hybridization at the interface because the double-helix structure of DNA is sur- rounded by negative ions in solution that provide a repelling force between the strands. Therefore, the stability of the duplex DNA structure is very sensitive to the surrounding hybridization buffer 0956-5663/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2011.11.045