Quantum-dot biosensor for hybridization and detection of R3500Q mutation of apolipoprotein B-100 gene Mohammad Mazloum-Ardakani a,n , Roghayyeh Aghaei a , Mohammad Mehdi Heidari b a Department of Chemistry, Faculty of Science, Yazd University, Yazd 89195-741, Iran b Department of Biology, Faculty of Science, Yazd University, Yazd 89195-741, Iran article info Article history: Received 21 March 2015 Received in revised form 5 May 2015 Accepted 6 May 2015 Available online 14 May 2015 Keywords: CdS quantum dot DNA biosensor DNA hybridization Apolipoprotein B-100 gene Electrochemical impedance spectroscopy abstract A quantum-dot electrode system was developed as a transducer surface for covalent immobilization of a designed synthetic ApoB-100 specific probe, DNA hybridization and monitoring of DNA synthesis for the sensitive detection of R3500Q mutation of apolipoprotein B-100 (ApoB-100) gene. CdS-QDs cause an improvement in the fundamental characteristics of the electrode interface, such as its electroactive surface area, diffusion coefficient and electron transfer kinetics. The sensing characteristics of this bio- sensor offer a suitable potential for detection of target oligonucleotide with a detection limit of 3.4 Â 10 À17 M. Also, the electrochemical responses of single-stranded DNA (ssDNA), DNA hybridization and DNA synthesis were investigated using electrochemical impedance spectroscopy (EIS). The extracted genomic DNA was detected based on changes in the charge transfer resistance (RCT) with [Fe(CN) 6 ] 3 À/4À as a redox probe. The proposed biosensor can distinguish between the normal sequence and the mutant sequence of ApoB-100 gene, promising a possibility to apply the QD-based biosensor for clinical in- vestigations. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Substantial progress over the past decade has led to dramatic improvements in the performance of biosensors. These improve- ments have, in turn, led to the fabrication of biosensors with capability of convenient measurement at less than subnanomolar (parts per trillion) levels (Wang and Liu, 2010, Benvidi et al., 2014; Thavanathan et al., 2014; Zhai et al., 2015; Amouzadeh-Tabrizi and Shamsipur, 2015; Huang et al., 2015). The best biosensor perfor- mance depends on biomolecular immobilization onto a suitable matrix. The interfacing of biomolecules with a nanomaterial may lead to producing a wide range of functional hybrid materials for biosensor applications. In comparison with bulk materials, nano- particles can exhibit modified physical properties due to their size. For this reason, nanoparticles are very attractive in analytical de- tection systems and sensors (Lin et al., 2007; Gill et al., 2008; De et al., 2008). Nanostructured devices exhibit some improved properties such as enhanced catalytic activity or sensitivity (Katz et al., 2004; Mazloum-Ardakani et al., 2013, 2014a, 2014b, 2015; Taleat et al., 2014; Chen et al., 2007). Quantum dots (QDs) are a novel class of inorganic nano- particles which are gaining widespread recognition due to their exceptional photophysical properties (Wang et al., 2006). Colloidal quantum dot films allow large-area solution processing and bandgap tuning through the quantum size effect (Kramer and Sargent, 2011). Rapidly being applied to existing and emerging technologies, these films can play an important role in many fields (Algar et al., 2009; Klostranec and Chan, 2006; Zhang et al., 2010). QD-biocomposites, as a result of interaction of QDs with biological molecules including proteins, peptides and DNA, have widespread applications in areas ranging from in vivo imaging and diagnostics in biomedicine to environmental monitoring for public health and security (Prasuhn et al., 2010). A number of reports have shown that QD-conjugated oligonucleotide sequences (attached via sur- face carboxylic acid groups) may be targeted to bind with DNA or mRNA (Pathak et al., 2001; Gerion et al., 2002). Electroanalytical chemists are attracted by QDs as a transducer surface for the development of electrochemical biosensing assays and keep in view various potentials of these nanoparticles (Shar- ma et al., 2013; Schubert et al., 2010). For instance, fabrication of a sensitive electrochemical biosensor using an interface based on QDs self-assembly for blood cancer detection has been reported by Sharma. Effective coupling of quantum dots to biomolecules sig- nificantly depends on different synthesis methods of QDs and methods of surface modification with different ligands and cap- ping agents (Murrar et al., 1993; Yu and Peng, 2002; Zhong et al., 2004). Therefore, solubilisation of QDs in water is essential for Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/bios Biosensors and Bioelectronics http://dx.doi.org/10.1016/j.bios.2015.05.014 0956-5663/& 2015 Elsevier B.V. All rights reserved. n Corresponding author. Fax: þ98 351 8210644. E-mail address: mazloum@yazd.ac.ir (M. Mazloum-Ardakani). Biosensors and Bioelectronics 72 (2015) 362–369