Ultrasensitive electrochemical detection for DNA arrays based on silver nanoparticle aggregates

Multiplexed DNA target detection is of great significance in many fields including clinical diagnostics, environmental monitoring, biothreat detection and forensics. Although the emergence of DNA chip technology has accelerated this process, it is still a challenge to perform ultrasensitive DNA assay at low attomol concentrations so that DNA detection can be directly achieved without a PCR protocol. In this work, an oligonucleotide-functionalized silver nanoparticle tag has been successfully developed for multiplexed DNA electrochemical detection with ultrahigh sensitivity. The multiprobes containing oligo(d)A and the reporting probes were anchored onto the silver nanoparticles, followed by hybridizing with the silver nanoparticle conjugate modified with oligo(d)T. The hybridization-induced tag was found to show an aggregated nanostructure 10 times larger than the individual nanoparticle, as revealed by TEM. For sandwich-based assays, the tag was specifically coupled to a gold electrode surface via target DNA. Compared to a single nanoparticle label, this novel tag has shown excellent electroactive property and produces 10(3)-fold amplification in the differential pulse voltammetric (DPV) method. Hepatitis B virus (HBV) sequence was employed as a sample model, and we have achieved a detection limit of 5 aM ( approximately 120 molecules in 40 muL volume), demonstrating ultrasensitive measurement for DNA. The property of the electrochemical process involving silver aggregates was further investigated and the integrative oxidation of the silver tag was observed. We further demonstrated the multiplexed DNA target detection using array chips functionalized with Herpes simplex virus (HSV), Epstein-Barr virus (EBV) and cytomegalovirus (CMV) sequences, which shows effective recognition of the relative sequences individually or simultaneously. The method offers a uniquely new approach for DNA detection with ultrahigh sensitivity as well as advantages of rapidity, throughput, and miniaturization.