Nanoparticle Signal Amplification Electrochemical Impedance Dna Biosensor

Deoxyribonucleic acid is the essential genetic material of the living organisms, which has the function of storing up, transferring information and guiding various types of protein synthesis. The sequence-specific detection of DNA based on the hybridization between a DNA target and its complementary probe has attracted considerable interest in a wide range of areas including molecular diagnostics, environmental monitoring, and forensic applications. Detection of genetic mutations at the molecular level opens up the possibility of performing reliable diagnostics even before any symptom of a disease appears. At present, numerous DNA detection systems have been described, the traditional DNA sequencing generally uses gel electrophoresis method. During the past decade, the DNA sensors overcomes the disadvantage of traditional methods of time-consuming, exhausting and low efficiency.Consequently, various optical, piezoelectric, and electronic transduction techniques have been employed for the development of DNA sensors. Among them, DNA sensors based on electrochemical impedance spectroscopy (EIS) have attracted great attention due to the fact that electrochemical detectors are label-free, simple, portable, inexpensive and high sensitivity. In order to improve the sensitivity, selectivity, and detection limit of the biosensor, gold nanoparticles (AuNPs) have been prepared and utilized recently for the electrochemical impedance spectroscopy DNA biosensor. This paper is consistsed of the following three chapters.Chapters 1:IntroductionFistly, it briefly describes the principle and classification of DNA biosensor,and then Introduce the key principles of DNA electrochemical biosensors (DNA probes immobilized on the electrode surface and electrochemical impedance method). Second, the application of gold nanoparticles on DNA biosensors was introduced. Finally, the background, research ideas, purpose and contents of this paper are described.Chapters 2:Highly sensitive impedimetric sensing of DNA hybridization based on the target DNA-induced displacement of gold nanoparticles attached to ssDNA probeAn impedimetric DNA sensor based on the displacement of gold nanoparticles (AuNPs) by target DNA(cDNA) was developed for the highly sensitive detection of DNA hybridization without signal amplification. Positively charged gold nanoparticles, in combination with Single-stranded DNA, were used to fabricate a impedimetric electrochemical DNA biosensor. A thiol modified probe ssDNA (PDNA) was immobilized on a gold electrode by self-assembly followed by backfill with mercaptohexanol. Subsequently, positively charged 5 nm AuNPs were attached to the immobilized PDNA by base-Au and electrostatic interaction. Attachment of AuNPs to the immobilized ssDNA probe significantly decreased the electron transfer resistance (Ret) of the DNA sensor. After hybridization of target ssDNA to immobilized PDNA, the AuNPs were displaced by target DNA, which led to an increase in the Ret value. Based on the displacement of AuNPs by target ssDNA, The results of experiment shows that the change of the electron transfer resistance of the biosensor is linear with the concentration of target DNA in the range from 5.0×10-14 to 1.0×10-12 mol·L-1. The detection limit for target DNA was 3×10-14 mol·L-1 fmol·L-1 (S/N= 3). The sensor surface clearly distinguished between complementary target ssDNA from single-base pair mismatches and non-complementary ssDNA.Chapters 3:impedimetric DNA electrochemical biosensors Based on the Enlargement of Surface-Charged Gold NanoparticlesA simple, label-free and cascaded signal amplification electrochemical impedimetric DNA biosensors for target DNA was fabricated. The sandwich system of DPDNA-AuNPs/ ssDNA/CPDNA was fabricated as the sensing platform. The change of the interfacial feature of the electrode was characterized by electrochemical impedance analysis with the redox probe [Fe(CN)6]3-/4-. For improving detection sensitivity, the three-level cascaded impedimetric signal amplification was developed:(1) DPDNA-AuNPs as the first-level signal enhancer. (2) the steric-hindrance between the enlarged DPDNA-AuNPs as the second-level signal amplification. (3) the electrostatic-repulsion between sodium dodecylsulfate (SDS) stabilized DPDNA-AuNPs and the redox probe [Fe(CN)6]3-/4- as the third-level signal amplification. The results of experiment shows that the change of the electron transfer resistance of the biosensor is linear with the concentration of target DNA in the range from 3.0×10-14 to 1.0×10-13 fmol·L-1. r=0.9879. The detection limit for target DNA was 1×10-14 mol·L-1 (S/N= 3). It presents a simple and general signal amplification model for impedimetric DNA sensors.