Electrochemical DNAzyme Sensor for Lead Based on Amplification of DNA−Au Bio-Bar Codes

Abstract

An electrochemical DNAzyme sensor for sensitive and selective detection of lead ion (Pb(2+)) has been developed, taking advantage of catalytic reactions of a DNAzyme upon its binding to Pb(2+) and the use of DNA-Au bio-bar codes to achieve signal enhancement. A specific DNAzyme for Pb(2+) is immobilized onto an Au electrode surface via a thiol-Au interaction. The DNAzyme hybridizes to a specially designed complementary substrate strand that has an overhang, which in turn hybridizes to the DNA-Au bio-bar code (short oligonucleotides attached to 13 nm gold nanoparticles). A redox mediator, Ru(NH3)6(3+), which can bind to the anionic phosphate of DNA through electrostatic interactions, serves as the electrochemical signal transducer. Upon binding of Pb(2+) to the DNAzyme, the DNAzyme catalyzes the hydrolytic cleavage of the substrate, resulting in the removal of the substrate strand along with the DNA bio-bar code and the bound Ru(NH3)6(3+) from the Au electrode surface. The release of Ru(NH3)6(3+) results in lower electrochemical signal of Ru(NH3)6(3+) confined on the electrode surface. Differential pulse voltammetry (DPV) signals of Ru(NH3)6(3+) provides quantitative measures of the concentrations of Pb(2+), with a linear calibration ranging from 5 nM to 0.1 microM. Because each nanoparticle carries a large number of DNA strands that bind to the signal transducer molecule Ru(NH3)6(3+), the use of DNA-Au bio-bar codes enhances the detection sensitivity by five times, enabling the detection of Pb(2+) at a very low level (1 nM). The DPV signal response of the DNAzyme sensor is negligible for other divalent metal ions, indicating that the sensor is highly selective for Pb(2+). Although this DNAzyme sensor is demonstrated for the detection of Pb(2+), it has the potential to serve as a general platform for design sensors for other small molecules and heavy metal ions.

Applications of gold nanoparticles in medicine and therapy

“…For examples, Shen et al 23 proposed an EC DNAzyme sensor based on AuNPs for sensitive and selective detection of Pb…”

“…To realize ultrasensitive detection of biomolecules, development of novel and robust detection methods for signal amplification of EC sensors is essential. In past work, a lot of photo or electro-active indicators, such as ferrocene, 98 methylene blue 99 and enzymes, 100 were immobilized onto AuNPs to realize the detection signals amplification. Zheng et al 101 prepared an ultrasensitive EC sensor based on networklike thiocyanuric acid/AuNPs for detection of thrombin.…”

Advanced AuNMs as nanomedicine’s central goals capable of active targeting in both imaging and therapy in biomolecules

“…For examples, Shen et al [92] proposed an EC DNAzyme sensor based on AuNPs for sensitive and selective detection of Pb 2+ . A label-free EC sensor was developed for the highly sensitive and selective detection of Hg 2+ by Tang et al [93].…”

A sensitive fluorescence anisotropy method for detection of lead (II) ion by a G-quadruplex-inducible DNA aptamer

“…Of these, [8][9][10][11][12][13][14][15][16][17] DNAzyme has attracted much more attention. They have been extensively explored for Pb 2+ detection via fluorescence [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29], fluorescence anisotropy [30], colorimetry [31][32][33][34], electrochemistry [35][36][37][38], electrochemiluminescence [39], dynamic light scattering [40,41], and surface enhanced Raman scattering [42].…”