Libing Fu

DNAzyme-based magneto-controlled electronic switch for picomolar detection of lead (II) coupling with DNA-based hybridization chain reaction

A novel magneto-controlled electrochemical DNA biosensor is designed for the ultrasensitive detection of lead coupling a lead-specific DNAzyme with DNA-based hybridization chain reaction (HCR). To construct such a magnetic lead sensor, DNAzyme-based molecular beacons, selective to cleavage in the presence of Pb(2+), are initially immobilized onto magnetic beads, which were used as the recognition elements. Upon addition of target lead, catalytic cleavage of substrate DNA segments in the double-stranded DNAzymes results in the capture of the initiator strands via the conjugated catalytic strands on magnetic beads. The captured DNA initiator strands trigger the hybridization chain reaction between two alternating hairpin DNA structures labeled with ferrocene to form a nicked double-helix on the magnetic beads. Numerous ferrocene molecules are formed on the neighboring probes, each of which produces an electrochemical signal within the applied potential. Under optimal conditions, the electrochemical signal of the magnetic lead sensor increases with the increasing lead level in the sample, and exhibits a linear response over a Pb(2+) concentration range of 0.1-75 nM with a detection limit of 37 pM. Quantitative measurement of Pb(2+) in the complex sample demonstrates the selectivity of the sensor scheme and points favorably to the application of such technologies to the analysis of environmental samples. The unique combination of a DNAzyme with hybridization chain reaction makes it possible to change the DNAzyme to select for other compounds of interest. This work represents the initial steps toward the creation of a robust field sensor for lead in groundwater or drinking water.

Enzyme-catalyzed silver deposition on irregular-shaped gold nanoparticles for electrochemical immunoassay of alpha-fetoprotein.

A new and disposable electrochemical immunosensor was designed for detection of alpha-fetoprotein (AFP), as a model analyte, with sensitivity enhancement based on enzyme-catalyzed silver deposition onto irregular-shaped gold nanoparticles (ISGNPs). The assay was carried out with a sandwich-type immunoassay protocol by using ISGNP-labeled anti-AFP antibodies conjugated with alkaline phosphatase (ALP-Ab(2)) as detection antibodies. The enzymatically catalytic deposition of silver on the electrode could be measured by stripping analysis in KCl solution due to the Ag/AgCl solid-state voltammetric process. Several labeling protocols including spherical gold nanoparticle-labeled ALP-Ab(2) and ISGNP-labeled ALP-Ab(2) were investigated for determination of AFP, and improved analytical properties were achieved with the ISGNP labeling. With the ISGNP labeling method, the effects of incubation time and incubation temperature for antigen-antibody reaction, and deposition time of silver on the current responses of the electrochemical immunosensors were also monitored. Under optimal conditions, the electrochemical immunosensor exhibited a wide dynamic range from 0.01 ng mL(-1) to 200 ng mL(-1) with a detection limit of 5.0 pg mL(-1) AFP. The immunosensor displayed a good stability and acceptable reproducibility and accuracy. No significant differences at the 95% confidence level were encountered in the analysis of 10 clinical serum samples between the developed immunoassay and the commercially available electrochemiluminescent method for determination of AFP.

Portable and quantitative monitoring of heavy metal ions using DNAzyme-capped mesoporous silica nanoparticles with a glucometer readout

A portable and quantitative monitoring protocol for sensitive detection of lead ions is designed, based on target-responsive cargo release from Pb2+-specific DNAzyme-capped mesoporous silica nanoparticles (MSNs), by coupling with a widely accessible personal glucose meter (PGM). Initially, glucose molecules are loaded into the pores of the MSNs, the pores are then capped with Pb2+-specific DNAzymes. Upon target introduction, the molecular gates open, resulting in release of the cargo from the pores. The released glucose can be quantitatively monitored using a portable PGM. Under optimal conditions, the as-prepared sensing platform presents good analytical properties for the determination of the target Pb2+ ions, and allows detection of Pb2+ at concentrations as low as 1.0 pM. Importantly, the portable sensing platform has the advantages of simple, on-site, user-friendly and low-cost assessment and has tremendous potential for quantitative detection of non-glucose targets by the public.

Hybridization-induced isothermal cycling signal amplification for sensitive electronic detection of nucleic acid.

This works reports a new signal-on amplification strategy for sensitive electronic detection of nucleic acid based on the isothermal circular strand-displacement polymerization (ICSDP) reaction. The assay mainly involves a hybridization of ferrocene-labeled hairpin DNA with blocker DNA, a strand-displacement process with target DNA, and an ICSDP-based polymerization reaction. The signal is amplified by the labeled ferrocene on the hairpin probe with target recycling. Upon addition of target analyte, the blocker DNA is initially displaced by target DNA from the hairpin/blocker DNA duplex owing to the difference of the folding free energy, then the newly formed target/blocker DNA duplex causes the ICSDP reaction with the aid of the primer and polymerase, and then the released target DNA retriggers the strand-displacement for target recycling. Numerous ferrocene molecules are close to the electrode surface due to the reformation of hairpin DNA, each of which produces an electronic signal within the applied potentials, thereby resulting in the amplification of electrochemical signal. Under the optimal conditions, the ICSDP-based amplification method displays good electrochemical responses for detection of target DNA at a concentration as low as 0.03pM.

Mesoporous nanogold–MnO2–poly(o-phenylenediamine) hollow microspheres as nanotags and peroxidase mimics for sensing biomolecules

A new electrochemical immunosensor was designed for the determination of carcinoembryonic antigen (CEA) with sensitivity enhanced by using nanogold-poly(o-phenylenediamine)-manganese dioxide organic-inorganic hybrid nanostructures (GNPM) as nanotags and peroxidase mimics. Initially, mesoporous poly(o-phenylenediamine)-manganese dioxide (PPD-MnO2) hollow microspheres were synthesized by an inorganic/organic interfacial polymerization technique. Then gold nanoparticles were assembled onto the surface of PPD-MnO2, which were used for the labelling of the anti-CEA detection antibody (pAb2). The prepared GNPM nanotags were characterized using transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), UV-vis absorption spectroscopy, N2 adsorption-desorption isotherm measurements and Fourier transform infrared spectroscopy (FTIR). The assay was carried out with a sandwich-type immunoassay format in pH 5.5 acetic acid-buffered saline solution containing 2.5 mmol L-1 H2O2. Experimental results indicated that the electrochemical immunosensor exhibited a wide dynamic range from 0.01 to 80 ng mL-1 towards the target CEA with a detection limit (LOD) of 6.0 pg mL-1. The immunosensor also displayed a good stability and acceptable reproducibility and selectivity. In addition, the methodology was evaluated by assaying 10 clinical serum samples, providing a good relationship between the electrochemical immunosensor and the commercialized electrochemiluminescent (ECL) method for determination of CEA.

A squaric acid-stimulated electrocatalytic reaction for sensing biomolecules with cycling signal amplification

Squaric acid, a 2-dimensional planar structure of squarate C4O4 units linked by protons in a layered sheet, was utilized for the first time as a catalytic substrate for ultrasensitive electronic determination of low-abundance proteins by coupling a target-induced electrocatalytic reaction with the in situ cycling signal amplification strategy.

DNA pseudoknot-functionalized sensing platform for chemoselective analysis of mercury ions.

A novel, simple, signal-enhanced electrochemical sensor was designed for sensitive and selective determination of mercury ions by using target-triggered conformational change of DNA pseudoknots with the assistance of auxiliary DNA strands.

Target-stimulated metallic HgS nanostructures on a DNA-based polyion complex membrane for highly efficient impedimetric detection of dissolved hydrogen sulfide

Target-stimulated metallic HgS nanostructures formed on the DNA-based polyion complex (PIC) membrane were for the first time utilized as an efficient scheme for impedimetric detection of hydrogen sulfide (H2S) by coupling insoluble precipitation with sensitivity enhancement.