Photoelectrochemical DNA Biosensors

N-doped TiO2 based visible light activated label-free photoelectrochemical biosensor for detection of Hg(2+) through quenching of photogenerated electrons

A novel photoelectrochemical (PEC) biosensor was fabricated based on N-doped TiO2 for the detection of Hg(2+) through the quenching of photogenerated electrons. The N-doped TiO2 was synthesized by a sol-gel method with urea and tetrabutyl titanate as the N and Ti sources. Compared with the undoped TiO2, the N-doped TiO2 showed an enhanced photocurrent response under visible light (λ > 420 nm). The sensing surface was functionalized with 5'-amino-modified T-rich oligonucleotides. The photoelectrochemical biosensor bound Hg(2+) on the surface by a highly specific T-Hg(2+)-T recognition. Hg(2+) on the surface of the N-doped TiO2 film withdrew the photogenerated electrons and decreased the recorded current signal. The dynamic linear range for Hg(2+) has been determined to be as low as 2-6 μM.

Biomolecule-free, selective detection of o-diphenol and its derivatives with WS2/TiO2-based photoelectrochemical platform

Herein, a novel photoelectrochemical platform with WS2/TiO2 composites as optoelectronic materials was designed for selective detection of o-diphenol and its derivatives without any biomolecule auxiliary. First, catechol was chosen as a model compound for the discrimination from resorcinol and hydroquinone; then several o-diphenol derivatives such as dopamine, caffeic acid, and catechin were also detected by employing this proposed photoelectrochemical sensor. Finally, the mechanism of such a selective detection has been elaborately explored. The excellent selectivity and high sensitivity should be attributed to two aspects: (i) chelate effect of adjacent double oxygen atoms in the o-diphenol with the Ti(IV) surface site to form a five/six-atom ring structure, which is considered as the key point for distinction and selective detection. (ii) This selected WS2/TiO2 composites with proper band level between WS2 and TiO2, which could make the photogenerated electron and hole easily separated and results in great improvement of sensitivity. By employing such a photoelectrochemical platform, practical samples including commercial clinic drugs and human urine samples have been successfully performed for dopamine detection. This biomolecule-free WS2/TiO2 based photoelectrochemical platform demonstrates excellent stability, reproducibility, remarkably convenient, and cost-effective advantages, as well as low detection limit (e.g., 0.32 μmol L(-1) for dopamine). It holds great promise to be applied for detection of o-diphenol kind species in environment and food fields.

Cyclometalated iridium complex-based label-free photoelectrochemical biosensor for DNA detection by hybridization chain reaction amplification

Photoactive material is the most crucial factor which intimately determines analytical performances of the photoelectrochemical sensor. On the basis of the high affinity of dipyrido [3,2-a:2',3'-c] phenazine (dppz) with DNA helix, a novel photoactive intercalator, [(ppy)2Ir(dppz)](+)PF6(-)(ppy = 2-phenylpyridine and dppz = dipyrido [3,2-a:2',3'-c] phenazine) was prepared and characterized by UV-vis absorption spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. The photoelectrochemical properties of the as-prepared iridium(III) complex immobilized on the ITO electrode was investigated. Either cathodic or anodic photocurrent generation can be observed when triethanolamine (TEOA) or dissolved O2 is used as a sacrificial electron donor/acceptor, respectively. The probable photocurrent-generation mechanisms are speculated. A highly sensitive iridium(III) complex-based photoelectrochemical sensor was proposed for DNA detection via hybridization chain reaction (HCR) signal amplification. Under optimal conditions, the biosensor was found to be linearly proportional to the logarithm of target DNA concentration in the range from 0.025 to 100 pmol L(-1) with a detection limit of 9.0 fmol L(-1) (3σ). Moreover, the proposed sensor displayed high selectivity and good reproducibility, demonstrating efficient and stable photoelectric conversion ability of the Ir(III) complex.

Photoresponsive DNA monolayer prepared by primer extension reaction on the electrode

We describe a simple and convenient method for the preparation of photoresponsive DNA-modified electrodes using primer extension (PEX) reactions. A naphthalimide derivative was used as the photosensitizer that was attached to the C5-position of 2'-deoxyuridine-5'-triphosphate (dUTP(NI)). It has been found that dUTP(NI) is a good substrate for the PEX reactions using KOD Dash and Vent (exo-) enzymes in solutions to incorporate naphthalimide (NI) moieties into the DNA sequences. On the electrode surface immobilized with the primer/template DNA, the PEX reactions to incorporate dUTP(NI) molecules into the DNA sequence were found to efficiently proceed. With this solid-phase method, the DNA monolayers capable of generating photocurrent due to the photoresponsive NI molecule can be constructed. It was shown that the photocurrent generation was significantly suppressed by a single-nucleotide mismatch included in the primer/template DNA, which is applicable for the design of photoelectrochemical sensors to discriminate single-nucleotide sequences.

Self assembled nanocages from DNA–protoporphyrin hybrid molecules

DNA–organic hybrid molecular building blocks are generated by covalent conjugation of the carboxyl groups of protoporphyrin IX with the amine functional groups of modified DNA oligomers.

Highly sensitive “signal-on” electrochemiluminescent biosensor for the detection of DNA based on dual quenching and strand displacement reaction

A “signal-on” electrochemiluminescent DNA biosensing platform was proposed based on dual quenching and the strand displacement reaction.

A label-free fluorescent molecular switch for a DNA hybridization assay utilizing a G-quadruplex-selective auramine O

A G-quadruplex molecular switch (G4-MS) assembled using auramine O and the G-rich single stranded DNA is developed for a DNA assay.

Homogeneous chemiluminescent DNA assay based on allosteric activation of peroxidase-mimicking DNAzyme

We developed a homogeneous chemiluminescent DNA assay based on allosteric activation of peroxidase-mimicking DNAzyme.

Photoelectrochemical bioanalysis: the state of the art

This review provides a panoramic snapshot of the state of the art in the dynamically developing field of photoelectrochemical bioanalysis.

Organometallic polymers for electrode decoration in sensing applications

Macromolecules containing metals combine the processing advantages of polymers with the functionality offered by the metal centers. The developments in the area of electrochemical chemo/biosensors based on organometallic polymers are reviewed.

Anatase TiO2 based photoelectrochemical sensor for the sensitive determination of dopamine under visible light irradiation

The sensitive photoelectrochemical determination of dopamine was achieved using an indium tin oxide electrode modified with TiO₂ nanoparticles.

A sensitive photoelectrochemical immunoassay based on mesoporous carbon/core–shell quantum dots as donor–acceptor light-harvesting architectures

A label-free PEC biosensor based on the amplification of mesoporous conductive material and core–shell QDs as light-harvesting architecture.

Application of CuS-functionalized ZnO nanoflakes for a paper-based photoelectrochemical immunoassay using an in situ electron donor producing strategy

Copper sulfide functionalized ZnO nanoflakes were used to construct a paper-based photoelectrochemical immunosensor using an in situ electron donor producing strategy.

A new visible-light-driven photoelectrochemical biosensor for probing DNA–protein interactions

A novel photoelectrochemical approach was achieved for the detection of a DNA binding protein via the protein–DNA interaction.

Flexible microfabricated film sensors for the in situ quantum dot-based voltammetric detection of DNA hybridization in microwells

A new flexible miniaturized integrated device was microfabricated for the in situ ultrasensitive voltammetric determination of DNA mutation in a microwell format, using quantum dots (QDs) labels. The integrated device consisted of thin Bi, Ag, and Pt films (serving as the working, reference, and counter electrode, respectively) deposited by sputtering on a flexible polyimide substrate. A DNA assay was employed in microwell format, where an immobilized complementary oligonucleotide probe hybridized with the biotinylated target oligonucleotide followed by reaction with streptavidin-conjugated PbS QDs. After the acidic dissolution of the QDs, the flexible sensor was rolled and inserted into the microwell and the Pb(II) released was determined in situ by anodic stripping voltammetry. Since the analysis took place directly in the microwell, the volume of the working solution was only 100 μL and the target DNA could be detected at a concentration down to 1.1 fmol L(-1). The proposed flexible microdevice addresses the restrictions of conventional rigid electrodes while it provides a low cost integrated transducer for the ultrasensitive detection of important biomolecules.

DNA adsorption by indium tin oxide nanoparticles

The high conductivity and optical transparency of indium tin oxide (ITO) has made it a popular material in the electronic industry. Recently, its application in biosensors is also explored. To understand its biointerface chemistry, we herein investigate its interaction with fluorescently labeled single-stranded oligonucleotides using ITO nanoparticles (NPs). The fluorescence of DNA is efficiently quenched after adsorption, and the interaction between DNA and ITO NPs is strongly dependent on the surface charge of ITO. At low pH, the ITO surface is positively charged to afford a high DNA adsorption capacity. Adsorption is also influenced by the sequence and length of DNA. For its components, In2O3 adsorbs DNA more strongly while SnO2 repels DNA at neutral pH. The DNA adsorption property of ITO is an averaging result from both components. DNA adsorption is confirmed to be mainly by the phosphate backbone via displacement experiments using free phosphate or DNA bases. Last, DNA-induced DNA desorption by forming duplex DNA is demonstrated on ITO, while the same reaction is more difficult to achieve on other metal oxides including CeO2, TiO2, and Fe3O4 because these particles adsorb DNA more tightly.

Dual switchable CRET-induced luminescence of CdSe/ZnS quantum dots (QDs) by the hemin/G-quadruplex-bridged aggregation and deaggregation of two-sized QDs

The hemin/G-quadruplex-catalyzed generation of chemiluminescence through the oxidation of luminol by H2O2 stimulates the chemiluminescence resonance energy transfer (CRET) to CdSe/ZnS quantum dots (QDs), resulting in the luminescence of the QDs. By the cyclic K(+)-ion-induced formation of the hemin/G-quadruplex linked to the QDs, and the separation of the G-quadruplex in the presence of 18-crown-6-ether, the ON-OFF switchable CRET-induced luminescence of the QDs is demonstrated. QDs were modified with nucleic acids consisting of the G-quadruplex subunits sequences and of programmed domains that can be cross-linked through hybridization, using an auxiliary scaffold. In the presence of K(+)-ions, the QDs aggregate through the cooperative stabilization of K(+)-ion-stabilized G-quadruplex bridges and duplex domains between the auxiliary scaffold and the nucleic acids associated with the QDs. In the presence of 18-crown-6-ether, the K(+)-ions are eliminated from the G-quadruplex units, leading to the separation of the aggregated QDs. By the cyclic treatment of the QDs with K(+)-ions/18-crown-6-ether, the reversible aggregation/deaggregation of the QDs is demonstrated. The incorporation of hemin into the K(+)-ion-stabilized G-quadruplex leads to the ON-OFF switchable CRET-stimulated luminescence of the QDs. By the mixing of appropriately modified two-sized QDs, emitting at 540 and 610 nm, the dual ON-OFF activation of the luminescence of the QDs is demonstrated.

Photoelectrochemical aptasensing of kanamycin using visible light-activated carbon nitride and graphene oxide nanocomposites

Photoactive material and recognition element are two crucial factors which determine the sensitivity and selectivity of the photoelectrochemical (PEC) sensor. Herein we developed a novel PEC aptamer sensor for the specific detection of kanamycin using water-dispersible graphite-like carbon nitride (w-g-C3N4) as visible light-active material and aptamer as the biorecognition element. While a suitable amount of graphene oxide (GO) was doped in w-g-C3N4, the visible light photocurrent response was enhanced, which was beneficial to the construction of PEC sensor. On the other hand, the large specific surface area and π-conjugated structure of GO/w-g-C3N4 provided an excellent platform for immobilizing the kanamycin-binding DNA aptamer on the surface of the sensor via π-π stacking interaction. On such a sensor, the capture of kanamycin molecules by aptamer resulted in increased photocurrent. The PEC response of the sensor was found to be linearly proportional to the concentration of kanamycin in the range from 1 nM to 230 nM with a detection limit (3S/N) of 0.2 nM. Moreover, the proposed sensor displayed high selectivity, good reproducibility, and high stability, demonstrating the successful combination of GO/w-g-C3N4 with aptamer in fabricating high performance PEC sensors.