Photoelectrochemical DNA Biosensors

Efficient Photocurrent Enhancement from Porphyrin Molecules on Plasmonic Copper Arrays: Beneficial Utilization of Copper Nanoanntenae on Plasmonic Photoelectric Conversion Systems

We demonstrated the usefulness of Cu light-harvesting plasmonic nanoantennae for the development of inexpensive and efficient artificial organic photoelectric conversion systems. The systems consisted of the stacked structures of layers of porphyrin as a dye molecule, oxidation-suppressing layers, and plasmonic Cu arrayed electrodes. To accurately evaluate the effect of Cu nanoantenna on the porphyrin photocurrent, the production of Cu₂O by the spontaneous oxidation of the electrode surfaces, which can act as a photoexcited species under visible light irradiation, was effectively suppressed by inserting the ultrathin linking layers consisting of 16-mercaptohexadecanoic acid, titanium oxide, and poly(vinyl alcohol) between the electrode surface and porphyrin molecules. The reflection spectra in an aqueous environment of the arrayed electrodes, which were prepared by thermally depositing Cu on two-dimensional colloidal crystals of silica with diameters of 160, 260, and 330 nm, showed clear reflection dips at 596, 703, and 762 nm, respectively, which are attributed to the excitation of localized surface plasmon resonance (LSPR). While the first dip lies within the wavelengths where the imaginary part of the Cu dielectric function is moderately large, the latter two dips lie within a region of a quite small imaginary part. Consequently, the LSPR excited at the red region provided a particularly large enhancement of porphyrin photocurrent at the Q-band (ca. 59-fold), compared to that on a Cu planar electrode. These results strongly suggest that the plasmonic Cu nanoantennae contribute to the substantial improvement of photoelectric conversion efficiency at the wavelengths, where the imaginary part of the dielectric function is small.

Synergy effect of specific electrons and surface plasmonic resonance enhanced visible-light photoelectrochemical sensing for sensitive analysis of the CaMV 35S promoter

A Ag/TiO₂/N-GNR ternary composite-based photoelectrochemical sensor for sensitive analysis of the CaMV 35S promoter.

Hemin/Au nanorods/self-doped TiO2nanowires as a novel photoelectrochemical bioanalysis platform

A sensitive photoelectrochemical platform for GSH was developed by modifying self-doped TiO₂nanowires with mixed Au nanorods at two different aspect ratios as the core sensing unit and hemin for recognition.

A potentiometric resolved ratiometric photoelectrochemical aptasensor

A novel ratiometric photoelectrochemical aptasensor based on the potentiometric resolved photocurrents generated from different PEC active materials was designed for the first time.

A one-pot hydrothermal synthesis of graphene/CdS:Mn photocatalyst for photoelectrochemical sensing of glutathione

The GR/CdS:Mn composite was fabricated by a simple hydrothermal synthesis which illustrates excellent performance for the photoelectrochemical detection of glutathione.

Photoelectrochemical DNA Biosensor Based on Dual-Signal Amplification Strategy Integrating Inorganic-Organic Nanocomposites Sensitization with λ-Exonuclease-Assisted Target Recycling

Sensitive and accurate analysis of DNA is crucial to better understanding of DNA functions and early diagnosis of fatal disease. Herein, an enhanced photoelectrochemical (PEC) DNA biosensor was proposed based on dual-signal amplification via coupling inorganic-organic nanocomposites sensitization with λ-exonuclease (λ-Exo)-assisted target recycling. The short DNA sequence about chronic myelogenous leukemia (CML, type b3a2) was selected as target DNA (tDNA). ZnO nanoplates were deposited with CdS nanocrystals to form ZnO/CdS hetero-nanostructure, and it was used as PEC substrate for immobilizing hairpin DNA (hDNA). CdTe quantum dots (QDs) covalently linked with meso-tetra(4-carboxyphenyl)porphine (TCPP) to form CdTe/TCPP inorganic-organic nanocomposites, which were utilized as sensitization agents labeling at the terminal of probe DNA (pDNA). When the hDNA-modified sensing electrode was incubated with tDNA and λ-Exo, hDNA hybridized with tDNA, and meanwhile it could be recognized and cleaved by λ-Exo, resulting in the release of tDNA. The rest of nonhybridized hDNA would continuously hybridize with the released tDNA, cleave by λ-Exo, and set free the tDNA again. After λ-Exo-assisted tDNA recycling, more amounts of short DNA (sDNA) fragments coming from digestion of hDNA produced on the electrode and hybridized with CdTe/TCPP-labeled pDNA (pDNA-CdTe/TCPP conjugates). In this case, the sensitization of CdTe/TCPP inorganic-organic nanocomposites occurred, which evidently extend the absorption range and strengthened the absorption intensity of light energy, and accordingly the photocurrent signal significantly promoted. Through introducing the dual-signal amplification tactics, the developed PEC assay allowed a low calculated detection limit of 25.6 aM with a wide detection scope from 0.1 fM to 5 pM for sensitive and selective determination of tDNA.

Electro-Photodynamic Visualization of Singlet Oxygen Induced by Zinc Porphyrin Modified Microchip in Aqueous Media

A porphyrin-based electro-photodynamic imaging system was fabricated for monitoring the concentration of oxygen. Distinct from the electrochemiluminescent (ECL) inability of numerous organic species in aqueous solutions, a strong and stable red irradiation at 634 nm could be stimulated electrochemically on zinc(II) meso-tetra(4-carboxyphenyl) porphine (ZnTCPP)/tetraoctylammonium bromide (TOAB) in the physiological condition. In terms of in situ electron paramagnetic resonance and ECL spectroscopies, the nature of ECL was thoroughly investigated, being exactly the chemiluminescence from singlet oxygen (¹O₂) produced during the successive electro-reduction of ZnTCPP. Meanwhile, the excellent film-making capacity of amphiphilic TOAB as a potent ion barrier granted the luminophores a micro-order and patternable electrode modification. Such platform was exceptionally tolerant of pH variation, facilitating a durable solid-state ECL visualization under potentiostatic electrolysis and time exposure in the charge-coupled device (CCD) camera. For flow-injection and real-time detection, a chip-mounted microfluidic cell was customized and manufactured. A sensitive and simple vision-sensing of O₂ was further achieved with a real determination limit as low as a few micromolar level. The developed ECL imaging system is a good prototype and an eco-friendly technique in the cathodic range, and thus, it would supplement the primary anodic imaging library, showing great promise for multiplexed and colorimetric assays as well as oxygen-involved activity studies in the future.

Ligating Dopamine as Signal Trigger onto the Substrate via Metal-Catalyst-Free Click Chemistry for "Signal-On" Photoelectrochemical Sensing of Ultralow MicroRNA Levels

The efficiency of photon-to-electron conversion is extremely restricted by the electron-hole recombinant. Here, a new photoelectrochemical (PEC) sensing platform has been established based on the signal amplification of click chemistry (CC) via hybridization chain reaction (HCR) for highly sensitive microRNA (miRNA) assay. In this proposal, a preferred electron donor dopamine (DA) was first assembled with designed ligation probe (probe-N₃) via amidation reaction to achieve DA-coordinated signal probe (P_DA-N₃). The P_DA-N₃ served as a flexible trigger to signal amplification through efficiently suppressing the electron-hole recombinant. Specifically, the P_DA-N₃ can be successfully ligated into the trapped hairpins (H1 and H2) via the superior ligation method of metal-catalyst-free CC, in which the electron donor DA was introduced into the assay system. Moreover, the enzyme-free HCR, employed as a versatile amplification way, ensures that lots of P_DA-N₃ can be attached to the substrate. This PEC sensing for miRNA-141 detection illustrated the outstanding linear response to a concentration variation from 0.1 fM to 0.5 nM and a detection limit down to 27 aM, without additional electron donors. The sensor is further employed to monitor miRNA-141 from prostate carcinoma cell (22Rv1), showing good quantitative detection capability. This strategy exquisitely influences the analytical performance and offers a new PEC route to highly selective and sensitive detection of biological molecules.

Graphitic Carbon Nitride Sensitized with CdS Quantum Dots for Visible-Light-Driven Photoelectrochemical Aptasensing of Tetracycline

Graphitic carbon nitride (g-C₃N₄) is a new type of metal-free semiconducting material with promising applications in photocatalytic and photoelectrochemical (PEC) devices. In the present work, g-C₃N₄ coupled with CdS quantum dots (QDs) was synthesized and served as highly efficient photoactive species in a PEC sensor. The surface morphological analysis showed that CdS QDs with a size of ca. 4 nm were grafted on the surface of g-C₃N₄ with closely contacted interfaces. The UV-visible diffuse reflection spectra (DRS) indicated that the absorption of g-C₃N₄ in the visible region was enhanced by CdS QDs. As a result, g-C₃N₄-CdS nanocomposites demonstrated higher PEC activity as compared with either pristine g-C₃N₄ or CdS QDs. When g-C₃N₄-CdS nanocomposites were utilized as transducer and tetracycline (TET)-binding aptamer was immobilized as biorecognition element, a visible light-driven PEC aptasensing platform for TET determination was readily fabricated. The sensor showed a linear PEC response to TET in the concentration range from 10 to 250 nM with a detection limit (3S/N) of 5.3 nM. Thus, g-C₃N₄ sensitized with CdS QDs was successfully demonstrated as useful photoactive nanomaterials for developing a highly sensitive and selective PEC aptasensor.

An ultrasensitive energy-transfer based photoelectrochemical protein biosensor

Using single stranded DNA (ssDNA) as a distance controller and Au nanoparticles (NPs) functionalized with ssDNA as novel energy-transfer nanoprobes, an ultrasensitive energy-transfer based photoelectrochemical protein biosensor was realized.

Dual Signal Amplification Using Gold Nanoparticles-Enhanced Zinc Selenide Nanoflakes and P19 Protein for Ultrasensitive Photoelectrochemical Biosensing of MicroRNA in Cell

Using Au nanoparticles (NPs)-decorated, water-soluble, ZnSe-COOH nanoflakes (NFs), an ultrasensitive photoelectrochemical (PEC) biosensing strategy based on the dual signal amplification was proposed. As a result of the localized surface plasmon resonance (SPR) of Au NPs, the ultraviolet-visible absorption spectrum of Au NPs overlapped with emission spectrum of ZnSe-COOH NFs, which generated efficient resonant energy transfer (RET) between ZnSe-COOH NFs and Au NPs. The RET improved photoelectric conversion efficiency of ZnSe-COOH NFs and significantly amplified PEC signal. Taking advantage of the specificity and high affinity of p19 protein for 21-23 bp double-stranded RNA, p19 protein was introduced. P19 protein could generate remarkable steric hindrance, which blocked interfacial electron transfer and impeded the access of the ascorbic acid to electrode surface for scavenging holes. This led to the dramatic decrease of photocurrent intensity and the amplification of PEC signal change versus concentration change of target. Using microRNA (miRNA)-122a as a model analyte, an ultrasensitive signal-off PEC biosensor for miRNA detection was developed under 405 nm irradiation at -0.30 V. Owing to RET and remarkable steric hindrance of p19 protein as dual signal amplification, the proposed strategy exhibited a wide linear range from 350 fM to 5 nM, with a low detection limit of 153 fM. It has been successfully applied to analyze the level of miRNA-122a in HeLa cell, which would have promising prospects for early diagnosis of tumor.

Recent advances in the use of quantum dots for photoelectrochemical bioanalysis

Photoelectrochemical (PEC) bioanalysis is a newly developed technique for innovative biomolecular detection. Quantum dots (QDs) with unique photophysical properties are key components in realization of various exquisite PEC bioanalyses. Particularly, significant progress has been made in the QD-based PEC bioanalysis. In this work, we briefly summarize the most recent and important developments in the use of traditional and newly emerging QDs for novel PEC bioanalytical applications. The future prospects in this dynamic field are also highlighted.

Photoelectrochemical CaMV35S biosensor for discriminating transgenic from non-transgenic soybean based on SiO2@CdTe quantum dots core-shell nanoparticles as signal indicators

A methodology for detection of the Cauliflower Mosaic Virus 35S(CaMV35S) promoter was developed to distinguish transgenic from non-transgenic soybean samples by using photoelectrochemical (PEC) biosensor. In this PEC biosensing system, the as-prepared gold nanoparticles-reduced graphene oxide acted as a nanocarrier to immobilize the thiol-functional probe (probe1), and the SiO₂@CdTe quantum dots (QDs) core-shell nanoparticles tagged with the amino-functional probe (probe2) acted as signal indicators, respectively. In the presence of target DNA (tDNA) of CaMV35S, the binding of tDNA with probe1 and probe2 through the high specific DNA hybridization led to the fabrication of sandwich structure, and thus the high loading of the signal indicators SiO₂@CdTe QDs at the electrode surface, which increased the PEC signal. The increased PEC signal depended on the concentration of tDNA, and a wide linear range from 0.1pM to 0.5nM with low detection limit of 0.05pM was obtained. In addition, the PEC biosensor has been successfully used for discriminating transgenic soybean from non-transgenic samples, which was consistent with the polymerase chain reaction (PCR) results, suggesting the proposed PEC biosensor is a feasible tool for the further daily genetically modified organism detection.

Electrochemical, Electrochemiluminescence, and Photoelectrochemical Aptamer-Based Nanostructured Sensors for Biomarker Analysis

Aptamer-based sensors have been intensively investigated as potential analytical tools in clinical analysis providing the desired portability, fast response, sensitivity, and specificity, in addition to lower cost and simplicity versus conventional methods. The aim of this review, without pretending to be exhaustive, is to give the readers an overview of recent important achievements about electrochemical, electrochemiluminescence, and photoelectrochemical aptasensors for the protein biomarker determination, mainly cancer related biomarkers, by selected recent publications. Special emphasis is placed on nanostructured-based aptasensors, which show a substantial improvement of the analytical performances.

A label-free photoelectrochemical aptasensor for bisphenol A based on surface plasmon resonance of gold nanoparticle-sensitized ZnO nanopencils

A simple and novel photoelectrochemical (PEC) aptasensor for selective detection of bisphenol A (BPA) was developed using surface plasmon resonance of Au nanoparticles activated ZnO nanopencils. With the irradiation of simulated light, the increased photocurrent of nano-Au/ZnO than that of pure ZnO nanopencil is induced by the hot electrons from excited Au nanoparticles. The perfect selectivity is attributed to the specific binding of BPA to its aptamer. With the addition of BPA, the conformation of aptamer changed to a G-quadruplex structure, which resulted in the blockages of photogenerated electron-transfer channels. Based on the above mechanisms and the optimized conditions, the assembled PEC aptasensor was linear with the concentration of BPA in the range of 1-1000nmolL(-1) with a detection limit of 0.5nmolL(-1). The presence of the same concentration and similar structure of other organics did not interfere in the detection of BPA and the recovery was between 96.2% and 108.4%. It has been successfully applied to the detection of BPA in drinking water and liquid milk samples. This PEC aptasensor has good performances in novelty, selectivity, sensitivity and low cost, and it provides an alternative approach to the detection of BPA.

Photoelectrochemical detection of metal ions

Depending on the situation, metal ions may either play beneficial roles or be harmful to human health and ecosystems. Sensitive and accurate detection of metal ions is thus a critical issue in the field of analytical sciences and great efforts have been devoted to the development of various metal ion sensors. Photoelectrochemical (PEC) detection is an emerging technique for the bio/chemical detection of metal ions, and features a fast response, low cost and high sensitivity. Using representative examples, this review will first introduce the fundamentals and summarize recent progress in the PEC detection of metal ions. In addition, interesting strategies for the design of particular PEC metal ion sensors are discussed. Challenges and opportunities in this field are also presented.

Sequence-Dependent Photocurrent Generation through Long-Distance Excess-Electron Transfer in DNA

Given its well-ordered continuous π stacking of nucleobases, DNA has been considered as a biomaterial for charge transfer in biosensors. For cathodic photocurrent generation resulting from hole transfer in DNA, sensitivity to DNA structure and base-pair stacking has been confirmed. However, such information has not been provided for anodic photocurrent generation resulting from excess-electron transfer in DNA. In the present study, we measured the anodic photocurrent of a DNA-modified Au electrode. Our results demonstrate long-distance excess-electron transfer in DNA, which is dominated by a hopping mechanism, and the photocurrent generation is sequence dependent.

Label-free electrochemical genosensor based on mesoporous silica thin film

A novel label-free electrochemical strategy for nucleic acid detection was developed by using gold electrodes coated with mesoporous silica thin films as sensing interface. The biosensing approach relies on the covalent attachment of a capture DNA probe on the surface of the silica nanopores and further hybridization with its complementary target oligonucleotide sequence, causing a diffusion hindering of an Fe(CN)6 (3-/4-) electrochemical probe through the nanochannels of the mesoporous film. This DNA-mesoporous silica thin film-modified electrodes allowed sensitive (91.7 A/M) and rapid (45 min) detection of low nanomolar levels of synthetic target DNA (25 fmol) and were successfully employed to quantify the endogenous content of Escherichia coli 16S ribosomal RNA (rRNA) directly in raw bacterial lysate samples without isolation or purification steps. Moreover, the 1-month stability demonstrated by these biosensing devices enables their advanced preparation and storage, as desired for practical real-life applications. Graphical abstract Mesoporous silica thin films as scaffolds for the development of novel label-free electrochemical genosensors to perform selective, sensitive and rapid detection of target oligonucleotide sequences. Application towards E. coli determination.

The Application of Graphene and Its Derivatives to Energy Conversion, Storage, and Environmental and Biosensing Devices

Graphene (GR) and its derivatives are promising materials on the horizon of nanotechnology and material science and have attracted a tremendous amount of research interest in recent years. The unique atom-thick 2D structure with sp(2) hybridization and large specific surface area, high thermal conductivity, superior electron mobility, and chemical stability have made GR and its derivatives extremely attractive components for composite materials for solar energy conversion, energy storage, environmental purification, and biosensor applications. This review gives a brief introduction of GR's unique structure, band structure engineering, physical and chemical properties, and recent energy-related progress of GR-based materials in the fields of energy conversion (e.g., photocatalysis, photoelectrochemical water splitting, CO2 reduction, dye-sensitized and organic solar cells, and photosensitizers in photovoltaic devices) and energy storage (batteries, fuel cells, and supercapacitors). The vast coverage of advancements in environmental applications of GR-based materials for photocatalytic degradation of organic pollutants, gas sensing, and removal of heavy-metal ions is presented. Additionally, the use of graphene composites in the biosensing field is discussed. We conclude the review with remarks on the challenges, prospects, and further development of GR-based materials in the exciting fields of energy, environment, and bioscience.

Electrosynthesis and characterization of nanostructured polyquinone for use in detection and quantification of naturally occurring dsDNA

The detection of naturally occurring desoxyribonucleic acid (DNA) has become a subject of study by the projections that would generate to be able to sense the genetic material for the detection of future diseases. Bearing this in mind, to provide new measuring strategies, in the current work the preparation of a low-cost electrode, modified with poly(1-amino-9,10-anthraquinone) nanowires using a SiO2 template, is carried out; the assembly is next modified by covalently attaching ssDNA strands. It must be noted that all this is accomplished by using solely electrochemical techniques, according to methodology developed for this purpose. SEM images of the modified surface show high order and homogeneity in the distribution of modified nanowires over the electrode surface. In turn, after the hybridization with its complementary strand, the voltammetric responses enable corroborating the linear relationship between hybridization at different DNA concentrations and normalized current response, obtaining a limit of detection (LOD) 5.7·10(-12)gL(-1) and limit of quantification (LOQ) 1.9·10(-11)gL(-1). The working dynamic range is between 1.4·10(-7) and 8.5·10(-9)gL(-1) with a correlation coefficient 0.9998. The successful obtaining of the modified electrode allows concluding that the high order reached by the nanostructures, guides the subsequent single strand of DNA (ssDNA) covalent attachment, which after hybridization with its complementary strand brings about a considerable current increase. This result allows foreseeing a guaranteed breakthrough with regard to the use of the biosensor in real samples.

Rational design of supramolecular hemin/G-quadruplex-dopamine aptamer nucleoapzyme systems with superior catalytic performance

The rational design of a set of hemin/G-quadruplex (hGQ)-dopamine binding aptamer (DBA) conjugates, acting as nucleoapzymes, is described. The nucleoapzyme constructs consist of a hGQ DNAzyme as a catalytic unit and DBA as a substrate binding unit that are brought into spatial proximity by a duplex scaffold composed of complementary oligonucleotide strands. When the hGQ unit is linked to the duplex scaffold via a single-strand DNA tether of variable length, the resulting nucleoapzymes reveal a moderate catalytic enhancement toward the H2O2-mediated oxidation of dopamine to aminochrome as compared to the process stimulated by the separated hGQ and DBA units (5-7 fold enhancement). This limited enhancement is attributed to inappropriate spatial positioning of the hGQ in respect to the dopamine binding site, and/or to the flexibility of the tether that links the hGQ catalytic site to the double-stranded scaffold. To solve this, rigidification of the hGQ/DBA conjugates by triplex oligonucleotide structures that anchor the hGQ to a duplex domain associated with the DBA units was achieved. By the sequential, programmed, triplex-controlled rigidification of the hGQ/DBA structure, a nucleoapzyme with superior catalytic activity toward the oxidation of dopamine to aminochrome is identified (30-fold catalytic enhancement). Molecular dynamics simulations reveal that in the resulting highly active rigidified nucleoapzyme structure, the hGQ catalytic site is positioned in spatial proximity to the opening of the DBA substrate binding site, thus rationalizing and supporting the enhanced catalytic functions of the system. Finally, the most active nucleoapzyme system was subjected to fuel- and anti-fuel strands that separate and re-assemble the nucleoapzyme structure, allowing "ON" and "OFF" switching of the nucleoapzyme catalytic functions.

One-pot hydrothermal route to fabricate nitrogen doped graphene/Ag-TiO2: Efficient charge separation, and high-performance "on-off-on" switch system based photoelectrochemical biosensing

Charge separation is crucial for increasing the performances of semiconductor-based materials in many photoactive applications. In this paper, we designed novel nanocomposites consisting of TiO2 nanocrystals, Ag nanoparticles (NPs) and nitrogen doped graphene (NGR) via a facile one-pot hydrothermal route. The as-prepared ternary nanocomposites exhibited enhanced photoelectrochemical (PEC) performances owing to the introduction of Ag NPs and NGR, which increase the excitons' lifetime and improve the charge transfer. In particular, it is shown by means of the transient-state surface photocurrent responses that the photocurrent intensity of the as-fabricated composites exhibited 18.2 times higher than that of pristine TiO2. Based on the robust photocurrent signal, a new kind of "on-off-on" PEC aptasensor was established with the assistance of Pb(2+) aptamer, which integrates the advantages of low background signal and high sensitivity. Under optimal conditions, a wide linear response for Pb(2+) detection was obtained from 1pM to 5nM as well as a detection limit down to 0.3pM. With its simplicity, selectivity, and sensitivity, this proposed strategy shows great promise for Pb(2+) detection in food and environment analysis.

Ultrasensitive Visual Detection of HIV DNA Biomarkers via a Multi-amplification Nanoplatform

Methodologies to detect disease biomarkers at ultralow concentrations can potentially improve the standard of living. A facile and label-free multi-amplification strategy is proposed for the ultrasensitive visual detection of HIV DNA biomarkers in real physiological media. This multi-amplification strategy not only exhibits a signficantly low detection limit down to 4.8 pM but also provides a label-free, cost-effective and facile technique for visualizing a few molecules of nucleic acid analyte with the naked eye. Importantly, the biosensor is capable of discriminating single-based mismatch lower than 5.0 nM in human serum samples. Moreover, the visual sensing platform exhibits excellent specificity, acceptable reusability and a long-term stability. All these advantages could be attributed to the nanofibrous sensing platform that 1) has a high surface-area-to-volume provided by electrospun nanofibrous membrane, and 2) combines glucose oxidase (GOx) biocatalysis, DNAzyme-catalyzed colorimetric reaction and catalytic hairpin assembly (CHA) recycling amplification together. This multi-amplification nanoplatform promises label-free and visual single-based mismatch DNA monitoring with high sensitivity and specificity, suggesting wide applications that range from virus detection to genetic disease diagnosis.