Ultrasensitive MicroRNA Photoelectric Assay Based on a Mimosa-like CdS-NiS/Au Schottky Junction.

Seeking and constructing superior photoactive materials have the potential to improve the performance of photoelectrochemical (PEC) biosensors. In this work, we proposed a novel mimosa-like ternary inorganic composite with a significantly enhanced light-harvesting ability and photogenerated carrier separation rate. This ternary photoactive material was obtained via electrodeposition of gold nanoparticles (Au) on the surface of transition metal sulfide composite of CdS and NiS (CdS-NiS/Au). The experimental results showed that the high initial photocurrent was acquired on CdS-NiS/Au (68-fold higher than that of individual CdS) with the synergistic effect of p-n heterojunction, Schottky junction, and the eminent optical properties of gold nanoparticles. Meanwhile, using silver nanoclusters prepared by link DNA protection as an effective quencher, integrating the duplex-specific nuclease-assisted rolling circle amplification strategy, a "Signal ON" PEC biosensor was fabricated for the detection of microRNA 21 (miRNA 21). With the release of the quencher, the recovered photocurrent is able to achieve determination of miRNA 21 within the range from 10 aM to 1 pM with a detection limit down to 4.6 aM (3σ). Importantly, this work not only provides a superb idea for designing ternary inorganic heteromaterials with exceptional photoactive ability but also allows the detection of other biomarkers by selecting appropriate recognition units.

Schottky-functionalized Z-scheme heterojunction: Improved photoelectric conversion efficiency and immunosensing.

Designing photovoltaic materials with good photoelectric activity is the crucial to boost the sensitivity of photoelectrochemical (PEC) biosensors. To meet this concern, a Schottky-functionalized direct Z-scheme heterojunction photovoltaic material was proposed by electrodeposition of gold nanoparticles on two kinds of bismuth oxyhalide composites surface (bismuth oxybromide and bismuth oxyiodide with different but matched band gaps) (depAu/BiOI/BiOBr). Specifically, synergistic effect was achieved through the direct Z-scheme heterojunction formed by BiOBr and BiOI as well as the gold Schottky junction, resulting in the enhanced light harvest and photoelectric conversion efficiency. Meanwhile, combined with sandwich immunotechnology, a "signal-off" PEC biosensor was fabricated for highly sensitive detection of carcinoembryonic antigen (CEA). In which, using depAu/BiOI/BiOBr modified glassy carbon electrodes both as the photoactive sensing interface and capture antibody loading matrix, polyethyleneimine copper complex encapsulated gold nanoclusters labeled detection antibody (Ab2-Au@PEI-Cu) as the quencher, the photocurrent decreased with the increasing target CEA introduced by sandwich immune reaction. The proposed smart PEC immunoassay platform exhibited a wide detection range (1.0 fg/mL-2.0 ng/mL) and a detection limit as low as 0.11 fg/mL with favorable selectivity and stability. In addition, this PEC sensing strategy can be easily extended for other tumor marker analysis, which offers a new perspective of using multiple bismuth oxyhalide as photoactive materials for early diseases diagnosis.

Highly Sensitive Photoelectrochemical Immunosensor Based on Organic Multielectron Donor Nanocomposite as Signal Probe.

Organic photoelectric materials with conjugated electron-rich structures and good biocompatibilities have broad application prospects in biosensors. Herein, we report a promising organic photoelectric multielectron donor nanocomposite for highly sensitive PEC immunoassays. Specifically, the organic multielectron donor nanocomposite (DA-ZnTCPP-g-C3N4) was prepared from dopamine (DA, polyphenol hydroxyl structure substance), zinc tetracarboxylate porphyrin (ZnTCPP, large p-π conjugated heterocyclic compound), and two-dimensional graphene-like nitrogen carbide (g-C3N4) via an amidation reaction. With a multielectron donor structure and photoelectricity, this nanocomposite can achieve sensitization by self-structure without the addition of an electron donor in the test solution. It was utilized to label the carcinoembryonic detection antibody as a immuno-probe (Ab2-DA-ZnTCPP-g-C3N4). Meanwhile, the glassy carbon electrode electrodeposited with gold nanoparticles anchoring the capture antibody was used as a PEC immunomatrix (Ab1/DpAu/GCE). The enhanced PEC current, "signal on", was confirmed by the immunosensor via sandwich immunorecognition of a carcinoembryonic antigen (CEA). Under optimal conditions, the as-prepared sensing platform displayed high sensitivity for CEA with a dynamic linear response range from 10 fg·mL-1 to 1 mg·mL-1 and a lower detection limit of 3.6 fg·mL-1. This organic nanocomposite showed good sensitivity and stability in an immunosensing system with a low background. This strategy affords a promising approach for biological applications of organic photoelectric materials.

Cluster-Dominated Electrochemiluminescence of Tertiary Amines in Polyethyleneimine Nanoparticles: Mechanism Insights and Sensing Application.

Designing and screening highly efficient and cost-effective luminophores have always been a challenge to develop sensitive electrochemiluminescence (ECL) biosensors. Herein, polyethyleneimine nanoparticles (PEI NPs), a kind of nonconjugated polymer (NCP) NPs with tertiary amine clusters, were developed as an ECL luminophore. Specifically, PEI NPs were synthesized by a one-step hydrothermal method using PEI and formaldehyde. The properties of PEI NPs were investigated in detail using photochemical and electrochemical techniques. The results showed cluster-dominated luminescence of tertiary amines in PEI NPs via "through-space conjugation". This non-negligible ECL performance (at 631 nm) was also verified by the initiated reduction-oxidation process. With persulfate as a coreactant, PEI NPs acted as both the luminophore and coreaction accelerator to enhance the ECL intensity remarkably, which was eightfold higher than that of isolated PEI. Moreover, choosing dopamine as the model target, a highly sensitive "signal off" ternary ECL sensor was constructed utilizing PEI NPs as the luminophore. Dopamine could be oxidized to benzoquinone at the sensing interface, quenching the signal via ECL energy transfer. Free from any signal amplification, the proposed sensor achieved a low detection limit (4.3 nM) for target monitoring with good selectivity and stability. This strategy not only provides a unique perspective for designing novel efficient and facile ECL luminophores of tertiary amines but also broadens the biological application of NCP NPs.

Self-enhanced photoelectrochemical sensor based on a Schottky heterostructure organic electron donor matrix.

A self-enhanced photoelectrochemical copper ions sensor was constructed using an organic electron donor matrix with a Schottky heterostructure prepared from dopamine and single walled carbon nanohorns. The determination of Cu2+ with no additional electron donor solution, with high sensitivity and low background, provides new inspiration for the development of photoelectric sensing.

Construction of self-enhanced photoelectrochemical platform for L-cysteine detection via electron donor-acceptor type coumarin 545 aggregates.

Self-enhanced electron donor-acceptor type coumarin 545 aggregates prepared via an anionic surfactant-assisted reprecipitation method provide an underlying approach for the photoelectrochemical detection of L-cysteine, which can be employed in aqueous solution without the addition of electron donors.

Novel optoelectronic metal organic framework material perylene tetracarboxylate magnesium: preparation and biosensing.

The pursuit for improving photoelectrochemical (PEC) performances of organic materials remains an urgent need. Here, we have proposed an envision of the preparation the metal-organic frameworks (MOFs) with arenes to realize high photo-to-current conversion efficiency and excellent PEC performances. Magnesium 3,4,9,10-perylene tetracarboxylic acid metal-organic frameworks (Mg-PTCA MOFs) were synthesized for the first time. The uniformly distributed and regular-shaped Mg-PTCA MOFs showed a much more stable and higher photocurrent than the single PTCA and its derivatives, which confirmed our hypothesis. A regenerated-biosensor was designed for microRNA analysis based on Mg-PTCA MOFs as a novel photoelectric material, target-triggered three-dimensional DNA Scaffold (3D-Sca) as an efficient signal amplifier, and gold nanoclusters (Au NCs) as quencher. The elaborately designed biosensor achieved ultrasensitive detection for miRNA 21 with a dynamic range from 10 aM to 10 pM and a detection limit of 2.8 aM. This biosensor showed good analytical performance in the extracts of different cancer cells, indicating the possibility for early diagnosis, timely staging assessment, and accurate prognostic judgment for diseases. The recommendable performances of Mg-PTCA MOFs highlight the significance of organic MOFs in PEC sensing.

An electron donor-acceptor organic photoactive composite with Schottky heterojunction induced photoelectrochemical immunoassay.

A signal enhancement photoelectrochemical (PEC) immunoassay system induced by the composite (PTCs@Au) of electron donor-acceptor with Schottky heterojunction was designed. Carcinoembryonic antigen (CEA) was selected as a model target. Initially, the capture anibody (Ab1) was linked to gold nanoparticles electrodeposited on glassy carbon electrode and sealed by bovine serum albumin. Meanwhile, the organic semiconductor (PTCs) with the structure of electron donor-acceptor was synthetized from perylene tetracarboxylic dianhydride (acceptor) and dopamine (donor) via amidation reaction. Then PTCs@Au composite with Schottky heterojunction was formed through gold nanoparticles in situ reduction and functionalization with PTCs. Next, the detection antibody was labeled by PTCs@Au composite (Ab2-PTCs@Au) as an immuno-probe. The PTCs@Au was introduced via sandwich immune reaction leading to enhancement PEC signal without additional electron donor nor acceptor for achieving quantitative detection of CEA under external light. The proposed immunoelectrode showed dynamic ranges of 0.5 fg mL-1 to 10 pg mL-1 and 10 pg mL-1 to 1 µg mL-1 with the detection limit of 0.17 fg mL-1. In addition, this PEC strategy with acceptable selectivity and stability can be potentially applied to detect other targets by choosing appropriate target recognition unit.

Gold Nanoparticles Photosensitization towards 3,4,9,10-Perylenetetracarboxylic Dianhydride Integrated with a Dual-Particle Three-Dimensional DNA Roller: A General "ON-OFF-ON" Photoelectric Plasmon-Enhanced Biosensor.

A high initial signal for the sensitive detection of analytes is critical in photoelectrochemical (PEC) biosensing systems. As a semiconductor, 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) possesses an appropriate optical band gap of 2.5 eV and inherently intense and stable PEC response. When gold nanoparticles (Au NPs) are electrodeposited on the surface of PTCDA to form a Schottky junction (Au NPs/PTCDA), a surprising and satisfactory PEC performance is unfolded before our eyes. Considering the outstanding PEC behaviors of Au NPs/PTCDA and the great quenching effect of gold nanoclusters (Au NCs), the "ON-OFF-ON" PEC sensing platform has been developed for microRNA 1246 (miRNA 1246) detection combined with the cascaded quadratic amplification strategy of the polymerization/nicking reaction and dual-particle 3D DNA roller. The higher initial PEC signals of the system can be acquired by regulating the deposition time for 35 s (-0.2 V), which is derived from the synergetic effect of localized surface plasmon resonance of Au NPs and the formation of a Schottky junction. The dual-particle 3D DNA roller has been designed to guarantee wide walking space, remarkable operation performances, and inhibition of derailment. The proposed biosensor shows a dynamic range from 10 aM to 1 pM at a low detection limit of 3.1 aM and exhibits good analytical behaviors while analyzing miRNA 1246 in healthy human serum samples. This work not only expands the application of organic photoelectric materials in bioanalysis but also provides potential possibility of detecting other biomarkers by choosing appropriate target units.

Efficient Curing Sacrificial Agent-Induced Dual-Heterojunction Photoelectrochemical System for Highly Sensitive Immunoassay.

A photoelectrochemical (PEC) biosensor is a very efficient and sensitive detection technology for the quick and effective conversion of light to electrical signals. However, the sensitivity and stability of the sensors are still unsatisfactory based on single-phase semiconductors or in the absence of sacrificial agents in the test solution. Herein, we present an efficient curing sacrificial agent-induced dual-heterojunction PEC system, which can detect the prostate-specific antigen (PSA) with high sensitivity. This PEC immune system was initially fabricated using single-walled carbon nanohorns (SWCNHs), p-type MoS2, and n-type Ag2S successively through a Schottky junction and p-n heterojunction on a glassy carbon electrode with electrodeposited gold nanoparticles. Then, the capture antibody (Ab1) was modified and the nonspecific binding sites were sealed off. Meanwhile, the ferrocene (Fc) solidified with hollow nanospheres of zinc ferrite (ZnFe2O4) served as a curing electronic sacrificial agent (Fc-ZnFe2O4). Next, the detection antibody labeled with Fc-ZnFe2O4 (Ab2-Fc-ZnFe2O4) was used as a bio-nanoprobe and captured by PSA and Ab1 via sandwich immunorecognition. Under white light, PEC signal amplification could be driven by the curing electronic sacrificial agent-induced dual-heterojunction to achieve the highly sensitive detection of the target. This proposed system exhibited excellent photocurrent performance within the working range from 1 fg·mL-1 to 100 ng·mL-1 at a low detection limit of 0.44 fg·mL-1 (S/N = 3). The proposed strategy features high sensitivity, selectivity, and stability that provides a new opportunity for the development of biosensors in the PEC field.

Novel Luminescent Nanostructured Coordination Polymer: Facile Fabrication and Application in Electrochemiluminescence Biosensor for microRNA-141 Detection.

A series of novel luminescent nanostructured coordination polymers (Ce-Ru-NCPs) with tunable morphologies have been successfully synthesized on a large scale at room temperature by a facile and rapid solution-phase method using Ce3+ and tris(4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium(II) dichloride (Ru(dcbpy)32+). Among them, the flowerlike Ce-Ru-NCP shows good cathodic electrochemiluminescence (ECL) characteristics. The ECL efficiency of the Ce-Ru-NCP/S2O82- system is about 2.34 times that of the classic tris(2,2'-bipyridyl) ruthenium(II) dichloride/S2O82- (Ru(bpy)32+/S2O82-) system. Hence, we report a sensitive ECL biosensor for microRNA-141 (miRNA-141) detection based on the flowerlike Ce-Ru-NCP as a cathodic ECL luminophore and a bipedal three-dimensional (3D) DNA walking machine as a signal amplifier. Through the bipedal 3D DNA walking machine, trace targets can be converted to substantial secondary targets (marked with the quencher dopamine), and a significant quenching effect on the ECL signal is achieved. As a result, the proposed biosensor exhibits a relatively good sensitivity for miRNA-141 detection and shows a dynamic range from 1.0 × 10-16 to 1.0 × 10-6 mol·L-1 with a limit of detection (LOD) of 33 amol·L-1 (S/N = 3). The Ce-Ru-NCP with tunable morphologies and high ECL efficiency, intensity, and stability possesses potential applications in ECL analysis.

A novel signal self-enhancement photoelectrochemical immunosensor without addition of a sacrificial agent in solution based on Ag2S/CuS/α-Fe2O3 n-p-n heterostructure films.

A novel signal self-enhancement photoelectrochemical immuno-sensor has been developed based on the curing of sacrificial agent SO32- coated-Au NPs sensitizing Ag2S/CuS/α-Fe2O3 n-p-n hetero-structure films for the first time. This strategy has acquired high sensitivity and low background without addition of a sacrificial agent in solution in the detection of prostate antigen.

Multifunctional Zinc Oxide Promotes Electrochemiluminescence of Porphyrin Aggregates for Ultrasensitive Detection of Copper Ion.

The design and exploration of highly efficient organic luminophores for an electrochemiluminescence (ECL) sensor is a fascinating and promising subject. Herein, we present a surfactant-assisted self-assembly of 5,10,15,20-tetrakis (4-carboxyphenyl) porphyrin (TCPP) J-aggregate as a robust organic luminophore to construct the solid-state ECL sensing platform with significantly enhanced and constantly stable signals, by using peroxydisulfate (S2O82-) as the coreactant, and l-cysteine capped zinc oxide nanoflowers (ZnO@Cys NFs) as the multifunctional energy donor and coreactant accelerator. Compared with TCPP monomer, this TCPP J-aggregate possesses a unique aggregation-induced electrochemiluminescence (AIECL) performance, which results in 5-fold enhancement in red-light ECL emission at 675 nm. The resonance energy transfer from the ZnO@Cys NFs (energy donor) to the TCPP J-aggregate (energy acceptor) substantially improves the ECL intensity and stability. ZnO@Cys NFs have also been used as a coreactant accelerator to promote the conversion of more S2O82- into SO4•-. The corresponding ECL mechanism has been investigated by UV-vis absorption spectrum, photoluminescence, ECL, and density functional theory. Since l-cysteine on ZnO@Cys NFs can efficiently realize bidentate chelation with Cu2+, the proposed ECL sensor shows a highly selective and sensitive quenching effect for the detection of Cu2+ with a wide linear range from 1.0 pmol·L-1 to 500 nmol·L-1 and a detection limit of 0.33 pmol·L-1, paving a bright research direction for the development of TCPP aggregates in ECL field.

Multi-functional electrochemiluminescence aptasensor based on resonance energy transfer between Au nanoparticles and lanthanum ion-doped cadmium sulfide quantum dots.

Novel lanthanum ion-doped cadmium sulfide quantum dots (CdS:La QDs) were synthesized and characterized by transmission electron microscopy (TEM) and photoluminescence (PL). Based on CdS:La QDs as the electrochemiluminescence (ECL) luminophores, a distance-dependent ECL intensity enhanced or quenched system between CdS:La QDs and gold nanoparticles (Au NPs) was designed. Firstly, ssDNA 1 was linked to the CdS:La QDs modified glassy carbon electrode via amide bond. Then the prepared Au NP-ssDNA 2 conjugates were used to hybridize with ssDNA 1, the surface plasmon resonances (SPR) of Au NPs enhanced ECL intensity (signal on) while Au NPs and CdS:La QDs were separated at a certain distance. Secondly, In the presence of Hg2+, the oligonucleotide conformation changed from linear chain to hairpin due to the thymine-Hg2+-thymine (T-Hg2+-T) base pairs. ECL quenching (signal off) achieved lie in resonance energy transfer (RET) between the CdS:La QDs and the proximal Au NPs at a close distance. Finally, after being incubated with TB, a strong and stable TB-aptamer complex was generated, which led to the release of Au NP-ssDNA 2 conjugates. The ECL signal of the CdS:La QDs was ultimately recovered (signal on again). The "on-off-on" approach was used to detect Hg2+ and TB, sensitively and respectively. The line ranges were 1.00 × 10-12 -1.00 × 10-5 mol L-1 and 1.00 × 10-16 -1.00 × 10-6 mol L-1, respectively. The low limits of detection (S/N = 3) were at 3.00 × 10-13 mol L-1 and 3.00 × 10-17 mol L-1. Moreover, the ECL sensor exhibited high selectivity and good stability, and was successfully applied to the detection of TB in real sample.

Nitrogen-doped graphene quantum dots coated with gold nanoparticles for electrochemiluminescent glucose detection using enzymatically generated hydrogen peroxide as a quencher.

Nitrogen-doped graphene quantum dots (N-GQDs) were prepared from dicyandiamide and then used as both an electrochemiluminescence (ECL) emitter and a reductant to produce gold nanoparticles (Au-N-GQDs) on their surface without using any reagent. In order to avoid resonance energy transfer, the Au-N-GQDs were stabilized with chitosan. Transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), UV-vis spectroscopy (UV-vis) and ECL methods were used to characterize the nanocomposite. The materials was placed on a glassy carbon electrode (GCE), and the ECL signals are found to be strongly quenched by hydrogen peroxide that is enzymatically produced by oxidation of glucose. With the applied typical potential of -1.7 V, the ECL of the Au-N-GQDs modified GCE decreases linearly in the 10 nM to 5.0 µM glucose concentration range, and the lower detection limit is 3.3 nM. The influence of H2O2 to the signal has been discussed and a possible mechanism has been presented. Graphical abstract Schematic presentation of the reduction of gold nanoparticles with nitrogen-droped graphene quantum dots (N-GQDs) to form Au-N-GQDs. They were used to detect glucose by electrochemiluminescence through a signal off strategy.

A widened emission window of the peroxydisulfate-oxygen system for the detection of L-alanine.

Peroxydisulfate-oxygen (S2O82--O2) system has become one of the most used systems in electrogenerated chemiluminscence (ECL) field. Due to S2O82- can be used as Fenton Reagent, this work designed an ECL biosensor based on the S2O82--O2 system for the detection of L-alanine in a widened emission window and using hemin/G-quadruplex and platinum and palladium nanowires (Pt-Pd NWs) to in situ generate O2 to amplify the ECL intensity. The proposed ECL sensor showed an excellent analytical property for the detection of L-alanine in a linear range of 5.0 × 10-3 M to 1.0 × 10-8 M with the detection limit of 3.3 × 10-9 M (S/N = 3). This work with high selectivity, stability and reproducibility may open a new door to apply S2O82- in ECL field.