Electrochemiluminescence Resonance Energy Transfer System: Mechanism and Application in Ratiometric Aptasensor for Lead Ion

Perylene-Based Photoactive Material as a Double-Stranded DNA Intercalating Probe for Ultrasensitive Photoelectrochemical Biosensing

Photoelectrochemical (PEC) sensing techniques have attracted considerable concerns because of the intrinsic merit of complete separation between the excitation light and responsive current but still remain a great challenge for further potential application. It is assigned to the scarcity of photoactive materials with narrow band gap, good biosafety, and high photon-to-electron conversion efficiency and unfavorable processing methods for photoactive materials on indium tin oxide. Herein, we employed a perylene-based polymer (PTC-NH₂) with exceptional photoelectrical properties to develop a red-light-driven PEC sensor for ultrasensitive biosensing based on its superior electrostatic intercalation efficiency in double-stranded DNA to that in single-stranded DNA, with DNA adenine methyltransferase (Dam MTase) as the model target. The prepared PTC-NH₂ was characterized by Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, and PEC techniques, and the results demonstrated that PTC-NH₂ rather than metal oxides/metal sulfides/C₃N₄/metal complexes enjoyed the prominent capacity of converting light to current. Benefiting from the unique PEC properties of PTC-NH₂ and target-initiated hybridization chain reaction (HCR) signal amplification, ultrasensitive detection of Dam MTase was accessibly realized with the detection limit of 0.015 U/mL, which is lower than that of PEC, electrochemical, or fluorescent biosensors previously reported. Furthermore, the proposed PEC sensor has been also applied in screening Dam MTase activity inhibitors. Therefore, the perylene-based PEC sensor exhibits great potential in early accurate diagnosis of DNA methylation-related diseases.

Electrostatic assembly of gold nanoparticles on black phosphorus nanosheets for electrochemical aptasensing of patulin

An aptamer based impedimetric assay for the mycotoxin patulin (PAT) is described. A glassy carbon electrode (GCE) was modified with black phosphorus nanosheets (BP NSs) and modified with PAT aptamer by electrostatic attraction. Detection is based on the variations of electron transfer resistance at the modified electrode surface. This assay can detect PAT over a linear range that extends from 1.0 nM to 1.0 μM with a 0.3 nM detection limit. To improve the performance of the sensor, the BP NS-GCE was further modified with gold nanoparticles and then with thiolated PAT aptamer. This modified electrode, operated at an applied potential of 0.18 V (vs. Ag/AgCl), has a wider linear range (0.1 nM to 10.0 μM) and a lower detection limits (0.03 nM). Both assays were successfully applied to the analysis of (spiked) genuine food samples. Graphical abstract Black phosphorus nanosheets (BP NSs) were used to fabricate an aptamer based assay for patulin. To further improve the performance of the electrode, gold nanoparticles (AuNP) were placed on the surface of black phosphorus nanosheets (AuNP-BP NSs) by electrostatic attraction for patulin aptasensing.

Dual-Wavelength Ratiometric Electrochemiluminescence Immunosensor for Cardiac Troponin I Detection

Ratiometric electrochemiluminescence (ECL) has attracted special focus in the biological analysis field, because it could eliminate the environmental interference and allow for precise measurement. Herein, a dual-wavelength ratiometric ECL biosensor was designed for the detection of cardiac troponin I (cTnI), where (4,4'-dicarboxylic acid-2,2'-bipyridyl) ruthenium(II) (Ru(dcbpy)₃²⁺) and Au nanoparticle-loaded graphene oxide/polyethylenimine (GPRu-Au) nanomaterial acts as an acceptor, and Au nanoparticle-modified graphitic phase carbon nitride nanosheet composite (Au-CNN) acts as donor. Au-CNN shows a high and steady ECL signal centered at 455 nm, which is well-matched with the adsorption of GPRu-Au; thereby, a highly efficient electrochemiluminescent resonance energy transfer (ECL-RET) sensing platform is designed. AuNPs facilitate the immobilization of antibody on the nanomaterials through a Au-N bond. The high surface area of graphene oxide/polyethylenimine allows a large number of Ru(dcbpy)₃²⁺ to be loaded, immensely amplifying the ECL signal. This sensing platform exhibits outstanding analytical performance toward cTnI with a detection limit of 3.94 fg/mL (S/N = 3). The high reliability, selectivity, and sensitivity of this ratiometric ECL biosensor provides a versatile sensing platform for the bioanalysis.

Ratiometric Electrogenerated Chemiluminescence Cytosensor Based on Conducting Polymer Hydrogel Loaded with Internal Standard Molecules

A sensitive and reliable bimodal electrochemiluminescent (ECL) system based on CdTe quantum dots (QDs) and luminol as double luminophores is constructed. CdTe QDs tagged with the aptamer (CdTe-Apt 2) of cancer cells are used as the detection signals, while luminol molecules are used as internal standards. The electrodeposited polyaniline-based conducting polymer hydrogel (CPH) on the electrode surfaces improves the biocompatibility and conductivity of the sensing interfaces effectively. Furthermore, electron transfer is probably much easier when luminol and coreactant potassium persulfate (K₂S₂O₈) are immobilized in the CPH in comparison to that in solution. Cancer cells are captured to the electrode surface by another aptamer linked to the Au nanoparticles immobilized in the CPH through Au-S bonds. In the developed bimodal ECL system, an internal standard method is used to quantify cancer cells by comparing the differences in sensitivity of the double-peak ECL signals with that of target analytes. The internal standard method of ECL strategy can provide very accurate detection results in a complex environment because interferences in the system can be eliminated through the self-calibration of two emission spectra. A linear relation is found on the basis of a plot of the ΔECL_CdTe/ΔECL_luminol against the concentration of cancer cells within 100-6500 cells mL^-1 under optimized conditions. The developed ratiometric ECL cytosensor with internal standard can significantly improve the accuracy and reliability of cell assays in complex biological media, demonstrating promising applications in healthcare monitoring and clinical diagnostics.

Recent trends in electrochemiluminescence aptasensors and their applications

Aptamers are single stranded DNA or RNA ligands which can be selected for different targets from proteins to small organic dyes. In the past few years great progress has been accomplished in the development of aptamer based bioanalytical assays with different detection techniques. Among them, electrochemiluminescence (ECL) aptasensors are very promising because they have the advantages of both electrochemical and chemiluminescence biosensors, such as high sensitivity, low background, cost effectiveness, and ease of control. In this review, we summarize the recent efforts to construct novel and improved ECL aptasensors and their application.

Direct Immunoassay for Facile and Sensitive Detection of Small Molecule Aflatoxin B1 based on Nanobody

Aflatoxin B₁ (AFB₁ ), one of the most toxic mycotoxins, is classified as a group I carcinogen and ubiquitous in various foods and agriproducts. Thus, accurate and sensitive determination of AFB₁ is of great significance to meet the criteria of food safety. Direct detection of AFB₁ is difficult by monoclonal antibody (mAb) with large molecular size (≈150 kD) since the target is too small to produce a detectable signal change. Herein, by combining the electrochemical properties of nanomaterials and the advantages of nanobodies, we developed a direct, highly selective and sensitive electrochemical immunosensor for small molecule detection. The proposed immunosensor had a wide calibration range of 0.01 to 100 ng mL^-1 and a low detection limit of 3.3 pg mL^-1 (S/N=3). Compared with the immunosensor prepared with mAb which was applied in the typical indirect immunoassay, the immunosensor in this work possessed two orders of magnitudes wider linear range and 10-fold more sensitivity. The as-obtained immunosensor was further successfully applied for sensing AFB₁ in real samples. This proposed assay would provide a simple, highly sensitive and selective approach for the direct immunoassay of small molecule AFB₁ , and is extendable to the development of direct immunosensing systems for other small molecules detection by coupling nanocarbon and nanobody.

An amperometric aptasensor for ultrasensitive detection of sulfadimethoxine based on exonuclease-assisted target recycling and new signal tracer for amplification

The risks caused by veterinary drug residues in animal foodstuffs are of great concern to the public. Accordingly, this work reported an amperometric aptasensor for highly sensitive detection of sulfadimethoxine (SDM). Functionalised fullerene (C₆₀)-doped graphene (C₆₀-rGO) nanohybrid was designed and prepared to load electroactive toluidine blue (Tb) through the π-π stacking, forming a C₆₀-rGO-Tb nanocomposite. Furthermore, the as-prepared nanocomposite was decorated with gold nanoparticles and used for the immobilization of signal probes to form a new signal tracer, which was coupled with exonuclease-catalyzed target recycling for amplification. To construct the aptasensor, a thiolated double-stranded DNA (dsDNA) of aptamer-capture probe complex was immobilised on a gold electrode surface through strong Au-S bond. In the presence of SDM, the aptamer preferred to form an aptamer-SDM complex, which led to the dissociation of dsDNA. Then aptamer could be selectively digested by RecJ_f exonuclease, resulting in liberated SDM molecules to participate in the next reaction cycling and achieve signal amplification. Then, capture probes released from the cyclic processes were hybridized with the signal tracer, which could further enhance electrochemical signal responses. On the basis of cascade signal amplification strategies, the proposed aptasensor exhibited a wide linear range from 10 fg/mL to 10 ng/mL for SDM with high sensitivity, good selectivity and satisfactory stability.

Ultrasensitive photoelectrochemical aptasensor for lead ion detection based on sensitization effect of CdTe QDs on MoS2-CdS:Mn nanocomposites by the formation of G-quadruplex structure

An ultrasensitive photoelectrochemical (PEC) aptasensor for lead ion (Pb²⁺) detection was fabricated based on MoS₂-CdS:Mn nanocomposites and sensitization effect of CdTe quantum dots (QDs). MoS₂-CdS:Mn modified electrode was used as the PEC matrix for the immobilization of probe DNA (pDNA) labeled with CdTe QDs. Target DNA (tDNA) were hybridized with pDNA to made the QDs locate away from the electrode surface by the rod-like double helix. The detection of Pb²⁺ was based on the conformational change of the pDNA to G-quadruplex structure in the presence of Pb²⁺, which made the labeled QDs move close to the electrode surface, leading to the generation of sensitization effect and evident increase of the photocurrent intensity. The linear range was 50 fM to 100 nM with a detection limit of 16.7 fM. The recoveries of the determination of Pb²⁺ in real samples were in the range of 102.5-108.0%. This proposed PEC aptasensor provides a new sensing strategy for various heavy metal ions at ultralow levels.

Strong Electrochemiluminescence from MOF Accelerator Enriched Quantum Dots for Enhanced Sensing of Trace cTnI

The development of a sensitive and practical electrochemiluminescence (ECL) bioassay relies on the use of ECL signal tags whose signal intensity is high and stable. In this work, strong ECL emission was achieved from metal organic framework (MOF) accelerator enriched quantum dots (CdTe), which were applied as an efficient ECL signal tag for trace biomarker detection. It is particularly noteworthy that a novel mechanism to drastically enhance the ECL intensity of CdTe is established because isoreticular metal organic framework-3 (IRMOF-3) with 2-amino terephthalic acid (2-NH₂-BDC) as the organic ligand not only allows for loading a large amount of CdTe via the encapsulating effect and internal/external decoration but also functions as a novel coreactant accelerator for promoting the conversion of coreactant S₂O₈^2- into the sulfate radical anion (SO₄^•-), further boosting the ECL emission of CdTe. On the basis of the simple sandwich immunoreaction approach, cardiac troponin-I antigen (cTnI), a kind of biomarker related with myocardial infarction, was chosen as a detection model using an IRMOF-3-enriched CdTe labeled antibody as the signal probe. This immunosensor demonstrated desirable assay performance for cTnI with a wide response range from 1.1 fg mL^-1 to 11 ng mL^-1 and a very low detection limit (0.46 fg mL^-1). This suggested that the IRMOF-3-enriched CdTe nanocomposite strategy can integrate the coreactant accelerator and luminophore to significantly enhance the ECL intensity and stability, providing a direction for promising ECL tag preparation with broad applications.

Dual-signal ratiometric electrochemiluminescence assay for detecting the activity of human methyltransferase

A ratiometric electrochemiluminescence assay using CdS:Eu NCs and luminol as signal emitters was fabricated for detecting the human methyltransferase activity.

Electrochemiluminescence biosensing based on different modes of switching signals

Electrochemiluminescence (ECL) has attracted much attention in various fields of analysis owing to low background signals, high sensitivity, and excellent controllability.

Electrochemiluminescent Pb2+-Driven Circular Etching Sensor Coupled to a DNA Micronet-Carrier

Herein, an ultrasensitive electrochemiluminescent (ECL) strategy was designed based on the fabrication of a multi-interface DNA micronet-carrier via layer by layer hybridization of double-stranded DNAzyme-substrate to immobilize large amounts of ECL indicator, [Ru(dcbpy)₂dppz]²⁺, in double-strand DNA on the electrode surface, generating enhanced ECL signals. When the double-stranded structures were cleaved circularly via Pb²⁺ in the detection sample, the ECL indicator was released, which resulted in a decreased ECL signal associated with the concentration of Pb²⁺, that had higher sensitivity and wider linear range. As a result, the developed ECL strategy exhibited a linear range from 50 pM to 500 μM with a detection limit of 4.73 pM, providing an alternative analytical strategy with excellent properties, including a high sensitivity and a wide linear range. Importantly, the ECL strategy could be readily expanded for various metal ions, proteins, nucleotide sequences, and cells, offering a simple and efficient technology for both environmentally safe assays and clinical diagnostics.

Electrochemiluminescence resonance energy transfer system between GNRs and Ru(bpy)32+: Application in magnetic aptasensor for β-amyloid

Electrochemiluminescent (ECL) assay has gradually drawn increasing interest in the biomedical analysis. This paper proposed a new methodology for ultrasensitive and facile detection of Alzheimer's disease marker β-amyloid (Aβ) by fabricating a sandwich-type ECL sensing platform. Herein, electrochemiluminescence resonance energy transfer (ECL-RET) was employed to determine Aβ concentration, which can be attributed to the quenching effect from RET between Ru(bpy)₃²⁺ and gold nanorods (GNRs) acting as ECL-RET electron donor and acceptor, respectively. In this protocol, mesoporous carbon nanospheres were adopted to immobilize ECL reactant Ru(bpy)₃²⁺ and antibody via nafion to acquire the RET donor nanocomposites (MOCs/nafion/Ru(bpy)₃²⁺/antibody), which were tightly interconnected with epoxy group functionalized Fe₃O₄ nanoparticles. It is of vital importance that GNRs with exquisite rod shape were synthesized and exhibited a typical absorption peak at 650nm to quench ECL signal of Ru(bpy)₃²⁺ effectively. In addition, the ECL emission decreased linearly with the logarithm of Aβ concentration in a wide linear range from 1.0 × 10^-5 to 100ng/mL with a detection limit of 4.2 × 10^-6ng/mL. Furthermore, distinctive and desirable properties were verified to declare the promise for being applicable to analyze the Aβ content in real Alzheimer's cerebrospinal fluid samples with satisfactory results.

Electrochemiluminescent resonance energy transfer of polymer dots for aptasensing

This work designed a three-component polymer for the preparation of polymer dots (Pdots). The polymer contained 9-(diphenylmethylene)-9H-fluorene (DPF), 9,9-dioctyl-9H-fluorene (DOF) and 1,1'-binaphthyl moieties, and was synthesized via Pd-catalyzed Suzuki reaction. It exhibited obvious yellow-colored aggregation-induced emission (AIE) for fluorescence enhancement at 543nm via an intramolecular fluorescence resonance energy transfer from DOF moiety to DPF moiety. The Pdots prepared by nanoprecipitation could be conveniently cast on electrode surface and showed a stable anodic electrochemiluminescence (ECL) emission in the presence of triethylamine as a co-reactant. The ECL emission could be effectively quenched by rhodamine B via resonance energy transfer, which led to an "off-on" switch for the design of ECL sensing methodology. Using Pb²⁺ as a target model, an ECL aptasensor for the detection of trace Pb²⁺ was proposed, which showed a linear range of 100pM to 1.0μM with a detection limit down to 38.0pM This work demonstrated the first Pdots prepared with AIE-active polymer for highly efficient ECL sensing.

Metal ion detection using functional nucleic acids and nanomaterials

Metal ion detection is critical in a variety of areas. The past decade has witnessed great progress in the development of metal ion sensors using functional nucleic acids (FNAs) and nanomaterials. The former has good recognition selectivity toward metal ions and the latter possesses unique properties for enhancing the performance of metal ion sensors. This review offers a summary of FNA- and nanomaterial-based metal ion detection methods. FNAs mainly include DNAzymes, G-quadruplexes, and mismatched base pairs and nanomaterials cover gold nanoparticles (GNPs), quantum dots (QDs), carbon nanotubes (CNTs), and graphene oxide (GO). The roles of FNAs and nanomaterials are introduced first. Then, various methods based on the combination of different FNAs and nanomaterials are discussed. Finally, the challenges and future directions of metal ion sensors are presented.

Highly Efficient Intramolecular Electrochemiluminescence Energy Transfer for Ultrasensitive Bioanalysis of Aflatoxin M1

The intermolecular electrochemiluminescence resonance energy transfer (ECL-RET) between luminol and Ru(bpy)₃²⁺ was studied extensively to achieve the sensitive bioanalysis owing to the perfect spectral overlap of the donor and acceptor, but it still suffers from the challenging issue of low energy-transfer efficiency. The intramolecular ECL-RET towards the novel ECL compound containing the donor of luminol and the acceptor of Ru(bpy)₂ (mcpbpy)²⁺ (Lum-Ru) was designed and investigated. With the high-efficient ECL-RET in one molecule, the highly intense ECL signal of Lum-Ru was obtained owing to the short path of energy transmission and less energy loss between luminol and Ru(bpy)₂ (mcpbpy)²⁺ . Lum-Ru was further applied to construct a signal-off electrochemiluminescence (ECL) aptasensor for ultrasensitive detection of a harsh carcinogen of Aflatoxin M1 (AFM1). This sensing platform also provides a significant boost for the trace detection of other biomolecules in clinical analysis.

Progress and challenges in electrochemiluminescent aptasensors

The importance of developing new diagnostic and detection technologies for the growing number of sensing challenges is rising each year. Here, we present a comprehensive and concise review on electrochemiluminescent (ECL) aptasensors by putting special emphasis on its characteristic features, advances, challenges, and applications of ECL based aptasensors. ECL is an ideal tool for constructing such sensors because of its inherent characteristics and can be easily integrated into aptamer based sensing platforms. This review summarizes the "synergistic benefits" of ECL aptamer-based sensors; classifications of ECL aptamer-based assay designs, and signal amplification strategies. This critical review highlights the effects of integration of nanomaterials, immobilization techniques, and amplification/detection strategies on the analytical performance of ECL based aptasensors. Moreover, several proof-of-concepts with appropriate figures and explanations have been shown to provide a general guide for the design of ECL aptasensors, and to stimulate further application of these ECL aptasensors. Finally, we conclude with the remaining challenges and opportunities to inspire further developments in ECL aptasensors.

Novel multifunctionalized peryleneteracarboxylic/amine supramolecules for electrochemical assay

In this work, a series of novel multifunctionalized peryleneteracarboxylic supramolecules were synthesized based on hydrogen bonding interactions between 3,4,9,10-perylenetetracarboxylic acid (PTCA) and amines, which possess large specific surface area, good membrane-forming properties and high stability. Importantly, an interesting phenomenon was found in that these series of supramolecules could conciliate disorderly redox peaks of PTCA and result in a pair of well-defined redox peaks, which were able to act as redox carriers for charge-generation and electron-transportion. And the probable mechanism for this phenomenon was discussed for the first time in detail through the integration of theoretical with practical research. To further reveal the advantages of these novel multifunctionalized supramolecule nanomaterials, PTCA/triethylamine (PTCA/TEA) was chosen as the best candidate for a redox carrier to participate in a "signal-on" aptasensor for thrombin (TB) detection by employing Fe₃O₄ magnetic beads (MBs) as a good enzyme mimic to catalyze the PTCA/TEA for signal amplification. As a result, a wide linear detection range of 0.0001-50 nM is acquired with a relatively low detection limit of 0.05 pM. And the proposed aptasensor exhibited good specificity and acceptable reproducibility and stability. After all, the explorations between PTCA and amines would set up a meaningful basis in seeking multifunctionalized supramolecule nanomaterials based on PTCA for extending the application of PTCA in a wider range of fields, and exploring the essential reason for the referred peculiar phenomenon for PTCA.

Electrochemiluminescence of Supramolecular Nanorods and Their Application in the "On-Off-On" Detection of Copper Ions

In this work, an "on-off-on" switch system has been successfully applied through the construction of an electrochemiluminscent biosensor for copper ion (Cu(2+) ) detection based on a new electrochemiluminescence (ECL) emitter of supramolecular nanorods, which was achieved through supramolecular interactions between 3,4,9,10-perylenetetracarboxylic acid (PTCA) and aniline. The initial "signal-on" state with strong and stable ECL emission was obtained by use of the supramolecular nanorods with a new signal amplification strategy involving a co-reaction accelerator. In addition, ECL quencher probes (Fc-NH2 /Cu-Sub/nano-Au) were fabricated by immobilizing aminoferrocene (Fc-NH2 ) on Cu-substrate strand modified Au nanoparticles. The quencher probes were hybridized with the immobilized Cu-enzyme strand to form Cu(2+) -specific DNAzyme. Similarly, the "signal-off" state was obtained by the high quenching effect of Fc-NH2 on the ECL of the excited-state PTCA ((1) PTCA*). As expected, the second "switch-on" state could achieved by incubating with the target Cu(2+) , owing to the Cu(2+) -specific DNAzyme, which was irreversibly cleaved, resulting in the release of the quencher probes from the sensor interface. Herein, on the basis of the ECL intensity changes (ΔIECL ) before and after incubating with the target Cu(2+) , the prepared Cu(2+) -specific DNAzyme-based biosensor was used for the determination of Cu(2+) concentrations with high sensitivity, excellent selectivity, and good regeneration.

A sensitive electrochemiluminescent aptasensor based on perylene derivatives as a novel co-reaction accelerator for signal amplification

Herein, a novel signal amplification strategy was designed using the perylene derivative as the co-reaction accelerator toward graphene-CdTe quantum dots (G-CdTe)/S2O8(2-) system to construct a highly sensitive electrochemiluminescent (ECL) aptasensor for thrombin (TB) detection. Firstly, the G-CdTe nanocomposites were prepared by one-step method of in situ generating CdTe quantum dots onto the surface of the graphene oxide by using 3-mercaptopropionic acid as the CdTe QDs stabilizer. Then, a kind of perylene derivative (PTC-Lys), was synthesized by covalently binding L-lysine to 3,4,9,10-perylenetetracarboxylic acid, which was further immobilized onto the G-CdTe by the π-π* stacking and cross-linked the detection thrombin aptamer (TBA II) to obtain the TBA II/PTC-Lys/G-CdTe signal probes. It is worth pointing out that PTC-Lys acting as an efficient co-reaction accelerator interacted with the co-reactant of S2O8(2-) rather than G-CdTe to promote the more oxidant mediators of SO4(•-), which could further react with G-CdTe to produce excited state species G-CdTe* for emitting light. Compared with the G-CdTe/S2O8(2-) ECL system, our proposed strategy with the introduction of co-reaction accelerator of PTC-Lys exhibited ultra-high sensitivity to quantify the concentration of TB from 1.0×10(-7)nM to 10nM with a detection limit of 34aM.