Electrogenerated Chemiluminescence Signal Research Articles

Heavily Labeled Signal Probe for Electrogenerated Chemiluminescence Peptide-based Biosensing of Matrix Metalloproteinase 2.

The field of electrogenerated chemiluminescence (ECL) biosensing has witnessed remarkable growth, emphasizing the need for precise detection of biomarkers. The synthesis approach of peptide-based signal probe with high recognition ability and high ECL efficiency is a significant issue in the ECL biosensing. Here, a heavily labeled signal probe was synthesized for ECL peptide-based biosensing tactic by using a new aldehyde bearing cyclometalated Ir(III) complex ([Ir(bt)2(bpy-CHO)PF6 (bt =2-phenylbenzothiazole, bpy-CHO=4'-methyl-[2,2'-bipyridine]-4-carbaldehyde, denoted as Ir1) as ECL signal reagent and streptavidin (SA) as carrier protein. One ECL peptide-based biosensing method was exemplified for the detection of matrix metalloproteinase 2 (MMP-2) by using Ir1 labeled SA (SA-Ir1) as heavily labeled signal probe and biotinylated peptide as molecular recognition substrate. MMP-2 was sensitively detected in the range from 5 to 100 ng/mL with a detection limit of 1.5 ng/mL. Importantly, two detection modes differing in the order of cleavage recognition by MMP-2 and signal transduction with SA-Ir1 were compared for the first time. First cleavage and second signal transduction were proposed to be beneficial to sensitive detection of target, which provides some ideas for biomarker diagnostics in disease screening at an early stage.

Electrogenerated Chemiluminescence Biosensor for Quantization of Matrix Metalloproteinase-3 in Serum via Target-Induced Cleavage of Oligopeptide

A highly sensitive and selective electrogenerated chemiluminescence (ECL) biosensor was developed for the determination of matrix metalloproteinase 3 (MMP-3) in serum via the target-induced cleavage of an oligopeptide. One ECL probe (named as Ir-peptide) was synthesized by covalently linking a new cyclometalated iridium(III) complex ([(3-pba)2Ir(bpy-COOH)](PF6)) (3-pba = 3-(2-pyridyl) benzaldehyde, bpy-COOH = 4′-methyl-2,2′-bipyridine-4-carboxylic acid) with an oligopeptide (CGVPLSLTMGKGGK). An ECL biosensor was fabricated by firstly casting Nafion and gold nanoparticles (AuNPs) on a glassy carbon electrode and then self-assembling both of the ECL probes, 6-mercapto-1-hexanol and zwitterionic peptide, on the electrode surface, from which the AuNPs could be used to amplify the ECL signal and Ir-peptide could serve as an ECL probe to detect the MMP-3. Thanks to the MMP-3-induced cleavage of the oligopeptide contributing to the decrease in ECL intensity and the amplification of the ECL signal using AuNPs, the ECL biosensor could selectively and sensitively quantify MMP-3 in the concentration range of 10–150 ng·mL−1 and with both a limit of quantification (26.7 ng·mL−1) and a limit of detection (8.0 ng·mL−1) via one-step recognition. In addition, the developed ECL biosensor showed good performance in the quantization of MMP-3 in serum samples, with a recovery of 92.6% ± 2.8%–105.6% ± 5.0%. An increased level of MMP-3 was found in the serum of rheumatoid arthritis patients compared with that of healthy people. This work provides a sensitive and selective biosensing method for the detection of MMP-3 in human serum, which is promising in the identification of patients with rheumatoid arthritis.

Femtoliter oil droplets act as CO2 micropumps for uninterrupted electrochemiluminescence at the water|oil interface

Interfacial effects are well-known to significantly alter chemical reactivity, especially in confined environments, where the surface to volume ratio increases. Here, we observed an inhomogeneity in the electrogenerated chemiluminescence (ECL) intensity decrease over time in a multiphasic system composed of femtoliter water droplets entrapping femtoliter volumes of the 1,2-dichloroethane (DCE) continuous phase. In usual electrochemiluminescence (ECL) reactions involving an ECL chromophore and oxalate ([C2O4]2−), the build-up of CO2 diminishes the ECL signal with time because of bubble formation. We hypothesised that relative solubilities of chemical species in these environments play a dramatic role in interfacial reactivity. Water droplets, loaded with the ECL luminophore [Ru(bpy)3]2+ and the coreactant [C2O4]2− were allowed to stochastically collide and adsorb at the surface of a glassy carbon macroelectrode. When water droplets coalesce on the surface, they leave behind femtoliter droplets of the DCE phase (inclusions). We report the surprising finding that the addition of multiple interfaces, due to the presence of continuous phase’s femtoliter inclusions, allows sustained ECL over time after successive potential applications at the triple-phase boundary between water droplet|electrode|DCE inclusion. When femtoliter droplets of DCE form on the electrode surface, bright rings of ECL are observed during the simultaneous oxidation of [Ru(bpy)3]2+ and [C2O4]2−. Control experiments and finite element modelling allowed us to propose that these rings arise because CO2 that is generated near the 1,2-dichloroethane droplet partitions in due to relative solubility of CO2 in 1,2-dichloroethane and builds up and/or is expelled at the top of the droplet. The small droplets of the DCE phase act as micropumps, pumping away carbon dioxide from the interface. These results highlight the unexpected point that confined microenvironments and their geometry can tune chemical reactions of industrial importance and fundamental interest.

Ratiometric electrogenerated chemiluminescence sensing microRNA based on electrochemically controlled release of lucigenin from silica/chitosan/lucigenin nanoparticles

The dye-doped silica nanoparticles-based electrogenerated chemiluminescence (ECL) has been widely explored for analytical purposes due to its high sensitivity, simplicity and wide dynamic concentration range. However, only a few of dye molecules located at the near surface of nanoparticles can participate in the ECL reaction due to the poor conductivity of silica nano-matrix. In addition, the ECL signal is easy to be affected by environmental interference, which results in poor accuracy. Herein, a ratiometric ECL sensing method is established based on the electrochemically controlled release of lucigenin molecules from silica/chitosan/lucigenin composite nanoparticles (Lu/CS NPs) with the aid of sulfide ions. Firstly, H+ produced from the electrochemical oxidation of HS− ions can combine with SiO− and displace lucigenin from Lu/CS NPs. The released lucigenin molecules react with the reactive oxygen species (ROS) generated from the electroreduction of dissolved oxygen to produce the cathodic ECL signal. In addition, the excited elemental sulfur from the electrooxidation of HS− ions transfers its energy to lucigenin molecules and makes them be excited to produce energy-transfer anodic ECL signal. Based on these findings, a ratiometric ECL sensor is developed taking the anodic ECL intensity of lucigenin as a reference signal for the cathodic ECL of lucigenin. The proposed ratiometric ECL sensor has been successfully applied to the detection of let-7a with a wide linear range of 0.1–9.0 pM, a low detection limit of 28 fM, high selectivity and good reproducibility. Moreover, the developed approach was used to detect let-7a in human serum composite samples with good recoveries.

Label-Free Electrogenerated Chemiluminescence Aptasensing Method for Highly Sensitive Determination of Dopamine via Target-Induced DNA Conformational Change.

A label-free electrogenerated chemiluminescence (ECL) aptasensing method for highly sensitive determination of dopamine (DA) was developed based on target-induced DNA conformational change. After anti-DA specific aptamer, as molecular recognition element, was hybridized with a capture ss-DNA (complementary with the aptamer), the formed double-strand DNA (ds-DNA) was self-assembled onto the surface of a gold electrode, and then Ru(phen)32+, as ECL reagent, was intercalated into ds-DNA to form an ECL biosensing platform. In the presence of DA, DA bound with its aptamer and target-induced DNA conformational change occurred, resulting in the dissociation of ds-DNA, the release of intercalated Ru(phen)32+ from the electrode surface, and the decrease of ECL intensity. For comparison, an ECL aptamer-based biosensing method using an ECL reagent-labeled aptamer was also developed for DA assay based on target-induced DNA conformational change. Because of the increase in the amount of ECL reagent into ds-DNA over that of the single-site ECL reagent-labeled aptamer, an obvious increase of ECL intensity was found at the ds-DNA modified electrode over the aptamer modified electrode. DA can be sensitively detected with a lower detection limit of 0.05 nM in the range from 0.1 to 100 nM. With the recognition of the aptamer for DA, DA can be selectively and sensitively detected in artificial cerebrospinal fluid and serum samples without interference from common small molecules. This work demonstrates that the combination of the direct transduction of specific recognition of DA and its aptamer into an ECL signal with Ru(phen)32+ intercalated ds-DNA amplification provides a promising strategy for the development of a simple, sensitive, and selective method for DA assay, which is of great importance in neurochemical assays and clinical diagnosis.

Washing-free electrogenerated chemiluminescence magnetic microbiosensors based on target assistant proximity hybridization for multiple protein biomarkers

This work reports washing-free electrogenerated chemiluminescence (ECL) magnetic microbiosensors based on target assistant proximity hybridization (TAPH) for multiple protein biomarkers for the first time. As a principle-of-proof, alpha-fetoprotein (AFP) was chosen as a model analyte, and biotin-DNA1 bound streptavidin-coated magnetic microbeads (MMB@SA⋅biotin-DNA1) were designed as the universal capture MMB, while the corresponding two antibodies tagged with DNA2 or DNA3 were utilized as hybrid recognition probes, and ruthenium complex-tagged DNA4-10A was designed as a universal ECL signal probe. When the capture MMB was added into the mixture solution (containing the analyte, hybrid recognition probes, signal probe and tri-n-propylamine), biocomplexes were formed on the MMB. After the resulting MMB was efficiently brought to the surface of a magnetic glassy carbon electrode (MGCE), ECL measurement was performed without a washing step, resulting in an increase in the ECL intensity. A model for ECL measuring the second-order rate constants of hybridization reactions on MMB was derived. It was found that the rate constants for hybridization reactions on MMB in rotating mode are 1.6-fold higher than those in shaking mode, and a suitable DNA length of the signal probe can improve the signal-to-noise ratio. The washing-free ECL method was developed for the determination of AFP with a much lower detection limit (LOD) of 0.04 ng mL−1. The developed flexible strategy has been extended to determine D-dimer with an LOD of 0.1 ng mL−1 and myoglobinglobin with an LOD of 1.1 ng mL−1. This work demonstrated that the proposed strategy of ECL TAPH on MMB at MGCE is a washing-free and flexible promising strategy, and can be extended to qualify other multiple protein biomarkers in real clinical assays.

Electrogenerated chemiluminescence resonance energy transfer between luminol and MnO2 nanosheets decorated with Cu2O nanoparticles for sensitive detection of RNase H.

In the present work, a novel approach was developed for the preparation of Cu2O nanoparticle decorated MnO2 nanosheets (Cu2O@MnO2). Uniformly dispersed Cu2O nanocrystals were produced on the surface of MnO2 nanosheets by in situ reduction under refluxing conditions. The unique structure of the used MnO2 nanosheet support played a vital role in the preparation of such Cu2O@MnO2 nanocomposites. The electrogenerated chemiluminescence (ECL) resonance energy transfer can occur between the luminol/H2O2 system and Cu2O@MnO2 nanocomposites, resulting in a decrease of the ECL intensity, which can be used to fabricate an ECL sensor. Cu2O@MnO2 nanocomposite modified heterologous DNA/RNA duplexes were modified on the GCE to construct an ECL-RET system, leading to the decrease of ECL intensity. As a highly conserved damage repair protein, RNase H can specifically hydrolyze RNA in DNA/RNA strands to release Cu2O@MnO2 nanocomposites and recover the ECL signal. As a result, an "off-on" mode ECL sensor for sensitive RNase H assay was fabricated. Under the optimal conditions, the detection limit of RNase H is 0.0005 U mL-1, which is superior to other approaches. The proposed method provides a universal platform for monitoring RNase H, and exhibits great potential in bioanalysis.

Label-free electrogenerated chemiluminescence biosensor for quantization of CD44 on basis of its heterodimerization with matrix metalloproteinase-14

CD44, which is expressed frequently and predominantly in invasive tumor cells, is substrate of a membrane-type matrix metalloproteinase (MT1-MMP, also named MMP-14) and its processing accompanies promotion of cell migration. The hemopexin-like domain of MMP-14 (PEX-14) is the region responsible for association with CD44. An electrogenerated chemiluminescence (ECL) biosensor was developed firstly for highly sensitive quantification of CD44 based on heterodimerization interaction between CD44 and PEX-14. In the work, PEX-14 was chosen to specially recognize target CD44. ECL emitter, ruthenium complex (Ru), was covalently coupled onto the surface of Co, Mo2C-carbon nanofiber@polydopamine (Co, Mo2C-CNF@PDA) modified glassy carbon electrode. PEX-14 was further attached to the modified surface, the ECL fabricated successfully. In theory, the ECL signal decreases after binding to CD44. Under the optimal experimental conditions, the designed biosensor exhibited excellent sensitivity with a wide linear range of 0.002–250 ng mL−1 and a detection limit of 0.001 ng mL−1. The biosensor is demonstrated by detecting of living cells expressing CD44 (MDA-MB-231 cancer cells as model). The development of the label-free ECL biosensor integrated with functionalized nanofiber will provide a prospect for studying invasion and metastasis of cancer cells based on the interaction between CD44 and PEX of MMPs.

Electrogenerated chemiluminescence biosensor for assay of matrix metalloproteinase-14 and protein-expressing cancer cells via inhibitory peptides-based sandwich assay

A novel electrogenerated chemiluminescence (ECL) biosensor based on sandwich structure between target and inhibitory peptides was firstly developed for determination of matrix metalloproteinase and its expressing cancer cells. Here, target MMP-14 was used as model protein. Inhibitory peptide (AP1) was used as capture probe. Ruthenium complex (Ru) tagged inhibitory peptide (AP2) was used as signal probe (Ru-AP2) in this work. The biosensors were fabricated by covalently coupling Cys group of AP1 onto the surface of functional fullerene-chitosan (C60-Chit) nanocomposite modified glassy carbon electrode. Upon binding of MMP-14, Ru-AP2 further specially bound to MMP-14 and a sandwich format formed, and increasing ECL signal was obtained. Under the optimal experimental conditions, the designed biosensor exhibited excellent sensitivity with a wide linear range of 0.05–7 pg mL−1 and a detection limit of 0.008 pg mL−1. The biosensor is demonstrated by detecting of living cells expressing MMPs (MDA-MB-231 cancer cells as model) and distinguish the expression MMPs in different cells. Our work firstly fabricated a sandwich ECL biosensor for determination of MMPs and MMPs relative cancer cells based on the interaction between peptide inhibitors and PEX of MMPs, which will provide a platform to study the mechanism of MMP and inhibitors.

Array of Interdigitated Bipolar Electrodes for the Selective Capture and Analysis of Melanoma Cells

In this work, we develop an array of biosensors for the selective dielectrophoretic capture and electrochemical detection of single to few melanoma cells. Each biosensor in the array consists of a gold thin film interdigitated bipolar electrode (IDBPE) patterned on a glass substrate. Microwells are patterned over the interdigitated end of each IDBPE to restrict the number of cells captured and to retain cells on the electrodes for subsequent analysis. An overlying microfluidic channel controls delivery of the cell sample to the microwells. Cells are attracted to the interdigitated electrode by a positive dielectrophoretic force, thereby pulling them into the microwells, where they remain trapped during the next step – introduction of reagents for electrochemical enzyme-linked immunosorbent assay (eELISA). The dimensions of the wells, solution flow rate, and AC voltage applied all support the retention of the cells on the electrodes once they are captured.A bipolar electrode (BPE) is a conductor, which in the presence of an externally applied electric field, facilitates electrically coupled faradaic reactions at its opposing ends. In the context of analysis, a sensing reaction at one pole of the BPE is coupled to a reporting reaction, which produces a visual signal at the opposite pole. Because of their wireless operation, arrays of tens to thousands of BPEs can be operated in parallel with a single power supply – an advantageous feature for parallel analysis of few or single cells. However, traditional BPEs with electrogenerated chemiluminescence (ECL) as the reporting reaction do not provide sufficient sensitivity for biologically relevant detection limits, and therefore, require a means of signal amplification for such applications. To address this issue, we previously developed IDBPEs, which facilitate redox cycling by interdigitation of the sensing pole of each BPE of an array with a shared driving electrode, thereby yielding more intense ECL at the reporting pole.1 In the present study, the interdigitated end of the IDBPE is utilized for eELISA to quantify the expression of a cell surface antigen, melanoma cell adhesion marker (MCAM). Cells are labelled with biotinylated anti-human MCAM and alkaline phosphatase (ALP) conjugated streptavidin. Once cells are captured, the redox inactive substrate, para-aminophenyl phosphate (PAPP), is flowed through the microchannels and ALP catalyzes its conversion to the redox active species para-aminophenol (PAP). The amplified current obtained at each IDBPE by the redox cycling of PAP and its oxidized form, quinone imine (QI), is reported by an ECL reaction on its opposing pole. The ECL signal obtained at each IDBPE is correlated to the expression level of MCAM on the melanoma cells isolated in the corresponding well. This work is significant because it allows for the sensitive detection of melanoma cells in a device amenable to point-of-care application by combining selective enrichment of malignant cells by dielectrophoresis with the amplification and facile arraying afforded by IDBPEs. Borchers, J.S., Campbell, C.R., Van Scoy, S.B., Clark, M.J. and Anand, R.K. (2021), Redox Cycling at an Array of Interdigitated Bipolar Electrodes for Enhanced Sensitivity in Biosensing. ChemElectroChem. https://doi.org/10.1002/celc.202100523

Sensitive and non-separation 5-hydroxymethylcytosine double-stranded DNA sensing in different mice tissues: Electrogenerated chemiluminescence biosensing method incorporating DNA nanomachine amplification and nanocomposite magnetic separation

Herein, a sensitive and non-separation electrogenerated chemiluminescence (ECL) biosensing method that combines poly (diallyl dimethyl ammonium chloride)/ferrosoferric oxide/molybdenum disulfide (PDDA/Fe3O4/MoS2) nanocomposite with DNA nanomachine was developed to determine 5-hydroxymethylcytosine modified double-strand DNA (5-hmC-dsDNA). A positively charged and magnetic PDDA/Fe3O4/MoS2 nanocomposite was proposed, which can be used to fix negatively charged 5-hmC-dsDNA to overcome the steric resistance problem and is available for magnetic fields separation. In addition, the DNA nanomachine with three elements was fabricated: a DNA walking probe for signal amplification, an ECL reagent labeled S1 DNA (Ru-S1), 5-hmC antibody (Ab) for specifically recognizing 5-hmC modification. In the presence of 5-hmC-dsDNA, sandwich-type conjugates were generated to incubate PDDA/Fe3O4/MoS2 and DNA nanomachine. After magnetic separation and the DNA walking driven by enzyme cleavage, a lot of ECL reagents were released and increased the ECL signal. ECL measurement was performed in a separation-free format. The method showed a broader linear range (0.0090–0.5761 %) and a low limit of detection (0.0024 %). Furthermore, the determination of 5-hmC-dsDNA in different mice tissues using the ECL biosensing method was also carried out, demonstrating that the established strategy may pave a novel avenue for the early clinical diagnosis of disease.

One-Step Fabrication of Highly Sensitive Tris(2,2'-bipyridyl)ruthenium(II) Electrogenerated Chemiluminescence Sensor Based on Graphene-Titania-Nafion Composite Film.

A highly sensitive tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+) electrogenerated chemiluminescence (ECL) sensor based on a graphene-titania-Nafion composite film has been prepared in a simple one-step manner. In the present work, a highly concentrated 0.1 M Ru(bpy)32+ solution was mixed with an as-prepared graphene-titania-Nafion composite solution (1:20, v/v), and then a small aliquot (2 µL) of the resulting mixture solution was cast on a glassy carbon electrode surface. This one-step process for the construction of an ECL sensor shortens the fabrication time and leads to reproducible ECL signals. Due to the synergistic effect of conductive graphene and mesoporous sol-gel derived titania-Nafion composite, the present ECL sensor leads to a highly sensitive detection of tripropylamine from 1.0 × 10−8 M to 2.0 × 10−3 M with a detection limit of 0.8 nM (S/N = 3), which is lower in comparison to that of the ECL sensor based on the corresponding ECL sensor based on the titania-Nafion composite containing carbon nanotube. The present ECL sensor also shows a good response for nicotinamide adenine dinucleotide hydrogen (NADH) from 1.0 × 10−6 M to 1.0 × 10−3 M with a detection limit of 0.4 µM (S/N = 3). Thus, the present ECL sensor can offer potential benefits in the development of dehydrogenase-based biosensors.

Electrogenerated chemiluminescence biosensor for microRNA detection incorporating enzyme-free dual DNA cyclic amplification and Ru(bpy)32+-functionalized metal-organic framework

Herein, a novel electrogenerated chemiluminescence (ECL) biosensor for the determination of microRNA was developed on the basis of enzyme-free dual signal amplification and Ru(bpy)32+-functionalized metal-organic frameworks (Ru@MIL-101(Al)–NH2) as ECL signal labels. MicroRNA-21 (miRNA-21) was used as a model target, which initiated the toehold-mediated strand displacement reaction (TSDR). The first cyclic amplification TSDR converted a small quantify of miRNA-21 to abundant report strands (RS), which then catalyzed the second cyclic amplification catalytic hairpin assembly (CHA). The CHA ran cyclically to produce numerous H1–H2 duplexes with the exposed segment. Finally, the newly exposed segment of H2 could bind with the ECL probe (DNA-Ru@MIL-101(Al)–NH2), leading to an evident ECL signal enhancement. The results showed that the ECL intensity varied linearly with the logarithm of the concentration of miRNA-21 ranging from 0.01 to 10,000 pM. The detection limit was as low as 4 fM because of the signal amplification through TSDR and CHA processes coupling with Ru@MIL-101(Al)–NH2. In addition, this biosensor has been successfully applied to detect miRNA-21 in MCF-7 cells, providing great potential for the related clinical diagnosis.

Potentiometric aptasensing of Escherichia coli based on electrogenerated chemiluminescence as a highly sensitive readout

We introduce here a versatile approach to read out potentiometric aptasensors by electrogenerated chemiluminescence (ECL), which can amplify the small potential changes induced by the bacterial concentrations via ECL signals. In the present system, the electrode modified with single-walled carbon nanotubes (SWCNTs) and aptamer molecules acts as the reference electrode and is placed in the sample solution for sensing the bacterial concentration changes, while the Ru(bpy)32+ modified gold electrode serves as the working electrode for generating ECL signals and is placed in the detection solution containing tripropylamine (TPA) spatially separated from the sample solution by a salt bridge. Ru(bpy)32+ is immobilized on the gold electrode's surface for enhancement of luminous efficiency and reduction of reagent consumption. A moving-part-free fluid flowing system is introduced to promote the mass transport of TPA from the detection solution to the surface of the ECL generating electrode. When a constant potential is imposed between the working and reference electrodes, the potential changes at the SWCNTs-aptamer modified electrode induced by the bacterial concentrations can modulate the potentials at the Ru(bpy)32+ modified electrode, thus generating the ECL signals. The developed sensing strategy shows a highly sensitive response to E. coli O157: H7 in the linear range of 5–1000 CFU mL−1 with a low detection limit of 2 CFU mL−1. We believe that the proposed approach is promising to develop aptasensors for sensitive detection of bacterial cells.

Sensitive and Selective Detection of N,N-Dimethyltryptamine with Molecularly Imprinted Polymer Coupled with Electrogenerated Chemiluminescence

One of the challenges in analytical chemistry is to develop a method that is not only sensitive but also selective for detection and quantification of a target analyte. Herein, we report a strategy that combines a molecularly imprinted polymer (MIP) as the selective element with electrogenerated chemiluminescence (ECL) as the sensitive analytical signal generator for detection of a hallucinogenic drug N,N-dimethyltryptamine (DMT). MIPs hold specific binding capability toward probed targets, and their molecular recognition behavior is similar to that of specific antibodies to antigens or probe single-strand DNAs to complemental target DNA sequencies. Additionally, MIPs are chemically stable, easily synthesized, and cost-effective. On the other hand, ECL has been regarded as one of the most sensitive analytical techniques for ultra-trace analyte determination. This is because ECL is a kind of spectroscopy initiated by electrochemistry without using any light source. For the present work, DMT specific MIPs were prepared by anodic electrodeposition of aminobenzoic acid as monomer mixed with DMT as template molecule on a glassy carbon electrode that had coated with a Ru(bpy)3 2+ trapped nafion film. ECL signals at the electrodes with DMT immobilized MIPs were acquired in a phosphate buffered solution upon the anodic potential scanning. A non-imprinted polymer (NIP) was also prepared in absence of template under similar conditions. The MIP-ECL sensor showed a wide dynamic range of 0.05 to 100 µM to DMT with an estimated detection limit of 0.05 µM. The reproducibility, stability, and selectivity of the sensor were also examined. Figure 1

In situ growth of TiO2 nanowires on Ti3C2 MXenes nanosheets as highly sensitive luminol electrochemiluminescent nanoplatform for glucose detection in fruits, sweat and serum samples

A sensitive electrogenerated chemiluminescence (ECL) biosensor for glucose was developed based on in situ growth of TiO2 nanowires on Ti3C2 MXenes (TiO2–Ti3C2) as the nanoplatform. Via tuning the alkaline oxidation time, different amount of TiO2 nanowires can be found on MXenes. An ECL biosensor for glucose was constructed by covalent immobilization of glucose oxidase (GODx) on the glycine functional TiO2–Ti3C2 surface, with the ECL signal depending on the in-situ formation of H2O2 via the specifically catalysis of glucose by GODx, resulting in the apparent increase of ECL signal. The TiO2–Ti3C2 can also act as the catalyst for the oxidation of H2O2 into O2 to enhance the ECL of luminol. Based on this strategy, a highly sensitive ECL biosensor for glucose was obtained in wide concentration range of 20 nM-12 mM with a low detection limit of 1.2 nM (S/N = 3). The synergistic effects of large surface area, excellent conductivity, and high catalytic activity of the TiO2–Ti3C2 make the sensor highly sensitive toward glucose; the specific enzyme catalysis reaction promises excellent selectivity of the ECL sensor. The proposed biosensor has been employed to detect glucose in human serum, fruits, and sweat samples with excellent performance, providing a universal approach for glucose in various samples, which shows great prospect in clinical diagnostics and wearable sensors.

A Comparison of Commercially Available Screen-Printed Electrodes for Electrogenerated Chemiluminescence Applications.

We examined a series of commercially available screen-printed electrodes (SPEs) for their suitability for electrochemical and electrogenerated chemiluminescence (ECL) detection systems. Using cyclic voltammetry with both a homogeneous solution-based and a heterogeneous bead-based ECL assay format, the most intense ECL signals were observed from unmodified carbon-based SPEs. Three commercially available varieties were tested, with Zensor outperforming DropSens and Kanichi in terms of sensitivity. The incorporation of nanomaterials in the electrode did not significantly enhance the ECL intensity under the conditions used in this evaluation (such as gold nanoparticles 19%, carbon nanotubes 45%, carbon nanofibers 21%, graphene 48%, and ordered mesoporous carbon 21% compared to the ECL intensity of unmodified Zensor carbon electrode). Platinum and gold SPEs exhibited poor relative ECL intensities (16% and 10%) when compared to carbonaceous materials, due to their high rates of surface oxide formation and inefficient oxidation of tri-n-propylamine (TPrA). However, the ECL signal at platinum electrodes can be increased ∼3-fold with the addition of a surfactant, which enhanced TPrA oxidation due to increasing the hydrophobicity of the electrode surface. Our results also demonstrate that each SPE should only be used once, as we observed a significant change in ECL intensity over repeated CV scans and SPEs cannot be mechanically polished to refresh the electrode surface.

Electrogenerated chemiluminescence aptamer-based biosensing for the determination of mucin and specific cells based on bio-bar-code amplification

<p indent=0mm>A highly sensitive electrogenerated chemiluminescence (ECL) aptamer-based biosensing based on bio-bar-code amplification was developed for the determination of cell surface proteins and specific cells. MCF-7 cells were used as target cells, mucin (MUC1) was used as target proteins, anti-MUC1 specific aptamers (rcDNA) were used as molecular recognition elements and Ru(phen)₃²⁺ was used as ECL signal molecules. A hairpin DNA (hpDNA) and a rcDNA were self-assembled on the surface of gold nanoparticles (AuNP) by self-assembly technique to obtain the bio-bar-code probe hpDNA/AuNP/rcDNA. rcDNA was modified onto the surface of gold electrodes to form a biosensing platform. A sandwich complex among rcDNA, target MUC1 (or MCF-7 cells) and hpDNA/AuNP/rcDNA was formed on the surface of electrodes. After Ru(phen)₃²⁺ was intercalated into hpDNA, strong ECL signals were generated in the presence of co-reactants at the constant potential of <sc>0.95 V</sc>. The increased ECL intensity was proportional to the logarithm of MUC1 concentration in the range of 4~800 pg/mL with a detection limit of 0.5 pg/mL. The increased ECL intensity was proportional to the logarithm concentration of MCF-7 cells in the range of 30~5×10⁴ cells/mL with a detection limit of 9 cells/mL. In addition, the developed ECL method was used to discriminate the MUC1 expression on different types of the cells and to monitor the dynamics of MUC1 on the surface of MCF-7 cells under the external drug stimulation, including apigenin and H₂O₂. The decline of MUC1 expression on the surface of MCF-7 cells was observed under apigenin treatment while inconspicuous MUC1 expression was observed under H₂O₂ treatment.

An electrogenerated chemiluminescence aptasensor for lysozyme based on the interaction between Ru(bpy)3 2+ and cucurbit[8]uril.

Strong anodic Ru(bpy)3 2+ electrogenerated chemiluminescence (ECL) was obtained at a cucurbil[8]uril (CB[8]) modified electrode in neutral conditions without the need of an additional coreactant. An ECL aptasensor was fabricated based on the strong ECL emission as well as the host-guest interaction between DNA and CB[8]. Firstly, amino group-terminated complementary DNA (DNA-NH2 ) was firmly immobilized on CB[8]/glass carbon electrode, which could further increase ECL intensity. Then, a ferrocene group-terminated lysozyme aptamer (Fc-DNA) was hybridized with complementary DNA. The inhibiting effect of ferrocene on Ru(bpy)3 2+ ECL resulted in the apparent decrease in ECL signal. When the modified electrode was incubated in lysozyme, specific binding between lysozyme and its aptamer could release the ferrocene group from the electrode surface, and the ECL emission was recovered. As a result, an 'on-off-on' mode ECL aptasensor for lysozyme was fabricated. In the range 0.14-140 pg ml-1 , the increased ECL intensities exhibited excellent linearity with the logarithm of lysozyme concentrations, and the detection limit was calculated as 0.093 pg ml-1 (3σ). The proposed ECL aptasensor exhibited satisfactory analytical performance, revealing the potential application of CB[n]s in an ECL sensing field.

Electrogenerated chemiluminescence biosensing method for DNA hydroxymethylation detection via glycosylation and a new multi-functional ECL signal compound

A simple electrogenerated chemiluminescence (ECL) biosensing method was proposed for specific detection of 5-hydroxymethylcytosine (5-hmC) in double-stranded DNA (5-hmC-dsDNA) on the basis of glycosylation and a new multi-functional ECL signal compound (N-(phthalhydrazide-4-yl)-thiophen-2-amino-5-boronic acid, PTAB). 5-hmC-dsDNA was chosen as the target, T4-β-Glucosyltransferase (β-GT) was as a molecular recognition element, and PTAB was as ECL signal reagent. PTAB includes the three main modules: 4-aminophthalhydrazide (isoluminol module), borinic acid module, and thiophene module. 5-hmC-dsDNA was glycosylated to glucosyl-5-hydroxymethylcytosine dsDNA (5-ghmC-dsDNA) by β-glucosyltransferase (β-GT); then, PTAB (boronic acid module) acted as a bridging agent to couple with 5-ghmC-dsDNA, yielding PTAB-5-ghmC-dsDNA; finally, the PTAB-5-ghmC-dsDNA (thiophene module) anchored to the gold surface via Au-S bond, the ECL signal parts (isoluminol module) was brought close to the biosensing electrode interface and the ECL enhanced simultaneously. The ECL intensity positively correlated with 5-hmC-dsDNA content in the range of 0.0090 % to 0.5761 %, with a detection limit of 0.0058 %. The proposed method was verified by detecting 5-hmC-dsDNA content in mice tissues. In addition, due to the multi-functional ECL signal compound, the presented strategy could be easily extended to ECL detection of various analytes with 1, 2- or 1, 3-diols sample, which provides a great potential for clinical applications.