Electrogenerated Chemiluminescence Detection Research Articles

Signal-on electrogenerated chemiluminescence detection of gonyautoxin 1/4 based on proximity ligation-induced an electrode-bound pseudoknot DNA

A “signal on” electrogenerated chemiluminescence (electrochemiluminescence, ECL) aptasensor based on proximity ligation-induced an electrode-bound pseudoknot DNA for sensitive detection of gonyautoxin 1/4 (GTX1/4) was developed on basis of the competitive type reaction mode. Aptamer was adopted as recognition element. Ru(bpy)32+ as ECL signal, was attached on the glassy carbon electrode (GCE) surface modified with nafion and gold nanoparticles (AuNPs) by electrostatic attraction to obtain the ECL platform. The pseudoknot DNA as capture probe, was immobilized onto the ECL platform via Au–S bond to obtain the ECL aptasensor. In the absence of GTX1/4, Y-shape proximate cooperative complex among aptamer, pseudoknot DNA and DNA1 was formed, drawing the ferrocene groups Fc, as ECL quencher) of both pseudoknot DNA and DNA1 near the electrode surface and resulting in low ECL signal. In the presence of GTX1/4, GTX1/4 competed with pseudoknot DNA and DNA1 for aptamer in homogeneous solution, preventing the formation of proximate cooperative complex and keeping the capture DNA in the pseudoknot conformation with Fc groups far away from the electrode surface, generating a high ECL signal. The recovery of ECL intensity increased with the GTX1/4 concentration and allowed the detection of GTX1/4 in the range of 0.01 ng/mL to 10 ng/mL with a detection of limit as low as 6.56 pg/mL. Additionally, the accuracy of this method was validated for analysis of spiked sea water samples with good recoveries, which indicates great potential in commercial application.

Sensitive and selective electrogenerated chemiluminescence aptasensing method for the determination of dopamine based on target-induced conformational displacement

Dopamine (DA) is an important neurotransmitter associated with many diseases. It is very significant to detect DA with high sensitivity and good selectivity. Here, a sensitive and selective electrogenerated chemiluminescence (ECL) aptasensing method was developed for the determination of DA based on target-induced conformational displacement. An anti-DA specific aptamer spliting into two ss-DNA (S1 and S2) was used as molecular recognition elements while an ss-DNA labeled with ferrocene (Fc-CS1, complementary to S1) was used as quenching probe. An ECL platform was prepared by dropping the mixture of Nafion, gold nanoparticles (AuNPs) and Ru(bpy)32+ onto glassy carbon electrode (GCE). After hybridization of S1 and Fc-CS1, ds-DNA (S1-CS1-Fc) was self-assembled onto the ECL platform to form an ECL aptasensing platform. In the presence of DA and S2, a S1-S2-DA complex was formed and then Fc-CS1 was released from the electrode surface, resulting in an increase of ECL intensity. DA can be sensitively detected in the range of 1.0 × 10-9 M to 5 × 10-8 M with a lower detection limit of 0.32 nM. This is first report of ECL aptasensing method for the determination of DA based on target-induced conformational displacement. The proposed ECL aptasensing method, exploiting both the aptamer recognition and ECL detection, allows direct detection of DA in diluted serum samples with high sensitivity and good selectivity, which may be further applicable in other neurochemicals assay and biomedical research.

Highly sensitive determination of capsaicin with tris(2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence

A highly sensitive tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy)32+] electrogenerated chemiluminescence (ECL) detection method for the determination of capsaicin has been developed. In this study, capsaicin was worked as a coreactant in the oxidative-reduction pathway of the Ru(bpy)32+ ECL. The oxidation of Ru(bpy)32+ together with coreactant capsaicin on a bare glassy carbon electrode at an applied potential of + 1.10 V vs. Ag/AgCl (3 M NaCl) led to a strong ECL emission. The Ru(bpy)32+ ECL emission of capsaicin was strongly dependent upon the buffer solution pH, in which a strong ECL was obtained in alkaline buffer solution. Under the optimized conditions, the present Ru(bpy)32+ ECL detection method showed a linear response to capsaicin in the linear range from 1.0 × 10-7 M to 1.0 × 10-4 M with a limit of detection of 9.4 × 10-8 M (S/N = 3). In addition, the present method can detect dihydrocapsaicin and nordihydrocapsaicin with a detection limit of 1.9 × 10-7 M and 2.2 × 10-7 M, respectively. The present ECL method shows good analytical performance for capsaicinoids in terms of linear dynamic range and detection limit compared to those obtained at other electrochemical methods even without the employment of additional modification of electrode surfaces to enhance the detection responses. In addition, no analyte preconcentration was required. The recovery tests performed for spiked capsaicin in real pepper samples were satisfactory with the recovery from 95% to 103%. To the best of our knowledge, this is the first report on the application of ECL for the quantitative determination of capsaicinoids. Since the present method is very simple, fast and sensitive, it could be applied for the determination of capsaicin in food and pharmaceuticals.

Anchoring luminol based on Ti3C2-mediated in situ formation of Au NPs for construction of an efficient probe for miRNA electrogenerated chemiluminescence detection.

An efficient electrogenerated chemiluminescence (ECL) nanoprobe (luminol-Au NPs-Ti3C2) was constructed based on Ti3C2Tx MXene (Ti3C2)-mediated in situ formation of Au NPs and anchoring luminol to fabricate a sensitive ECL biosensor for miRNA-155 detection. Herein, Ti3C2 with rich Ti vacancy defects was used as reducing agent, and Au NPs were generated in situ and anchored on the Ti3C2 (Au NPs-Ti3C2). Moreover, the Au NPs-Ti3C2 composites were used as a carrier and provided a large number of sites for the efficient linking of luminol through Au-N bonds to form stable luminol-Au NPs-Ti3C2. The immobilization of ECL emitters is a versatile strategy which not only shortens the electron transmission distance between luminol and electrode, but also provides naked catalytic predominated (111) facets of Au NPs with high electrocatalytic activity, significantly improving the ECL signal of luminol. Furthermore, a catalytic hairpin assembly (CHA) reaction was used, resulting in further amplification of the signal. As a result, the as-prepared ECL biosensor exhibited a linear range from 0.3 fM to 1nM with a detection limit of 0.15 fM, and demonstrated high reliability of miRNA-155 detection even in human serum samples. The construction of a multifunctional ECL probe with excellent ECL emission opens a new chapter for the application of Ti3C2 in the field of bioanalysis. Herein, Au NPs were generated in situ and anchored on the Ti3C2 (Au NPs-Ti3C2). Moreover, the Au NPs-Ti3C2 was used as a carrier and linked luminol through Au-N bonds to form a stable luminol-Au NPs-Ti3C2 nanoprobe. The strategy displayed versatility which not only shortened the electron transmission distance between luminol and the electrode, but also provided a catalytic surface with high electrocatalytic activity of Au NPs that significantly improved the ECL signal of luminol.

Electrogenerated chemiluminescence detection of single entities.

Electrogenerated chemiluminescence, also known as electrochemiluminescence (ECL), is an electrochemically induced production of light by excited luminophores generated during redox reactions. It can be used to sense the charge transfer and related processes at electrodes via a simple visual readout; hence, ECL is an outstanding tool in analytical sensing. The traditional ECL approach measures averaged electrochemical quantities of a large ensemble of individual entities, including molecules, microstructures and ions. However, as a real system is usually heterogeneous, the study of single entities holds great potential in elucidating new truths of nature which are averaged out in ensemble assays or hidden in complex systems. We would like to review the development of ECL intensity and imaging based single entity detection and place emphasis on the assays of small entities including single molecules, micro/nanoparticles and cells. The current challenges for and perspectives on ECL detection of single entities are also discussed.

Determination of tranexamic acid in essential cosmetics by pre-column derivatization capillary electrophoresis coupled with electrogenerated chemiluminescence detection

N-Methylation of tranexamic acid yields an unique derivative, which generates strong co-luminescence signals in the presence of an electrochemiluminescence reagent such as Ru(bpy)32+. Using this principle, we established a highly selective analytical method based on pre-column derivatization capillary electrophoresis coupled with electrogenerated chemiluminescence detection for determining the tranexamic acid content in essential cosmetics. The addition of a ternary ionic association gel, Mg2+-trehalose-SiO32-, in the components of background electrolyte greatly improved the electrophoretic separation efficiency. Under the optimized assay conditions, two electrophoretic peaks attributed to the derivatives of tranexamic acid and its internal standard (sarcosine) were completely separated in 500 s, and their electrophoretic peak intensities ratio showed a good linear relationship with the initial concentration of tranexamic acid in the range of 10-750 μmol/L (correlation coefficient r2=0.9993). The limit of detection was estimated to be 3.6 μmol/L (S/N=3). Moreover, the internal standard method was further applied to the quantitative determination of tranexamic acid content in three kinds of toothpaste and two kinds of nutrient solutions in facial masks. The results showed that the average tranexamic acid content in three toothpaste samples was 4.05, 0.24, and 6.06 mg/g, while that in two facial masks was 51.3 and 7.98 mg/mL. The recoveries for the above-mentioned samples were within the range 92.5% to 104.0%, implying satisfactory results.

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.

Reaction-Based Electrochemiluminescent Sensors for Selective Detection of Biochemical and Environmental Targets

Electrogenerated chemiluminescence (ECL) is a luminescent process which generates light through sequential electron transfer reactons on the electrode surface. ECL-based molecular sensors have several advantages over the conventional analytical techniques such as high sensitivity and low background signal. Additionally, the ECL provides the possibility of potential point-of-care-testing and field-monitoring with the simplicity of equipment and the method. However, ECL detection of small molecules is still a great challenge because most of ECL detection methods have been developed via specific biomacromolecular recognition such as antibody-antigen and aptamer-protein interactions. Herein, we report ECL molecular sensors for qualitative and quantitative detection of biologically important and environmentally toxic molecules.In the first part, a chemodosimetric approach will be introduced for one-step analysis of Hcy levels based on the ECL. A rationally designed cyclometalated iridium(III) complex possessing a phenylisoquinoline main ligand underwent a selective ring-formation reaction with Hcy to generate a binding adduct, which produced highly luminescent excited states, and yielded strong ECL signals on the surface of an electrode. The level of Hcy was successfully monitored by the ECL increment with a linear correlation between 0–40 µM in 99.9% aqueous media. The approach required neither sample preparation nor bulky instrument, suggesting the point-of-care testing of Hcy levels, and is potentially useful for routine, cost-effective, and precautionary diagnosis of various cardiovascular diseases. ECL sensors for other biologically important analytes (pyrophosphate, hydrogen sulfide, cysteine, H2O2) and environmentally toxic molecules (thiophenol, glyphosate, Hg(II)) will also be presented.In the second part, we report a totally different approach to discriminate a target among various interferences. This is called potential-dependent electrochemiluminescence. The iridium complex having a dicyanovinyl group on the main ligand cannot perfectly distinguish cyanide from sulfide and cysteine because not only cyanide but also sulfide and cysteine can attack the beta position of the dicyanovinyl group to increase the PL intensity. However, cyanide adduct is electrochemically oxidized at much less positive potential (~ 1.0 V) than those of sulfide and cysteine adducts, and this enables the discrimination of cyanide via ECL approach. This method enables complete removal of the interfering signals from sulfide and other thiols by controlling the potential range (0 – 1.4 V).

Enhanced biosensing strategies using electrogenerated chemiluminescence: recent progress and future prospects.

Ultrasensitive and highly accurate bioassays are critically required for the early detection of various biomarkers and diagnosis of cancer. Electrogenerated chemiluminescence (ECL) is one such technique which shows powerful analytical ability by incorporating ECL active species for sensitive detection of targets. In this regard, the development of ECL as an assay technique is constantly being pushed for better performance and lower detection limits. Incorporation of sensitive immunosensing and aptasensing methods with ECL has the ability to multiply the advantages several-fold. The recent progress in and methods utilized for the enhancement and amplification of ECL detection techniques based on highly sensitive immunosensors and aptasensors have been discussed in this review with regard to widely popular techniques.

Closed Bipolar Electrochemistry for the Detection of Human Immunodeficiency Virus Short Oligonucleotide

Although a monumental progress has been made in case of Human Immunodeficiency Virus researches, there are still more than 34 million people living with this viral disease. Therefore, the development of a fast and cost-effective protocol that can sensitively and selectively detect HIV gene sequence is essential. In the present study, a protocol for the molecular detection of HIV genome taking advantage of closed bipolar electrochemistry integrated with electrogenerated chemiluminescence detection is described. In this case, a closed split bipolar electrochemical cell is applied to detect the short specific oligonucleotide target of HIV1. Anthraquinone disulfonic acid, as a negative electroactive reporter, intercalates with hybridized double-strand DNA on the sensing site. By reduction of redox reporter (AQDS) on the cathodic pole, luminol is oxidized on the anodic pole and subsequent oxidized diazo product generates light that is followed using a photomultiplier tube. The experimental condition is optimized to obtain the highest sensitivity. The results demonstrate the high sensitivity and selectivity of this fast and economical method toward Human Immunodeficiency Virus genome detection in the range of 0.1 to 300nM with the detection limit of 30pM (S/N=3).

Investigation of perfluorooctanoic acid induced DNA damage using electrogenerated chemiluminescence associated with charge transfer in DNA.

An electrogenerated chemiluminescence (ECL)-DNA sensor was designed and fabricated for the investigation of DNA damage by a potential environmental pollutant, perfluorooctanoic acid (PFOA). The ECL-DNA sensor consisted of a Au electrode that had a self-assembled monolayer of 15 base-pair double-stranded (ds) DNA oligonucleotides with covalently attached semiconductor CdSe quantum dots (QDs) at the distal end of the DNA. Characterization of the ECL-DNA sensor was conducted with X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), ECL, and cyclic voltammetry before and after the exposure of the sensor to PFOA. Consistent data revealed that the dsDNA on Au was severely damaged upon the incubation of the electrode in PFOA, causing significant increase in charge (or electron) transfer(CT) resistance within DNA strands. Consequently, the cathodic coreactant ECL responses of the Au/dsDNA-QDs electrode in the presence of K2S2O8 were markedly decreased. The strong interaction between DNA and PFOA via the hydrophobic interaction, especially the formation of F···H hydrogen bonds by insertion of the difluoro-methylene group of PFOA into the DNA base pairs, was believed to be responsible for the dissociation or loosening of dsDNA structure, which inhibited the CT through DNA. A linear relationship between the ECL signal of the sensor and the logarithmical concentration of PFOA displayed a dynamic range of 1.00 × 10(-14)-1.00 × 10(-4) M, with a limit of detection of 1.00 × 10(-15) M at a signal-to-noise ratio of 3. Graphical Abstract Illustration of ECL detection of PFOA on a Au/dsDNA-QDs ECL-DNA sensor.

Considering the chemical energy requirements of the tri-n-propylamine co-reactant pathways for the judicious design of new electrogenerated chemiluminescence detection systems.

The introduction of a 'co-reactant' was a critical step in the evolution of electrogenerated chemiluminescence (ECL) from a laboratory curiosity to a widely utilised detection system. In conjunction with a suitable electrochemiluminophore, the co-reactant enables generation of both the oxidised and reduced precursors to the emitting species at a single electrode potential, under the aqueous conditions required for most analytical applications. The most commonly used co-reactant is tri-n-propylamine (TPrA), which was developed for the classic tris(2,2'-bipyridine)ruthenium(II) ECL reagent. New electrochemiluminophores such as cyclometalated iridium(III) complexes are also evaluated with this co-reactant. However, attaining the excited states in these systems can require much greater energy than that of tris(2,2'-bipyridine)ruthenium(II), which has implications for the co-reactant reaction pathways. In this tutorial review, we describe a simple graphical approach to characterise the energetically feasible ECL pathways with TPrA, as a useful tool for the development of new ECL detection systems.

Observation of Local Redox Events at Individual Au Nanoparticles Using Electrogenerated Chemiluminescence Microscopy

Au nanoparticles (NPs) are known to be able to enhance the oxidation of tripropylamine (TrPA) and the generation of electrogenerated chemiluminescence (ECL) from Ru(bpy)32+ when TrPA is used as a coreactant. Local redox activities of single Au NPs can therefore be investigated using the combined methods of voltammetry and ECL imaging. Our study shows that ECL generation at individual Au NPs increases with particle size (diameters from 30 to 300 nm) and is affected by the local chemical and charge transfer environment of the NPs. Such an ECL detection scheme can allow one to study the local redox activities of single nanoparticles with improved spatial resolution. ECL at single Au NPs shows slight temporal variations in intensity attributed to the oxidation and reconstruction of small clusters on the Au surface during ECL generation. Quantitative agreement between calculations and experiment concerning the effect of particle size and electrode potential on spatial and transient ECL profiles is presented.

Highly sensitive electrogenerated chemiluminescence biosensor based on hybridization chain reaction and amplification of gold nanoparticles for DNA detection

A one-target-triggered hybridization chain reaction (HCR) strategy was designed for high sensitive electrogenerated chemiluminescence (ECL) detection of DNA. The sensor was constructed by immobilizing a capture probe (CP) on a gold electrode via an Au–S bond. When target DNA (tDNA) was introduced, its 5′ terminus hybridized with the CP and the 3′ terminus hybridized with a concatamer. Then the long DNA concatamer, self-assembled by numerous biotinylated probes (auxiliary 1 and auxiliary 2), was firmly immobilized on the gold electrode via tDNA and CP. At last a large number of gold nanoparticles-streptavidin assembling on the DNA sensor surface by biotin–streptavidin system, which generates a magnificently amplified ECL signal in carbonate buffer solution (CBS) contains luminol. With the use of Human Immunodeficiency Virus type 1 (HIV-1) as a proof-of-principle analyte, this newly designed protocol provides highly sensitive ECL detection of HIV-1 with a limit of detection down to 5.0 fM, and also exhibit good selectivity in complex matrixes. Therefore, the proposed ECL-based method should have wide applications in diagnosis of genetic diseases due to its simplicity, low cost, and high sensitivity at extremely low concentrations.

Electrogenerated Chemiluminescence Bioanalytic System Based on Biocleavage of Probes and Homogeneous Detection.

A novel electrogenerated chemiluminescence (ECL) bioanalytic system based on biocleavage of a ECL probe and homogeneous detection was designed and utilized for the first time for highly sensitive quantification of proteases to overcome drawbacks from probes directly immobilized on electrodes and commercial ECL biosystems, based on bioaffinity reactions. Prostate-specific antigen (PSA) was taken as a model analyte and ruthenium complex-tagged specific peptide (CHSSKLQK) was designed as an ECL probe (peptide-Ru1). ECL bioconjugated magnetic beads were synthesized through a simple solid-phase synthesis. When analyte PSA was introduced into the suspension of ECL bioconjugated magnetic beads, a biocleavage of the peptide occurred and the cleaved Ru1 part was released from the magnetic beads. ECL measurement was carried out in the presence of co-reactant tripropylamine, using two models. One is homogeneous ECL detection on a bare graphite pencil electrode (PGE), and the other is enriching ECL detection after the cleaved Ru1 part of the peptide was concentrated into the surface film of Nafion/gold nanoparticles modified PGE (AuNPs/Nafion/PGE). The extremely low detection limit of 80 fg/mL and high reproducibility (relative standard deviation (RSD) of 5.4% for six measurements of 0.5 pg/mL) for the detection of PSA were achieved at AuNPs/Nafion/PGE. This work demonstrates that the bioanalytic system designed can not only quantify proteases with high sensitivity and selectivity, but also diminish the complicated electrode process and improve the reproducibility by conducting the biocleavage and transduction steps at different surfaces. It can be easily extended for ECL analysis of other proteases in this system and other detection techniques, including optics and electrochemistry.

Determination of Miglitol by Column-Switching Ion-Pair HPLC with Tris(2,2'-bipyridine)ruthenium(II)-Electrogenerated Chemiluminescence Detection.

We have developed a highly sensitive, simple method for the quantitative determination of miglitol in standard serum samples using column-switching ion-pair HPLC with tris(2,2'-bipyridine)ruthenium(II)-electrogenerated chemiluminescence detection. The serum samples were directly injected into a column-switching HPLC system with a Shim-pack MAYI-SCX precolumn to remove the serum matrix. Chromatographic separation of miglitol was achieved on a TSKgel ODS 100-V column using a mobile phase containing sodium 1-octanesulfonate as an ion-pair reagent. The detection and quantification limits of miglitol were 3 and 10 ng/mL, respectively. The calibration curve for miglitol in the serum samples showed good linearity (r(2)=0.9997) in the range of 10-2500 ng/mL. The recovery rate of miglitol from the serum samples was more than 94% as calculated from blank serum samples spiked with miglitol 50, 100, 500, 1000, and 2000 ng/mL. Therefore, this method can be applied to routine therapeutic monitoring of miglitol in serum samples.

Determination of Cyromazine and Melamine Based on Capillary Electrophoresis Coupled with Electrogenerated Chemiluminescence at Gold Nanoparticles Modified Electrode

A method has been developed for the detection of cyromazine and melamine using capillary electrophoresis (CE) coupled with electrogenerated chemiluminescence (ECL). The method utilized gold nanoparticles modified electrode as a working electrode because it can improve sensitivity of ECL detection. It has been found that acetonitrile can improve stacking in electrokinetic injection with field amplified sample stacking. The detection limits of 0.5 ng/mL and 1.0 ng/mL were obtained for cyromazine and melamine, respectively. The established method was successfully applied for milk sample analysis with good reproducibility, precision, accuracy, and high recovery.

Dual-peak electrogenerated chemiluminescence of carbon dots for iron ions detection.

Carbon dots (CDs) have rigorously been investigated on their unique fluorescent properties but rarely their electrogenerated chemiluminescence (ECL) behavior. We are here to report a dual-peak ECL system of CDs, one at -2.84 V (ECL-1) and the other at -1.71 V (ECL-2) during the cyclic sweep between -3.0 and 3.0 V at scan rate of 0.2 V s(-1) in 0.1 M tetrabutyl ammonium bromide (TBAB) ethanol solution, which is more efficiency to distinguish metallic ions than single-peak ECL. The electron transfer reaction between individual electrochemically reduced nanocrystal species and coreactants led to ECL-1, in which the electron injected to the conduction band of CDs in the cathodic process. Ion annihilation reactions induced direct formation of exciplexes that produced another ECL signal, ECL-2. ECL-1 showed higher sensitivity to the surrounding environment than ECL-2 and thus was used for ECL detection of metallic ions. Herein, we can serve as an internal standard method to detect iron ions. A linear relationship of the intensity ratio R of ECL-1 and ECL-2 to iron ions was observed in the concentration extending from 5 × 10(-6) to 8 × 10(-5) M with a detection limit of 7 × 10(-7) M.

Lab-on-paper-based devices using chemiluminescence and electrogenerated chemiluminescence detection

As an analytical support, paper, being low cost, highly abundant, of high porosity, disposable or biodegradable, and easy to use, store, transport, and print, has excellent chemical compatibility with many applications. Since the first microfluidic paper-based analytical device (μ-PAD or lab-on-paper) was proposed, the paper-based assay has never attracted as much attention as it does now. There has recently been rapidly increasing interest in using sensitive luminescence methods, for example chemiluminescence (CL) and electrogenerated chemiluminescence (ECL), as the detection strategy for lab-on-paper devices. Because of their intrinsic characteristics, CL and ECL provide outstanding performance while retaining the simplicity, low cost, multifunctionality, versatility, flexibility, and disposability of μ-PADs. The objective of this review is to cover the development of lab-on-paper-based devices using CL and ECL detection, including fabrication of paper devices, construction of sensing interfaces, signal amplification strategies, external instruments used, and applications. We believe that lab-on-paper devices with CL and ECL detection methods will meet the diverse requirements of point-of-care diagnosis.

Understanding Electrogenerated Chemiluminescence Efficiency in Blue‐Shifted Iridium(III)‐Complexes: An Experimental and Theoretical Study

Compared to tris(2-phenylpyridine)iridium(III) ([Ir(ppy)3 ]), iridium(III) complexes containing difluorophenylpyridine (df-ppy) and/or an ancillary triazolylpyridine ligand [3-phenyl-1,2,4-triazol-5-ylpyridinato (ptp) or 1-benzyl-1,2,3-triazol-4-ylpyridine (ptb)] exhibit considerable hypsochromic shifts (ca. 25-60 nm), due to the significant stabilising effect of these ligands on the HOMO energy, whilst having relatively little effect on the LUMO. Despite their lower photoluminescence quantum yields compared with [Ir(ppy)3 ] and [Ir(df-ppy)3 ], the iridium(III) complexes containing triazolylpyridine ligands gave greater electrogenerated chemiluminescence (ECL) intensities (using tri-n-propylamine (TPA) as a co-reactant), which can in part be ascribed to the more energetically favourable reactions of the oxidised complex (M(+) ) with both TPA and its neutral radical oxidation product. The calculated iridium(III) complex LUMO energies were shown to be a good predictor of the corresponding M(+) LUMO energies, and both HOMO and LUMO levels are related to ECL efficiency. The theoretical and experimental data together show that the best strategy for the design of efficient new blue-shifted electrochemiluminophores is to aim to stabilise the HOMO, while only moderately stabilising the LUMO, thereby increasing the energy gap but ensuring favourable thermodynamics and kinetics for the ECL reaction. Of the iridium(III) complexes examined, [Ir(df-ppy)2 (ptb)](+) was most attractive as a blue-emitter for ECL detection, featuring a large hypsochromic shift (λmax =454 and 484 nm), superior co-reactant ECL intensity than the archetypal homoleptic green and blue emitters: [Ir(ppy)3 ] and [Ir(df-ppy)3 ] (by over 16-fold and threefold, respectively), and greater solubility in polar solvents.