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Hot electron-induced electrochemiluminescence at cellulose derivatives-based composite electrodes
Abstract
The possibility of using cellulose derivative films as (i) insulating material on metal electrodes or (ii) in composite electrode films on metal to produce hot electron-induced electrochemiluminescence (HECL) was studied. It was shown that the luminophores known to produce HECL at thin insulating film coated cathodes (e.g. Si/SiO2 and Al2O3 electrodes) produced HECL with the present novel electrodes. In the case of composite films consisting of cellulose material doped with conducting carbon particles, the optimal cellulose/carbon black ratios were investigated by measuring the time-resolved HECL (TR-HECL) of an aromatic Tb(III) chelate. In addition to Tb(III) chelate, other well-known labels, fluorescein and Ru(bpy)3²⁺ chelate, were demonstrated to produce strong HECL at the present composite electrodes, which are more environmental friendly in disposable assay cartridges as the plastic-based composites we have studied previously. Thus, it is now possible on the present basis to manufacture biodegradable paper-based assay cartridges with HECL detection of labels at biodegradable electrodes. It was shown that the present composite films are stable over wide pH range, and also time-resolved detection of Ru(bpy)3²⁺ chelate is possible although its luminescence lifetime if quite short. The calibration curves were measured for presently used aromatic Tb(III) chelate and for Ru(bpy)3²⁺. The detection limit (s/n = 3) was 2 · 10⁻¹⁰ M for the Tb(III)-chelate and 4 · 10⁻⁹ M for Ru(bpy)3²⁺ in time-resolved detection mode. The relative standard deviation for Tb(III)-L1 (n = 5) emission at 10⁻⁵ M concentration was 2%. Wide linear range and low detection limits suggests that cellulose based composite electrodes can be used in HECL bioaffinity assays which was finally demonstrated here by an immunometric immunoassay.
... The main advantage of these novel electrodes over traditional insulating thin-film covered electrodes is their insensitivity to composite layer thickness and composition of the film [9,15,21,22]. Compared to thin insulating film-coated electrode materials, such as aluminum or silicon, composite electrodes are found to have a more stable and reproducible HECL output in a wider pH range, and most importantly, without considerable background emission [15,23,24]. Our research group has studied a few different composite electrode materials and found that the combination of (i) carbon black as a conductive material and (ii) polystyrene or ethyl cellulose as insulating binder materials is one of the best composite material to obtain a polymer layer doped with small conducting particles [15,24]. ...
... Compared to thin insulating film-coated electrode materials, such as aluminum or silicon, composite electrodes are found to have a more stable and reproducible HECL output in a wider pH range, and most importantly, without considerable background emission [15,23,24]. Our research group has studied a few different composite electrode materials and found that the combination of (i) carbon black as a conductive material and (ii) polystyrene or ethyl cellulose as insulating binder materials is one of the best composite material to obtain a polymer layer doped with small conducting particles [15,24]. ...
... Polystyrene is one of the most commonly used supportive substrate material in a wide variety of bioanalytical protocols, such as enzyme-linked immunosorbent assays and fluoroimmunoassays [15]. We have also studied cellulose derivatives to explore more environmentally friendly composite cathode materials and found ethyl cellulose to be a very suitable insulating material for composite film-coated cathodes [24]. The low material cost of these composite electrodes combined with the possibility of manufacturing them in mass with low technology methods (e.g., screen or inkjet printing), makes them an ideal disposable electrode choice for things like point-of-care testing. ...
Novel hot electron-emitting working electrodes and conventional counter electrodes were created by screen printing. Thus, low-cost disposable electrode chips for bioaffinity assays were produced to replace our older expensive electrode chips manufactured by manufacturing techniques of electronics from silicon or on glass chips. The present chips were created by printing as follows: (i) silver lines provided the electronic contacts, counter electrode and the bottom of the working electrode and counter electrode, (ii) the composite layer was printed on appropriate parts of the silver layer, and (iii) finally a hydrophobic ring was added to produce the electrochemical cell boundaries. The applicability of these electrode chips in bioaffinity assays was demonstrated by an immunoassay of human C-reactive protein (i) using Tb(III) chelate label displaying long-lived hot electron-induced electrochemiluminescence (HECL) and (ii) now for the first time fluorescein isothiocyanate (FITC) was utilized as an a low-cost organic label displaying a short-lived HECL in a real-world bioaffinity assay.
... Cellulose derivative continued to be a topic of research interest according to its abundant, easy handling, biodegradation [1][2][3]. Carboxymethyl cellulose which is termed CMC, is one of famous examples of cellulose derivatives. Even it is considered as the most used cellulose derivatives in the industry. ...
With the development of modern industrial technology, the residual heavy metal ions in environment-related matrices poses a serious threat to environmental and public health, because they could accumulate in human body and affect human health through the exposure of food chain. On account of this, it is of great significance to develop an efficient environmental surveillance and traceability assay toward heavy metal ions for thus establishing an efficient warning-early mechanism to safeguard environmental and public health. In this case, as an emerging technology, electrochemiluminescence (ECL)-based sensors have exhibited the promising potentials in various heavy metal ions monitoring with high sensitivity, near zero background signal, wide detection range, and low cost. To better promote the development of this field, we here summarized the recent progresses of the innovative ECL sensors for quantitative monitoring the residual levels of heavy metal ions (e.g., Hg²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Ni²⁺, Co²⁺, Ag⁺, Cr³⁺, Cr⁶⁺, Fe³⁺, & their coexistence) in environment-related matrices, profiled the inevitable challenges, and discussed the future perspectives. We expected that this timely and systematic review might offer the significant insights to develop the ECL technique-driven novel management systems, commercial point-of-care sensors, and efficient warning-early mechanisms for monitoring and controlling the residual pollutions of heavy metal ions in environment-related matrices, thus ensuring environmental and public health.
For hot electron-induced electrochemiluminescence (HECL), developing facile and controllable insulating layer on the electrode surface is key to the effective electron tunneling. Herein, a polystyrene modified glassy carbon electrode based the spin-coating was proposed for HECL. The constructed interface was characterized by atomic force microscopy (AFM). And HECL performance was investigated in details using the system of Ru(bpy)3²⁺ and S2O8²⁻. The as-prepared film shows the stable and reproducible HECL performance and the HECL mechanism was discussed using ECL spectra and hydrated electron quenchers. Finally, on the basis of the inhibition of SO4•-, the present polystyrene film was applied to the detection of rutin in the range of 0.1-1.3 μM with a detection limit of 90 nM (S/N = 3).
Electrochemiluminescence (ECL) is the light production triggered by reactions at the electrode surface. Its intrinsic features based on a dual electrochemical/photophysical nature have made it an attractive and powerful method across diverse fields in applied and fundamental research. Herein, we review the combination of ECL with semiconductor (SC) materials presenting various typical dimensions and structures, which has opened new uses of ECL and offered exciting opportunities for (bio)sensing and imaging. In particular, we highlight this particularly rich domain at the interface between photoelectrochemistry, SC material chemistry and analytical chemistry. After an introduction to the ECL and SC fundamentals, we gather the recent advances with representative examples of new strategies to generate ECL in original configurations. Indeed, bulk SC can be used as electrode materials with unusual ECL properties or light-addressable systems. At the nanoscale, the SC nanocrystals or quantum dots (QDs) constitute excellent bright ECL nano-emitters with tuneable emission wavelengths and remarkable stability. Finally, the challenges and future prospects are discussed for the design of new detection strategies in (bio)analytical chemistry, light-addressable systems, imaging or infrared devices.
The development of the hot electron‐induced cathodic electrochemiluminescence (HECL) often accompanied with the advance in the electrode materials and instruments. In this work, dimethyl silicone oil was employed as the coating layer for initiating the HECL. The insulating layer was obtained by simple drop casting and subsequent polishing, which can withstand high voltage and meet the requirement of HECL. With the as‐prepared interface, the quantitative detection of puerarin in the aqueous solution was achieved based on the quenching effect on the SO4·‐.
This paper presents a simple and inexpensive method to fabricate chemically and mechanically resistant hot electron-emitting composite electrodes on reusable substrates. In this study, the hot electron emitting composite electrodes were manufactured by doping a polymer, nylon 6,6, with few different brands of carbon particles (graphite, carbon black) and by coating metal substrates with the aforementioned composite ink layers with different carbon-polymer mass fractions. The optimal mass fractions in these composite layers allowed to fabricate composite electrodes that can inject hot electrons into aqueous electrolyte solutions and clearly generate hot electron-induced electrochemiluminescence (HECL). An aromatic terbium (III) chelate was used as a probe that is known not to be excited on the basis of traditional electrochemistry but to be efficiently electrically excited in the presence of hydrated electrons and during injection of hot electrons into aqueous solution. Thus, the presence of hot, pre-hydrated or hydrated electrons at the close vicinity of the composite electrode surface were monitored by HECL. The study shows that the extreme pH conditions could not damage the present composite electrodes. These low-cost, simplified and robust composite electrodes thus demonstrate that they can be used in HECL bioaffinity assays and other applications of hot electron electrochemistry.
Inflammation is widely considered to be an important contributing factor of the pathophysiology of coronary heart disease (CHD), and the inflammatory cascade is particularly important in the atherosclerotic process. In consideration of the important role that inflammatory processes play in CHD, recent work has been focused on whether biomarkers of inflammation may help to improve risk stratification and identify patient groups who might benefit from particular treatment strategies. Of these biomarkers, C-reactive protein (CRP) has emerged as one of the most important novel inflammatory markers. CRP an acute phase protein is synthesized by hepatocytes in response to proinflammatory cytokines, in particular interleukin-6. Many large-scale prospective studies demonstrate that CRP strongly and independently predicts adverse cardiovascular events, including myocardial infarction, ischemic stroke, and sudden cardiac death in individuals both with and without overt CHD. CRP is believed to be both a marker and a mediator of atherosclerosis and CHD. CRP plays a pivotal role in many aspects of atherogenesis including, activation of complement pathway, lipids uptake by macrophage, release of proinflammatory cytokines, induces the expression of tissue factor in monocytes, promotes the endothelial dysfunction and inhibits nitric oxide production. The commercial availability of CRP high sensitive assays has made screening for this marker simple, reliable, and reproducible and can be used as a clinical guide to diagnosis, management, and prognosis of CHD.
This work focused on studying the sensing efficiency of tetrahydrofuran (THF) by composite films made of thin layers of a cellulose-based polymer and carbon black. We analyze the reproducibility, durability, desorption time, and the sensitivity percent as a function of the amount of solvent. Two types of experiments were conducted, (1) progressive sensing test (PST) which consisted of progressively increasing the amount of solvent from 0.1 mL increments up to 1.0 mL and (2) multiple sensing test (MST) where the layers were subjected to consecutive pulses of the same amount of solvent, with a minimum of 0.1 mL and a maximum of 0.4 mL. The response and desorption times were a few seconds, and the sensitivity percent ranged from 1% to 170% and was dependent on the solvent quantity.
Spin-coated films of cellulose acetate (CA), cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB) and carboxymethylcellulose
acetate butyrate (CMCAB) have been characterized by ellipsometry, atomic force microscopy (AFM) and contact angle measurements.
The films were spin-coated onto silicon wafers, a polar surface. Mean thickness values were determined by means of ellipsometry
and AFM as a function of polymer concentration in solutions prepared either in acetone or in ethyl acetate (EA), both are
good solvents for the cellulose esters. The results were discussed in the light of solvent evaporation rate and interaction
energy between substrate and solvent. The effects of annealing and type of cellulose ester on film thickness, film morphology,
surface roughness and surface wettability were also investigated.
Celluloses and nanofibrillar celluloses, and the basis of their luminescence are studied. Comparative studies of photoluminescence of birch kraft pulp and microfibrillar and nanofibrillar celluloses manufactured from the same pulp were made with the aim to investigate their luminescence properties. Comparison was made with the earlier literature and the origin of the photoluminescence of these cellulose variants is discussed.
Aromatic Tb(III) chelates can be detected down to subnanomolar concentrations at polystyrene-carbon black composite electrodes on the basis of hot electron-induced electrochemiluminescence, and used as electrochemiluminescent labels in bioaffinity assays. The excitation mechanism is based on chemiluminescent reactions that are initiated by the field emission/tunnel emission of hot electrons from the composite electrode. The composition and the properties of the novel composite electrodes were studied in detail. Hot electron-induced electrochemiluminescence intensities obtainable with the present composite electrodes are comparable to the previously used metal/insulator-type electrodes without exhibiting considerable long-lived solid state electroluminescence background emission, unlike e.g. oxide-coated silicon and aluminum electrodes.
C-reactive protein was finally determined in a heterogeneous sandwich-assay by using the present composite electrodes as a solid support material for the capture antibodies. The detection antibody was labeled with a commercially available Tb(II) chelate. Calibration curve for the determination of C-reactive protein was linear over two orders of magnitude and the detection limit was well below the clinical reference value, approx. 1 μg l⁻¹. Disposable polystyrene-carbon black composite electrodes are superior alternatives for e.g. silicon-based electrodes due to the low cost, easier manufacturing process and a very good performance e.g. in immunoassays.
Hot electron-induced electrochemiluminescence (HECL) of calcein and calcein-Tb(III) complex was generated at oxide-covered aluminum electrode during cathodic pulse polarization. The excitation of calcein as a molecule or as a ligand is based on subsequent one-electron oxidation and reduction steps by oxidizing radicals and solvated electrons. During HECL excitation of calcein-Tb(III) solution a reaction product of the calcein is formed that also enables the photoexcitation of Tb(III) via the formed ligand derivative by ligand-sensitized mechanism. The determination of low concentrations of calcein with aluminum electrodes was complicated by a relatively strong background electroluminescence originating from the Al2O3-layer. Polyvinyl butyral-carbon black composite electrodes coated on brass were fabricated to solve this problem and a fifty-fold lower background emission was obtained for these novel composite electrodes in comparison to that of oxide-covered 99.9% pure aluminum electrodes. The obtained detection limits were 3.2·10⁻¹⁰ M for calcein and 6.4·10⁻⁹ M for calcein-Tb(III) at the present composite electrodes. These species could potentially be utilized as electrochemiluminescent labels in bioaffinity assays.
Tb(III) chelates exhibit intense hot electron-induced electrogenerated chemiluminescence during cathodic polarization of metal/polystyrene-graphite (M/PG) electrodes in fully aqueous solutions. The M/PG working electrode provides a sensitive means for the determination of aromatic Tb(III) chelates at nanomolar concentration levels with a linear log-log calibration curve spanning more than five orders of magnitude. The charge transport and other properties of these novel electrodes were studied by electrochemiluminescence measurements and cyclic voltammetry. The present composite electrodes can by utilized both under pulse polarization and DC polarization unlike oxide-coated metal electrodes which do not tolerate cathodic DC polarization. The present cost-effective electrodes could be utilized e.g. in immunoassays where polystyrene is extensively used as a solid phase for various bioaffinity assays by using electrochemiluminescent Tb(III) chelates or e.g. Ru(bpy)3²⁺as labels.
Various luminophores produce strong electrogenerated chemiluminescence during cathodic pulse polarization of the present insulating film-covered carbon paste electrodes in fully aqueous solutions. First electrodes made of a commercial conductive carbon paste were successfully utilized as working electrodes and their surface was characterized by ESCA. Then custom in-laboratory made improved composite electrodes were manufactured from the same insulating polymer and conducting carbon black particles. The relationship between the amount of carbon present on the composite electrode, in the bulk and on the surface, and the intensity of electrogenerated chemiluminescence was studied further. The overall performance of these composite electrodes makes them viable low-cost replacements for metal/insulator type electrodes such as oxide-coated silicon electrodes.
The heterogeneous immunoassay of thyroid stimulating hormone (TSH) was detected by the time-resolved cathodic electrochemiluminescence immunoassay (tr-CECLIA) method using magnetic beads as a mobile support. The magnetic beads coated with sandwich type TSH immunoassay were captured with a magnet for washing and detection processes. The time-resolved cathodic electrochemiluminescence (tr-CECL) signal of Tb(III) chelate label was generated by cathodic pulse polarization in the aluminum working electrode and platinum counter electrode system. The detection method causes injection of high energy electrons into the aqueous solution near the aluminum electrode and creates rigid simultaneous oxidative and reductive conditions that excitate the Tb(III) chelate used as a label luminophore in the heterogeneous sandwich type immunoassay of TSH in the surface of the magnetic beads. The limit of detection of the method was about 50 mIU L⁻¹. The precision of it was noticed to be good; the coefficient variation percentage was realized to be lower than 10 %. Unfortunately the limit of detection is not good enough for determination of analyte levels of very low concentrations for instance TSH in body fluids. The possible application areas of the method are in highly sophisticated micro or nano fluidic detection and sensor systems where the aspiration level of the analyte detection limit is not very high and the mobility and manageability and the large surface area of the magnetic beads can be utilized efficiently in separating, washing, moving, coating and detecting processes. In the case of tr-CECLIA the presented method makes possible to use multipurpose working electrodes instead of disposable ones.
Tris(2,2′-bipyridine)ruthenium(II) chelate exhibits strong electrogenerated chemiluminescence during cathodic high-voltage pulse-polarization of pointed Pt electrode in aqueous solutions. The present method is based on a field emission or other type of tunnel emission of hot electrons into an aqueous electrolyte solution. The method allows the detection of tris(2,2′-bipyridine)ruthenium(II) and its derivatives below nanomolar concentration levels and yields linear log-log calibration plots spanning several orders of magnitude of concentration.
La profesion –formacion- docente es un tema crucial en los actuales debates educativos. La existencia de dos decretos y el desplazamiento del verdadero sentido del ser maestro reclaman de los analisis un ejercicio de comprension del orden discursivo oficial. La calidad es el sustrato de la sociedad de control. En este marco se agencia nuevas practicas de subjetivacion del maestro los cuales podriamos situar en la calidad, flexibilidad, adaptabilidad, eficiencia, eficacia. En cualquier caso, el esfuerzo por hacer del maestro un intelectual de la educacion fue borrado. La gran cuestion consiste en saber que discursos regula el saber del docente a la luz de la sociedad de control.
Hot electron induced cathodic electrochemiluminescence (ECL) was observed at screen printed carbon electrodes (SPCEs) during pulse polarization. The thin insulating film resulted from the printing inks was found to be suitable for generating hot electrons, which can further be converted to hydrated electrons and induce the subsequent luminescence. Compared with disposable Al/Al2O3 electrode, SPCEs show more stable and reproducible ECL in a wider pH range without background emission. A sensitive ECL method for determination of quercetin is proposed. The detection limit is 8.0×10−10 mol L−1(S/N=3), which is two magnitudes lower than that of common ECL method.
Kinetic data for the radicals H⋅ and ⋅OH in aqueous solution,and the corresponding radical anions, ⋅O− and eaq−, have been critically pulse radiolysis, flash photolysis and other methods. Rate constants for over 3500 reaction are tabulated, including reaction with molecules, ions and other radicals derived from inorganic and organic solutes.
This paper deals with the preparation, structural characterization, and physical performances of composites composed of biomass-based cellulose acetate propionate (CAP) and exfoliated graphene (EG). As a reinforcing nanofiller, EG is thus prepared by an oxidation/thermal expansion process of natural graphite flakes and it is characterized to consist of disordered graphene platelets. Structural features, thermal stability, mechanical modulus, and electrical resistivity of CAP/EG composites are investigated as a function of EG content. SEM and X-ray diffraction data demonstrate that graphene platelets of EG are well dispersed and exfoliated in the CAP matrix for the composites with up to ∼1 wt.% EG, although they are partially aggregated in the composites with higher EG contents above ∼3 wt.%. Thermo-oxidative stability of CAP/EG composites under active oxygen gas condition is improved substantially due to the gas barrier effect of graphene platelets of EG dispersed in the CAP matrix. Dynamic mechanical modulus of the composites is also enhanced significantly with increasing the EG content. This mechanical enhancement of CAP/EG composites is analyzed by adopting the Halpin–Tsai model. The electrical volume resistivity of CAP/EG composites prepared by melt-compounding is decreased dramatically from ∼1015 to ∼106 Ω cm by forming the electrical conduction path at a certain EG content between 5 and 7 wt.%.
Luminol-specific extrinsic lyoluminescence of UV-irradiated potassium peroxodiphosphate and potassium nitrate has been studied. UV irradiation of solid peroxodiphosphate can induce rupture of the peroxide bond and produce a stable solid solution of phosphate radicals in potassium peroxodiphosphate. The dissolution of the irradiated salt can liberate phosphate radicals which initiate a luminol chemiluminescence-generating pathway in alkaline solution. UV irradiation of solid potassium nitrate induces partial photoisomerisation to potassium peroxonitrite, which has been previously reported to generate hydroxyl radicals during dissolution in aqueous solution. Support for hydroxyl radical generation was obtained and the hydroxyl radical was observed to be a key intermediate for strong chemiluminescence of luminol during dissolution of irradiated KNO3 in luminol sample solutions. Both lyoluminescence systems allow the detection of luminol down to sub-nM levels with linear calibration curves spanning five orders of magnitude of luminol concentration, suggesting that they can be used as tools in bioaffinity assays utilising luminol and isoluminol derivatives as labels.
Light emission from aluminium oxide during cathodic pulse-polarisation of oxide-covered aluminium in aqueous solution was observed to be strongly enhanced in the presence of peroxydisulfate ions. The spectrum of the light emission had a broad maximum between 400 and 450 nm being attributed to F-centre luminescence of aluminium oxide. The mechanism of the luminescence is associated with the two-step reduction of peroxydisulfate anions near the oxide-covered cathode where the first one-electronic reduction step occurs either (i) by tunnel-emission generated hydrated electrons or (ii) by trickling down the surface states to the energy level of peroxydisulfate ion or (iii) by direct heterogeneous electron transfer from the bottom of the aluminium oxide conduction band to peroxydisulfate ions during strong downward band bending induced by cathodic pulse-polarisation. The second step occurs by electrons from F- or F
+
-centres at the oxide/electrolyte interface. Transitions of aluminium oxide conduction band electrons to fill the sulfate radical-emptied electron trapping sites (oxygen vacancies) produces analogous F- and F
+
-centre luminescence to that occurring during photoluminescence and thermoluminescence of aluminium oxide. No enhancement of light emission was observed in the presence of hydrogen peroxide which is also reduced in a two-step process at oxide-covered aluminium electrode. This can be explained by the fact that the energy level of hydroxyl radical under the present conditions lies ca. 1 eV above, whereas the energy level of sulfate radical lies somewhat below the colour-centre sub-band of aluminium oxide. Therefore, the sulfate radical is a sufficiently strong oxidant but the hydroxyl radical is too weak an oxidant to abstract electrons from F- and F
+
-centres.
Hot electron injection into aqueous electrolyte solutions
from metal/insulator/metal/electrolyte and
metal/insulator/electrolyte tunnel junctions is considered
and the possibility of an electrochemical generation of
hydrated electrons is discussed. The hot electron-induced UV
electrochemiluminescence of (9-fluorenyl)methanol was used
to demonstrate the presence of highly energetic transient
species in aqueous solution at several
metal/insulator/electrolyte hot electron tunnel emitters.
These transient species cannot be produced electrochemically
in fully aqueous solutions at any active metal electrodes. A
detailed mechanism for the present electrochemiluminescence
is suggested.
Experimental evidence for the production of hot electrons in an acetonitrile solution from a Ta2O5-covered Ta electrode was provided by electrogenerated chemiluminescence (ECL) and electrochemical measurements. Electron transfer to solution species occurred via the Ta2O5 conduction band, as demonstrated by comparative measurements with a number of one-electron redox couples at Pt and Ta electrodes. The oxidized forms of thianthrene and a heptamethine cyanine dye were selected as the species capable of direct formation of the excited state and ECL upon hot electron injection. The observation of ECL emission upon a cathodic potential step (a process that does not occur at a metal electrode) confirmed the occurrence of this process. ECL emission at Ta/Ta2O5 was also observed during reduction of Ru(bpy)33+ (bpy = bipyridine). Reasons for the low efficiency of the ECL process via hot electrons at the metal/metal oxide/solution interface are discussed.
Ruthenium(II) tris-(2,2‘-bipyridine) chelate exhibits strong electrogenerated chemiluminescence during cathodic pulse polarization of oxide-covered aluminum electrodes in aqueous solutions. The present method is based on a tunnel emission of hot electrons into an aqueous electrolyte solution. The method allows the detection of ruthenium(II) tris-(2,2‘-bipyridine) and its derivatives below nanomolar concentration levels and yields linear log−log calibration plots spanning several orders of magnitude of concentration. This method allows simultaneous excitation of derivatives of ruthenium(II) tris-(2,2‘-bipyridine) and Tb(III)-chelates. The former label compounds have a luminescence lifetime of the order of microseconds, while the latter compounds generally have a luminescence lifetime of around 2 ms. Thus, the combined use of these labels easily provides the basis for two-parameter bioaffinity assays by either using wavelength or time discrimination or their combination.
Paper-based analytical devices are the subject of growing interest for the development of low-cost point-of-care diagnostics, environmental monitoring technologies, and research tools for limited-resource settings. However, there are limited chemistries available for the conjugation of biomolecules to cellulose for use in biomedical applications. Herein, divinyl sulfone (DVS) chemistry was demonstrated to immobilize small molecules, proteins, and DNA covalently onto the hydroxyl groups of cellulose membranes through nucleophilic addition. Assays on modified cellulose using protein-carbohydrate and protein-glycoprotein interactions as well as oligonucleotide hybridization showed that the membrane's bioactivity was specific, dose-dependent, and stable over a long period of time. The use of an inkjet printer to form patterns of biomolecules on DVS-activated cellulose illustrates the adaptability of the DVS functionalization technique to pattern sophisticated designs, with potential applications in cellulose-based lateral flow devices.
In this chapter, we discuss the basics of cathodic hot electron-induced electrogenerated chemiluminescence (HECL). In the
applications of HECL, we discuss, e.g., the usable electrode materials and their advantages as well as the applicable solution
conditions in aqueous media. We also summarize the luminophore types excitable by this method and their usability as labels
in practical bioaffinity assay applications.
Aromatic Gd(III) and Y(III) chelates produce ligand-centered emissions during cathodic pulse polarization of oxide-covered
aluminum electrodes, while the corresponding Tb(III) chelates produce metal-centered5D4 →7Fj emissions. It was observed that a redox-inert paramagnetic heavy lanthanoid ion, Gd(III), seems to enhance strongly intersystem
crossing in the excited ligand and direct the deexcitation toward a triplet-state emission, while a lighter diamagnetic Y(III)
ion directs the photophysical processes toward a singlet-state emission of the ligand. The luminescence lifetime of Y(III)
chelates was too short to be measured with our apparatus, but the luminescence lifetime of Gd(III) chelates was between 20
and 70 μs. The mechanisms of the ECL processes are discussed in detail.
The question posed in the title has been addressed by studying the swelling of celluloses at 20 °C by twenty protic solvents, including water; linear- and branched-chain aliphatic alcohols; unsaturated aliphatic alcohols, and alkoxyalcohols. The biopolymers investigated included microcrystalline cellulose, MC, native and never-dried mercerized cotton cellulose, cotton and M-cotton, and native and never-dried mercerized eucalyptus cellulose, eucalyptus and M-eucalyptus, respectively. In most cases, better correlations with the physico-chemical properties of the solvents were obtained when the swelling was expressed as number of moles of solvent/anhydroglucose unit, nSw, rather than as % increase in sample weight. The descriptors employed in these correlations included, where available, Hildebrand’s solubility parameters, Gutmann’s acceptor and donor numbers, solvent molar volume, VS, as well as solvatochromic parameters. The latter, employed for the first time for correlating the swelling of biopolymers, included empirical solvent polarity, ET(30), solvent “acidity”, αS, “basicity”, βS, and dipolarity/polarizability, π
S*, respectively. Small regression coefficients and large sums of the squares of the residues were obtained when values of nSw were correlated with two solvent parameters. Much better correlations were obtained with three solvent parameters. The most statistically significant descriptor in the correlation equation depends on the cellulose, being π
S* for MC, cotton, and eucalyptus, and VS for M-cotton and M-eucalyptus. The best correlations were obtained with the same set of four parameters for all celluloses, namely, solvent pKa (or αS) βS, π
S*, and VS, respectively. These results indicate that the supra-molecular structure of the biopolymer, in particular the average sizes of crystallites and micro-pores, and the presence of its chains in parallel (cellulose I) or anti-parallel (cellulose II) arrangements control its swelling. At least for the present biopolymer/solvent systems, use of solvatochromic parameters is a superior alternative to Hildebrand’s solubility parameters and/or Gutmann’s acceptor and donor numbers. The relevance of these results to the accessibility of the hydroxyl groups of cellulose, hence to its reactivity, is briefly discussed.
Hot electron injection into aqueous electrolyte solution was studied with electrochemiluminescence and electron paramagnetic
resonance (EPR) methods. Both methods provide further indirect support for the previously proposed hot electron emission mechanisms
from thin insulating film-coated electrodes to aqueous electrolyte solution. The results do not rule out the possibility of
hydrated electron being as a cathodic intermediate in the reduction reactions at cathodically pulse-polarized thin insulating
film-coated electrodes. However, no direct evidence for electrochemical generation of hydrated electrons could be obtained
with EPR, only spin-trapping experiments could give information about the primary cathodic steps.
High amplitude cathodic pulse polarization of ultra thin oxide film-coated heavily doped silicon electrodes induces tunnel emission of hot electrons into aqueous electrolyte solution, which probably results in the generation of hydrated electrons in the vicinity of the electrode surface. The method allows the detection of tris (2,2'-bipyridine) ruthenium(II) chelate at subnanomolar concentration level. This paper shows that both n- and p-type heavily doped silicon electrodes can be used, illustrates the effect of oxide film thickness upon the silicon electrode on the intensity of ECL of tris (2,2'-bipyridine) ruthenium(II) and discusses the basic features of tris (2,2'-bipyridine) ruthenium(II) chelate-specific ECL at these electrodes. Thin oxide film-coated silicon electrodes provide a lower blank emission and a higher ECL intensity of the present ruthenium chelate than oxide-covered aluminium electrodes. This suggests that thin oxide film-coated silicon is a very promising working electrode material, especially in microanalytical systems made fully or partly of silicon. (c) 2004 Elsevier B.V. All rights reserved.
The primary processes occurring at cathodically polarized oxide-covered aluminum electrode are discussed in detail. It is pointed out that more energetic cathodic processes can be induced in aqueous media at thin insulating film-coated electrodes than at any semiconductor or active metal electrode. It is proposed that tunnel emission of hot electrons with energies well above the level of the conduction band edge of water occur, and the thermalization and solvation of the emitted electrons can result in generation of hydrated electrons. The cathodically pulse-polarized oxide-covered aluminum also generates a strong oxidant (or oxidants) at the oxide/electrolyte interface, and it is proposed that this species is the hydroxyl radical which is generated either by cathodic high field-induced ejection of self-trapped holes as oxygen dianions (i.e. oxide radical ions) into the electrolyte solution, or by the action of anion vacancies and/or F+-centers as the primary oxidants capable of oxidizing hydroxide ions or the hydroxyl groups of the hydroxylated surface on the oxide film. These radicals, hydrated electrons/hydroxyl radicals, can act as mediating reductants/oxidants in reduction/oxidation of solutes. The formation of the primary species is monitored by electrochemiluminophores which cannot be cathodically excited at active metal electrodes in fully aqueous solutions, but which can be chemically excited in aqueous media in the simultaneous presence of highly reducing and highly oxidizing radicals.
Hot electrons emitted from thin oxide film-coated heavily doped silicon electrodes by cathodic pulse polarization can induce electrochemiluminescence from luminophores. The intensity of electrochemiluminescence produced at the electrode surface is dependent on the features of thin oxide films formed by thermal oxidation. As a preliminary study, we investigated the effect of thermal oxide growth conditions on the intensity of electrochemiluminescence produced at these electrodes, such as oxidation atmospheres, oxidation temperature, oxidation time and pre-treatment of wafers, using ruthenium(II) tris-(2,2′-bipyridine) chelate as a model luminophore. Optimal oxidation conditions of heavily doped silicon electrodes were obtained for the generation of intense electrochemiluminescence at this kind of silicon electrodes.
C-reactive protein (CRP) was determined in the concentration range 0.01-10 mg L(-1) using hot electron induced electrochemiluminescence (HECL) with devices combining both working and counter electrodes and sample confinement on a single chip. The sample area on the electrodes was defined by a hydrophobic ring, which enabled dispensing the reagents and the analyte directly on the electrode. Immunoassay of CRP by HECL using integrated electrodes is a good candidate for a high-sensitivity point-of-care CRP-test, because the concentration range is suitable, miniaturisation of the measurement system has been demonstrated and the assay method with integrated electrodes is easy to use. High-sensitivity CRP tests can be used to monitor the current state of cardiovascular disease and also to predict future cardiovascular problems in apparently healthy people.
Cathodic electrochemiluminescence (ECL) is firstly observed at a carbon oxide covered glassy carbon (C/C(x)O(1-x)) electrode as a large cathodic pulse polarization is applied. This insulating carbon oxide (C(x)O(1-x)) film is constructed on a glassy carbon (GC) substrate by electrochemical oxidization in basic media. The film properties, such as the composition of carbon and oxygen, and the thickness as well, can be controlled by the potential and the duration in the oxidizing process. X-Ray photoelectron spectroscopy (XPS) studies show that carbonyl and carboxyl dominate at the oxidized surface, to which antibodies can be covalently bound. The specific immunoreaction between antigen (Ag) and antibody (Ab) resulted in a decrease in the ECL intensity, thus creating an interesting basis for the development of a label-free cathodic ECL immunosensor. As an example, human IgG (hIgG) was sensitively determined in the concentration range of 0.01-100 ng mL(-1), and the detection limit was ca. 1.0 pg mL (-1) (S/N = 3). In addition, the content of hIgG in human serum has been assayed by the developed immunosensor and a commercially available immune turbidimetry method, respectively, and consistent results were obtained. The prepared immunosensor provides a promising approach for the clinical determination of IgG levels in human serum, because it is simple, rapid, highly sensitive, specific, and without the need of tedious labeling operations.
Cathodic pulse polarisation of thin insulating film-coated electrodes enables the generation of electrochemiluminescence (ECL) by tunnel emission of hot electrons from the Fermi level of the conductor material of the conductor–insulator–aqueous electrolyte solution junction to the solutes at the vicinity of the electrode surface and probably also to the conduction band of water. The latter process can generate hydrated electrons as strongly reducing slightly longer-lived cathodic intermediates, which are known to be able to induce chemiluminescence (CL) of various types of luminophores having very different photophysical and chemical properties. The generation of the above-mentioned cathodic primary species provides good possibilities to use many types of luminophores as label molecules in sensitive immuno and DNA-probing assays. This paper introduces an electrochemiluminoimmunoassay (ECLIA) for human thyroid stimulating hormone (hTSH) at oxide-coated n-silicon electrodes and demonstrates the suitability of silicon electrodes covered with thermally grown silicon dioxide film as disposable working electrodes (WEs) in sensitive time-resolved ECL (tr-ECL) measurements in aqueous solution. The label chelate can be detected almost down to picomolar level and the calibration curve of the chelate covers more than five orders of magnitude of chelate concentration. Also the calibration curve of the immunometric hTSH assay was found to be linear over a wide range of hTSH concentration, the detection limit of the hormone being below 1 mU l−1 (4 pmol l−1).
Electrochemiluminescence (ECL) of aromatic Tb(III) chelates at thin insulating film-coated electrodes provides a means for extremely sensitive detection of Tb(III) chelates and also of biologically interesting compounds if these chelates are used as labels in bioaffinity assays. The suitability of silicon electrodes coated with thermally grown silicon dioxide film as disposable working electrodes in sensitive time-resolved ECL measurements is demonstrated, and a rapid electrochemiluminoimmunoassay (ECLIA) of human C-reactive protein (hCRP) is described. Tb(III) chelate labels can be detected almost down to picomolar level, and the calibration curve of these labels covers more than 6 orders of magnitude of chelate concentration. The calibration curve of the present immunometric hCRP assay was found to be linear over a wide range, approximately 4 orders of magnitude of hCRP concentration, the detection limit of the protein being 0.3 ng mL(-1) (mean background + 2SD) on CV values of about 10-30%, depending on the immunoassay incubation time. In the ECLIA measurements, different incubation times were tested from 15 min (giving above-mentioned performance) to as short as only 2 min, which still gave successful results with approximately 20,000 times better detection limit levels than traditional commercial assay methods. During the ECLIA process, also the Si electrode surface morphology was also investigated by atomic force microscope monitoring.
Strong electrogenerated chemiluminescence (ECL) of fluorescein is generated during cathodic pulse polarization of oxide-covered aluminum electrodes and the resulting decay of emission is so sluggish that time-resolved detection of fluorescein is feasible. The present ECL in aqueous solution is based on the tunnel emission of hot electrons into the aqueous electrolyte solution, which probably results in the generation of hydrated electrons and hydroxyl radicals acting as redox mediators. The successive one-electron redox steps with the primary radicals result in fluorescein in its lowest excited singlet state. The method allows the detection of fluorescein (or its derivatives containing usable linking groups to biomolecules) over several orders of magnitude of concentration with detection limits well below nanomolar concentration level. The detection limits can still be lowered, e.g., by addition of azide or bromide ions as coreactants. The results suggest that the derivatives of fluorescein, such as fluorescein isothiocyanate (FITC), can be detected by time-resolved measurements and thus be efficiently used as electrochemiluminescent labels in bioaffinity assays.
This paper describes a heterogeneous DNA-hybridization assay based on electrochemiluminescence (ECL) detection on gold electrodes. Short, 15-mer oligonucleotides were conjugated with a synthesized electrochemiluminescent label, bis(2,2'-bipyridine)-5-isothiocyanato-1,10-phenanthroline ruthenium(II) at the amino-modified 5'-end. Gold electrodes were derivatized with 15-mer oligonucleotide probes via 1-(3-(dimethylamino)propyl)-3-ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) cross-linking reaction and hybridized with Ru-labeled strands. Two types of self-assembled-monolayers have been utilized for the immobilization reaction, 3-mercaptopropanoic acid (3-MHA) and 16-mercaptohexadecanoic acid (16-MHA). Longer thiols were more stable at high electrode potentials needed for the ECL generation. The system was sensitive down to 1 fmol of labeled complementary strand, detected in 30 microL of buffer. Mismatch discrimination was achieved both passively by washing and actively by application of negative electrode potential on electrodes prior to detection, but active denaturing lead to better results. Two base-pair mismatches were discriminated at room temperature.
Generation of free radicals and electrochemiluminescence at pulse-polarized oxide-covered silicon electrodes in aqueous solutions
- T Ala-Kleme
- S Kulmala
- M Latva
T. Ala-Kleme, S. Kulmala, M. Latva, Generation of free radicals and electrochemiluminescence at pulse-polarized oxide-covered silicon electrodes in aqueous
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Bioanalytical advances in assays for C-reactive protein
- S K Vashist
- A G Venkatesh
- E Marion Schneider
- C Beaudoin
- P B Luppa
- J H T Luong
S.K. Vashist, A.G. Venkatesh, E. Marion Schneider, C. Beaudoin, P.B. Luppa,
J.H.T. Luong, Bioanalytical advances in assays for C-reactive protein, Biotechnol.
Adv. 34 (2016) 272-290, https://doi.org/10.1016/j.biotechadv.2015.12.010.
- P Grönroos
P. Grönroos et al.
Journal of Electroanalytical Chemistry 833 (2019) 349-356