Definition and Mechanism of Electrochemiluminescence
– Electrochemiluminescence (ECL) is a type of luminescence produced during electrochemical reactions in solutions.
– ECL occurs when electrochemically generated intermediates undergo a highly exergonic reaction, resulting in the emission of light.
– The wavelength of the emitted light corresponds to the energy gap between the excited and lower-level states of the intermediates.
– ECL can be induced by energetic electron transfer reactions of electrogenerated species.
– Luminescent species can be produced in both oxidized and reduced forms in organic solvents by sweeping the electrode potential.
Applications of Electrochemiluminescence
– ECL is widely used in analytical applications due to its high sensitivity and selectivity.
– It combines the advantages of chemiluminescent analysis with easy control of reactions through electrode potential.
– ECL analysis is versatile, with a simplified optical setup compared to photoluminescence and good temporal and spatial control compared to chemiluminescence.
– Ruthenium complexes, particularly [Ru(bpy)(bpy = 2,2-bipyridine), are commonly used in ECL analysis.
– ECL has various applications, including biosensors, immunoassays, DNA probes, and clinical lab testing.
Electrochemiluminescence in Aqueous Medium
– Simultaneous oxidation and reduction of luminescent species in aqueous medium is challenging due to the electrochemical splitting of water.
– In aqueous ECL, a coreactant is used to facilitate the oxidation of luminescent species at the electrode.
– The coreactant undergoes chemical transformations, generating a strong reducing agent for the oxidative reduction mechanism.
– Aqueous ECL is commonly used in analytical applications and offers good sensitivity and dynamic range.
– The detection of ECL in aqueous medium is crucial for bio-related applications.
Comparison with Other Analytical Methods
– ECL analysis presents advantages over other common analytical methods.
– It offers enhanced selectivity by controlling the species that are oxidized or reduced at the electrode.
– Compared to photoluminescence, ECL has a simplified optical setup.
– Compared to chemiluminescence, ECL provides better temporal and spatial control.
– ECL techniques have been well established and heavily used commercially for clinical lab applications.
References
– Forster RJ, Bertoncello P, Keyes TE (2009). Electrogenerated Chemiluminescence. Annual Review of Analytical Chemistry.
– Valenti G, Fiorani A, Li H, Sojic N, Paolucci F (2016). Essential Role of Electrode Materials in Electrochemiluminescence Applications. ChemElectroChem.
– Electrogenerated Chemiluminescence, Edited by Allen J. Bard, Marcel Dekker, Inc., 2004.
– Valenti G, Rampazzo R, Bonacchi S, Petrizza L, Marcaccio M, Montalti M, Prodi L, Paolucci F (2016). Variable Doping Induces Mechanism Swapping in Electrogenerated Chemiluminescence of Ru(bpy)32+ Core−Shell Silica Nanoparticles. J. Am. Chem. Soc.
– Miao W, Choi J, Bard A (2002). Electrogenerated Chemiluminescence 69: The Tris(2,2′-bipyridine)ruthenium(II), (Ru(bpy)2+)/Tri-n-propylamine (TPrA) System RevisitedsA New Route Involving TPrA•+ Cation Radicals (PDF). J. Am. Chem. Soc. Source: https://en.wikipedia.org/wiki/Electrochemiluminescence
Electrochemiluminescence or electrogenerated chemiluminescence (ECL) is a kind of luminescence produced during electrochemical reactions in solutions. In electrogenerated chemiluminescence, electrochemically generated intermediates undergo a highly exergonic reaction to produce an electronically excited state that then emits light upon relaxation to a lower-level state. This wavelength of the emitted photon of light corresponds to the energy gap between these two states. ECL excitation can be caused by energetic electron transfer (redox) reactions of electrogenerated species. Such luminescence excitation is a form of chemiluminescence where one/all reactants are produced electrochemically on the electrodes.
ECL is usually observed during application of potential (several volts) to electrodes of electrochemical cell that contains solution of luminescent species (polycyclic aromatic hydrocarbons, metal complexes, quantum dots or nanoparticles) in aprotic organic solvent (ECL composition). In organic solvents both oxidized and reduced forms of luminescent species can be produced at different electrodes simultaneously or at a single one by sweeping its potential between oxidation and reduction. The excitation energy is obtained from recombination of oxidized and reduced species.
In aqueous medium, which is mostly used for analytical applications, simultaneous oxidation and reduction of luminescent species is difficult to achieve due to electrochemical splitting of water itself so the ECL reaction with the coreactants is used. In the latter case luminescent species are oxidized at the electrode together with the coreactant which gives a strong reducing agent after some chemical transformations (the oxidative reduction mechanism).
