Coreactant System Research Articles

Immunosensing of Cardiac Troponin I (cTnI) Using a Two-Electrode Electrochemiluminescence Platform with Near Persisting Luminescence Generated on a Ru(bpy)32+-Tripropylamine System.

An economical, rapid, and ultrasensitive detection of biomolecules in clinical settings is very crucial, particularly for the early detection of Cardiac Troponin I (cTnI), which is the gold standard biomarker for Acute Myocardial Infarction (AMI). Electrochemiluminescence (ECL) has risen in prominence as an important technique for in vitro diagnosis and detection by virtue of its high sensitivity reaching a femtomolar level. This study introduces an economically feasible nanoplatform for ECL immunosensing, consisting of a gold nanoparticle (AuNP) with Ru(bpy)32+ and tripropylamine (TPA) system, which is a potential ECL luminophore and coreactant system. AuNPs serve the role of an ECL signal enhancer as well as the carrier of antibody, which enables the creation of a label-free immunosensor for antigen-antibody interactions. The prepared immunosensor detected cTnI with a detection limit (LOD) of 0.03 ng/mL. This potential immunosensor provides appreciable results in the detection of cTnI from spiked real serum analysis, which shows its potential application in low-resource clinical settings.

Study on the Electrochemiluminescence Emission Mechanism of HOF-14 and Its Multimode Sensing and Imaging Application.

A novel hydrogen-bonded organic framework (HOF-14) has attracted much attention due to its excellent biocompatibility and low toxicity, but its research in the electrochemiluminescence (ECL) field has not been reported. In this work, the annihilation-type and coreactant-type ECL emission mechanisms of HOF-14 were studied systematically for the first time. It was found that the ECL quantum efficiency of HOF-14/TEA coreactant system was the highest, which was 1.82 times that of Ru(bpy)32+/TEA. Further, the ECL emission intensity of HOF-14/TEA system could achieve colorimetric (CL) imaging of mobile phone. We also discovered that HOF-14 had superior photoelectrochemical (PEC) performance. Based on the above research results, a unique HOF-14-based multimode sensing and imaging platform was constructed. The antibiotic Enrofloxacin (ENR) was selected as the detection target, and the Cu-Zn bimetallic single-atom nanozyme (Cu-Zn/SAzyme) with excellent peroxidase (POD)-like activity was used to prepare quenching probes. When the target ENR was present, Cu-Zn/SAzyme quenching probes were introduced to the surface of HOF-14 by the dual-aptamer sandwich method. Cu-Zn/SAzyme could catalyze diaminobenzidine (DAB) to produce brown precipitations to quench the ECL, PEC, and CL signals of HOF-14, realizing multimode detection of ENR. This work not only discovered excellent ECL and PEC property of new HOF-14 material but also systematically studied the ECL emission mechanism of HOF-14, and proposed a novel multimode sensing and imaging platform, which greatly improved the detection accuracy of target and showed great contributions to the field of ECL analysis.

Novel Efficient Selenium-Based D-π-A NIR Polymer Dots Anodic Electrochemiluminescence Emitter and Its Application in Simultaneous Detection of Two Pneumonia Pathogens with CdS Quantum Dots.

Community-acquired pneumonia (CAP) is a major cause of death in children under 5 years old globally. With Streptococcus pneumoniae (S. pneumoniae) and Mycoplasma pneumoniae (M. pneumoniae) being the main pathogens linked to CAP that requires hospitalization, there is an urgent need for a straightforward, cost-efficient, and highly accurate diagnostic method for immediate and early detection of CAP. In this work, benzo[1,2-c;4,5-c']bis([1,2,5]thiadiazole) (BBT) as π-bridge spacer with the donor unit of poly(9,9-dioctylfluorene) (PF) and the acceptor unit of dithienylbenzoselenadiazole (DBS) has been successfully copolymerized to unprecedentedly prepare novel D-π-A selenium-based polymer dots with efficient NIR electrochemiluminescence (named as Se-Pdots in this work). Se-Pdots exclusively generated excellent anodic ECL in the two-component coreaction system comprising TPrA and K2S2O8. Moreover, a potential-resolved ECL biosensor to simultaneously detect S. pneumoniae and M. pneumoniae has also been successfully constructed based on this novel Se-based NIR Pdots as an anodic emitter with CdS QDs as a cathodic emitter. Under optimal conditions, the biosensor has a wide linear range for S. pneumoniae (10-15 to 10-9 M) and M. pneumoniae (10-15 to 10-9 M), with low detection limits for S. pneumoniae (0.56 fM) and M. pneumoniae (0.96 fM). The proposed ECL biosensor provides a simple, sensitive, and reliable method for the simultaneous detection of CAP pathogens in clinical applications.

Bimodal Oxidation Electrochemiluminescence Mechanism of Coreactant-Embedded Covalent Organic Frameworks via Postsynthetic Modification.

Electrochemiluminescence (ECL) efficiency is determined by charge transfer between coreactants and emitters in coreactant systems, which are usually limited by their slow intermolecular charge transfer. In this study, a covalent organic framework (COF) with aldehyde residue was synthesized, and then coreactants were covalently integrated into the skeleton through the postsynthetic modification strategy, resulting in a crystalline coreactant-embedded COF nanoemitter (C-COF). Compared to the pristine COF with an equivalent external coreactant, C-COF exhibited an extraordinary 1008-fold enhancement of ECL intensity due to the rapid intrareticular charge transfer. Significantly, with the pH increase, C-COF shows protonation-induced ECL enhancement for the first ECL peaked at +1.1 V and an opposite trend for the second ECL at +1.4 V, which were attributed to the antedating oxidation of coreactant in framework and COF self-oxidation, respectively. The resulting bimodal oxidation ECL mechanism was rationalized by spectral characterization and density functional theory calculations. The postsynthetic coreactant-embedded nanoemitters present innovative and universal avenues for advancing ECL systems.

Bimodal Oxidation Electrochemiluminescence Mechanism of Coreactant‐Embedded Covalent Organic Frameworks via Postsynthetic Modification

AbstractElectrochemiluminescence (ECL) efficiency is determined by charge transfer between coreactants and emitters in coreactant systems, which are usually limited by their slow intermolecular charge transfer. In this study, a covalent organic framework (COF) with aldehyde residue was synthesized, and then coreactants were covalently integrated into the skeleton through the postsynthetic modification strategy, resulting in a crystalline coreactant‐embedded COF nanoemitter (C–COF). Compared to the pristine COF with an equivalent external coreactant, C–COF exhibited an extraordinary 1008‐fold enhancement of ECL intensity due to the rapid intrareticular charge transfer. Significantly, with the pH increase, C–COF shows protonation‐induced ECL enhancement for the first ECL peaked at +1.1 V and an opposite trend for the second ECL at +1.4 V, which were attributed to the antedating oxidation of coreactant in framework and COF self‐oxidation, respectively. The resulting bimodal oxidation ECL mechanism was rationalized by spectral characterization and density functional theory calculations. The postsynthetic coreactant‐embedded nanoemitters present innovative and universal avenues for advancing ECL systems.

Combined Strategies Enable Highly Selective Light Olefins and para-Xylene Production on Single Catalyst Bed.

Achieving multiple high-value-added chemical production through novel reaction processes and shape-selective catalytic strategy is the key to realizing efficient low-carbon catalytic processes. In this work, a methanol-toluene coreaction system was developed, and combined control strategies of reaction pathway guidance and shape-selective catalysis were applied for the successful production of light olefins and para-xylene on single HZSM-5 catalyst bed. Cofeeding toluene additionally provides reactive and flowing aromatic hydrocarbon pool species that change the dominant reaction pathway in the complex network of the methanol reaction on HZSM-5 and promote the formation of ethylene. For the first time, the key reaction intermediates methylmethylenecyclodiene are directly captured and identified by experimental and theoretical techniques. This helps to propose the catalytic cycle for the dominant generation of ethylene and, more importantly, enriches the methanol-to-hydrocarbons (MTH) chemistry and hydrocarbon pool mechanism. Furthermore, 0.4HZSM-5@S-1-CLD, an optimized HZSM-5 catalyst modified by the silicalite-1 epitaxial growth followed by silanization approach, realizes highly selective production of light olefins (especially ethylene) and para-xylene, while excellent reactant activity is maintained. This highly efficient coreaction route gives an important leading significance in synthesizing the raw materials for the polyolefin and polyester industries. The establishment of the combined control strategies provides a model for the joint production of multiple target chemicals in complex catalytic processes.

Smartphone-based portable electrochemical-colorimetric dual-mode biosensor for glucose detection in a co-reaction system

Regular monitoring of blood sugar levels is essential for diabetics, both for adjusting medication or insulin doses and for preventing complications like blindness, nerve damage, heart disease, and kidney failure. This paper presents a novel smartphone-based electrochemical-colorimetric dual-mode detecting system for detecting glucose at low concentrations. This system utilizes a smartphone as a mobile terminal to control the electrochemical circuit board and enable data analysis. The circuit board integrates cyclic voltammetry and differential pulse voltammetry, providing a low-cost and palm-sized solution for glucose detection. Additionally, digital image colorimetry is employed to enable efficient and accurate colorimetric detection. The use of glucose oxidase and horseradish peroxidase (GOx/HRP) in combination with 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) ABTS substrates facilitates glucose dual-mode quantitative analysis in a-coreaction system. The electrochemical and colorimetric methods exhibit limits of detection of 0.467 µM and 10 µM, respectively. This system shows a point-of-care testing (POCT) potential for reliable and convenient monitoring of blood glucose levels, particularly for individuals with diabetes.

Retraction notice to “4-dimethylaminopyridine: Discovery of a co-reactant system providing outstanding and reliable emission in electrochemiluminescence” [J. Electroanal. Chem. 921 (2022) 116507

Retraction notice to “4-dimethylaminopyridine: Discovery of a co-reactant system providing outstanding and reliable emission in electrochemiluminescence” [J. Electroanal. Chem. 921 (2022) 116507

Aerosol-Assisted Chemical Vapor Deposition of MoS2 with a Thiourea Sulfur Source: Single-Source Precursors vs Coreactant Mixtures.

Aerosol-assisted chemical vapor deposition of MoS2 from solutions containing the single-source precursors cis-Mo(CO)4(TMTU)2 and Mo(CO)5(TMTU) in toluene was compared to depositions from the coreactant solution containing Mo(CO)6 and uncoordinated TMTU in toluene. The results were used to assess the significance of ligand precoordination on the properties of the deposited films. Raman spectra and GI-XRD patterns of the films show that the single-source precursors produced more intense and sharper signals for 2H-MoS2 as compared to the coreactant system of Mo(CO)6 and TMTU, which is indicative of improved crystallinity. SEM and XPS were also used to assess morphology and film composition. Thermolysis of cis-Mo(CO)4(TMTU)2 and analysis of the pyrolysis products by GC-MS and 1H NMR suggested a decomposition mechanism of the TMTU ligand where a terminal sulfido is generated on the molybdenum center with loss of a heteroatom stabilized carbene.

Highly efficient electrochemiluminescence of nitrogen-doped carbon quantum dots

Nitrogen-doped carbon quantum dots (N-CQDs) are nanocomposites that can be synthesized by the hydrothermal method. In this work, N-CQDs with the size of 3.2 ± 1.7 nm was prepared from 1 g citric acid and 2 g urea precursor in 10 mL water. Electrochemiluminescence (ECL) of the prepared N-CQDs with K2S2O8 as a coreactant was found to reach a high ECL efficiency up to 109% relative to that of the Ru(bpy)32+/K2S2O8, coreactant system, revealing their great potential for electroanalysis. It is probably because that N elements were doped well in this N-CQDs and increased presence of surface states per mass of N-CQDs. From the spooling ECL spectroscopy, it can be found that the ECL spectra exhibited both a red shift compared with their photoluminescence (PL) spectrum and a wavelength shift during the potentiodynamic scan in the ECL evolution and devolution processes, due to various emissive excited states of N-CQDs leading to higher ECL efficiency. This work gives an insight into development of high ECL efficiency N-CQDs for bioanalytical and light emitting applications.

A metal-organic framework regulated graphdiyne-based electrochemiluminescence sensor with a electrocatalytic self-acceleration effect for the detection of di-(2-ethylhexyl) phthalate.

In this work, a super-sensitive electrochemiluminescence (ECL) aptamer sensor was constructed using a multiple signal amplification strategy to realize ultra-sensitive detection of di-(2-ethylhexyl) phthalate (DEHP). The incorporation of a highly efficient electrocatalytic metal-organic framework (NH2-Zr-MOF) and graphdiyne (GDY) composite has significantly enhanced the overall electrochemically active surface area, facilitating electron transfer during the entire electrochemical reaction process, and the large number of pores in graphdiyne and NH2-Zr-MOF limited a series of redox reactions within a certain range. This resulted in the generation of a greater number of SO4˙- radicals, thereby boosting the ECL intensity of the GDY in the K2S2O8 system. To increase the performance of the sensor even further, sodium ascorbate (NaAsc) as an accelerator was added to the co-reactant system. Additionally, nitrogen micro-nano bubbles with higher stability and stronger mass transfer have been introduced into the ECL system for the first time. Based on these, the aptamer as the recognition element realized the ultra-sensitive detection of DEHP in the linear range of 1.0 × 10-12 to 1.0 × 10-4 mg mL-1 with the limit of detection (LOD) of 2.43 × 10-13 mg mL-1. In summary, we have utilized the electrocatalytic activity of the porous MOF and the reducing capability of sodium ascorbate to enhance the ECL emission of GDY, which has been successfully applied to the detection of DEHP in water samples.

Electrochemistry and electrochemiluminescence of resorufin dye: Synergetic reductive-oxidation boosted by hydrogen peroxide

To develop robust field diagnostic systems capable of responding to medical needs, miniaturization of devices and high target sensitivity remain significant challenges. Electrochemiluminescence (ECL) is an ideal analysis tool to meet these challenges, and developing novel ECL materials is essential. Here we report the reversible electrochemical properties of resorufin, a commercial fluorescent dye, and its highly stable cathodic ECL. We find the cathodic ECL emission from the resorufin quantitatively changes upon the H2O2 content and propose the selective ECL molecular sensor against it. Resorufin undergoes reversible two-electron-transfer electrochemical reduction, and it generates cathodic ECL via a reductive-oxidation pathway with the S2O82− co-reactant. Interestingly, highly enhanced, synergetic ECL is produced in the dual K2S2O8–H2O2 co-reactant system, and especially, it can be used for selective molecular recognition of H2O2. Via the chronoamperometric application, the resorufin ECL signal reveals the linear correlation with the H2O2 concentration range of 0–150 µM with a detection limit of 6.8 µM. Resorufin exhibits strong potential as a new ECL luminophore. Also, selective enhancement of ECL suggests potential applicability to various immunoassays using H2O2.

Enhanced Electrochemiluminescence of A Macrocyclic Tetradentate Chelate Pt(II) Molecule through Its Collisional Interactions with the Electrode.

A macrocyclic tetradentate chelate Pt(II) molecule (Pt1) served as an excellent luminophore in electrochemiluminescence (ECL) processes. The blue ECL of Pt1/S2 O8 2- coreactant system in N,N'-dimethylformamide was found to be 46 times higher than that of the Ru(bpy)2+ /S2 O8 2- system or 30 times higher than that of the 9,10-diphenylanthracene/S2 O8 2- system. The unprecedented high ECL quantum efficiencies were caused by the cyclic generation of monomer excited states through collisional interactions of Pt1 molecules with the electrode at an elevated frequency. The ECL is tunable from bright blue to pure white by simply changing the solvent from N,N'-dimethylformamide to dichloromethane. The white ECL of Pt(II) molecule was reported for the first time and the mechanism was proposed to be the simultaneous emissions from the monomer excited state (blue) and excimer (red).

Insights into enhanced electrochemiluminescence of a multiresonance thermally activated delayed fluorescence molecule

AbstractThe electrochemiluminescence (ECL) behavior of a multiresonance thermally activated delayed fluorescence molecule has been investigated for the first time by means of ECL‐voltage curves, newly designed ECL‐time observatory, and ECL spectroscopy. The compound, Mes3DiKTa, shows complex ECL behavior, including a delayed onset time of 5 ms for ECL generation in both the annihilation pathway and the coreactant route, which we attribute to organic long‐persistent ECL (OLECL). Triplet‐triplet annihilation, thermally activated delayed fluorescence and uncompensated solution resistance cannot be ruled out as contributing mechanisms to the ECL. A very long ECL emission decay was attributed to OLECL as well. The absolute ECL efficiencies of Mes3DiKTa were enhanced and reached 0.0013% in annihilation route and 1.1% for the coreactant system, which are superior to those of most other organic ECL materials. It is plausible that ECL materials with comparable behavior as Mes3DiKTa are desirable in applications such as ECL sensing, imaging, and light‐emitting devices.

RETRACTED: 4-dimethylaminopyridine: Discovery of a co-reactant system providing outstanding and reliable emission in electrochemiluminescence

• 4-DMAP, a novel co-reactant, has been explored for improving Ru(bpy)32 + ECL. • Ru(bpy)32+/4-DMAP system enhances 28 times stronger ECL emission than Ru(bpy)32+/TPrA system. • It exhibits electrochemical oxidation behaviour like TPrA. • The efficient ECL is in the pH range of an environmental and biological system or immunoassay. Ru(bpy) 3 2+ has received significantly increasing interest in clinical diagnosis and scientific research because of its high sensitivity, wide dynamic range, good stability, solubility, and ECL efficiency in aqueous solutions. As the electrochemiluminescence (ECL) results from electrochemical reactions between Ru(bpy) 3 2+ and co-reactant, extensive research has been focused on exploring novel co-reactants for the highly sensitive determination of Ru(bpy) 3 2+ . Therefore, co-reactant plays a critical role for the electrochemiluminescence (ECL) application. Herein, 4-DMAP has been explored as a potential co-reactant for enhancing Ru(bpy) 3 2+ ECL. It is much more effective than tripropylamine (TPrA) at gold and platinum electrodes, although it shows an ECL emission mechanism similar to TPrA. The presence of amine group at para position with pyridine ring in 4-DMAP structure considerably enhances ECL intensity. The ECL intensities of the Ru(bpy) 3 2+ /4-DMAP system are approximately 28 and 25 times stronger than that of the Ru(bpy) 3 2+ /TPrA system at gold and platinum electrode, respectively.

Imaging electrochemiluminescence layer to dissect concentration-dependent light intensity for accurate quantitative analysis

As one of most advanced transduction techniques, electrochemiluminescence (ECL), such as that generated by tris(2,2′-bipyridyl)ruthenium (Ru(bpy)32+), has been extensively used in chemical sensing and analysis, but the reaction mechanism has not been fully resolved. Aiming at gaining insightful mechanistic information on the coreactant system involving (Ru(bpy)32+) and tri-n-propylamine (TPrA), herein we investigate the variation of thickness of ECL layer (TEL) with the concentration ratio of (Ru(bpy)32+) to TPrA (cRu/cTPrA) by ECL microscopy. Using carbon fiber as the working electrode, TEL was observed to grow with the increase of cRu/cTPrA remarkably. In conjunction with finite element simulations, the extension of ECL layer was rationalized to be associated with the incremental contribution of so-called “catalytic route”. This route offers an additional channel of generating remote light emission in solution, apart from surface-confined emission produced by the “oxidative-reduction route”. Given the quantitative analysis of coreactant-type analytes is often based on the calibration curve, namely a graph generated by plotting the measured light intensity of a series of standard solutions against their concentrations, the contribution of “catalytic route” particularly at a low concentration of analyte (equivalent to a relatively large cRu/cTPrA) is favorable to the analytical sensitivity. Moreover, the presence and absence of this route will result in a nonlinear and linear calibration curve, respectively, for example in the detection of TPrA and pyruvate. The results highlight the microwire-based imaging approach can provide insightful mechanistic information and help unveil the concentration dependence of measured ECL intensity for precise quantitative analysis.

Quantum Efficiency of Electrochemiluminescence Generation by Tris(2,2’‐bipyridine)ruthenium(II) and Tri‐n‐propylamine Revisited from a Kinetic Reaction Model

AbstractElectrochemiluminescence quantum efficiency (ECL‐QE) is an important parameter to evaluate the energy conversion ability of luminophores and analytical sensitivity of corresponding ECL systems. Herein, taking tris(2,2’‐bipyridine)ruthenium(II) (Ru(bpy)32+) and tri‐n‐propylamine (TPrA) coreactant system as an example, the ECL‐QE was evaluated in terms of a kinetic reaction model, in which Ru(bpy)33+ was considered to be the key intermediate in a reaction scheme consisting of competitive oxidative reduction and catalytic reaction routes. It was calculated as the product of electrochemical excitation efficiency (ηex) and light emission efficiency (i. e., photoluminescence quantum yield, PLQY). We used finite element simulations to examine the variation of ηex with the electrode material, applied potential, concentration and distance from the electrode surface. ηex was found to be largely determined by the electrochemical oxidation rate of TPrA that varied by several orders of magnitude with the electrode material. The estimation of ECL‐QE helped in selecting the appropriate conditions for efficient ECL generation and sensitive analysis.

Ultrasensitive molecularly imprinted electrochemiluminescence sensor based on highly-conductive rGO-COOH synergically amplify TCPP luminophor signal in aqueous phase system for “switches-controlled” detection of tryptamine

An efficient and innovative molecularly imprinted electrochemiluminescence sensor (MIECLS) based on the reduced carboxylated graphene oxide (rGO-COOH) amplifying aqueous phase meso-tetra(4-carboxyphenyl)porphyrin (TCPP) signal was constructed for “switches-controlled” detection of tryptamine (Tryp). The conductive rGO-COOH uninterruptedly accelerated the high-energy electrons injection into the aqueous co-reaction system of green metal-free TCPP, and more excited state molecules (TCPP*) were generated to obtain excellent ECL signal. Benefiting from the large specific surface area provided by rGO-COOH, molecularly imprinted polymer (MIP) with specific recognition cavities can be firmly electropolymerized on the surface of rGO-COOH/glassy carbon electrode (GCE), which regulated electrons transfer rate to realize “switches-controlled” detection by elution and recombination of Tryp. Under optimal conditions, the MIECLS exhibited a favorable linear relationship with Tryp in the concentration range of 1 × 10−9–1 × 10−4 mol L−1 and the limit of detection (LOD) was 0.25 × 10−9 mol L−1. The MIECLS was used for Tryp detection in actual samples with the satisfactory results (recovery rate, 83.19–91.32%) and consistent with that of HPLC. The dual application of TCPP and MIP/rGO-COOH/GCE can create nicely synergistic effect for the Tryp detection, making a novel avenue to the rapid analysis of other food hazards.

A catalyst-free co-reaction system of long-lasting and intensive chemiluminescence applied to the detection of alkalinephosphatase.

A catalyst-free co-reaction luminol-H2O2-K2S2O8 chemiluminescence (CL) system was developed, with long-life and high-intensity emission, and CL emission lasting for 6h. A possible mechanism of persistent and intense emission in this CL system was discussed in the context of CL spectra, cyclic voltammetry, electron spin resonance (ESR), and the effects of radical scavengers on luminol-H2O2-K2S2O8 system. H2O2 and K2S2O8 co-reactants can promote each other to continuously generate corresponding radicals (OH•, 1O2, O2•-, SO4•-) that trigger the CL emission of luminol. H2O2 can also be constantly produced by the reaction of K2S2O8 and H2O to further extend the persistence of this CL system. CL emission can be quenched via ascorbic acid (AA), which can be generated through hydrolysis reaction of L-ascorbic acid 2-phosphate trisodium salt (AAP) and alkaline phosphatase (ALP). Next, a CL-based method was established for the detection of ALP with good linearity from 0.08 to 5 U·L-1 and a limit of detection of 0.049 U·L-1. The proposed method was used to detect ALP in human serum samples.

Metal-Insulator-Semiconductor Anodes for Ultrastable and Site-Selective Upconversion Photoinduced Electrochemiluminescence.

Photoinduced electrochemiluminescence (PECL) allows the electrochemically assisted conversion of low-energy photons into high-energy photons at an electrode surface. This concept is expected to have important implications, however, it is dramatically limited by the stability of the surface, impeding future developments. Here, a series of metal-insulator-semiconductor (MIS) junctions, using photoactive n-type Si (n-Si) as a light absorber covered by a few-nanometer-thick protective SiOx /metal (SiOx /M, with M=Ru, Pt, and Ir) overlayers are investigated for upconversion PECL of the model co-reactant system involving the simultaneous oxidation of tris(bipyridine)ruthenium(II) and tri-n-propylamine. We show that n-Si/SiOx /Pt and n-Si/SiOx /Ir exhibit high photovoltages and record stabilities in operation (35 h for n-Si/SiOx /Ir) for the generation of intense PECL with an anti-Stokes shift of 218 nm. We also demonstrate that these surfaces can be employed for spatially localized PECL. These unprecedented performances are extremely promising for future applications of PECL.