Studying the synergy between photons and electrons
- Electrogenerated chemiluminescence
- Electrochemical microscopy and photoelectrochemistry
- Coupling electrochemistry and fluorescence microscopy
- Nanostructured optical fibers
- Electrogenerated chimiluminescence
Electrogenerated ChemiLuminescence (ECL) is the light emission of a luminophore resulting from an initial electrochemical step. It combines thus intimately electrochemistry and photochemistry. Due to its intrinsic characteristics, ECL is a powerful analytical technique and it is widely commercialized for immunoassays and clinical diagnostics by several companies. Our goal is to decipher the ECL mechanistic pathways and, based on this fundamental knowledge, to propose original (bio)analytical applications. For this, we develop a holistic approach at the differetn scales to push back the limits of ECL:
(1)at the molecular scale: discovery and study of new efficient ECL luminophores [1,2,3]
(2) at the nanometer scale: stimuli-responsive hydrogel nanomaterials (nanoparticles and thin films)[4,5,6] and nanoelectrodes[7,8] are exploited to miniaturize analytical systems
(3) at the micrometer scale: immunoassays,[8,9] analytical (bio)swimmers and 3D ECL,[10,11,12] and cell imaging[13]
(4) at the macroscale: to develop integrated (bio)analytical ECL-based platforms[14,15]
Potential applications : bioassays, cell microscopy, ECL imaging, ultrasensitive detection
From left to right : ECL luminophores, stimuli-responsive NPs, bead-based ECL immunoassays, cell imaging, (bio)swimmers developed by the synergy between ECL and bipolar electrochemistry, microelectrode arrays.
Electrochemical microscopy and photoelectrochemistry
Scanning Electrochemical Microscopy (SECM) has been first described in the early 90’s and is nowadays widely used to analyze interfacial phenomenon. The principle of SECM is to use a microelectrode, that can move in the three directions of space to study a substrate. The electrochemical response of the tip is disturbed by the substrate, providing information about its nature and its properties. SECM recently find applications in the field of solar energy, by coupling the microelectrode with an optical fiber, it is called scanning photoelectrochemical microscopy (SPECM). We used the SPECM to rapidly screen the photoelectrochemical properties of TiO2 spots prepared in different conditions. We simultaneous measured the water oxidation photocurrent and the reduction current of the produced oxygen. By placing the optoelectrode at a constant distance and by scanning the surface in the X-Y direction, an image was obtained, allowing to observe the most efficient photocatalyst.
Potential applications : Chemical surface patterning,[16] rapid screening of photocatalysts[17]
a) Scheme of local generation and screening of TiO2 by SECM; b) Photoelectrochemical image of different type of TiO2 generated by local anodization.
Coupling electrochemistry and fluorescence microscopy
Nowadays, the coupling between electrochemistry and fluorescence microscopy is gaining a considerable interest. The collection of both analytical signals provides simultaneously a space- and time-resolved information, thus enabling the detection of spatial or temporal heterogeneities of electrode processes. We have implemented fluorescence confocal laser scanning microscopy (FCLSM) under electrochemical control to map in situ various reaction layers in 3D (xy plane at different z positions with respect to the electrode surface). The main objectives are: (1) the study of the (electro)chemical reactivity of biorelevant fluorogenic dyes used as analytical probes in medicinal/clinical diagnostics and (2) the control and/or improvement of the coverage homogeneity of modified electrodes used as biosensing platforms.
Fluorescence intensity mapping along the z-direction perpendicular to the electrode surface collected by confocal laser scanning microscopy for an extinction (left) or activation of fluorescence (right) upon electron transfer
Nanostructured optical fibers for imaging and analysis
Optical fiber bundles are well-established tools in analytical chemistry for sensing and imaging. For instance, we fabricated high density nanoprobe arrays[1,2] for DNA detection and for remote imaging of the human skin (corneocytes) by wet etching optical fiber bundles. Such bundles are composed of thousands of micrometric optical fibers arranged in a coherent optical way (for example: 6000 optical fibers with a 3µm-core diameter assembled in a 350µm bundle). The bundles are micro/nanostructured by well-controlled wet etching with regular 3D patterns such as nano-tips, micro/nano-wells, micro-pillars, micro/nano-beads or more complex shapes[3,4] can also be achieved. The resulting optical nanostructures keep the initial architecture of the bundle and therefore its intrinsic imaging properties. Remote imaging and detection based on fluorescence, ECL, Surface-Enhanced Raman Scattering (SERS), Fluorescence Correlation Spectroscopy (FCS), Surface Plasmon Resonance (SPR) were demonstrated through the bundle itself.[5,6] We also developed with an industrial partner (L’Oréal) a remote imaging technique of living corneocytes directly on the human skin.
a) SERS with etched nanotip. b) Remote imaging of corneocytes on the forearm. c) Fluorescence image of the DNA spots electropolymerized on the nanotip array.