The light-addressable electrochemical sensor (LAES) is a recently emerged bioanalysis technique combining electrochemistry with the photoelectric effect in a semiconductor. In an LAES, a semiconductor substrate is illuminated locally to generate charge carriers in a well-defined area, thereby confining the electrochemical process to a target site. Benefiting from the unique light addressability, an LAES can not only detect multiple analytes in parallel within a single sensor plate but also act as a bio(chemical) imaging sensor to visualize the two-dimensional distribution of specific analytes. An LAES usually has three working modes: a potentiometric mode using light-addressable potentiometric sensors (LAPS) and an impedance mode using scanning photoinduced impedance microscopy (SPIM), while an amperometric mode refers to light-addressable electrochemistry (LAE) and photoelectrochemical (PEC) sensing. In this review, we describe the detection principles of each mode of LAESs and the concept of light addressability. In addition, we highlight the recent progress and advance of LAESs in spatial resolution, sensor system design, multiplexed detection, and bio(chemical) imaging applications. An outlook on current research challenges and future prospects is also presented.
electrochemical properties of the constituent materials as well as intra-and intermolecular interactions. Molecular self-assembly in π-conjugated systems is essential because it opens up an avenue to organic materials with desired spectroscopic properties and electrochemical activities. [1] While organic π-conjugated structures have been considerably studied, the exploration of aggregates or gels containing metalorganic materials is relatively rare. [2] Platinum emitters produce long-lived and phosphorescent 3 π,π* triplet excited states caused by heavy-atom-induced spin-orbital coupling; [3] the device performance could be dramatically improved by the insertion of metal centers into organic semiconductors. [4] Therefore, the triplet emitter, which structurally feature a four-coordinated square planar platinum(II) center with the chemical structure P−CC−Pt(PBu 3) 2 −CC−T− CC−Pt(PBu 3) 2 −CC−P (PPtTPtP, where T = 2,5-thienylene and P = phenyl), is investigated to explore the photophysical and electrochemical properties. The organic-based molecules, as the most common organic dyes and supramolecules in the ECL device have been extensively studied in the past decade. [5] The ECL is a phenomenon that involves the annihilation of radical ions generated The comprehension of triplet exciton mechanisms in organic-inorganic semiconductors has a significant impact on emerging optoelectronic and biosensing technologies. The capability to mutually integrate the photophysical properties of conjugated organic semiconductor with those of well-characterized heavy metals is therefore of utmost importance. Due to heavy-atom effect, the platinum-based triplet emitter, PPtTPtT, achieves highly efficient phosphorescence. Here, it is first demonstrated that π-conjugated PPtTPtT organometallics in electrochemiluminescence (ECL) devices exhibit precisely dual and blueshifted phosphorescence simultaneously induced by thermally activated delayed phosphorescence (TADP) and interchromophore exciton interaction in H-aggregates. Utilizing a combination of photophysical and electrochemical techniques, the distinctive ECL process involving energy sufficient singlet route (S-route), intersystem crossing, as well as triplet relaxation, hereafter called SIT-route, is reported for the first time. The hybrid TADP materials designed with donor-acceptor-donor system enable potential applications, including but not limited to organic light-emitting diodes, light-emitting electrochemical cells, imaging devices, and other bio-related detections.
Here, we describe a new photoelectrochemical imaging method termed light-addressable square wave voltammetry (LASWV). It measures local SWV currents at an unstructured electrolyte/insulator/semiconductor (EIS) fieldeffect substrate by illuminating and addressing the substrate with an intensityconstant laser. Due to the continuous generation of charge carriers in the lightirradiated semiconductor, the drift and diffusion of photoinjected carriers within the semiconductor bulk would slow down the equilibrium processes of charge and discharge in one potential pulse cycle. Therefore, even though SWV is sampled at the end of the direct and reverse pulses to reject capacitive currents, in our approach, photoinduced capacitive current can still be detected as an effective sensory signal. The obtained current−potential (I−V) curve shows a typical shape corresponding to the accumulation, depletion, and inversion regions of field-effect devices. We demonstrated that LASWV can be used as a field-effect chemical sensor to measure the solution pH and monitor enzymatic reactions. More importantly, since the charge carriers are only generated in the illuminated area, the laser spot in the device can be used as a virtual probe to record local electrochemical properties such as impedance with microresolution.
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