Lighting Up Electrochemiluminescence-Inactive Dyes via Grafting Enabled by Intramolecular Resonance Energy Transfer.

Due to near-zero optical background and photobleaching, electrochemiluminescence (ECL), an optical phenomenon excited by electrochemical reactions, has drawn extensive attention, especially for ultrasensitive bioassays. Developing diverse ECL emitters is crucial to unlocking their multiformity and performances but remains a formidable challenge due to the rigorous requirements for ECL. Herein, we report a general strategy to light up ECL-inactive dyes in an aqueous solution via grafting, a well-developed concept for plant propagation since 500 BCE. As a proof of concept, a series of luminol donor-dye acceptor-based ECL emitters were grafted with near-unity resonance energy transfer (RET) efficiency and coarse/fine-tunable emission wavelengths. Rather than the sophisticated design of new skeleton-based molecules to meet all of the prerequisites for ECL in a constrained manner, each unit in the proposed ECL ensemble performed its functions maximally. As a result, beyond traditional two-dimensional (2D) ones, a three-dimensional (3D) coordinate biosensing system, simultaneously showing a calibration curve and selectivity, was established using the new ECL emitter. This lighting up strategy would generally address the scarcity of ECL emitters and enable unprecedented functions.

Bound oxygen-atom transfer endows peroxidase-mimic M-N-C with high substrate selectivity.

Advances in nanoscience have stimulated the wide exploration of nanozymes as alternatives to enzymes. Nonetheless, nanozymes often catalyze multiple reactions and are not specialized to a specific substrate, restricting their broad application. Here, we report that the substrate selectivity of the peroxidase-mimic M-N-C can be significantly altered via forming bound intermediates with variable interactions with substrates according to the type of metal. Taking two essential reactions in chemical sensing as an example, Fe-N-C and Co-N-C showed opposite catalytic selectivity for the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) and 3-aminophthalhydrazide (luminol), respectively, by factors of up to 200-fold. It was revealed that specific transition metal-N coordination was the origin of the selective activation of H2O2 forming critically bound oxygen intermediates (M[double bond, length as m-dash]O) for oxygen-atom transfer and the consequent oxidization of substrates. Notably, owing to the embedded ligands in the rigid graphitic framework, surprisingly, the selectivity of M-N-C was even superior to that of commonly used horseradish peroxidase (HRP).

Ultrafast Condensation of Carbon Nitride on Electrodes with Exceptional Boosted Photocurrent and Electrochemiluminescence.

Semiconducting polymeric carbon nitride (CN) has drawn wide attention ranging from photocatalysis to more recent biosensing owing to unique defect-tolerated optoelectronic properties and being metal-free, cheap, and highly stable. However, at the core of electrical-optical interconversion, the preparation of the CN photoelectrode is still challenging. Now, the growth of CN on electrodes is achieved simply by microwave-assisted condensation in seconds. The ultrafast heating not only addressed the thermodynamic contradiction of precursor volatilization during polymerization but also led to strongly adhesive CN layer on electrodes with gradient carbon-rich texture, greatly accelerating the electron-hole separation and mobility. Consequently, the CN photoelectrode exhibited a remarkable photocurrent and a record cathodic efficiency of electrochemiluminescence up to 7 times that of benchmark Ru(bpy)3 Cl2 in aqueous solution.

Exfoliation and Sensitization of 2D Carbon Nitride for Photoelectrochemical Biosensing under Red Light.

Two-dimensional carbon nitride (CN) has drawn increasing attention as a conjugated metal-free polymer for photoelectrochemical (PEC) biosensing. However, CN only absorbs ultraviolet and very limited visible light (λ<460 nm), which poses potential risks for biomolecules and also cannot pass through tissue for in vivo detection. Herein, simultaneous exfoliation and functionalization of CN nanosheets (CNNS) with copper phthalocyanine (TsCuPc) simply by mechanical milling, thanks to the delicate π-π interaction between them, is reported. Moreover, due to energy-level matching, an effective donor-acceptor (D-A) interaction with much-improved photocurrent under irradiation with red light (λ>630 nm) was observed for the as-prepared CNNS-TsCuPc. As an example, dopamine in blood was detected by using red light by a CNNS-TsCuPc photoelectrode with uncompromised linear range and detection limit, as well high selectivity. As one of the few successful demonstrations of red-light-responsive PEC sensing systems, this work takes a first step toward future in vivo applications by enriching the optoelectronic properties of CN with task-specific antenna molecules via D-A interaction.

Magneto-controlled aptasensor for simultaneous electrochemical detection of dual mycotoxins in maize using metal sulfide quantum dots coated silica as labels.

Currently there is an urgent need for multi-mycotoxin detection methods due to the co-occurrence of multiple mycotoxins in food raw materials and their augmented toxicity. Herein, a magneto-controlled aptasensor has been developed for simultaneous electrochemical detection of ochratoxin A (OTA) and fumonisin B1 (FB1), two typical mycotoxins found in food crops world-wide. This aptasensor was designed using the high specificity between the target and aptamer with heavy CdTe or PbS quantum dots (QDs) coated silica as labels and the complementary DNA functionalized magnetic beads as capture probes. In presence of targets, the aptamer preferred to form the target-aptamer binding which forced the partial release of the preloaded labels from the magnetic beads. After a one-step incubation and a simple magnetic separation, the electrochemical signals of Cd2+ and Pb2+ dissolved from the reserved labels which had negative correlation with targets contents, was measured based on the difference of peak potentials. This aptasensor provided a wide detection range of 10pgmL-1 to 10ngmL-1 for OTA and 50pgmL-1 to 50ngmL-1 for FB1, and succeeded in real maize samples. This method provides a new avenue for high throughput screen of mycotoxins due to the advantages of simple instrument, low sample consumption, short assay times, and lower detection costs per assay. Moreover, it could be readily expanded for the simultaneous detection of a large panel of mycotoxins by using different metal sulfide QDs when their specific aptamers are available.