Visible-Light Driven Photoelectrochemical Platform Based on the Cyclometalated Iridium(III) Complex with Coumarin 6 for Detection of MicroRNA

A cathodic photoelectrochemical biosensor based on CRISPR/Cas12a trans-cleavage mediated p-n heterojunction quenching mode for microRNA determination

In this study, a cathodic photoelectrochemical (PEC) bioanalysis for sensitive determination of microRNA (miRNA) has been constructed based on CRISPR/Cas12a trans-cleavage mediated [(C6)₂Ir(dcbpy)]⁺PF₆^- (C6 represents coumarin-6 and dcbpy represents 4,4'-dicarboxyl-2,2'-bipyridine)-sensitized NiO photocathode and p-n heterojunction quenching mode. The [(C6)₂Ir(dcbpy)]⁺PF₆^--sensitized NiO photocathode exhibits a stable and dramatically improved photocurrent signal due to highly effective photosensitization of [(C6)₂Ir(dcbpy)]⁺ PF₆^-. Then Bi₂S₃ quantum dots (Bi₂S₃ QDs) is captured on the photocathode, resulting in markedly quenching of the photocurrent. When target miRNA is specifically recognized by the hairpin DNA to stimulate the trans-cleavage activity of CRISPR/Cas12a, leading to the leave of the Bi₂S₃ QDs. The photocurrent is gradually recovered with the increasing target concentration. Thus, the quantitative signal response to target is achieved. Benefiting from excellent performance of NiO photocathode, intense quenching effect of p-n heterojunction and accurate recognition ability of CRISPR/Cas12a, the cathodic PEC biosensor shows a wider linear range over 0.1 fM-10 nM, with a low detection limit of 36 aM. Also, the biosensor exhibits satisfying stability and selectivity.

Target-Induced In Situ Formation of Organic Photosensitizer: A New Strategy for Photoelectrochemical Sensing

Small-molecule photosensitizers have great application prospects in photoelectrochemical (PEC) sensing due to their defined composition, diversified structure, and adjustable photophysical properties. Herein, we propose a new strategy for PEC analysis based on the target-induced in situ formation of the organic photosensitizer. Taking thiophenol (PhSH) as a model analyte, we designed and synthesized a 2,4-dinitrophenyl (DNP)-caged coumarin precursor (Dye-PhSH), which was then covalently coupled onto the TiO₂ nanoarray substrate to obtain the working photoanode. Due to the intramolecular photoinduced electron transfer process, Dye-PhSH has only a very weak photoelectric response. Upon reacting with the target, Dye-PhSH undergoes a tandem reaction of the detachment of the DNP moiety and the intramolecular cyclization process, which leads to a coumarin dye with a pronounced photoelectric effect, thus achieving a highly selective turn-on PEC response to PhSH. For the first time, this study was to construct a PEC sensor by exploiting specific organic reactions for the in situ generation of small molecule-based photoactive material. It can be anticipated that the proposed strategy will expand the paradigm of PEC sensing and holds great potential for detecting various other analytes.

Cyclometalated Iridium(III) Complex-Sensitized NiO-Based-Cathodic Photoelectrochemical Platform for DNA Methyltransferase Assay

This work reports an efficient [(C6)₂Ir(dppz)]⁺PF₆^- (C6 = coumarin 6 and dppz = dipyridophenazine)-sensitized NiO photocathode and its application in photoelectrochemical (PEC) bioanalysis field for the first time. This dye-sensitized NiO photocathode was found to exhibit a markedly enhanced cathodic photocurrent. A sensitive cathodic PEC platform was proposed integrating the as-prepared photocathode with enzyme-free cascaded amplification strategies of the catalytic hairpin assembly (CHA) and the hybridization chain reaction (HCR) for DNA methyltransferase (MTase) assay. A hairpin DNA(H_Dam) with specific recognition site of Dam MTase in its stem was designed. The site of H_Dam was methylated in the presence of Dam MTase and then cut by endonuclease DpnI. The released loop fragment, as an initiator, triggered the CHA circuit and the follow-up HCR circuit, resulting in long dsDNA concatemers on the ITO electrode. Numerous [(C6)₂Ir(dppz)]⁺PF₆^- were intercalated into dsDNA, and highly efficient signal amplification was realized. Benefiting from the superior iridium(III) complex-sensitized NiO photocathode and effective amplification strategy, a detection limit of 0.0028 U/mL for the determination of Dam MTase was achieved. Moreover, this work further demonstrated that these proposed tactics could be applied to screen Dam MTase activity inhibitors.

Recent Trends in Electrochemical Sensors for Vital Biomedical Markers Using Hybrid Nanostructured Materials

This work provides a succinct insight into the recent developments in electrochemical quantification of vital biomedical markers using hybrid metallic composite nanostructures. After a brief introduction to the biomarkers, five types of crucial biomarkers, which require timely and periodical monitoring, are shortlisted, namely, cancer, cardiac, inflammatory, diabetic and renal biomarkers. This review emphasizes the usage and advantages of hybrid nanostructured materials as the recognition matrices toward the detection of vital biomarkers. Different transduction methods (fluorescence, electrophoresis, chemiluminescence, electrochemiluminescence, surface plasmon resonance, surface-enhanced Raman spectroscopy) reported for the biomarkers are discussed comprehensively to present an overview of the current research works. Recent advancements in the electrochemical (amperometric, voltammetric, and impedimetric) sensor systems constructed with metal nanoparticle-derived hybrid composite nanostructures toward the selective detection of chosen vital biomarkers are specifically analyzed. It describes the challenges involved and the strategies reported for the development of selective, sensitive, and disposable electrochemical biosensors with the details of fabrication, functionalization, and applications of hybrid metallic composite nanostructures.

Visualization of materials using the confocal laser scanning microscopy technique

The development of materials science always benefits from advanced characterizations. Currently, imaging techniques are of great technological importance in both fundamental and applied research on materials. In comparison to conventional visualization methods, confocal laser scanning microscopy (CLSM) is non-invasive, with macroscale and high-contrast scanning, a simple and fast sample preparation procedure as well as easy operation. In addition, CLSM allows rapid acquisition of longitudinal and cross-sectional images at any position in a material. Therefore, the CLSM-based visualization technique could provide direct and model-independent insight into material characterizations. This review summarizes the recent applications of CLSM in materials science. The current CLSM approaches for the visualization of surface structures, internal structures, spatial structures and reaction processes are discussed in detail. Finally, we provide our thoughts and predictions on the future development of CLSM in materials science. The purpose of this review is to guide researchers to build a suitable CLSM approach for material characterizations, and to open viable opportunities and inspirations for the development of new strategies aiming at the preparation of advanced materials. We hope that this review will be useful for a wide range of research communities of materials science, chemistry, and engineering.

A Dynamic DNA Machine via Free Walker Movement on Lipid Bilayer for Ultrasensitive Electrochemiluminescent Bioassay

Herein, an ultrasensitive electrochemiluminescent (ECL) strategy was proposed based on a highly efficient dynamic DNA machine based on microRNA triggered free movement on the lipid bilayer interface. Typically, the lipid bilayer is constructed on the electrode surface modified with nafion@ECL luminophore and gold nanoparticles to immobilize the DNA walker labeled with cholesterol and hairpin nucleotides labeled with cholesterol and ferrocene (Fc), based on the cholesterol-lipid interaction. On this state, Fc was close to the ECL luminophore, performing a quenched ECL emission. In the presence of target microRNA 21, it could trigger the entropy beacon-based DNA amplification to convert microRNA to massive special DNA sequences, which could further hybridize with the blocking DNA on DNA walker to reactivate the DNA walker and thus trigger the DNA walker-based amplification to make Fc to be far from the ECL luminophore, performing a recovered ECL emission related with the concentration of microRNA 21. Compared with the conventional DNA walker immobilized on the interface via chemical bonds or physical adsorption, a higher reaction efficiency could be achieved due to the free movements of DNA walker and its substrates on the interface. As expected, satisfactory performances for the detection of microRNA 21 were achieved with a detection limit of 0.4 fM and quantitative estimation in cells. Furthermore, this dynamic DNA machine-based ECL strategy could be readily expanded for the detection of other biomarkers for clinical diagnosis.

Avenues Toward microRNA Detection In Vitro: A Review of Technical Advances and Challenges

Over the decades, the biological role of microRNAs (miRNAs) in the post-transcriptional regulation of gene expression has been discovered in many cancer types, thus initiating the tremendous expectation of their application as biomarkers in the diagnosis, prognosis, and treatment of cancer. Hence, the development of efficient miRNA detection methods in vitro is in high demand. Extensive efforts have been made based on the intrinsic properties of miRNAs, such as low expression levels, high sequence homology, and short length, to develop novel in vitro miRNA detection methods with high accuracy, low cost, practicality, and multiplexity at point-of-care settings. In this review, we mainly summarized the newly developed in vitro miRNA detection methods classified by three key elements, including biological recognition elements, additional micro-/nano-materials and signal transduction/readout elements, their current challenges and further applications are also discussed.

Photofunctions of iridium(iii) complexes in vesicles: long-lived excited states and visible-light sensitization for hydrogen evolution in aqueous solution

Utilization of DPPC vesicles allows water-insoluble photoactive Ir(iii) complexes to be dispersed in bulk aqueous solution.