A Tetraphenylethylene-Based Aggregation-Induced Emission Probe for Fluorescence Turn-on Detection of Lipopolysaccharide in Injectable Water with Sensitivity Down to Picomolar

Phosphine-Catalyzed 1,2-cis-Diboration of 1,3-Butadiynes

Trialkyl phosphines PMe3 and PEt3 catalyze the 1,2-cis-diboration of 1,3-butadiynes to give 1,2-diboryl enynes. The products were utilized to synthesize 1,1,2,4-tetraaryl enynes using a Suzuki-Miyaura protocol and can readily undergo proto-deborylation.

Electrochemiluminescence aptasensing method for ultrasensitive determination of lipopolysaccharide based on CRISPR-Cas12a accessory cleavage activity

In this study, an ultrasensitive electrochemiluminescence (ECL) aptasensing method was developed for lipopolysaccharide (LPS) determination based on CRISPR-Cas12a accessory cleavage activity. Tris (2,2'-bipyridine) dichlororuthenium (II) (Ru(bpy)32+) was adsorbed on the surface of a glassy carbon electrode (GCE) coated with a mixture of gold nanoparticles (AuNPs) and Nafion film via electrostatic interaction. The obtained ECL platform (Ru(bpy)32+/AuNP/Nafion/GCE) exhibited strong ECL emission. Thiol-functionalized single-stranded DNA (ssDNA) was modified with a ferrocenyl (Fc) group and autonomously assembled on the ECL platform of Ru(bpy)32+/AuNP/Nafion/GCE via thiol-gold bonding, resulting in the quenching of ECL emission. After hybridization of the LPS aptamer strand (AS) with its partial complementary strand (CS), the formed double-stranded DNA (dsDNA) could activate CRISPR-Cas12a to indiscriminately cleave ssDNA-Fc on the surface of Ru(bpy)32+/AuNP/Nafion/GCE, resulting in recovery of the ECL intensity of Ru(bpy)32+ due to the increasing distance between Fc and the electrode surface. The combination of LPS and AS suppressed the formation of dsDNA, inhibited the activation of CRISPR-Cas12a, and prevented further cleavage of ssDNA-Fc. This mechanism aided in upholding the integrity of ssDNA-Fc on the surface of the electrode and was combined with ECL quenching induced by the target. The ECL intensity decreased linearly as the concentration of LPS increased from 1 to 50,000 pg/mL and followed a logarithmic relationship. This method exhibited a remarkably low detection limit of 0.24 pg/mL, which meets the requirement for low-concentration detection of LPS in the human body. The proposed method demonstrates the capacity of CRISPR-Cas12a to perform non-specific cutting of single-stranded DNA and transform the resultant cutting substances into changes in the ECL signal. By amalgamating this approach with the distinct identification abilities of LPS and its aptamers, a simple, responsive, and discriminatory LPS assay was established that holds immense significance for clinical diagnosis.

Ultramicro and ultrasensitive detection of lipopolysaccharides based on triple-signal amplification via ultrafast ATRP and an ultramicroelectrode

Highly sensitive testing of trace lipopolysaccharides (LPS) is very important due to their high toxicity to the human body. Here, an ultrasensitive electrochemical sensor requiring only 5 μL solution was developed for LPS detection via triple-signal amplification based on ultrafast atom transfer radical polymerization (UATRP) and a Au ultramicroelectrode (UME). Firstly, the Au UME was modified with gold nanoparticles (nAu) and an LPS aptamer (Apt) in turn. When the Apt recognized LPS, the ATRP initiator of 4-(bromomethyl)phenylboronic acid (BPA) could be tethered to the electrode by covalent cross-linking between the phenylboronic acid moiety and the cis-diol site of LPS. Then UATRP was conducted for 2.5 min with nitrogen-doped carbon quantum dots (N-CQDs) as the photocatalyst and methylacrolein (MLA) as the monomer. After the electroactive probes of Ag nanoparticles (AgNPs) were formed on the surface of poly(MLA) by the silver mirror reaction, the electrochemical sensor was successfully prepared. Under the optimal conditions, the sensor exhibited a lower detection limit and a wider linear range when it was compared with a similar assay for LPS. In particular, the LOD of 7.99 × 10-2 pg mL-1 was better than that of the limulus amoebocyte lysate (LAL)-based technique, which is the gold standard for LPS detection. In the end, the sensor reported in this paper showed good selectivity and satisfactory feasibility for LPS detection in real biological samples and food products. The results obtained from the drug, blood and potable water samples laid a strong foundation for its clinical applications and application in other fields.

Dansyl-labelled cellulose as dual-functional adsorbents for elimination and detection of mercury in aqueous solution via aggregation-induced emission

Dansyl chloride fluorophore exhibits typical aggregation induced fluorescence emission behavior in acetone/water solution. To realize the integration of detective and adsorptive functions, dansyl chloride is covalently immobilized on cellulose substrate to fabricate an efficient adsorbent for mercury ions in water. The as-prepared material exhibits excellent fluorescence sensing performance exclusively for Hg (II) with the presence of other metal ions. A sensitive and selective fluorescence quenching across the concentration range of 0.1-8.0 mg/L is observed with a detection limit of 8.33 × 10^-9 M as a result of the inhibition of aggregation induced emission caused by the coordination between adsorbent and Hg (II). Besides, the adsorption properties for Hg (II) including the influence of initial concentration and contact time are investigated. Langmuir model and pseudo-second-order kinetics are demonstrated to fit well with the adsorption experiment for the uptake of Hg (II) by the functionalized adsorbent, also, intraparticle diffusion kinetic model is proved to aptly describe the Hg (II) removal in aqueous solution. In addition, the recognition mechanism is considered to originate from the Hg (II) triggered structural reversals of naphthalene ring units which are verified by the X-ray photoelectron spectroscopy and density functional theory calculation. Moreover, the synthesis method used in this work also provides a strategy for the sensing application of organic sensor molecules with AIE properties in which the aggregated behavior could be appropriately realized.

Peptide-modified carbon dot aggregates for ultrasensitive detection of lipopolysaccharide through aggregation-induced emission enhancement

This study fabricated yellow-emitting CDs (Y-CDs) by hydrothermal treatment of citric acid and urea and applied them as a fluorescence turn-on platform for sensitive and selective detection of lipopolysaccharide (LPS) based on the non-shifted AIEE of peptide-stabilized CD aggregates. The designed peptide (named K3) consisting of aggregation-active and LPS-recognition units triggered the aggregation of Y-CDs, switching on their fluorescence through the blue-shifted AIEE process. The formed K3-stabilized Y-CD aggregates (K3-YCDAs) specifically interacted with LPS at neutral pH, demonstrating that the sequence of the decorated peptide was highly connected with their selectivity and sensitivity. The K3-YCDAs provided a fast response time (within 5 min) to detect LPS with a quantification range of 0.5-100.0 nM and a limit of detection (LOD, signal-to-noise ratio of 3) of 300.0 pM. By integrating ultrafiltration membranes as a concentration device with K3-YCDAs as a sensing probe, the LOD for LPS was further reduced to 3.0 pM. The determination of picomolar levels of plasma LPS by the K3-YCDAs coupled to the centrifugation ultrafiltration was demonstrated to fall within the specificity range of clinical interest for sepsis patients. Also, the K3-YCDAs served as a fluorescent probe to selectively image and quantify E. coli cells. The distinct advantages of the K3-YCDAs for LPS include fast response time, wide linear range, low detection limit, and excellent selectivity compared to previously reported sensors.

Simple and Rapid Endotoxin Recognition Using a Dipicolylamine-Modified Fluorescent Probe with Picomolar-Order Sensitivity

Endotoxin is a lipopolysaccharide (LPS) that is found in the outer membrane of the cell wall of Gram-negative bacteria. Due to its high toxicity, the allowable endotoxin limit for water for injection is set at a very low value. Conventional methods for endotoxin detection are time-consuming and expensive and have low reproducibility. A previous study has shown that dipicolylamine (dpa)-modified pyrene-based probes exhibit fluorescence enhancement in response to LPS; however, the application of such probes to the sensing of LPS is not discussed. Against this backdrop, we have developed a simple and rapid endotoxin detection method using a dpa-modified pyrenyl probe having a zinc(II) center (Zn-dpa-C4Py). When LPS was added into Zn-dpa-C4Py solution, excimer emission of the pyrene moiety emerged at 470 nm. This probe can detect picomolar concentrations of LPS (limit of detection = 41 pM). The high sensitivity of the probe is ascribed to the electrostatic and hydrophobic interactions between the probe and LPS, which result in the dimer formation of the pyrene moieties. We also found that Zn-dpa-C4Py has the highest selectivity for LPS compared with other phosphate derivatives, which is probably caused by the co-aggregation of the probe with LPS. We propose that Zn-dpa-C4Py is a promising chemical sensor for the detection of endotoxin in medical and pharmaceutical applications.

A Flexible Chemosensor Based on Colorimetric and Fluorescent Dual Modes for Rapid and Sensitive Detection of Hypochlorite Anion

A flexible chemosensor has been developed based on colorimetric and fluorescent dual modes using tetraphenylethylene-centered tetraaniline (TPE4A) for rapid and sensitive detection of hypochlorite anion. The fluorescent probe TPE4A exhibits a unique aggregation-induced emission (AIE) character which is proved by a blue shift of the fluorescent peak from 544 to 474 nm with the water equivalents increasing. With the addition of hypochlorite in solution, the absorbance of the probe changes and the responding fluorescence color can be observed to change from light green to purple. The detection limit of hypochlorite is 1.80 × 10-4 M in solution, and the visual detection limit is 1.27 µg/cm2 with the naked eye for the flexible paper-based chemosensor. The proposed flexible chemosensors show a good selectivity and sensitivity which has great potential for effective detection of hypochlorite anions without any spectroscopic instrumentation.

Hydrazone ligation assisted DNAzyme walking nanomachine coupled with CRISPR-Cas12a for lipopolysaccharide analysis

In this work, hydrazone ligation assisted DNAzyme walking nanomachine is explored to couple with CRISPR-Cas12a trans-cleavage. Hydrazone ligation with high efficiency can mediate signal input which can be induced by target binding, thereby regulating the performance of DNAzyme walking nanomachine. The product strand from DNAzyme walking nanomachine can further activate the trans-cleavage of Cas12a. So, cascade signal amplification can be achieved to enhance the sensitivity for target detection. Subsequently, hydrazone ligation assisted DNAzyme walking nanomachine coupled with CRISPR-Cas12a has been further developed as a biosensor to analyze lipopolysaccharides. The developed biosensor exhibits a linear range from 0.05 ng/mL to 10⁶ ng/mL and a lowest limit of detection of 7.31 fg/mL. This research provides a new mode for the signal output of DNAzyme walking nanomachine, so as to sensitively analyze different biomolecules.

Fluorescent AIE-Active Materials for Two-Photon Bioimaging Applications

Fluorescence imaging has been widely used as a powerful tool for in situ and real-time visualization of important analytes and biological events in live samples with remarkably high selectivity, sensitivity, and spatial resolution. Compared with one-photon fluorescence imaging, two-photon fluorescence imaging exhibits predominant advantages of minimal photodamage to samples, deep tissue penetration, and outstanding resolution. Recently, the aggregation-induced emission (AIE) materials have become a preferred choice in two-photon fluorescence biological imaging because of its unique bright fluorescence in solid and aggregate states and strong resistance to photobleaching. In this review, we will exclusively summarize the applications of AIE-active materials in two-photon fluorescence imaging with some representative examples from four aspects: fluorescence detection, in vitro cell imaging, ex vivo tissue imaging, and in vivo vascular imaging. In addition, the current challenges and future development directions of AIE-active materials for two-photon bioimaging are briefly discussed.