Aggregation-driven fluorescence quenching of imidazole-functionalized perylene diimide for urea sensing

A perylene-based fluorescent probe for highly efficient SDS detection

Sodium dodecyl sulfate (SDS) is widely used in numerous household products and pharmaceuticals due to its excellent water solubility, emulsification, foaming, and dispersing properties. However, the extensive use of SDS has made it a significant environmental pollutant, posing a great threat to aquatic ecosystems. Therefore, developing a rapid, efficient, and sensitive probe for detecting SDS in aqueous environments is crucial. In this study, we present a cationic imidazolium-conjugated perylene bisimide (PBI) compound, as an effective probe for detecting SDS in aqueous media. The probe exhibits a distinct color change from dark pink to light pink upon interaction with SDS, making it a simple yet powerful tool for naked-eye detection. Moreover, the strong electrostatic interaction between the positively charged PBI compound and the negatively charged sulfate group in SDS leads to the formation of closely packed molecular aggregates. This results in significant quenching of fluorescence emission, enabling the detection of SDS at micromolar concentrations. We further demonstrate the practical application of PBI compound for sensitive and selective fluorometric detection of SDS in home-care items and tap water samples. These findings highlight the potential of such compounds as versatile tools for both environmental monitoring and product safety applications involving sulfate-containing species.

A review on forensic analysis of bio fluids (blood, semen, vaginal fluid, menstrual blood, urine, saliva): Spectroscopic and non-spectroscopic technique

The accurate detection, identification, and analysis of biofluids at crime scenes play a critical role in forensic investigations. Various biofluids, such as blood, semen, vaginal fluid, menstrual blood, urine, and saliva, can be crucial evidence. In a murder case involving a knife attack, for instance, bloodstains from both the victim and perpetrator might be present. Sexual assault cases often involve the analysis of semen and vaginal secretions. Biofluid analysis employs a two-tiered approach: presumptive tests for initial identification and confirmatory tests for definitive analysis. This review article focuses on six key biofluids and their forensic significance. In this review, we comprehensively explore the relevant analytical techniques, including non-spectroscopic methods like immunoassays, spot tests, and cytokine profiling, alongside spectroscopic techniques such as Infrared (IR) spectroscopy, Mass Spectrometry (MS), and Raman Spectroscopy (RS).

Aggregation-Induced Emission Luminogen: Role in Biopsy for Precision Medicine

Biopsy, including tissue and liquid biopsy, offers comprehensive and real-time physiological and pathological information for disease detection, diagnosis, and monitoring. Fluorescent probes are frequently selected to obtain adequate information on pathological processes in a rapid and minimally invasive manner based on their advantages for biopsy. However, conventional fluorescent probes have been found to show aggregation-caused quenching (ACQ) properties, impeding greater progresses in this area. Since the discovery of aggregation-induced emission luminogen (AIEgen) have promoted rapid advancements in molecular bionanomaterials owing to their unique properties, including high quantum yield (QY) and signal-to-noise ratio (SNR), etc. This review seeks to present the latest advances in AIEgen-based biofluorescent probes for biopsy in real or artificial samples, and also the key properties of these AIE probes. This review is divided into: (i) tissue biopsy based on smart AIEgens, (ii) blood sample biopsy based on smart AIEgens, (iii) urine sample biopsy based on smart AIEgens, (iv) saliva sample biopsy based on smart AIEgens, (v) biopsy of other liquid samples based on smart AIEgens, and (vi) perspectives and conclusion. This review could provide additional guidance to motivate interest and bolster more innovative ideas for further exploring the applications of various smart AIEgens in precision medicine.

Enhanced Photocatalytic Oxygen Evolution Using Copper-Coordinated Perylene Diimide Nanorod Assemblies

A crystalline supramolecular photocatalyst is prepared through metal-induced self-assembly of perylene diimide with imidazole groups at the imide position (PDI-Hm). Exploiting the metal-coordination ability of imidazole, a crystalline assembly of copper-coordinated PDI-Hm (CuPDI-Hm) in a nanorod shape is prepared which displays an outstanding photocatalytic oxygen evolution rate of 25,900 μmol g-1 h-1 without additional co-catalysts. The imidazole-copper coordination, along with π-π stacking of PDI frameworks, guides the arrangement of PDI-Hm molecules to form highly crystalline assemblies. The coordination of copper also modulates the size of the CuPDI-Hm supramolecular assembly by regulating the nucleation and growth processes. Furthermore, the imidazole-copper coordination constructs the electric field within the PDI-Hm assembly, hindering the recombination of photo-induced charges to enhance the photoelectric/photocatalytic activity when compared to Cu-free PDI-Hm assemblies. Small CuPDI-Hm assembly exhibits higher photocatalytic activity due to their larger surface area and reduced light scattering. Together, the Cu-imidazole coordination presents a facile way for fabricating size-controlled crystalline PDI assemblies with built-in electric field enhancing photoelectric and photocatalytic activities substantially.

Fluorescent detection of tartrazine based on the supramolecular self-assembly of cationic perylene diimide

A cationic perylene probe was designed and synthesized for sensitive determination of tartrazine. In the presence of tartrazine, the fluorescence of the perylene probe was quenched by efficient supramolecular self-assembly of the perylene derivate. The quenching is caused by the synergistic effect of noncovalent interactions including static electricity, π-π stacking, and hydrophobic interaction. Benefiting from these advantages, the probe exhibited excellent sensing performance to tartrazine within 2 min. The detection and quantification limit of tartrazine are as low as 2.42 and 8.07 nmol L-1, respectively, with a wide linear operation range from 15 to 500 nmol L-1. Most importantly, due to the high binding affinity (3.22 × 107 mol L-1) between the perylene probe and tartrazine, the sensing system shows great anti-interference capacity. Subsequently, the visualization application of the approach was evaluated by portable device, and the limits of detection for visual detection for test strip, membrane, and hydrogel were 0.5, 0.5, and 5 μmol L-1, respectively. The approach has been applied to monitor tartrazine in various food condiments with recoveries in the range 91.29-108.83%. As far as we know, this is the first report of using perylene-based probe for tartrazine determination, offering a promising strategy for the construction of perylene-based detection system in the field of food safety.

Highly Bright Gold Nanowires Arrays for Sensitive Detection of Urea and Urease

In this work, highly fluorescent gold nanowire arrays (Au NWs) are successfully synthesized by assembling Zn²⁺ ions and non-emissive oligomeric gold-thiolate clusters using mercaptopropionic acid both as a reducing agent and a growth ligand. The synthesized Au NWs exhibited strong bluish green fluorescence with an absolute quantum yield up to 32% and possessed ultrasensitive pH stimuli-responsive performance in the range of 7.0-7.8. Based on the excellent properties of the as-prepared nanowire arrays, we developed a facile, sensitive, and selective fluorescent method for quantitative detection of urea and urease. The fabricated nanoprobe showed superior biosensing response characteristics with good linearities in the range of 0-100 μM for urea concentration and 0-12 U/L for urease activity. In addition, this fluorescent probe afforded relatively high sensitivity with the detection limit as low as 2.1 μM and 0.13 U/L for urea and urease, respectively. Urea in human urine and urease in human serum were detected with satisfied results, exhibiting a promising potential for biomedical application.

Red to NIR-emissive anthracene-conjugated PMI dyes with dual functions: singlet-oxygen response and lipid-droplet imaging

The rich chemistry of solution-processable red and near-infrared (NIR) organic emitters has emerged as an attractive and progressive research field because of their particular applications in organic optoelectronics and bioimaging. Also, one can see that the research area of perylene monoimide-based red and NIR-emissive fluorophores is underexplored, which prompted us to design and synthesize three anthracene-conjugated PMI dyes exhibiting strong emission in the red and NIR window in solution. Three PMI-based fluorophores were synthesized via conjoining anthracene and donor moieties (-Ph, -N,N-PhNMe₂) with a PMI core via an acetylene linkage at the peri-position, which helped to attain extensive electronic conjugation, which was reflected in red and NIR-emission in solution. The key molecular features to be highlighted here are: all three dyes are strongly emissive in solution, as unveiled by the excellent absolute fluorescence QYs; and they possess tuneable emission properties, guided by the donor strength and a profound Stokes shift (100-200 nm). The three fluorescent dyes demonstrated appreciable singlet-oxygen (¹O₂) sensitivity when photoirradiated with methylene blue (MB) in solution, showing a substantial blue-shift in emission in a ratiometric manner. Further, the treatment of dye-MB solution with α-tocopherol (¹O₂ scavenger) validated the presence of ¹O₂ as the only oxidizing species generated by MB in solution. Computational investigations gave insight into the twisting of donor moieties in their ground-state optimized geometries, the modulation of the FMO energy gap, and the thermodynamic feasibility of the ¹O₂ reaction. Finally, via taking advantage of the red and NIR-emission, we successfully utilized one of the fluorophores as a lipid-droplet marker for bioimaging in HepG2 cells.

Urea detection in milk by urease-assisted pH-sensitive carbon dots

Excessive urea in milk will lead to serious health problems. To detect whether the urea concentration in milk exceeds the standard and ensure the quality of milk, it is necessary to develop detection technology for urea in milk. But it is difficult to detect urea in milk conveniently and accurately by traditional methods. To measure the concentration of urea in milk, stable green light carbon dots (CDs) were synthesized by a one-step method as a fluorescent probe. Then, 3, 5-diaminobenzoic acid was used as the precursor for CD synthesis. Experimental results showed that CDs can generate strong fluorescence when excited by light (350-450 nm). The fluorescence peak wavelength is 490 nm, and the optimum excitation wavelength is 390 nm. The fluorescence intensity of CDs has a significant change with variations of pH (pH of 6-9), and the higher the pH, the lower the fluorescence intensity. Additionally, urea can be hydrolyzed by urease to produce ammonia and carbon dioxide. Ammonia is ionized in water to produce OH^-, which increases the pH of the solution. After adding standard urea to milk, urease and CDs are added. The fluorescence intensity of CDs in the mixed solution decreases as the concentration of standard added urea increases. Thus the concentration of urea in milk can be calculated. The experimental results show that the CD method for detecting urea in milk has advantages of high sensitivity and wide measurement range. The linear interval is 25-500 mg/L, R² is 0.998, and the limit of detection is 6.27 mg/L. The concentration of urea in the milk used in the experiment is 265.46 mg/L. CDs are easy to fabricate, and the advantages of the method are simple operation, no pretreatment, safety, and low cost. A new method for the detection of urea in milk was established, to the best of our knowledge, and this method can aid in food quality control.