Synthesis of novel organic-inorganic hybrid fluorescent microspheres and their applications as Fe(III), Hg(II) and biothiols probes

Review on Carbon Dot-Based Fluorescent Detection of Biothiols

Biothiols, such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH), play a vital role in gene expression, maintaining redox homeostasis, reducing damages caused by free radicals/toxins, etc. Likewise, abnormal levels of biothiols can lead to severe diseases, such as Alzheimer's disease (AD), neurotoxicity, hair depigmentation, liver/skin damage, etc. To quantify the biothiols in a biological system, numerous low-toxic probes, such as fluorescent quantum dots, emissive organic probes, composited nanomaterials, etc., have been reported with real-time applications. Among these fluorescent probes, carbon-dots (CDs) have become attractive for biothiols quantification because of advantages of easy synthesis, nano-size, crystalline properties, low-toxicity, and real-time applicability. A CDs-based biothiols assay can be achieved by fluorescent "Turn-On" and "Turn-Off" responses via direct binding, metal complex-mediated detection, composite enhanced interaction, reaction-based reports, and so forth. To date, the availability of a review focused on fluorescent CDs-based biothiols detection with information on recent trends, mechanistic aspects, linear ranges, LODs, and real applications is lacking, which allows us to deliver this comprehensive review. This review delivers valuable information on reported carbon-dots-based biothiols assays, the underlying mechanism, their applications, probe/CDs selection, sensory requirement, merits, limitations, and future scopes.

Facile preparation of fluorescent water-soluble non-conjugated polymer dots and fabricating an acetylcholinesterase biosensor

Acetylcholinesterase (AChE) has been demonstrated as a crucial enzyme in the development and treatment of Alzheimer's disease (AD). The present work reported the preparation of high fluorescence emission, water-soluble, non-conjugated polymer dots (NCPDs) via Schiff base reaction, and its self-assembly between hyperbranched poly(ethylenimine) (PEI) and pyrogallol in aqueous solutions. A one-pot method was introduced, which made the preparation process of the NCPDs more convenient, energy-efficient, and environmentally friendly. The mechanism of the inherent fluorescence of NCPDs and its fluorescence properties were investigated. This study, for the first time, explored the application of NCPDs to a nanoquencher biosensing system, discovering the reversible quenching effect of MnO2 nanosheets for NCPDs. Furthermore, the quenching mechanism of MnO2 for NCPDs was demonstrated to be an inner filter effect (IFE). The NCPDs-MnO2 biosensing system showed a broader detection range from 12.3 to 3675 U L-1 for AChE and the limit of detection (LOD) was as low as 4.9 U L-1. The sensing system has been applied to screen AChE inhibitors, and the result of the positive drug was highly consistent with previous studies. The established method showed a promising prospect in screening for leading compounds in new drug discoveries for AD.

Highly selective fluorescence probe with peptide backbone for imaging mercury ions in living cells based on aggregation-induced emission effect

Mercury is an anthropogenic toxic heavy metal found in the environment. It is highly desirable to develop a fluorescence probe that can selectively and sensitively detect mercury ions using a turn-on response. This paper reports the successful development of a peptide fluorescence probe, TP-2 (TPE-Trp-Pro-Gln-His-Glu-NH₂), which uses aggregation-induced emission effects and high selectivity to detect Hg²⁺. After fluorescence was activated, Hg²⁺ was efficiently detected using the change in fluorescence intensity. The detection limit for Hg²⁺ in the buffer solution was 41 nM (R² = 0.9952). Owing to its high sensitivity, high cell permeability, and low biotoxicity, the probe could perform live cell imaging under biological conditions. This study demonstrated that TP-2 can detect Hg²⁺ in complex biological environments.

The bright fluorescence of non-aromatic molecules in aqueous solution originates from pH-induced CTE behavior

Non-aromatic fluorescent materials with inherent visible light emission have received widespread attention. In this work, a biomimetic fluorescent molecule CA-AEP with a dipeptide structure is introduced. CA-AEP will emit bright biomimetic fluorescence in aqueous solutions by adjusting the pH, which has never been reported. This unique luminescent characteristic can be rationalized by the clustering-triggered emission (CTE) mechanism. In addition, CA-AEP can be used to monitor the maximum dynamic pH in the alkaline range of aqueous systems. Finally, the cytotoxicity assay to A549 cells showed that CA-AEP was non-toxic. Therefore, this work provides a new type of luminogen, which has potential application prospects in the field of environmental monitoring and cell biology.

A Microfluidic Biosensor Based on Magnetic Nanoparticle Separation, Quantum Dots Labeling and MnO2 Nanoflower Amplification for Rapid and Sensitive Detection of Salmonella Typhimurium

Screening of foodborne pathogens is an effective way to prevent microbial food poisoning. A microfluidic biosensor was developed for rapid and sensitive detection of Salmonella Typhimurium using quantum dots (QDs) as fluorescent probes for sensor readout and manganese dioxide nanoflowers (MnO2 NFs) and as QDs nanocarriers for signal amplification. Prior to testing, amino-modified MnO2 nanoflowers (MnO2-NH2 NFs) were conjugated with carboxyl-modified QDs through EDC/NHSS method to form MnO2-QD NFs, and MnO2-QD NFs were functionalized with polyclonal antibodies (pAbs) to form MnO2-QD-pAb NFs. First, the mixture of target Salmonella Typhimurium cells and magnetic nanoparticles (MNPs) modified with monoclonal antibodies (mAbs) was injected with MnO2-QD-pAb NFs into a microfluidic chip to form MNP-bacteria-QD-MnO2 complexes. Then, glutathione (GSH) was injected to dissolve MnO2 on the complexes into Mn2+, resulting in the release of QDs. Finally, fluorescent intensity of the released QDs was measured using the fluorescent detector to determine the amount of Salmonella. A linear relationship between fluorescent intensity and bacterial concentration from 1.0 × 102 to 1.0 × 107 CFU/mL was found with a low detection limit of 43 CFU/mL and mean recovery of 99.7% for Salmonella in spiked chicken meats, indicating the feasibility of this biosensor for practical applications.

Fluorescence Emission of Polyethylenimine-Derived Polymer Dots and Its Application to Detect Copper and Hypochlorite Ions

Polymer dots with nonconjugated groups that are facile to synthesize and environmentally friendly generally attract substantial interest. However, their fluorescence-emitting mechanisms are not clear. In this paper, nonconjugated polymer dots (N-PDs) are synthesized by amidation reaction between polyethylenimine (PEI) and citric acid (CA), then self-assemble into rice-like dots in aqueous phase with a high fluorescence quantum yield. Such nitrogen-containing nonconjugated compounds N-PDs are believed to be inherently fluorescent, and the reported reasons for fluorescence-emitting are discussed. Importantly, these N-PDs can be used as an excellent fluorescent probe to detect Cu²⁺ and ClO^- in aqueous solutions. Cu²⁺ could combine with the PEI moiety of the N-PDs to form a copper amine complex and then quench the fluorescence by an internal filtration effect. ClO^- could oxidize the hydroxyl groups on the surface of the N-PDs to form a positive charge, blocking electron transfer between the hydroxyl groups and the chromophore groups. Finally, the sensor was successfully applied to the detection of Cu²⁺ and ClO^- in environmental water samples.