Analyte-directed formation of emissive excimers for the selective detection of polyamines

Hydrogel Nanocomposite Towards Optical Sensing of Spermine in Biomedical and Real-Life Food Samples and Remediation of Toxic Dyes from Wastewater

Nanocomposites such as graphene oxide (GO) have been incorporated into hydrogels to enhance conventional hydrogels' properties and develop new functions. Unique and strong molecular interactions between GO and low molecular weight gelators allow the fabrication of various functional hydrogels suitable for different applications. In the present study, we report a stable and soft nanocomposite hydrogel comprising a pyrene-based chiral amphipath having an amino acid (l-phenylalanine) core with pendant oligo-oxyethylene hydrophilic chains and GO. The mechanical and viscoelastic properties of the nanocomposite hydrogel were thoroughly studied using various spectroscopic, microscopic, and mechanical techniques. Even without GO, native hydrogels could form a self-supported thermoreversible and thixotropic hydrogel composed of the fibrillar network. Unlike native hydrogels, the morphological investigation of nanocomposite gels shows the presence of cross-linked nanosheet-like structures. The combined effect of π-π stacking and H-bonding interactions is the driving force for the formation of such composite hydrogels. Moreover, the nanocomposite hydrogels possess significantly superior mechanical stiffness than the native hydrogels. Interestingly, the thixotropic properties observed with the parent gel were retained even in the presence of carbon nanomaterials (GO). The nanocomposite hydrogel could be employed in the optical sensing of a biogenic polyamine, spermine, resulting in a visible gel-to-sol transition. The superior electrostatic interaction between the GOs and spermine molecules might have led to the release of entrapped fluorogenic dyes from the hydrogel network and a turn-on emission response. The sensory system was employed to analyze spermine content in human urine samples and decomposed food items. A gel-coated paper strip was also developed for onsite detection of the spermine. The nanocomposite hydrogel was further utilized to remove toxic organic dyes such as methylene blue (MB) and rhodamine B (RhB) from the aqueous media. The nanocomposite hydrogel thus showed excellent dye removal capabilities and was also found to be recyclable. Calculations of different mechanical parameters suggest that the dye removal efficiency of the nanocomposite hydrogel was better for MB than for RhB.

Order-order assembly transition-driven polyamines detection based on iron-sulfur complexes

Innovative modes of response can greatly push forward chemical sensing processes and subsequently improve sensing performance. Classical chemical sensing modes seldom involve the transition of a delicate molecular assembly during the response. Here, we display a sensing mode for polyamine detection based on an order-order transition of iron-sulfur complexes upon their assembly. Strong validation proves that the unique order-order transition of the assemblies is the driving force of the response, in which the polyamine captures the metal ion of the iron-sulfur complex, leading it to decompose into a metal-polyamine product, accompanied by an order-order transition of the assemblies. This mechanism makes the detection process more intuitive and selective, and remarkably improves the detection efficiency, achieving excellent polyamines specificity, second-level response, convenient visual detection, and good recyclability of the sensing system. Furthermore, this paper also provides opportunities for the further application of the iron-sulfur platform in environment-related fields.

Recent Advances in Fluorescent Methods for Polyamine Detection and the Polyamine Suppressing Strategy in Tumor Treatment

The biogenic aliphatic polyamines (spermine, spermidine, and putrescine) are responsible for numerous cell functions, including cell proliferation, the stabilization of nucleic acid conformations, cell division, homeostasis, gene expression, and protein synthesis in living organisms. The change of polyamine concentrations in the urine or blood is usually related to the presence of malignant tumors and is regarded as a biomarker for the early diagnosis of cancer. Therefore, the detection of polyamine levels in physiological fluids can provide valuable information in terms of cancer diagnosis and in monitoring therapeutic effects. In this review, we summarize the recent advances in fluorescent methods for polyamine detection (supramolecular fluorescent sensing systems, fluorescent probes based on the chromophore reaction, fluorescent small molecules, and fluorescent nanoparticles). In addition, tumor polyamine-suppressing strategies (such as polyamine conjugate, polyamine analogs, combinations that target multiple components, spermine-responsive supramolecular chemotherapy, a combination of polyamine consumption and photodynamic therapy, etc.) are highlighted. We hope that this review promotes the development of more efficient polyamine detection methods and provides a comprehensive understanding of polyamine-based tumor suppressor strategies.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Spermine and Spermidine Detection through Restricted Intramolecular Rotations in a Tetraphenylethylene Derivative

Biogenic polyamines, especially spermine and spermidine, are associated with cell growth and development. These amines can be found at high concentrations in the tumor cells, tissues, and urine of cancer patients. In contrast, spermidine levels drop with age, and a possible connection between low endogenous spermidine concentrations and age-related deterioration has been suggested. Thus, the quantification of these amines in body fluids like urine could be used in the diagnosis of different pathological situations. Here a new fluorescent molecular probe based on a tetraphenylethylene derivative is reported. This probe is able to selectively detect these amines through the enhancement of the fluorescence emission of the resulting complex. This fluorescence enhancement may be related to restricted intramolecular rotations of TPE phenyl rings induced by the analyte. Theoretical studies were carried out to shed light on the observed selectivity. Finally, the detection of these amines in urine was performed with limits of detection of 0.70 µM and 1.17 µM for spermine and spermidine, respectively.

Supramolecular imaging of spermine in cancer cells

As an important biomarker, the overexpressed spermine has been widely investigated for cancer diagnosis and treatment. However, bioimaging of spermine in living cells is still a formidable challenge. Herein, we design a supramolecular imaging ensemble for spermine by the host-guest complexation of amphiphilic sulfonatocalix[5]arene (SC5A12C) assembly with lucigenin (LCG). Strong binding ability and complexation-induced fluorescence quenching properties enable SC5A12C to quench the fluorescence of LCG dramatically and to recover it completely due to the competition of overexpressed spermine in cancer cells. SC5A12C also exhibits excellent biocompatibility and promotes cellular uptake due to its ability to form ultra-stable assembly. Co-assembling folate further promotes the cellular uptake of folate receptor overexpressed cancer cells, contributing to enhanced bioimaging.

Ratiometric fluorescent detection of silver nanoparticles in aqueous samples using peptide-based fluorogenic probes with aggregation-induced emission characteristics

The quantification of silver nanoparticles and Ag⁺ contamination in the aquatic ecosystem has attracted considerable interest. Benzoimidazolyl-cyanovinylene (1) was synthesized as an aggregation-induced emission fluorophore, and a fluorescent peptidyl probe (2 and 3) bearing this fluorophore was developed. The fluorescent peptidyl probes coordinated with Ag⁺ selectively among various metal ions, leading to a ratiometric response to Ag⁺ in pure aqueous solutions. Furthermore, an "in situ" protocol was developed to quantify AgNPs using 2 with H₂O₂ as an oxidizing reagent. The fluorescent detection method for Ag⁺ and AgNPs showed promising detection properties such as high selectivity, high sensitivity, fast response, visible light excitation, well-operations in pure aqueous solution, and large fluorescent signal change. The detection limits of Ag⁺ (0.64 ppb) and AgNPs (1.1 ppb) were significantly low. According to the binding mode study, Ag⁺ induced the formation of a 2:1 complex between 2 and Ag⁺ and the chirality of the peptide part of the probe was not critical for this process. The formation of aggregates of the probe triggered by Ag⁺ from AgNPs induced a significant change in fluorescence. Furthermore, the amounts of spiked AgNPs in groundwater and tap water were quantified using the fluorescent detection method with 2.

A narrative review on biogenic amines in fermented fish and meat products

Biogenic amines (BAs) are organic nitrogenous compounds, formed mostly by decarboxylation of corresponding amino acids. BAs are responsible for several biological events. However, if the concentration of BAs reached the threshold level, it causes mild to serious health problems in human. The objective of this manuscript was to summarize the prevalence and prevention of Bas formation, detection methods and factors affecting the BAs formation in fermented fish and meat products. Meat sausages are the fermented meat product that contains high BAs. Fish sauces are reported to have high BAs compared to other fish products. Several chemosensors and chromatography methods are available to screen and detect BAs in foods. The prevention measures are vital to avoid toxic outbreaks. The use of starter culture, application of physical factors, control of environmental factors, and use of polyphenols could prevent or diminish the formation of BAs in fermented foods. The literature survey warrants that the development of potent starter with desirable characters, maintenance of hygienic food production and regular monitoring of commercial products are necessary to ensure the quality and safety of fermented fish and meat product.

Activatable Formation of Emissive Excimers for Highly Selective Detection of β-Galactosidase

Small-molecular fluorescence sensors have become promising detection tools in many fields attributing to their high sensitivity, excellent temporal and spatial resolution, and low cytotoxicity. However, high concentration or aggregation-induced fluorescence quenching effect has usually hindered the development of traditional fluorescence dyes. Herein, a new fluorophore cyanovinylene dye BMZ with excimer emission property has been constructed. It shows an obvious enhanced and red-shift emission upon aggregation in aqueous solution, which overmatches the conventional pyrene with longer absorption and emission wavelengths. Using this unique optical property, a new fluorescence probe BMZ-Gal has been developed for trapping of β-galactosidase (β-Gal) activity with high selectivity, low limit of detection of 0.17 U, and rapid recognition, which is based on the β-Gal-induced formation of red-shift emitting excimer. β-Gal has a strong affinity for BMZ-Gal, which is verified through the Michaelis-Menten constants (K_m, 1.87 μM) and the hydrolysis efficiencies (K_cat/K_m, 1.78 × 10³ M^-1 s^-1). Furthermore, the assay system has been successfully used for detecting endogenous β-Gal in living ovarian cancer cells and can passively targeted to identify β-Gal in organelle level and determine its subcellular location with satisfactory accuracy. We anticipate that the new fluorophore cyanovinylene dye herein may inaugurate new opportunities for the development of excimer emission sensors.

Perylene diimide-Cu2+ based fluorescent nanoparticles for the detection of spermine in clinical and food samples: a step toward the development of a diagnostic kit as a POCT tool for spermine

The sustainable development of point-of-care testing (POCT) for spermine detection is important to check for food spoilage, early diagnosis of various malignancies and diminished anticonvulsant drug carbamazepine response in chronic epilepsy. Herein, the synthesis, characterization and spectroscopic properties of perylene diimide EA-PDI∩Cu²⁺ complex based nanoparticles towards spermine were studied in detail. This EA-PDI∩Cu²⁺ complex can be used for the ultrasensitive detection of spermine as low as 86.3 nM (UV-vis) and 90 pM (fluorescence) in aqueous medium, in urine and blood serum samples (recovery 99 ± 3) and in the solid state (0.1 μg L^-1), and EA-PDI shows minimal cytotoxicity to cells and can easily enter into Human Osteosarcoma MG-63 cells for bio-imaging of Cu²⁺ and spermine. This EA-PDI∩Cu²⁺ complex can be established as a cost-effective method to develop a diagnostic kit for POCT of spermine in terms of a solution-based test kit for real time detection of spermine in vapor and solution form released from fermented food samples.

Chemosensors for biogenic amines and biothiols

There is burgeoning interest among supramolecular chemists to develop novel molecular systems to detect biogenic amines and bio-thiols in aqueous and non-aqueous media due to their potential role in biological processes. Biogenic amines are biologically important targets because of their involvement in the energy metabolism of human biological systems and their requirement is met through food and nutrition. However, the increasing instances of serious health problems due to food toxicity have raised the quality of food nowadays. Biogenic amines have been frequently considered as the markers or primary quality parameters of foods like antioxidant properties, freshness and spoilage. For instance, these amines such as spermine, spermidine, cadavarine, etc. may originate during microbial decarboxylation of amino acids of fermented foods/beverages. These amines may also react with nitrite available in certain meat products and concomitantly produce carcinogenic nitrosamine compounds. On the other hand, it is also well established that biothiols, particularly, thiol amino acids, provide the basic characteristics to food including flavor, color and texture that determine its acceptability. For instance, the reduction of thiol groups produces hydrogen sulfide which reduces flavour as in rotten eggs and spoiled fish, and the presence of hydrogen sulfide in fish is indicative of spoilage. Thus, biogenic amines and bio-thiols have attracted the profound interest of researchers as analytical tools for their quantification. Much scientific and technological information is issued every year, where the establishment of precise interactions of biogenic amines and bio-thiols with other molecules is sought in aqueous and non-aqueous media. This review summarizes the optical chemosensors developed for the selective detection of biogenic amines and bio-thiols.