A novel peptide-based fluorescent chemosensor for Cd(II) ions and its applications in bioimaging

Design of C2-symmetric pseudopeptides for in vivo detection of Cu(II) through controlled supramolecular nano-assembly

Pseudopeptides are emerging next-generation soft bioinspired materials for biological applications. Therefore, a new class of C2-symmetric L-valine-derived pseudopeptides has been designed and developed. The newly developed pseudopeptides exhibit intracellular Cu(II) ion detection in live-cell fluorescence studies on RAW264.7 cells. We find that the changes in the amino acid side chain in desired pseudopeptidic moieties lead to a drastic change in their selectivity towards different metal ions. The L-valine-derived pseudopeptides exhibit selectivity towards Cu(II) ions through turn-off fluorescence, and the L-phenylalanine-derived pseudopeptides exhibit selectivity towards Zn(II) ions through turn-on fluorescence. In addition, the L-valine-derived pseudopeptides show an increase in spherical-shaped structures upon incubation with Cu(II) ions during supramolecular nano-assembly formation. In contrast, the L-phenylalanine-derived pseudopeptides show a decrease in spherical-shaped structures upon adding Zn(II) ions. The judiciously designed L-valine-derived and L-phenylalanine-derived bioinspired pseudopeptides are promising for exploring similar effects in various peptidomimetics in advanced biological applications.

Sustainable and reusable probe-encapsulated porous poly(AMST-co-TRIM) monolithic sensor for the selective and ultra-sensitive detection of toxic cadmium(II) from industrial/environmental wastewater

This study focuses on a new type of fast responsive solid-state visual colorimetric sensor, custom engineered with dual-entwined porous polymer imbued with chromoionophoric 4-(sec-butyl)- 2-((5-mercapto-1,3,4-thiadiazol-2-yl)diazenyl)phenol (SMDP) probe for selective and ultra-sensitive colorimetric sensing of Cd(II). The polymer monolith, i.e., poly(aminostyrene-co-trimethylolpropanetrimethacrylate) denoted as poly(AMST-co-TRIM), is designed through a stoichiometric blending of monomer, crosslinker, and porogens leading to superior surface area, pore and adsorption properties for the voluminous incorporation of SMDP probe for target specific ion sensing. The porosity, surface and structural characteristics of the poly(AMST-co-TRIM)monolith and poly(AMST-co-TRIM)SMDP sensor are investigated using p-XRD, XPS, TG-DTA, FT-IR, BET/BJH, FE-SEM, HR-TEM, EDAX, and SAED techniques. The poly(AMST-co-TRIM)SMDP sensor reveals a frozen geometrical orientation of SMDP molecules to bind selectively with Cd(II), forming stable charge-transfer complexes by exhibiting transitional visible color shifts from light yellow to dark green (λmax 608 nm). The sensor imposes a linear response from 0-200 ppb, with quantification and detection limits of 0.95 and 0.28 ppb. The fabricated sensor material is cost-effective and versatile in its solid-state naked-eye sensing, with excellent reusability. The sensor performance has been verified using various environmentally contaminated water and commercial cigarette samples, with a recovery of ≥ 99.12% and an RSD of ≤ 1.95%, thus reflecting exceptional data reproducibility/reliability.

Methodologies to Evaluate the Hair Follicle-Targeted Drug Delivery Provided by Nanoparticles

Nanotechnology has been investigated for treatments of hair follicle disorders mainly because of the natural accumulation of solid nanoparticles in the follicular openings following a topical application, which provides a drug "targeting effect". Despite the promising results regarding the therapeutic efficacy of topically applied nanoparticles, the literature has often presented controversial results regarding the targeting of hair follicle potential of nanoformulations. A closer look at the published works shows that study parameters such as the type of skin model, skin sections analyzed, employed controls, or even the extraction methodologies differ to a great extent among the studies, producing either unreliable results or precluding comparisons altogether. Hence, the present study proposes to review different skin models and methods for quantitative and qualitative analysis of follicular penetration of nano-entrapped drugs and their influence on the obtained results, as a way of providing more coherent study protocols for the intended application.

Fluorescent Sensors for Detecting and Imaging Metal Ions in Biological Systems: Recent Advances and Future Perspectives

Metal ions play a crucial role in many biochemical processes, and when in a state of scarcity or surplus, they can lead to various diseases. Therefore, the development of a selective, sensitive, cost-effective, and fast-responding sensor to detect metal ions is critical for in vitro medical diagnostics. In recent years, fluorescent sensors have been extensively investigated as potent kits for the effective assessment of metal ions in living systems due to their high sensitivity, selectivity, ability to perform real-time, non-invasive monitoring, and versatility. This review is an overview of recent advances in fluorescent sensors for the detection and imaging of metal ions in biosystems from 2018 to date. Specifically, we discuss their application in detecting essential metal ions and non-essential metal ions for in vitro diagnostics, living cell imaging, and in vivo imaging. Finally, we summarize remaining challenges and offer a future outlook on the above topics.

A phenazine-imidazole based ratiometric fluorescent probe for Cd2+ ions and its application in in vivo imaging

A new phenazine-imidazole based Schiff base (PIS) fluorescent probe has been developed for the ratiometric detection of Cd²⁺ ions in aqueous media at physiological pH. PIS upon binding with Cd²⁺ ions shows red shifted fluorescence and thereby, permits ratiometric detection of Cd(II) ions. A detection limit down to 2.10 × 10^-8 M was determined for Cd²⁺ quantitation. Also, the accompanying apparent fluorescence color change (from yellow to orange red) is noticeable to the naked eye under a UV-lamp. The sensing mechanism could be attributed to the 1 : 1 PIS-Cd complexation, followed by extension of the conjugation due to better planarity and modulation of the charge transfer efficiency in the probe. This was complemented by solvatochromism and density functional theory calculations. Furthermore, PIS was used to detect Cd²⁺ in Oxya chinensis cells, zebrafish larvae and live tissues of Arabidopsis thaliana under a fluorescence microscope, showing great potential in analyzing living biosystems.

Recent progress in cadmium fluorescent and colorimetric probes

Cadmium is a heavy metal which exists widely in industrial and agricultural production and can induce a variety of diseases in organisms. Therefore, its detection is of great significance in the fields of biology, environment and medicine. Fluorescent probe has been a powerful tool for cadmium detection because of its convenience, sensitivity, and bioimaging capability. In this paper, we reviewed 98 literatures on cadmium fluorescent sensors reported from 2017 to 2021, classified them according to different fluorophores, elaborated the probe design, application characteristics and recognition mode, summarized and prospected the development of cadmium fluorescent and colorimetric probes. We hope to provide some help for researchers to design cadmium fluorescent probes with higher selectivity, sensitivity and practicability.

Cadmium is a heavy metal which exists widely in industrial and agricultural production and can induce a variety of diseases in organisms.

Peptide-Engineered Fluorescent Nanomaterials: Structure Design, Function Tailoring, and Biomedical Applications

Fluorescent nanomaterials have exhibited promising applications in biomedical and tissue engineering fields. To improve the properties and expand bioapplications of fluorescent nanomaterials, various functionalization and biomodification strategies have been utilized to engineer the structure and function of fluorescent nanomaterials. Due to their high biocompatibility, satisfied bioactivity, unique biomimetic function, easy structural tailoring, and controlled self-assembly ability, supramolecular peptides are widely used as versatile modification agents and nanoscale building blocks for engineering fluorescent nanomaterials. In this work, recent advance in the synthesis, structure, function, and biomedical applications of peptide-engineered fluorescent nanomaterials is presented. Firstly, the types of different fluorescent nanomaterials are introduced. Then, potential strategies for the preparation of peptide-engineered fluorescent nanomaterials via templated synthesis, bioinspired conjugation, and peptide assembly-assisted synthesis are discussed. After that, the unique structure and functions through the peptide conjugation with fluorescent nanomaterials are demonstrated. Finally, the biomedical applications of peptide-engineered fluorescent nanomaterials in bioimaging, disease diagnostics and therapy, drug delivery, tissue engineering, antimicrobial test, and biosensing are presented and discussed in detail. It is helpful for readers to understand the peptide-based conjugation and bioinspired synthesis of fluorescent nanomaterials, and to design and synthesize novel hybrid bionanomaterials with special structures and improved functions for advanced applications.

A novel peptide-based fluorescent probe for sensitive detection of zinc (II) and its applicability in live cell imaging

In this work, we report SPSS synthesis of a new peptide-based fluorescent probe (L) capable of detecting Zn²⁺ with little interference in 100% aqueous solutions at physiological pH. Furthermore, L showed excellent sensitivity, with a detection limit of 26.77 nM. The 2:1 binding ratio between L and Zn²⁺ was determined using fluorometric titration, Job's plot and ESI-MS analyses. The "off-on-off" type fluorescence change of L was demonstrated by alternately adding Zn²⁺ and EDTA based on a formation-separation process of the complex, indicating that L could serve as a reversible probe. Moreover, MTT studies demonstrated that L has low biotoxicity, and could be successfully used for detection of Zn²⁺ and EDTA in live cells.

A simple fluorescent probe for detection of Ag+ and Cd2+ and its Cd2+ complex for sequential recognition of S2

In this study, we designed and synthesized a simple probe 2-(8-((8-methoxyquinolin-2-yl)methoxy)quinolin-2-yl)benzo[d]thiazole (DQT) for detection of Ag⁺ and Cd²⁺ in a CH₃OH/HEPES (9 : 1 v/v, pH = 7.30) buffer system. Its structure was characterized by NMR, ESI-HR-MS and DFT calculations, and its fluorescence performance was also investigated. Probe DQT showed fluorescence quenching in response to Ag⁺ and Cd²⁺ with low detection limits of 0.42 μM and 0.26 μM, respectively. Importantly, the complexation of the probe with Cd²⁺ resulted in a red shift from blue to green, making it possible to detect Ag⁺ and Cd²⁺ by the naked eye under an ultraviolet lamp. The DQT-Cd²⁺ complex could be used for sequential recognition of S^2-. The recovery response could be repeated 3 times by alternate addition of Cd²⁺ and S^2-. A filter paper strip test further demonstrated the potential of probe DQT as a convenient and rapid assay.

Highly sensitive turn-on detection of mercury(II) in aqueous solutions and live cells with a chemosensor based on tyrosine

Herein, we reported a novel fluorescent chemosensor (DY) based on dansyl group and tyrosine by solid phase peptide synthesis (SPPS) for the detection of mercury(II) ions with excellent selectivity among 17 different metal ions. As designed, DY exhibited a sensitive fluorescence "turn-on" response to Hg²⁺ with low detection limits of 22.65 nM. A stoichiometric ratio (2: 1) of chemosensor DY and Hg²⁺ ions was determined by a Job's plot, fluorescent titration and the ESI-MS spectra. Especially, the reversible of DY-Hg with EDTA establishes the reuse of DY, and the circulation effect was very good. Furthermore, the wide pH range of 6-10 makes it capable of application in biological systems. Moreover, DY has been successfully applied to the detection of Hg²⁺ ions and EDTA in living HeLa and HK2 cells based on low cytotoxicity and good membrane permeability.

A novel fluorescent chemosensor for detection of mercury(II) ions based on dansyl-peptide and its application in real water samples and living LNcap cells

Mercury is one of the most hazardous pollutants, and mercury pollution is a serious hazard to our environment. Herein, we designed and synthesized a new peptide-based fluorescent chemosensor (L) based on a Fmoc-Lys (Fmoc)-OH backbone conjugated with two Serines and dansyl groups using solid phase peptide synthesis (SPPS) technology. L exhibited highly selective and excellent sensitive detection of Hg²⁺ ions in 100% aqueous solutions through fluorescence quenching. The chemosensor L forms a 2:1 stoichiometry with high binding constants (4.89×10⁶M^-1) and the detection limit for Hg²⁺ ions of the proposed assay was 7.59nM. In addition, the recovery test results of Hg²⁺ concentration in actual water samples showed that the quantitative detection of Hg²⁺ ions can be realized in two water samples. Moreover, L showed low cytotoxicity and excellent membrane permeability in HK2 cells, which has been successfully applied for monitoring Hg²⁺ ions in living LNCaP cells.

A new bio-compatible Cd2+-selective nanostructured fluorescent imprinted polymer for cadmium ion sensing in aqueous media and its application in bio imaging in Vero cells

Schematic representation of Cd²⁺ recognition by the imprinted polymer and fluorescence signal creation as a result of the mentioned recognition process.

A novel fluorescent chemosensor for detection of Zn(II) ions based on dansyl-appended dipeptide in two different living cells

This paper describes a new fluorescent chemosensor (DSH) based on dipeptide conjugated with dansyl group, which was synthesized by solid phase peptide synthesis (SPPS) technology. DSH exhibited a highly selective and sensitive toward Zn²⁺ ions by "turn-on" response based on generation of monomer-excimer mechanism in aqueous solutions, and the detection limit was calculated at 11.2 nM. In addition, the reversible of DSH-Zn with Na₂EDTA establishes the reuse of DSH, and the circulation effect was very good. Moreover, DSH had good water solubility, and was successfully applied to bioimage intracellular Zn²⁺ ions and Na₂EDTA in two different living cells with exciting cellular permeability and low cytotoxicity, which indicated that DSH had great potential in the application of biological imaging.

Methods to Evaluate Skin Penetration In Vitro

Dermal and transdermal drug therapy is increasing in importance nowadays in drug development. To completely utilize the potential of this administration route, it is necessary to optimize the drug release and skin penetration measurements. This review covers the most well-known and up-to-date methods for evaluating the cutaneous penetration of drugs in vitro as a supporting tool for pharmaceutical research scientists in the early stage of drug development. The aim of this article is to present various experimental models used in dermal/transdermal research and summarize the novel knowledge about the main in vitro methods available to study skin penetration. These techniques are: Diffusion cell, skin-PAMPA, tape stripping, two-photon microscopy, confocal laser scanning microscopy, and confocal Raman microscopic method.