A new fluorescent chemosensor for copper ions based on tripeptide glycyl-histidyl-lysine (GHK)

Synergistic integration of a rhodamine-labelled tripeptide into AIE-active fluorogenic probe: Enabling nanomolar detection of Al3+ ions through test strips, thin films, and Arduino-assisted optosensing platform

Peptide-fluorophore conjugates (PFCs) have been expeditiously utilized for metal ion recognition owing to their distinctive characteristics. Selective detection and quantification of aluminum is essential to minimize health and environmental risks. Herein, we report the synthesis and characterization of a new chemoprobe with aggregation-induced emission characteristics by chemically conjugating rhodamine-B fluorophore with a tripeptide. The probe revealed β-sheet secondary conformation in both solid and solution states, as confirmed by FT-IR, PXRD, and CD experiments. AIE characteristics of the probe in water-MeCN mixtures revealed the formation of spherically shaped nanoaggregates with an average size of 353 ± 7 nm, as confirmed by SEM, TEM, and DLS studies. The probe exhibited a large stokes shift (175 nm) and displayed selective colorimetric and fluorometric responses towards Al3+ ions with an extremely low detection limit (51 nm) and a fast response time (≤15 s). Comparative NMR studies confirmed the cleavage of spirolactam ring upon aluminum binding. The probe's practicality was enhanced through integration into test strips and thin films, allowing solid-phase detection of Al3+ ions. Furthermore, an RGB-Arduino enabled optosensing device has been developed to enable instant quantifiable analysis of aluminum concentrations in real-time conditions.

Development of a novel hypochlorite ratio probe based on coumarin and its application in living cells

Hypochlorous acid is a reactive oxygen species that is widely present in the body and has been found to exhibit an elevated concentration in tumors. As a result, fluorescent probes for tumor detection have recently gained significant attention. In this study, we designed and synthesized a novel ratiometric fluorescent probe, LW-1, using coumarin as a scaffold, and characterized its spectral properties. LW-1 displayed indigo blue fluorescence at low concentrations of hypochlorous acid. As the concentration of hypochlorous acid increased, the probe underwent a reaction, resulting in a red shift in its fluorescence peak and exhibiting green fluorescence. The fluorescence intensity ratio (green/blue) was a susceptible detection signal for HClO. LW-1 exhibited favorable characteristics, including a low detection limit, high sensitivity, good stability, and low background interference. The detection limit has reached 2.4642 nM. Moreover, we successfully employed LW-1 to image normal human liver and colon cancer cells in vitro, demonstrating its potential as a promising tool for tumor detection. Overall, our findings suggest that LW-1 could serve as a valuable addition to the current arsenal of fluorescent probes for tumor detection, with potential applications in the diagnosis and treatment of cancer.

Spiroindeno-pyridineindoles (SIPIs) as new visible colorimetric pH indicators

Some new, highly selective, and sensitive colorimetric pH indicators, spiro[4H-indeno-[1,2-b]pyridine-4,3'-[3H]indoles] (SIPIs) in aqueous solution were developed. SIPIs were synthesized via a one-pot four-component condensation of isatin derivatives, β-diketones 1,3-indandione, and ammonium acetate using FSi-PrNH-BuSO₃H as a nanocatalyst in EtOH. According to the experimental evaluations, it was found that SIPI derivatives are pH indicators for naked-eye detection of OH- ion with intense color changes from orange to purple in the pH range of 10.3-12.

A novel isatin-based probe for ratiometric and selective detection of Hg2+ and Cu2+ ions present in aqueous and environmental samples

A novel isatin derivative (1) is UV-Visible active and displays about 90 nm bathochromic shift upon interaction with only Hg²⁺ and Cu²⁺, but not with other common metal ions. Also, the colorless probe 1 turns to brick-red and yellow in the presence of Hg²⁺ and Cu²⁺, respectively. Addition of increasing amounts of Hg²⁺ or Cu²⁺ to 1 leads to the emergence of a new absorption at ~470 nm (due to LMCT), with a concomitant decrease in the intensity of absorption of 1 at ~380 nm, and thereby provides a ratiometric response. Common metal ions and anions do not interfere with the interactions of 1 with Hg²⁺or Cu²⁺ ions. Probe 1 shows very high sensitivity and selectivity towards Hg²⁺ and Cu²⁺ as revealed by their very low detection limits 0.95 × 10^-9 M and 1.5 × 10^-9 M, respectively. Formation of 1:1 complex with Hg²⁺ and 2:1 complex with Cu²⁺ is confirmed using NMR, ESI-MS and FT-IR techniques, Job plot and DFT calculations. Selective detection of Hg²⁺ from Cu²⁺ is established from the ratiometric response caused by β-mercaptoethanol. Advantages of the probe 1 in terms of high sensitivity, stability in the physiological pH and suitability for dual detection are presented. Probe impregnated silica plates for onsite detection of Hg²⁺ and Cu²⁺ present in environmental samples is also demonstrated.

Antioxidants as an Epidermal Stem Cell Activator

Antioxidants may modulate the microenvironment of epidermal stem cells by reducing the production of reactive oxygen species or by regulating the expression of extracellular matrix protein. The extracellular membrane is an important component of the stem cell niche, and microRNAs regulate extracellular membrane-mediated basal keratinocyte proliferation. In this narrative review, we will discuss several antioxidants such as ascorbic acid, plant extracts, peptides and hyaluronic acid, and their effect on the epidermal stem cell niche and the proliferative potential of interfollicular epidermal stem cells in 3D skin equivalent models.

Drug-Bearing Supramolecular MMP Inhibitor Nanofibers for Inhibition of Metastasis and Growth of Liver Cancer

Treatment of hepatocellular carcinoma (HCC) requires sustained suppression of tumor cell growth and metastasis for long-term efficacy. However, traditional intratumoral drug delivery system always exhibits burst release with less therapeutic outcomes. Here, a new self-assembling amphiphilic peptide drug conjugate (SAAPDC) is fabricated as a "two-in-one" nanofiber system comprising a hexapeptide as a matrix metalloproteinases (MMP) inhibitor and doxorubicin (DOX) for the treatment of HCC. The results indicate that doxorubicin-conjugated peptide (DOX-KGFRWR) self-assembles to form long nanofibers showing sustained release property for inhibiting the enzymatic activities of MMP-2 and MMP-9. This nanofiber not only inhibits tumor growth in situ but also effectively prevents pulmonary metastasis in an SMMC7721 cell line-based mouse model. In summary, this hexapeptide-based supermolecule system represents a promising nanoscale platform to sustain drug release with high loading capacity for intratumoral administration. Moreover, the delivery of chemotherapeutic drugs via drug-bearing supramolecular MMP inhibitor nanofibers simultaneously inhibits metastasis and tumor growth to achieve synergistic effects for metastatic HCC therapy.

A new Schiff-base chemosensor for selective detection of Cu2+ and Co2+ and its copper complex for colorimetric sensing of S2- in aqueous solution

A new Schiff-base colorimetric chemosensor 1 was developed for the detection of Cu²⁺, Co²⁺ and S^2-. Sensor 1 could simply monitor Cu²⁺ and Co²⁺ by a color change from colorless to yellow. The binding modes of 1 to Cu²⁺ and Co²⁺ were determined to be a 2 : 1 complexation stoichiometry through Job's plot and ESI-mass spectrometry analysis. The detection limits (0.02 μM and 0.63 μM) for Cu²⁺ and Co²⁺ were lower than the recommended values (31.5 μM and 1.7 μM) by the World Health Organization (WHO) for Cu²⁺ and the Environmental Protection Agency (EPA) for Co²⁺, respectively. Importantly, 1 could detect and quantify Cu²⁺ in real water samples. In addition, the Cu²⁺-2·1 complex could be used as a highly selective colorimetric sensor for S^2- in the presence of other anions without any interference. Moreover, the sensing mechanisms of Cu²⁺ and Co²⁺ by 1 were explained by theoretical calculations.

Selective recognition of Cu (II) and Fe (III) using a pyrene based chemosensor

A pyrene-based colorimetric chemosensor 1-(pyren-1-yl)-N,N-bis-(pyridine-2-ylmethyl)methanamine (1) was synthesised for selective detection of Cu (II) and Fe (III) over the other metal cations Ni²⁺, Mg²⁺, Cd²⁺, Hg²⁺, Na⁺, K⁺, Ca²⁺, Co²⁺, Cr³⁺, Pb²⁺ and Zn²⁺. The significant changes in UV-vis absorption band of receptor 1 and the emergence of 660nm band in presence of Cu²⁺ ion indicates the selective binding of Cu²⁺ ion as compared to other metal cations which could easily be identified from the naked eye strong colour change. Job plots suggest a 1:1 and 2:1 stoichiometric binding of Cu²⁺ and Fe³⁺, respectively, which was evidenced by ESI-MS analysis. Chemosensor 1 explores a cost-effective and selective colorimetric sensor for naked eye detection of trace amount of Cu²⁺ and Fe³⁺ ions in presence of other metal cations.

Spirolactam capped cyanine dyes for designing NIR probes to target multiple metal ions

This work reports cyanine based spirocyclic metal ion probes, showing a fluorescence turn-on response to various metal ions in the near-infrared spectral region.

Cooperative, ion-sensitive co-assembly of tripeptide hydrogels

Computational simulations and experimental validation of cooperative co-assembly of structural and functional tripeptides shows selective hydrogel formation in response to complexation with copper.

A colorimetric sensor for the sequential detection of Cu(2+) and CN(-) in fully aqueous media: practical performance of Cu(2+)

A new highly selective colorimetric chemosensor 1 (E)-9-(((5-mercapto-1,3,4-thiadiazol-2-yl)imino)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol was designed and synthesized for the sequential detection of Cu(2+) and CN(-). This sensor 1 exhibited an obvious color change from yellow to orange in the presence of Cu(2+) in a fully aqueous solution. The detection limit (0.9 μM) of 1 for Cu(2+) is far lower than the WHO limit (31.5 μM) for drinking water. In addition, the resulting Cu(2+)-2· 1 complex can be further used to detect toxic cyanide through a color change from orange to yellow, indicating the recovery of 1 from Cu(2+)-2·1. Importantly, chemosensor 1 could be used to detect and quantify Cu(2+) in water samples, and a colorimetric test strip of 1 for the detection of Cu(2+) could be useful for all practical purposes.

A novel displacement-type colorimetric chemosensor for the detection of Cu2+and GSH in aqueous solution

A new selective and sensitive chemosensor1for the sequential detection of Cu²⁺and GSHvianaked-eye has been developed.

Highly selective ratiometric peptide-based chemosensors for zinc ions and applications in living cell imaging: a study for reasonable structure design

The relationship between the structure and activity for the fluorescent sensing of zinc ions with H₂L peptides has been studied experimentally and computationally.

A colorimetric and fluorometric investigation of Cu(ii) ion in aqueous medium with a fluorescein-based chemosensor

A colorimetric and fluorometric chemosensor, 1,4-bis(1-fluorescein)-2,3-diaza-1,3-butadiene (L, 3) as Schiff base is developed for naked-eye detection of Cu²⁺ ion in aqueous medium due to the formation of a 1 : 1 copper–ligand complex.

A peptide-based fluorescent chemosensor for measuring cadmium ions in aqueous solutions and live cells

A novel peptide fluorescent chemosensor (H2L) with a lysine backbone and both -NH2 sites conjugated with cysteine and dansyl groups has been designed and synthesized by solid phase peptide synthesis with Fmoc chemistry. This chemosensor is a promising analytical tool for detecting Cd(2+) based on the photo-induced electron transfer (PET) effect by turn-on response in 100% aqueous solutions. As designed, H2L exhibits excellent cell permeation and low biotoxicity as well as displaying relatively high selectivity and sensitivity. The chemosensor penetrated live HeLa cells and detected intracellular Cd(2+) by turn-on response. The binding stoichiometry and affinity, interference test, pH sensitivity, fluorescence quantum yield, quantum mechanical calculations, lifetimes, and cytotoxicity of the chemosensor H2L to Cd(2+) were also investigated. Moreover, H2L exhibits low biotoxicity with a limit of detection (LOD) for Cd(2+) of about 52 nM, implying that H2L can be used as a highly selective and sensitive peptide fluorescent chemosensor in biological systems.

Specific fluorescent sensing of aluminium using naphthalene benzimidazole derivative in aqueous media

Naphthalene benzimidazole conjugate bearing a hydroxyl group was synthesized. Its binding properties towards various metal ions were examined and it showed a high selectivity and sensitivity towards Al(3+) ions in aqueous media. The recognition processes follows a photo induced electron transfer (PET) mechanism assisted with the restricted intramolecular C-C single bond rotation and are scarcely influenced by other coexisting metal ions. In addition, determination of Al(3+) in a variety of sewage water samples was also determined.

Optimization of an analytical method for the spectrophotometric determination of copper in tea and water samples after ultrasonic assisted cloud point extraction using a benzothiazole fluorescein derivative complexing agent

BTF is exists with spirolactone species with adding Cu²⁺, which leads to the absorbance intensity is decreased gradually and the decrease of the absorbance value is linear for Cu²⁺.

A highly selective and sensitive single click novel fluorescent off–on sensor for copper and sulfide ions detection directly in aqueous solution using curcumin nanoparticles

Graphical representation of the binding of CURNPs to Cu²⁺(fluorescence off) and release of CURNPs (fluorescence on) by the reaction of S²⁻with copper bound to CURNPs.

Selective electrochemical determination of trace level copper using a salicylaldehyde azine/MWCNTs/Nafion modified pyrolytic graphite electrode by the anodic stripping voltammetric method

Schematic illustration of Cu²⁺in solution detection using a SA/MWCNTs/Nafion modified PGE.

A novel peptide-based fluorescent chemosensor for measuring zinc ions using different excitation wavelengths and application in live cell imaging

A novel peptide-based fluorescent chemosensor containing both tryptophan and a dansyl fluorophore has been designed to detect Zn²⁺ in 100% aqueous solution and living cells via two pathways including fluorescence resonance energy transfer and chelation enhanced fluorescence.

DNA as sensors and imaging agents for metal ions

Increasing interest in detecting metal ions in many chemical and biomedical fields has created demands for developing sensors and imaging agents for metal ions with high sensitivity and selectivity. This review covers recent progress in DNA-based sensors and imaging agents for metal ions. Through both combinatorial selection and rational design, a number of metal-ion-dependent DNAzymes and metal-ion-binding DNA structures that can selectively recognize specific metal ions have been obtained. By attachment of these DNA molecules with signal reporters such as fluorophores, chromophores, electrochemical tags, and Raman tags, a number of DNA-based sensors for both diamagnetic and paramagnetic metal ions have been developed for fluorescent, colorimetric, electrochemical, and surface Raman detection. These sensors are highly sensitive (with a detection limit down to 11 ppt) and selective (with selectivity up to millions-fold) toward specific metal ions. In addition, through further development to simplify the operation, such as the use of "dipstick tests", portable fluorometers, computer-readable disks, and widely available glucose meters, these sensors have been applied for on-site and real-time environmental monitoring and point-of-care medical diagnostics. The use of these sensors for in situ cellular imaging has also been reported. The generality of the combinatorial selection to obtain DNAzymes for almost any metal ion in any oxidation state and the ease of modification of the DNA with different signal reporters make DNA an emerging and promising class of molecules for metal-ion sensing and imaging in many fields of applications.

A colorimetric “naked-eye” Cu(ii) chemosensor and pH indicator in 100% aqueous solution

A highly selective and sensitive colorimetric Cu²⁺-chemosensor and pH probe for practical use in water has been developed.

NIR- and FRET-based sensing of Cu2+ and S2- in physiological conditions and in live cells

We have synthesized a new indole functionalized rhodamine derivative L(1) which specifically binds to Cu(2+) in the presence of large excess of other competing ions with visually observable changes in their electronic and fluorescence spectral behavior. These spectral changes are significant enough in the NIR and visible region of the spectrum and thus enable naked eye detection. The receptor, L(1), could be employed as a resonance energy transfer (RET) based sensor for detection of Cu(2+) based on the process involving the donor indole and the acceptor Cu(2+) bound xanthene fragment. Studies reveal that L(1)-Cu complex is selectively and fully reversible in presence of sulfide anions. Further, fluorescence microscopic studies confirmed that the reagent L(1) could also be used as an imaging probe for detection of uptake of these ions in HeLa cells.

A molecular beacon and graphene oxide-based fluorescent biosensor for Cu(2+) detection

In this work, we report a "turn-on" fluorescent strategy for the direct detection of Cu(2+) in solutions using molecular beacons (MBs) and graphene oxide (GO). MBs are special single-stranded DNA and carry fluorescence sources. GO is a new nanomaterial having remarkable physical properties. In the sensing system, GO was used as an efficient fluorescence quencher upon the adsorption of MBs, which reduced the background signal and made the detection method highly sensitive. In the presence of Cu(2+), the MBs were cut into short pieces and released by the GO, leading to fluorescence restoration. The detection limit of the sensing strategy was ∼50nM, which is sufficiently sensitive for practical applications. The sensing method also exhibited high selectivity in testing samples containing other metal ions. The application of the method for drinking water is demonstrated.

Through bond energy transfer: a convenient and universal strategy toward efficient ratiometric fluorescent probe for bioimaging applications

Fluorescence resonance energy transfer (FRET) strategy has been widely applied in designing ratiometric probes for bioimaging applications. Unfortunately, for FRET systems, sufficiently large spectral overlap is necessary between the donor emission and the acceptor absorption, which would limit the resolution of double-channel images. The through-bond energy transfer (TBET) system does not need spectral overlap between donor and acceptor and could afford large wavelength difference between the two emissions with improved imaging resolution and higher energy transfer efficiency than that of the classical FRET system. It seems to be more favorable for designing ratiometric probes for bioimaging applications. In this paper, we have designed and synthesized a coumarin-rhodamine (CR) TBET system and demonstrated that TBET is a convenient strategy to design an efficient ratiometric fluorescent bioimaging probe for metal ions. Such TBET strategy is also universal, since no spectral overlap between the donor and the acceptor is necessary, and many more dye pairs than that of FRET could be chosen for probe design. As a proof-of-concept, Hg(2+) was chosen as a model metal ion. By combining TBET strategy with dual-switch design, the proposed sensing platform shows two well-separated emission peaks with a wavelength difference of 110 nm, high energy transfer efficiency, and a large signal-to-background ratio, which affords a high sensitivity for the probe with a detection limit of 7 nM for Hg(2+). Moreover, by employing an Hg(2+)-promoted desulfurization reaction as recognition unit, the probe also shows a high selectivity to Hg(2+). All these unique features make it particularly favorable for ratiometric Hg(2+) sensing and bioimaging applications. It has been preliminarily used for a ratiometric image of Hg(2+) in living cells and practical detection of Hg(2+) in river water samples with satisfying results.