A novel peptide-based fluorescent probe for highly selective detection of mercury (II) ions in real water samples and living cells based on aggregation-induced emission effect

Ru@UiO-66-NH2 MOFs-Based Dual Emission Ratiometric Fluorescence for Sensitive Sensing of Arginine

Arginine has been widely applied in the food industry as coloring agents, flavoring agents, and nutritional fortifiers. It is also one of the major components of feed additives. Currently, methods for the highly selective detection of arginine remain absent. For accurate and sensitive detection of L-arginine, a novel ratiometric fluorescence assay based on Ru@UiO-66-NH2 was developed and demonstrated in this study. Under optimized detection conditions, the limit of detection (LOD) of this assay for L-arginine was 2.32 μM, which is superior to most assays reported to date. Meanwhile, Ru@UiO-66-NH2 showed good stability within 30 days, demonstrating the wide applicability of the proposed assay. The spike-and-recovery rates of the proposed assay for L-arginine in real samples (e.g., tea, grape juice, and serum) were 84.27-113.09%. Overall, the proposed assay showed high sensitivity, good reproducibility, and excellent stability in the detection of L-arginine in both buffer and real samples.

A highly sensitive and selective fluorescent "on-off-on" peptide-based probe for sequential detection of Hg2+ and S2- ions: Applications in living cells and zebrafish imaging

Mercury ions (Hg2+) and sulfur ions (S2-), have caused serious harm to the ecological environment and human health as two kinds of highly toxic pollutants widely used. Therefore, the visual quantitative determination of Hg2+ and S2- is of great significance in the field of environmental monitoring and medical therapy. In this study, a novel fluorescent "on-off-on" peptide-based probe DNC was designed and synthesized using dipeptide (Asn-Cys-NH2) as the raw material via solid phase peptide synthesis (SPPS) technology with Fmoc chemistry. DNC displayed high selectivity in the recognition of Hg2+, and formed non-fluorescence complex (DNC-Hg2+) through 2:1 binding mode. Notably, DNC-Hg2+ complex generated in situ was used as relay response probe for highly selective sequential detection of S2- through reversible formation-separation. DNC achieved highly sensitive detection of Hg2+ and S2- with the detection limits (LODs) of 8.4 nM and 5.5 nM, respectively. Meanwhile, DNC demonstrated feasibility for Hg2+ and S2- detections in two water samples, and the considerable recovery rate was obtained. More importantly, DNC showed excellent water solubility and low toxicity, and was successfully used for consecutive discerning Hg2+ and S2- in test strips, living cells and zebrafish larvae. As an effective visual analysis method in the field, smartphone RGB Color Picker APP realized semi-quantitative detections of Hg2+ and S2- without the need for complicated device.

Construction of a novel fluorescent probe for sensitive determination of glyphosate in food and imaging living cells

Glyphosate is a widely used broad-spectrum herbicide in agriculture and horticulture to control a variety of weeds and undesirable plants. However, the excessive use of glyphosate has raised a number of environmental and human health concerns. It is urgent to develop tools to detect glyphosate. Herein, a novel dual-signal probe CCU-Cu2+ was designed and synthesized on the basis of CCU. CCU exhibited excellent selectivity and great sensitivity for Cu2+ which were based on both fluorescence "turn-off" reaction and comparative color visualisation methods. Due to the strong chelating ability of glyphosate on Cu2+, the CCU-Cu2+ complex was applied to glyphosate detection in practical samples. The experimental results in vitro showed that the CCU-Cu2+ complex was highly selective and rapid, with a low detection limit (1.6 μM), and could be recognised by the naked eye in the detection of glyphosate. Based on the excellent properties of the CCU-Cu2+ complex, we also constructed a smartphone-assisted detection sensing system for glyphosate detection, which has the advantages of precision, sensitivity, and high interference immunity. Moreover, the CCU-Cu2+ complex was also successfully employed for exogenous glyphosate imaging in living cells. These characteristics demonstrated that CCU-Cu2+ holds significant potential for detection and imaging of glyphosate in bio-systems.

A novel colormetric and light-up fluorescent sensor from flavonol derivative grafted cellulose for rapid and sensitive detection of Hg2+ and its applications in biological and environmental system

Mercury ion (Hg2+) is one of harmful heavy metal ions that can accumulate inside the human organism and cause some health problems. In the article, a highly effective fluorescent probe named EC-T-PCBM was prepared by grafting flavonol derivatives onto ethyl cellulose for the specific recognition of Hg2+. EC-T-PCBM exhibited a remarkable fluorescence light-up response toward Hg2+ with excellent sensitivity. EC-T-PCBM possessed several prominent sensing properties for Hg2+, such as low detection limit (43.9 nM), short response time (5 min), and wide detection pH range (6-9). The response mechanism of EC-T-PCBM to Hg2+ has been verified through 1H NMR titration and DFT computation. Additionally, EC-T-PCBM not only can be used for accurately determining trace amount of Hg2+ in actual environmental water samples, but also can serve as a portable and rapid device by loading it on test strips for sensitive and selective visualization of Hg2+. More importantly, the confocal fluorescence imaging of onion cells suggested the favorable cell membrane permeability of EC-T-PCBM and its prominent ability to continuously monitor the enrichment from Hg2+ within fresh plant tissues.

A novel ratiometric peptide-based fluorescent probe for sequential detection of Hg2+ and S2- ions and its application in living cells and zebrafish imaging

A new ratiometric peptide-based fluorescent probe DWPH was designed and synthesized, comprising dansyl fluorophore as a fluorescent dye, and tripeptide backbone (Trp-Pro-His-NH2) as a recognition group. The addition of Hg2+ caused the maximum emission peak of DWPH to blue shift from 560 nm to 510 nm. DWPH exhibited large Stokes shift (230 nm), satisfactory water solubility (100 % aqueous medium), good selectivity (only Hg2+), high sensitivity (24.6 nM), rapid response (within 50 s) and strong anti-interference ability for Hg2+ detection over a wide pH range (7-11). Additionally, the complex DWPH-Hg2+ as a relay response probe could also be applied to S2- according to displacement approach. Notably, the detection limit for S2- was calculated as 23.3 nM, exhibiting that DWPH showed great potential for environmental monitoring and bioimaging. In addition, DWPH were successfully used to determine Hg2+ and S2- in living cells and zebrafish based on excellent permeability and low cytotoxicity. What's more, the gradient concentration color changes of Hg2+ and S2- were combined with the smartphone APP to obtain red-green-blue (RGB) values, thus enabling rapid semi-quantitative detection of Hg2+ and S2- without expensive instruments.

Naphthalimide-based fluorescent probe for Hg2+ detection and imaging in living cells and zebrafish

A simple naphthalimide-based fluorescent probe was designed and synthesized for the determination of mercury ion (Hg2+ ). The probe showed a noticeable fluorescence quenching response for Hg2+ . When added with Hg2+ , the fluorescence intensity of the probe at 560 nm was remarkably decreased with the color changed from yellow to colorless under ultraviolet (UV) light. The probe had a notable selectivity and sensitivity for Hg2+ and displayed an excellent sensing performance when detecting Hg2+ at low concentration (19.5 nM). The binding phenomenon between the probe and Hg2+ was identified by Job's method and high-resolution mass spectrometry (HRMS). Moreover, the probe was not only utilized to identify Hg2+ in real samples with satisfactory results (92.00%-110.00%) but also was successfully used for bioimaging in cells and zebrafish. The recognition mechanism has been verified by transmission electron microscopy (TEM) for the first time. All the results showed that the probe could be used as a potent useful tool for detection of Hg2+ .

Novel design of near-infrared fluorescent sensors for the detection of Hg2+ in living cells and real water samples

Mercury sensing and imaging in the bio-system is essential for comprehending its toxicity and therapies. Based on the merocyanine scaffold, we designed and synthesized two novel near-infrared (NIR) fluorescent probes for detecting Hg2+. The release of chloro-substituted merocyanine structure on the probe CyHg-Cl enables fluorescence enhancement rapidly by introducing Hg2+. In addition, the probe CyHg-Cl exhibits NIR emission and a low detection limit of 0.59 µM. Finally, the probe CyHg-Cl was used to detect Hg2+ in live cells and real water samples.

A novel Cu(II)-assisted peptide fluorescent probe for highly sensitive detection of glyphosate in real samples: real application in test strips and smartphone

Glyphosate (Glyp) is an organophosphorus herbicide, and its abuse causes potential harm to the environment and human health. Thus, the development of simple and portable methods for rapid and visual detection of glyphosate is of great importance. Herein, we successfully developed a new fluorescent probe L with dansyl fluorophore as a fluorescent dye and tetrapeptide (Ala-Ser-Arg-His-NH2) as a recognition group. According to the design, L exhibited a specific fluorescence quenching response to Cu2+ and formed an L-Cu2+ ensemble with a molecular ratio of 2:1, demonstrating a limit of detection (LOD) as low as 12.04 nM. Interestingly, the L-Cu2+ ensemble as a relay response probe exhibited a specific fluorescence "off-on" response to glyphosate without interference from other pesticides and anions based on the strong complexation of glyphosate and Cu2+. The LOD of the L-Cu2+ ensemble for glyphosate was calculated as 12.59 nM. Additionally, the results of three recovery experiments with real samples showed that L has good practicability and accuracy in detecting glyphosate. Test strips were also fabricated to achieve facile detection of glyphosate to demonstrate the practical application potential of the L-Cu2+ ensemble. The L-Cu2+ ensemble was integrated with a smartphone for semi-quantification of glyphosate in a field environment under a 365 nm UV lamp.

A reversible CHEF-based NIR fluorescent probe for sensing Hg2+ and its multiple application in environmental media and biological systems

Hg²⁺ poses a great threat to human health and the environment due to its bioaccumulation and permanent damage. Herein, a reversible CHEF-based near-infrared fluorescent probe 2-(3-((E)-4-((E)-4-(diethylamino)-2- hydroxybenzylidene)amino)styryl)-5,5-dimethylcyclohex-2-en-1-ylidene)propanedinitrile (DHEY) capable of specifically recognizing Hg²⁺ was constructed. DHEY exhibits advantages of large Stokes shift (157 nm), excellent selectivity, high sensitivity (LOD = 3.2 μg/L), and fast response efficiency (<3 min). Interestingly, DHEY can also realize rapid and effective detection of Hg²⁺ after being recycled 7 times. The successful recovery of trace Hg²⁺ in different environmental water samples fully demonstrates the potential of DHEY for actual applications. In particular, DHEY enables real-time observation of the distribution and translocation pattern of exogenous Hg²⁺ in HeLa cells and zebrafish. This work provides important theoretical support for investigating the fate of heavy metal ions in the environment using fluorescence techniques.

A novel fluorescent probe based on a tripeptide-Cu(II) complex system for detection of histidine and its application on test strips and smartphone

Herein, we reported a novel peptide-based fluorescent probe DSSH for highly selective and sensitive detections of both Cu²⁺ and _l-histidine (_l-His). DSSH exhibited different color changes and fluorescence "on-off" response toward Cu²⁺ with a 2:1 binding stoichiometry, and the limit of detection (LOD) for Cu²⁺ was calculated to be 22.9 nM. The in situ formed DSSH-Cu²⁺ ensemble showed obvious fluorescence "off-on" response to _l-His based on replacement reaction with Cu²⁺, as well as the discernable color changes under 365 nm UV lamp irradiation with "naked eye". The specificity of Cu²⁺/_l-His interactions allowed _l-His to be determined without interference from other amino acids, and the detection limit of DSSH-Cu²⁺ ensemble response to _l-His was determined as 25.7 nM. Notably, DSSH was successfully applied for detecting Cu²⁺ and _l-His in RKO living cells owing to its remarkable fluorescence behavior and low cytotoxicity. Test strips experiments suggested that DSSH can recognize Cu²⁺ and _l-His together by a remarkable fluorescence change. More importantly, smartphone was combined with _l-His solutions of different concentrations and converted into digital values through RGB channels, which was successfully used for semi-quantitative identification of _l-His, and the limit of detection (LOD) was 0.97 μM.

A novel peptide-based relay fluorescent probe with a large Stokes shift for detection of Hg2+ and S2- in 100 % aqueous medium and living cells: Visual detection via test strips and smartphone

Herein, a novel relay peptide-based fluorescent probe DGRK was synthesized via solid phase peptide synthesis (SPPS) technology. DGRK exhibited excellent water-solubility, good stability, remarkably large Stokes shift (230 nm) and high selectivity response to Hg²⁺ with a non-fluorescence complex DGRK-Hg²⁺ formation via a 1:1 binding mode. Further studies indicated that the DGRK-Hg²⁺ complex could act as a secondary probe for rapidly and sequentially detecting S^2- based on fluorescent "off-on" response, and without interference from a range of anions. The limit of detection (LOD) for Hg²⁺ and S^2- were calculated to be 33.6 nM and 60.9 nM, respectively. In addition, The reversibility of interaction of confirmed that the continuous and reversible recognition behavior of Hg²⁺ and S^2- by the probe DGRK, and could be cycled more than 5 times. In addition, DGRK could be successfully applied to the fluorescence imaging of Hg²⁺ and S^2- in two living cells based on excellent cells permeability and low cytotoxicity. Meanwhile, DGRK was successfully used to create the low-cost and portable test strips for visual detection and rapid analysis under 365 nm UV lamp, and the test strips combined with a smartphone (RGB color) was successfully applied to the semi-quantitative analysis and monitoring of dynamic changes of Hg²⁺ levels.