Selective Turn-on Fluorescence Research Articles

Highly selective fluorescence turn-on sensor for·thiol compounds detection

As a kind of commonly-used synthetic materials for many pesticides, thiol compounds, once being leaked, can cause serious harm to the environment and humans. Therefore, the efficient detection of thiol compounds is essential. In this study developed a turn-on fluorescent probe (Cu@Zn-CP) for the highly sensitive fluorescence detection of thiol compounds. The probe was constructed based on a zinc coordination polymer (Zn-CP), whose fluorescence was quenched through the effective doping of Cu2+ ions. After the introduction of methyl thioglycolate (MTC), a rapid fluorescence turn-on response was generated within 90 s with a low detection limit of 23 ppb. Even after being reused for five cycles, the sensor maintains excellent detection performance and demonstrates good recyclability. It can also detect MTC in river water, with a spike recovery rate between 98–103 %. Furthermore, the designed Cu@Zn-CP exhibits good universality for detecting multifarious thiol compounds, including L-cysteine, glutathione, monothioglycerol, and 2-hydroxy-1-ethanethiol. This result provides a potential recyclable fluorescent sensor for thiol compounds.

Fluorescence Turn-on Detection of Perfluorooctanoic Acid (PFOA) by Perylene Diimide-Based Metal-Organic Framework.

A novel, water-stable, perylene diimide (PDI) based metal-organic framework (MOF), namely, U-1, has been synthesized for selective and sensitive detection of perfluorooctanoic acid (PFOA) in mixed aqueous solutions. The MOF shows highly selective fluorescence turn-on detection via the formation of a PFOA-MOF complex. This PFOA-MOF complex formation was confirmed by various spectroscopic techniques. The detection limit of the MOF for PFOA was found to be 1.68 μM in an aqueous suspension. Upon coating onto cellulose paper, the MOF demonstrated a significantly lower detection limit, down to 3.1 nM, which is mainly due to the concentrative effect of solid phase extraction (SPE). This detection limit is lower than the fluorescence sensors based on MOFs previously reported for PFAS detection. The MOF sensor is regenerable and capable of detecting PFOA in drinking and tap water samples. The PDI-MOF-based sensor reported herein represents a novel approach, relying on fluorescence turn-on response, that has not yet been thoroughly investigated for detecting per- and polyfluoroalkyl substances (PFAS) until now.

A turn-on fluorescent probe based on pyrene for hydrazine detection

This paper presents a novel fluorescent probe (GNEM) based on a pyrene fluorophore, with dicarboximide as the recognition unit for hydrazine. The fluorescence probe can be synthesized in a simple one-step process. A highly selective and sensitive fluorescence turn-on GNEM synthesized. GNEM react with hydrazine through nucleophilic addition, leading to the deprotection of dicarboximide and the release of dicarboximide hydrazine, resulting in significant blue fluorescence. This enhanced emission is attributed to the intramolecular charge transfer (ICT) sensing mechanism of GNEM. In addition, detection of hydrazine in soil and water is conducted. By designing a simple detection device, the hydrazine content in the air can be quantitatively measured.

The carbon dots based on Nile red: The preparation and application to probe α-synuclein fibrils

The aggregation of α-synuclein often links to the occurrence and development of Parkinson’s disease (PD). It is crucial to detect the α-synuclein fibril or monitor the aggregation of monomer for pharmacological and pathological researches, drug development and clinical diagnosis, etc. In this study, the Nile red (NR)-based carbon dots (NR-CDs) were meticulously designed and prepared. The NR-CDs were sensitive to the microenvironment, exhibiting enhanced fluorescence intensity with the elevated viscosity and decreased polarity. Thus, the NR-CDs exhibited high affinity towards α-synuclein fibril with remarkable red fluorescence enhancement, but did not respond to its monomer. Hence, the NR-CDs were used as the turn-on fluorescence probe to detect and image α-synuclein fibrils both in vitro and in vivo, as well as to monitor the aggregation process of the amyloids. Superior to NR dye, NR-CDs were characteristic of lower toxicity, better water dispersibility and anti-photobleaching resistance. In addition, the NR-CDs were demonstrated to inhibit the aggregation of α-synuclein, holding the potential as the therapeutic agent. The present study provided an effective way of designing the CDs using the small molecular dye as the carbon source to improve the biocompatibility and detectability, while reserve the selective turn-on fluorescence towards amyloid aggregates. This strategy may be generalized to construct more fluorescence probes with desired properties.

Water bridges as the trigger in an amino functionalized Zn-MOF for highly selective and sensitive fluorescent sensing of water

Water is a fundamental element for life. The highly selective and sensitive sensing of water is always attractive for mankind in activities such as physiological processes study and extraterrestrial life exploration. Fluorescent MOFs with precise channels and functional groups might specifically recognize water molecules with hydrogen-bond interaction or coordination effects and work as water sensors. As a proof of concept, herein, an amino functionalized Zn-MOF (named as complex 1) with pores that just right for water molecules to form hydrogen bond bridges is revealed for highly selective and sensitive fluorescent sensing of water. The single-crystal X-ray diffraction analysis indicates that the 3D framework of complex 1 is functionalized with free amino groups in the channels. Hydrogen bonds formed in the channel along b-axis as water bridges to connect two adjacent NH2bdc ligands and result in the restriction of intramolecular motions (RIM) which could responsible for the selective turn-on fluorescence response to water. Complex 1 exhibits high sensitive to trace amount of water in organic solvents and could be used for water detection in a wide range water contents. Take advantages of complex 1, portable sensors (complex 1@PMMA) were prepared and used in the highly sensitive water sensing.

Highly Selective and Portable Fluorescence Turn-On Detection of Sc3+ in Ore and Water Based on Strong Lewis Acid-Base Coordination.

Detecting scandium (Sc) with high selectivity and sensitivity is a challenging task due to its chemical similarity to other rare earth ions. Our findings show that the fluorescence of the complex fluorescent indicator calcein (CL) is quenched under acidic conditions (pH = 2), and Sc3+ strongly inhibits this process. The results demonstrate that CL forms multimers and precipitates out of the solution under acidic conditions, while Sc3+ causes a significant decrease in the scattering intensity of the solution. Additional experiments revealed that the strong Lewis acid nature of Sc3+ complexes with the carboxyl groups of CL leads to increased dispersion of CL even under acidic conditions, thus enhancing its absorption and fluorescence. The complexation ratio of Sc3+ and CL was investigated through spectral titrations and theoretical calculations. The interaction between Sc3+ and CL is the strongest among rare earth and common metal ions due to the smallest ionic radius, resulting in high selectivity. The fluorescence turn-on strategy had a linear range of 0.04 to 2.25 μM under optimal conditions, with a detection limit of 20 nM for Sc3+. The combination of 3D printing and a smartphone program allows for portable on-site analysis of Sc3+. Mineral and water samples were used to demonstrate the potential of this strategy for the rapid, selective, and sensitive analysis of low levels of Sc3+.

A phenothiazine coumarin based fluorescent probe with AIE feature for real-time detecting lysosomal ClO– in living cell

A new phenothiazine coumarin based probe WX-Lyso for detection of ClO– was developed. The probe showed obvious aggregation-induced emission (AIE) characteristic and exhibited a highly selective and sensitive turn-on fluorescence signal at 544 nm for ClO– with a large Stokes shift of 144 nm. The limit of detection (LOD) of ClO– was measured as low as 0.99 μM and a good line equation was obtained in the 0–50 μM concentration range. The detection mechanism was elucidated FT-IR, ESI-MS analysis and DFT. Furthermore, the probe had been demonstrated successfully has good lysosomal-targeting and high-contrast imaging abilities, which has the potential to become a new chemical tool and provide help for detecting ClO– in living systems.

Selective fluoride detection based on modulation of red emissive carbon dots fluorescence by zirconium-alizarin complex: Application to Nile River water and human saliva samples

Fluoride is an essential ion for dental health that is optimally supplemented through drinking water, toothpastes, and other oral hygiene products. This work reports a selective, simple, and inexpensive fluorescent sesnor for fluoride quantification. The sensor exploits the red fluorescence of carbon dots coupled with the colorimetric response of a zirconium-alizarin complex. The zirconium-alizarin exhibits an absorption band at 530 nm that overlaps the carbon dot excitation peak, resulting in inner filter effect-based quenching of the 612 nm red emission. However, in the presence of fluoride, binding disrupts the zirconium complex, releasing free alizarin with an absorption blue shifted to 420 nm. This reduces spectral overlap and restores carbon dot fluorescence. The carbon dots were synthesized by a hydrothermal method and exhibited excellent fluorescence quantum yield (16.3 %). Structural and optical characterizations were performed using TEM, XRD, XPS, FTIR, UV–vis, and fluorescence techniques. Under optimized conditions, the probe provided selective turn-on fluorescence detection of fluoride with a linear response from 1.0 to 130.0 μM and limit of detection (S/N = 3) of 0.32 μM. Practical utility was demonstrated by accurate quantification of fluoride in Nile River water and human saliva samples. This dual nanoprobe strategy offers a rapid and cost-effective platform for fluoride analysis in support of healthcare and environmental monitoring applications.

Antibody-functionalized gold nanoclusters/gold nanoparticle platform for the fluorescence turn-on detection of cardiac troponin I.

A selective fluorescence turn-on immunosensor for the specific detection of cardiac troponin I (cTnI), the potent biomarker for myocardial infarction diagnosis, was developed with a nano couple comprised of protein-stabilized gold nanocluster and gold nanoparticle. The red fluorescence of cTnI-specific antibody tagged bovine serum albumin stabilized gold nanoclusters was quenched with gold nanoparticles (AuNP) via the intensive interaction between amine and hydroxyl functionalities of BSA and AuNP. Through this, the adsorption of gold nanoclusters at the surface of AuNP, resulting in a core-satellite assembly, was assumed to quench the fluorescence emission. While in the presence of cTnI antigen, this gets disturbed due to the formation of immunocomplex between cTnI antigen and antibody, which restricts the close interaction between gold clusters and nanoparticles, thereby restoring quenched fluorescence. The enhancement in fluorescence signal is directly related to the concentration of cTnI, and this facilitates the selective detection of cTnI in the linearconcentration range 0.7 to 10ng/mL without any interference from other potentially interfering co-existing biomolecules. An appreciable limit of detection of 0.51ng/mL and a limit of quantification of 0.917ng/mL for cTnI is comparable to that of the previous report.

Highly selective near-infrared fluorescent turn-on probe with a large Stokes shift for the detection of hydrogen sulfide and imaging in live cells

The signalling molecules of hydrogen sulphide (H2S) play an important role in a variety of physiological and pathological processes, and its abnormal concentration causes Down's syndrome, Alzheimer's disease and diabetes mellitus. Thus, the development of an effective detection tool is of vital importance and challenge. In this paper, we synthesized a new “turn-on” hydrogen sulfide near-infrared fluorescent probe (DCM-H2S). Remarkably, this probe demonstrated an unanticipated level of selectivity for hydrogen sulfide (H2S) over other analytes, rendering it suitable for the precise determination of H2S in both in vitro and in vivo settings. Expectedly, the probe exhibited unexpectedly heightened selectivity for H2S compared to other analytes, making it a viable option for the specific determination of H2S in both in vitro and in vivo applications. With the addition of H2S, the probe exhibited distinct turn-on near-infrared (NIR) fluorescence intensity alterations in the DMSO/H2O system, together with a high sensitivity (LOD = 0.13 μM) and large Stokes shift (121 nm). More importantly, the probe has been successfully applied to bioimaging for real-time, dynamic tracking of exogenous and endogenous H2S. The outcomes showed that the probe (DCM-H2S) provides a rapid and effective detection tool for monitoring H2S in vivo.

A versatile sensor capable of ratiometric fluorescence detection of trace water and turn-on detection of Cu2+ modulating the binding interaction of a Cu(II) complex with BSA and DNA complemented by docking studies.

A fluorescent molecule, pyridine-coupled bis-anthracene (PBA), has been developed for the selective fluorescence turn-on detection of Cu2+. Interestingly, the ligand PBA also exhibited a red-shifted ratiometric fluorescence response in the presence of water. Thus, a ratiometric water sensor has been utilized as a selective fluorescence turn-on sensor for Cu2+, achieving a 10-fold enhancement in the fluorescence and quantum yield at 446 nm, with a lower detection limit of 0.358 μM and a binding constant of 1.3 × 106 M-1. For practical applications, sensor PBA can be used to detect Cu2+ in various types of soils like clay soil, field soil and sand. The interaction of the PBA-Cu(II) complex with transport proteins like bovine serum albumin (BSA) and ct-DNA has been investigated through fluorescence titration experiments. Additionally, the structural optimization of PBA and the PBA-Cu(II) complex has been demonstrated by DFT, and the interaction of the PBA-Cu(II) complex with BSA and ct-DNA has been analyzed using theoretical docking studies.

A pyrene–calix[4]triazolium conjugate for fluorescence recognition of hydrogen sulfate

A photoinduced electron transfer (PET) based pyrene–calix[4]triazolium conjugate was developed that exhibits selective turn-on fluorescence for HSO4−.

Selective fluorescence turn-on detection of combination cisplatin-etoposide chemotherapy based on N-CDs/GSH-CuNCs nanoprobe.

Cisplatin (CIS) and etoposide (ETP) combination therapy is highly effective for treating various cancers. However, the potential for pharmacokinetic interactions between these drugs necessitates selective sensing methods to quantitate both CIS and ETP levels in patient's plasma. This work develops a dual fluorescence probe strategy using glutathione-capped copper nanoclusters (GSH-CuNCs) and nitrogen-doped carbon dots (N-CDs) for the simultaneous analysis of CIS and ETP. The fluorescence signal of GSH-CuNCs at 615 nm increased linearly with CIS concentration while the N-CD emission at 480 nm remained unaffected. Conversely, the N-CD fluorescence was selectively enhanced by ETP with no interference with the CuNC fluorescence. Extensive materials characterization including UV-vis, fluorescence spectroscopy, XRD, and TEM confirmed the synthesis of the nanoprobes. The sensor showed high sensitivity with limits of detection of 6.95 ng mL-1 for CIS and 7.63 ng mL-1 for ETP along with excellent selectivity against potential interferences in rabbit plasma. Method feasibility was demonstrated with application to real rabbit plasma samples. The method was further applied to estimate the pharmacokinetic parameters of CIS before and after ETP coadministration. The dual nanoprobe sensing strategy enables rapid and selective quantitation of CIS and ETP levels to facilitate therapeutic drug monitoring and optimization of combination chemotherapy regimens.

A Kumujian-C based highly selective fluorescence turn-on probe enables the detection of sulfite in real samples and living cells

Kumujian-C as a small molecular fluorescent probe as a turn-on sensor for sulfite ions.

A coumarin-based multifunctional chemosensor for Cu2+/Al3+ as an AD theranostic agent: Synthesis, X-ray single crystal analysis and activity study

The pathogenesis of Alzheimer's disease (AD) is complex. So far there is no effective drug to treat the disease. The pathological changes of AD began 30 years before symptoms, so early diagnosis is considered to be important for AD treatment. Integrating diagnosis and therapy into a single regent has provided a new opportunity for AD treatment. Given that metal dyshomeostasis is thought to be one of the key factors to cause AD, a Schiff base substituted coumarin (probe 1) has been designed and synthesized as a selective metal chelator for multi-factor anti-AD in this work. The results of metal ions recognition showed that probe 1 had high selective fluorescent turn-on response to Al3+ and fluorescent turn-off response to Cu2+, due to intramolecular charge transfer (ICT) mechanism. Meanwhile, the results of both in vitro and in vivo bioactivities evaluation including metal chelation, reactive oxide species (ROS) elimination, self-/Cu2+-induced Aβ aggregation showed that 1 and 1-Cu(II) complex had excellent synergistic anti-AD activities. In addition, 1 had low cytotoxicity and was predicted to cross the blood-brain barrier (BBB). Noticeably, X-ray single crystal diffraction of 1-Cu(II) provided molecular level information to explain the structure and theranostic activity relationship. To sum up, 1 may be a promising candidate for the development of AD theranostic agent.

A highly selective fluorescence turn-on sensor for Hg2+ based on quinolimide in aqueous media and its applications

Herein, a novel fluorescent sensor QPE based on quinolimide was developed, which displayed the highly selective response to Hg2+ through the turn-on signal in aqueous media. The corresponding recognition mechanism of QPE for Hg2+ was investigated by the titration experiments, Job’s plots, HRMS, and DFT calculations analysis. QPE could detect Hg2+ in a broad pH range (pH = 4–9) with the LOD of 20 nM and the LOQ of 66 nM. Meanwhile, QPE-loaded test strips were demonstrated in the visual detection of Hg2+. Importantly, QPE exhibited the reliable capability to track Hg2+ in real water and soil samples and yeast cells, indicating that QPE could be used as a prospective tool for monitoring Hg2+ in wide fields.

Development of turn-on fluorescent sensor based on green emissive carnosine-modified tannic acid carbon dots for the selective detection of ascorbic acid

Ascorbic acid (AA) is an indispensable biological antioxidant with anti-aging potential in neurological disorders such as Parkinson’s and Alzheimer’s. Its abnormal concentrations in physiological fluids like human serum can lead to neurological complications. In this study, a turn-on fluorescent sensor was developed using dipeptide (i.e., carnosine) modification of the polyphenolic tannic acid (TA) carbon dots (CDs) (TATA-CDs) for AA detection. Blue-fluorescent TATA-CDs were synthesized using the hydrothermal treatment of the TA and ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) as a nitrogen (N) dopant. TATA-CDs were functionalized with carnosine (TATA-Car CDs) using a facile stirring reaction. Their morphological and optical properties were studied via TEM, XRD, UV–Vis, and fluorescence spectroscopy. TATA-Car CDs displayed green fluorescence with excitation and emission wavelength maxima of 400 and 509 nm, respectively. These novel CDs are responsible for the selective turn-on fluorescence sensing of AA (0 to 15 nM) when mixed with copper (Cu2+) ions and deliver a low detection limit of 1.34 nM. The practicality and feasibility of TATA-Car CDs were investigated in human serum samples. From this perspective, the proposed fluorescent sensor is more suitable for the real-time monitoring of AA in different neurological disorders.

Naphthalimide-based multiresponsive copper metal-organic framework for ratiometric detection of ClO− and turn-on sensing Fe3+, Cr3+, and Al3+ in water

Developing a single fluorescent sensor for multi-analytes with distinguishable output signals is significant but challenging. Herein a novel 2D copper metal-organic framework, namely NBCu, has been facilely prepared based on the assembling of imidazole and morpholine functionalized 1, 8-naphthalimide, 1, 3, 5-benzenetricarboxylic acid and Cu2+ ions, which presents solvent and pH stability (2.0–12.0) and thermostability. In addition, NBCu shows a significant and selective ratiometric fluorescent response to ClO− with more than 200-fold enhancement in fluorescence ratio (F473/F394), mainly due to an inhibited photoinduced electron transfer (PET) process by the hydrogen bonding interactions between morpholine and HClO that generated from ClO− in water. Meanwhile, the ClO− detection limit is determined as 82.95 nM, and the sensor can be regenerated and reused 5 times. Moreover, NBCu exhibits selective turn-on fluorescence (F394) to Fe3+, Cr3+, and Al3+ with the detection limit down to 10−8 M level and can be reused up to 5 cycles. Turn-on sensing behaviors are mainly the result of the absorbance-caused enhancement (ACE) effect and hydrogen bond destruction related to the interactions between the metal ions and the MOF. Significantly, using real water samples, NBCu can be employed as a tracer for ClO− detection.

N-Nitrosation Based Fluorescence Turn-On Nitric Oxide Probe: Kinetic and Cell Imaging Studies.

Nitric oxide (NO) is a ubiquitous messenger molecule playing a key role in various physiological and pathological processes. However, producing a selective turn-on fluorescence response to NO is a challenging task due to (a) the very short half-life of NO (typically in the range of 0.1-10 s) in the biological milieu and (b) false positive responses to reactive carbonyl species (RCS) (e.g., dehydroascorbic acid and methylglyoxal etc.) and some other reactive oxygen/nitrogen species (ROS/RNS), especially with o-phenylenediamine (OPD) based fluorosensors. To avoid these limitations, NO sensors should be designed in such a way that they react spontaneously with NO to give turn-on response within the time frame of t1/2 (typically in the range of 0.1-10 s) of NO and λem in the visible wavelength along with good cell permeability to achieve biocompatibility. With these views in mind, a N-nitrosation based fluorescent sensor, NDAQ, has been developed that is highly selective to NO with ∼27-fold fluorescence enhancement at λem = 542 nm with high sensitivity (LOD = 7 ± 0.4 nM) and shorter response time, eliminating the interference of other reactive species (RCS/ROS/RNS). Furthermore, all the photophysical studies with NDAQ have been performed in 98% aqueous medium at physiological pH, indicating its good stability under physiological conditions. The kinetic assay illustrates the second-order dependency with respect to NO concentration and first-order dependency with respect to NDAQ concentration. The biological studies reveal the successful application of the probe to track both endogenous and exogenous NO in living organisms.

Highly Selective Turn-on Fluorescence Sensor for Cd2+ Ions by TripodalOrganic Ligand.

Organic fluorescence sensor for selectively detecting and quantifying toxic heavy metal ions has received significant interest due to their environmental hazards. Herein, we have designed and synthesized a simple tripodal Schiff base ligand (1) based on hydroxy-naphthaldehyde and tris(2-aminoethyl)amine (TREN) and demonstrated highly selective turn-on fluorescence sensing of Cd2+ ions. The free ligand did not show any fluorescence in DMF. In contrast, Cd2+ (10- 4M) addition exhibited a strong enhancement of fluorescence at 450nm. Interestingly, other metal ions including Zn2+, which exhibit similar chemistry, did not show any turn-on fluorescence. The concentration-dependent studies of 1 with Cd2+ showed the detection limit of 6.78 × 10- 8M. NMR spectra of 1 with Cd2+ and computational studies were performed to understand the mechanism of sense.