Dual-emission fluorescent silica nanoparticle-based probe for ultrasensitive detection of Cu2+

Construction of a New Probe Based on Copper Chaperone Protein for Detecting Cu2+ in Cells

Biomacromolecular probes have been extensively employed in the detection of metal ions for their prominent biocompatibility, water solubility, high selectivity, and easy modification of fluorescent groups. In this study, a fluorescent probe FP was constructed. The probe FP exhibited high specificity recognition for Cu2+. With the combination of Cu2+, the probe was subjected to fluorescence quenching. The research suggested that the probe FP carried out the highly sensitive detection of Cu2+ with detection limits of 1.7 nM. The fluorescence quenching of fluorescamine was induced by Cu2+ perhaps due to the PET (photoinduced electron transfer) mechanism. The FP-Cu2+ complex shows weak fluorescence, which is likely due to the PET quenching effect from Cu2+ to fluorescamine fluorophore. Moreover, the probe FP can be employed for imaging Cu2+ in living cells. The new fluorescent probe developed in this study shows the advantages of good biocompatibility and low cytotoxicity. It can be adopted for the targeted detection of Cu2+ in cells, and it has promising applications in the mechanism research and diagnosis of Cu2+-associated diseases.

All-in-One Zinc-Doped Prussian Blue Nanozyme for Efficient Capture, Separation, and Detection of Copper Ion (Cu2+ ) in Complicated Matrixes

Copper is a vital micronutrient for lives and an important ingredient for bactericides and fungicides. Given its indispensable biological and agricultural roles, there is an urgent need to develop simple, affordable, and reliable methods for detecting copper in complicated matrixes, particularly in underdeveloped regions where costly standardized instruments and sample dilution procedures hinder progress. The findings that zinc-doped Prussian blue nanoparticle (ZnPB NP) exhibits exceptional efficiency in capturing and isolating copper ions, and accelerates the generation of dissolved oxygen in a solution of H2 O2 with remarkable sensitivity and selectivity, the signal of which displays a positive correlation with the copper level due to the copper-enhanced catalase-like activity of ZnPB NP, are presented. Consequently, the ZnPB NP serves as an all-in-one sensor for copper ion. The credibility of the method for copper assays in human urine and farmland soil is shown by comparing it to the standard instrumentation, yielding a coefficient of correlation (R2 = 0.9890), but the cost is dramatically reduced. This ZnPB nanozyme represents a first-generation probe for copper ion in complicated matrixes, laying the groundwork for the future development of a practical copper sensor that can be applied in resource-constrained environments.

Stimuli-directed selective detection of Cu2+ and Cr2O72- ions using a pH-responsive chitosan-poly(aminoamide) fluorescent microgel in aqueous media

In this work, the preparation of a pH-responsive fluorescent microgel, (NANO-PAMAM-CHT), is presented for the selective detection of Cu2+ and Cr2O72- ions. The NANO-PAMAM-CHT (nanosized polyaminoamide-chitosan microgel) is synthesized via aza-Michael addition reactions in a controlled and stepwise manner in water, using easily affordable starting materials like 1,4-diaminobutane, N,N'-methylene-bis-acrylamide, NIPAM and chitosan. NANO-PAMAM-CHT shows pH-responsive fluorescent properties, whereas the fluorescence intensity shows a pH-responsive change. Due to the selective fluorescence quenching, the microgel can detect both Cu2+ ions and Cr2O72- ions selectively at ambient pH in aqueous medium. Moreover, it can selectively differentiate between Cu2+ ion and Cr2O72- ions at pH ∼3 in water. The limits of detection for Cu2+ ions and Cr2O72- ions are reported as 16.9 μM and 2.62 μM, respectively (lower than the minimum allowed level in drinking water) at pH ∼7. Mechanistic study further reveals the dynamic quenching phenomenon in the presence of Cu2+ ions and static quenching in the presence of Cr2O72- ions.

Aggregation-Induced Emission via the Restriction of the Intramolecular Vibration Mechanism of Pinacol Lanthanide Complexes

Pinacol lanthanide complexes PyraLn (Ln = Dy and Tb) with the restriction of intramolecular vibration were obtained for the first time via an in situ solvothermal coordination-catalyzed tandem reaction using cheap and simple starting materials, thereby avoiding complex, time-consuming, and expensive conventional organic synthesis strategies. A high-resolution electrospray ionization mass spectrometry (HRESI-MS) analysis confirmed the stability of PyraLn in an organic solution. The formation process of PyraLn was monitored in detail using time-dependent HRESI-MS, which allowed for proposing a mechanism for the formation of pinacol complexes via in situ tandem reactions under one-pot coordination-catalyzed conditions. The PyraLn complexes constructed using a pinacol ligand with a butterfly configuration exhibited distinct aggregation-induced emission (AIE) behavior, with the αAIE value as high as 60.42 according to the AIE titration curve. In addition, the PyraLn complexes in the aggregated state exhibit a rapid photoresponse to various 3d metal ions with low detection limits. These findings provide fast, facile, and high-yield access to dynamic, smart lanthanide complex emissions with bright emission and facilitate the rational construction of molecular machines for artificial intelligence.

Preparation and application of carbon quantum dot fluorescent probes combined with rare earth ions

Globally, antibiotic abuse, organic contamination, and excessive heavy metal ion pollution pose serious threats to human health. In this case, ratiometric fluorescent probes can eliminate the errors caused by environmental factors and provide more accurate detection results than single-emission intensity nanoprobes. Accordingly, based on the excellent biocompatibility and abundant surface functional groups of carbon quantum dots (CQDs) and the properties of large Stokes shifts and narrow emission bands of rare earth ions (RE3+), RE-CQD fluorescent probes have attracted widespread attention. Herein, firstly we review the combination of carbon quantum dots with rare earth ions (rare earth complexes) using various functionalization approaches to improve the defects of rare earth complexes and realize the functionalization of carbon quantum dots and their applications in many fields, such as biology and environmental science. In addition, we classify the methods for the synthesis of RE-CQD hybrids into three groups according to the different binding modes of the RE and CQDs, including doping, covalent grafting, and direct coordination. The excellent properties of these fluorescent probes are also briefly described. Finally, a comprehensive overview of the important applications of RE-CQD fluorescent probes in the fields of public safety sensing, chemical sensing, biomedical sensing, temperature sensing, and pH sensing is presented. In this review, the recent research progress in the field of ratiometric fluorescence sensing based on carbon quantum dots and rare earth ions is summarized and an outlook on the future development of RE-CQD fluorescent probes regarding their construction and potential applications is provided.

Red-emitting carbon dots aggregates-based fluorescent probe for monitoring Cu2

R-CDAs have been synthesized in a one-pot solvothermal procedure starting from 3,4-diaminobenzoic acid in an acidic medium. Transmission electron microscopy (TEM) revealed that R-CDAs nanoparticles exhibited a much larger diameter of 7.2-28.8 nm than traditional monodisperse carbon dots. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) revealed the presence of polar functional groups (hydroxyl, amino, carboxyl) on the surface of R-CDAs. Upon excitation with visible light (550 nm), R-CDAs emit stable, red fluorescence with a maximum at 610 nm. Under the optimum conditions, Cu²⁺ ions quench the fluorescence of this probe, and the signal is linear in a concentration range of copper ions between 5 and 600 nM with the detection limit of only 0.4 nM. Recoveries from 98.0 to 105.0% and relative standard deviations (RSD) from 2.8 to 4.5% have been obtained for detection of Cu²⁺ in real water samples. Furthermore, the R-CDAs fluorescent probe showed negligible cytotoxicity toward HeLa cells and good bioimaging ability, suggesting its potential applicability as a diagnostic tool in biomedicine.

A toxicological profile of silica nanoparticles

Humans are regularly exposed to silica nanoparticles in environmental and occupational contexts, and these exposures have been implicated in the onset of adverse health effects. Existing reviews on silica nanoparticle toxicity are few and not comprehensive. There are natural and synthetic sources by which crystalline and amorphous silica nanoparticles are produced. These processes influence physiochemical properties, which are factors that can dictate toxicological effects. Toxicological assessment includes exposure scenario (e.g. environmental, occupational), route of exposure, toxicokinetics, and toxicodynamics. Broader considerations include pathology, risk assessment, regulation, and treatment after injury. This review aims to consolidate the most relevant and up-to-date research in these areas to provide an exhaustive toxicological profile of silica nanoparticles.

Facile synthesis of sulfur and oxygen co-doped graphitic carbon nitride quantum dots for on-off detection of Cu2+in real samples and living cells

A fluorescent sulfur and oxygen co-doped graphitic carbon nitride quantum dots (S,O-CNQDs) were prepared from ethylenediaminetetraacetic acid disodium salt dihydrate and thiourea as the carbon and sulfur sources. The morphology and surface functional groups of S,O-CNQDs were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The fluorescence of S,O-CNQDs could be quenched efficiently by Cu²⁺under the optimum conditions. The S,O-CNQDs could function as an excellent fluorescent probe for Cu²⁺detection with a wide linear range of 0.50-15μM and a low detection limit of 0.58 nM. In addition, this fluorescent probe was employed for monitoring Cu²⁺in samples of tap water, lake water, human serum and urine with good recoveries from 99.0% to 110.0%. Moreover, the S,O-CNQDs with high cell penetration and low cytotoxicity were utilized for Cu²⁺detection in living cells. Owing to the excellent properties of S,O-CNQDs, the as-prepared S,O-CNQDs can be a potential candidate for biological applications.

A Novel Reversible Fluorescent Probe for Cu2+and S2-Ions and Imaging in Living Cells

A novel fluorescent probe TSOC (thiazole salicylaldehyde oxazole chlorinated) was synthesized based on benzothiazole conjugated olefinic bond with salicylicaldehyde unit as fluorophore and a phenyl oxazole unit as bonding unit. The probe could reversibly detect of Cu2+ and S2- over other common ions with longer emission and large stokes shift in an aqueous solution at pH 7.3 (DMSO-Hepes, v/v, 5:1, 10 mM). The bonding mechanism was supported through the titration experiment of fluorescence and absorption spectroscopy, 1H-NMR titration, HR-MS and DFT calculations. Moreover, the probe further exhibited good cell permeability and were successfully used to visualize Cu2+ and S2- in living cells.

Mn2+-activated dual-wavelength emitting materials toward wearable optical fibre temperature sensor

Photothermal sensing is crucial for the creation of smart wearable devices. However, the discovery of luminescent materials with suitable dual-wavelength emissions is a great challenge for the construction of stable wearable optical fibre temperature sensors. Benefiting from the Mn²⁺-Mn²⁺ superexchange interactions, a dual-wavelength (530/650 nm)-emitting material Li₂ZnSiO₄:Mn²⁺ is presented via simple increasing the Mn²⁺ concentration, wherein the two emission bands have different temperature-dependent emission behaviours, but exhibit quite similar excitation spectra. Density functional theory calculations, coupled with extended X-ray absorption fine structure and electron-diffraction analyses reveal the origins of the two emission bands in this material. A wearable optical temperature sensor is fabricated by incorporating Li₂ZnSiO₄:Mn²⁺ in stretchable elastomer-based optical fibres, which can provide thermal-sensitive emissions at dual- wavelengths for stable ratiometric temperature sensing with good precision and repeatability. More importantly, a wearable mask integrated with this stretchable fibre sensor is demonstrated for the detection of physiological thermal changes, showing great potential for use as a wearable health monitor. This study also provides a framework for creating transition-metal-activated luminescence materials.

Dual-wavelength emission materials can provide fluorescence intensity ratio technology with self-calibration features; their fabrication however, remains a challenge. Here, authors design a dual-wavelength emitting material Li₂ZnSiO₄:Mn²⁺ and present a wearable optical fibre temperature sensor, functioning in both contact and noncontact modes.

Integration of Metal-Organic Frameworks with Bi-Nanoprobes as Dual-Emissive Ratiometric Sensors for Fast and Highly Sensitive Determination of Food Hazards

Functional nanoprobes which detect specific food hazards quickly and simply are still in high demand in the field of food-safety inspection research. In the present work, a dual-emission metal-organic framework-based ratiometric fluorescence probe was integrated to detect Cu²⁺ and Pb²⁺ with rapidness and ease. Specifically, quantum dots (QDs) and carbon quantum dots (CQDs) were successfully embedded into zeolitic imidazolate framework-67 (ZIF-67) to function as a novel ratiometric fluorescent sensing composite. The ratiometric fluorescence signal of CQDs/QDs@ZIF-67 was significantly aligned with the concentration of metal ions to give an extremely low detection limit of 0.3324 nM. The highly sensitive and selective CQDs/QDs@ZIF-67 composite showed potential for the rapid and cost-effective detection of two metal ions.

Fluorescence and Colorimetric Dual-Mode Ratiometric Sensor Based on Zr-Tetraphenylporphyrin Tetrasulfonic Acid Hydrate Metal-Organic Frameworks for Visual Detection of Copper Ions

As a special heavy metal ion, copper ions (Cu²⁺) play an indispensable role in the fields of environmental protection and safety. Their excessive intake not only easily leads to diseases but also affects human health. Therefore, it is particularly important to construct a facile, effective, and highly selective Cu²⁺ probe. Herein, a novel Zr-tetraphenylporphyrin tetrasulfonic acid hydrate (TPPS) metal-organic framework (ZTM) was fabricated using TPPS as the ligand and exhibited strong red fluorescence with a high quantum yield of 12.22%. In addition, we designed a ratiometric fluorescent probe by introducing green fluorescein isothiocyanate (FITC), which was not subject to environmental interference and had high accuracy. When exposed to different amounts of Cu²⁺, the fluorescence emission at 667 nm from ZTMs is remarkably quenched, while that at 515 nm from FITC is enhanced, accompanied by a change in the solutions' fluorescence color from red to green under a UV lamp. Besides, the ZTMs solutions display an excellent ratiometric colorimetric response for Cu²⁺ and produce an obvious color change (from green to colorless) that is visible to the naked eye. The fabricated ZTMs@FITC fluorescent probe exhibits distinguished performance for Cu²⁺ detection with linear ranges of 0.1 to 5 μM and 5 to 50 μM, as well as a low detection limit of 5.61 nM. Moreover, a colorimetric sensor based on ZTMs exhibits a good linear range from 0.1 to 20 μM for Cu²⁺ with the detection limit of 4.96 nM. Furthermore, the dual-signal ratiometric sensor has significant specificity for Cu²⁺ and is successfully applied for monitoring Cu²⁺ in water samples, which proves its practical application value in the environment and biological systems.

Optical chemosensors for environmental monitoring of toxic metals related to Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia and progresses from mild memory loss to severe decline in thinking, behavioral and social skills, which dramatically impairs a person's ability to function independently. Genetics, some health disorders and lifestyle have all been connected to AD. Also, environmental factors are reported as contributors to this illness. The presence of heavy metals in air, water, food, soil and commercial products has increased tremendously. Accumulation of heavy metals in the body leads to serious malfunctioning of bodily organs, specifically the brain. For AD, a wide range of heavy metals have been reported to contribute to its onset and progression and the manifestation of its hallmarks. In this review, we focus on detection of highly toxic heavy metals such as mercury, cadmium, lead and arsenic in water. The presence of heavy metals in water is very troubling and regular monitoring is warranted. Optical chemosensors were designed and fabricated for determination of ultra-trace quantities of heavy metals in water. They have shown advantages when compared to other sensors, such as selectivity, low-detection limit, fast response time, and wide-range determination under optimal sensing conditions. Therefore, implementing optical chemosensors for monitoring levels of toxic metals in water represents an important contribution in fighting AD.

This review briefly summarizes evidence that links toxic metals to onset and progression of Alzheimer's disease. It discusses the structure and fabrication of optical chemosensors, and their use for monitoring toxic metals in water.

Carbon dots and gold nanoclusters assisted construction of a ratiometric fluorescent biosensor for detection of Gram-negative bacteria

A core-satellite nanocomposite was prepared by encapsulating the photostable blue carbon dots (BCDs) in the core of silica as the reference signal readout, and the target-sensitive gold nanoclusters (AuNCs) covalently linked to the surface of silica as the respond signal readout. The nanocomposite (BCD@SiO₂@AuNC) was used as a ratiometric fluorescent sensor to realize the selective detection of Gram-negative bacteria. The detection principle was based on the quenching of Cu²⁺ toward AuNCs and the reduction of Gram-negative bacteria toward Cu²⁺. The sensor exhibited good selectivity toward Gram-negative bacteria owing to the copper-homeostasis mechanism possessed by the bacteria. The sensor demonstrated linear response to the logarithm concentration of Gram-negative bacteria with determination coefficients higher than 0.912. The feasibility of the sensor was verified by analysis of Gram-negative bacteria in eggshell, swimming pool water, as well as Chinese cabbage samples with recoveries ranging from 93.9% to 109%.

Enzyme Method-Based Microfluidic Chip for the Rapid Detection of Copper Ions

Metal ions in high concentrations can pollute the marine environment. Human activities and industrial pollution are the causes of Cu²⁺ contamination. Here, we report our discovery of an enzyme method-based microfluidic that can be used to rapidly detect Cu²⁺ in seawater. In this method, Cu²⁺ is reduced to Cu⁺ to inhibit horseradish peroxidase (HRP) activity, which then results in the color distortion of the reaction solution. The chip provides both naked eye and spectrophotometer modalities. Cu²⁺ concentrations have an ideal linear relationship, with absorbance values ranging from 3.91 nM to 256 μM. The proposed enzyme method-based microfluidic chip detects Cu²⁺ with a limit of detection (LOD) of 0.87 nM. Other common metal ions do not affect the operation of the chip. The successful detection of Cu²⁺ was achieved using three real seawater samples, verifying the ability of the chip in practical applications. Furthermore, the chip realizes the functions of two AND gates in series and has potential practical implementations in biochemical detection and biological computing.

Intrinsic dual-emissive carbon dots for efficient ratiometric detection of Cu2+ and aspartic acid

Herein, novel intrinsic dual-emitting carbon dots (CDs) are prepared through a one-step hydrothermal treatment of glucose and 3-nitroaniline in sulfuric acid solution and utilized for ratiometric determination of Cu²⁺ and aspartic acid (Asp). The CDs exhibited an interesting pH-switchable emission behavior displaying an intrinsic dual-emitting peak with emission maxima at 400 and 610 nm at pH 4.0-5.0. The presence of Cu²⁺ intensively quenched the first emission peak at 400 nm, but it had a negligible effect on the second emission peak. The ratiometric signal displayed a high selectively for Cu²⁺ over other metal ions and provided a linear response over the concentration range of 0.01-1.00 μM with a detection limit of 7.0 nM. Moreover, at pH 4.0, Asp was able to restore the quenched fluorescence of the CDs-Cu²⁺ system with a much more successful performance than other amino acids. This on-off-on fluorescence behavior provided a selective ratiometric fluorescence method for the determination of Asp in the concentration range of 0.2-15 μM. The acceptable detection results for Cu²⁺ in a river water sample (compared to Inductively Coupled Plasma (ICP) method) and for Asp in human serum samples confirmed the potential application of this ratiometric nanoprobe for sensing in real samples.

Silicon-based fluorescent platforms for copper(ii) detection in water

The potential of silicon-based fluorescent platforms for the detection of trace toxic metal ions was investigated in an aqueous environment. To this aim, silicon chips were first functionalized with amino groups, and fluorescein organic dyes, used as sensing molecules, were then covalently linked to the surface via formation of thiourea groups. The obtained hybrid heterostructures exhibited high sensitivity and selectivity towards copper(ii), a limit of detection compatible with the recommended upper limits for copper in drinking water, and good reversibility using a standard metal–chelating agent. The fluorophore–analyte interaction mechanism at the basis of the reported fluorescence quenching, as well as the potential of performance improvement, were also studied. The herein presented sensing architecture allows, in principle, tailoring of the selectivity towards other metal ions by proper fluorophore selection, and provides a favorable outlook for integration of fluorescent chemosensors with silicon photonics technology.

Covalent linkage of fluorescein to silanized silicon chips yields solid-state platforms for detection of copper(ii) in water. This architecture represents a step forward towards the fabrication of sensors for remote water analysis applications.

Simple assay for colorimetric quantification of unamplified bacterial 16S rRNA in activated sludge using gold nanoprobes

Domestic and industrial wastewater treatment systems are vital in the protection of natural ecosystems and human health. Identification of microbial communities in the systems is essential to stable treatment performance. However, the current tools of microbial community analysis are labor intensive and time consuming, and require expensive equipment. Therefore, we developed a simple assay for colorimetric quantification of bacterial 16S rRNA extracted from environmental samples. The assay is based on RNA extraction with commercial kits, mixing the unamplified RNA sample with Au-nanoprobes and NaCl, and analyzing the absorbance spectra. Our experimental results confirmed that the assay format was valid. By analyzing the synthesized DNA, we optimized the operational parameters affecting the assay. We achieved adequate capture DNA density by setting the capture DNA probe concentration at 10 μM during the functionalization step. The required incubation time after NaCl addition was 30 min. The binding site of the target had negligible effect on DNA detection. Under the optimized condition, a calibration curve was created using 16S rRNA extracted from activated sludge. The curve was linear above 5.0 × 10⁷ copies/μL of bacterial 16S rRNA concentration, and the limit of detection was 1.17 × 10⁸ copies/μL. Using the calibration curve, the bacterial 16S rRNA concentration in activated sludge samples could be quantified with deviations between 48% and 208% against those determined by RT-qPCR. The findings of our study introduce an innovative tool for the quantification of 16S rRNA concentration as the activity of key bacteria in wastewater treatment processes, achieving stable treatment performance.

Sensitive and selective colorimetric detection of Cu (II) in water samples by thiazolylazopyrimidine-functionalized TiO2 nanoparticles

In this study, a new thiazolylazopyrimidine-functionalized TiO₂ nanosensor (TiO₂-TAP) has been developed for sensitive and selective colorimetric detection of Cu²⁺ in water samples. Thiazolylazopyrimidine (TAP) as an azo ligand and TiO₂-TAP as highly selective nanosensor were successfully prepared through the diazo coupling reaction and surface chemical modification, respectively. Characterization of TiO₂-TAP NPs using Fourier transmission infrared (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive X- ray spectroscopy (EDX), and X-ray diffraction (XRD) analysis revealed that the TiO₂ NPs were effectively modified with the synthesized epoxy-activated thiazolylazopyrimidine. The synthesized azo ligand containing azo chromophore (N=N) produce color and make a stable complex formation with Cu²⁺ based on charge-transfer transduction in the detection system. The color change of TiO₂-TAP solution from yellow to red occur directly after few seconds of addition of Cu²⁺ ions, as a result of surface complexation. The TiO₂-TAP has revealed high affinity, sensitivity and selectivity for copper ion over other competing metal ions in aqueous media. The experimental data revealed that the Cu²⁺ ions was sensed and adsorbed by the TiO₂-TAP at optimal pH 5.0. The results also confirmed that the TiO₂-TAP has a wide linear detection range for Cu²⁺ (0.01 to 12.5 μM). From UV-vis titration experiment, the limit of detection (LOD) for Cu²⁺ ions was found to be 2.51 nM. The proposed method was successfully applied for the sensitive and selective detection of Cu²⁺ in tap water, sea water and well water. In addition, Cu²⁺ recovery improved using the TiO₂-TAP containing N, S and O atoms as chelating sites. Therefore, the developed nanosensor with great features like the cost-effective, excellent sensitively and selectively, short response times and high adsorption efficiency for Cu²⁺ can be utilized in any physical and biological conditions.

Polyethylenimine-Assisted Generation of Optical Nanoprobes for Biosensing Applications

Detection of analytes in biological systems is pivotal to explore their physiological roles and provide diagnostic and treatment options for related diseases, which however remains a great challenge. Optical nanoprobes that exhibit absorption or fluorescence signal changes in response to the targets of interest have emerged as a versatile class of biosensors in the field. Polyethylenimine (PEI) with abundant amine groups plays indispensable roles in the construction of optical nanoprobes and mediating the sensing processes. After interaction with analytes, PEI-based optical nanoprobes can be induced to form aggregates, be disassembled or separated into individual units, or undergo structure/component alterations. As such, the optical properties of these nanoprobes have corresponding changes, allowing for sensitive and selective detection of a wide variety of analytes in biological environment. Up to now, detections of reactive oxygen species, pH, metal ions, biothiols, neurotransmitters, therapeutic agents, oxygen levels, enzyme activities, and virus/bacteria have been successfully demonstrated using PEI-based optical nanoprobes. Herein, we summarize the recent developments of PEI-based optical nanoprobes for biosensing applications and highlight the probe designs and sensing mechanisms. The existing challenges and prospects regarding biosensing applications of PEI-based optical nanoprobes are also briefly discussed.

A Metallosupramolecular Coordination Polymer for the 'Turn-on' Fluorescence Detection of Hydrogen Sulfide

A coumarin based probe for the efficient detection of hydrogen sulfide in aqueous medium is reported. The investigated coumarine-based derivative forms spherical nanoparticles in aqueous media. In presence of Pd2+, a metallosupramolecular coordination polymer is formed, which is accompanied by quenching of the coumarin emission at 390 nm. Its Pd2+ complex could be used as a probe for chemoselective detection of monohydrogensulfide (HS-). Presence of HS- leads to a'turn-on' fluorescence signal, resulting from decomplexation of Pd2+ from the metallosupramolecular probe. The probe was successfully applied for qualitative and quantitative detection of HS- in different sources of water directly collected from sea, river, tap and laboratory drain water, as well as in growth media for aquatic species.

Self-Enhanced Chemiluminescence of Tris(bipyridine) Ruthenium(II) Derivative Nanohybrids: Mechanism Insight and Application for Sensitive Silver Ions Detection

In recent years, self-enhanced tris(bipyridine) ruthenium(II)-based luminescence systems have achieved great development in electrochemiluminescence (ECL) but are seldom mentioned in chemiluminescence (CL). Herein, a self-enhanced CL luminophore with excellent CL behavior was synthesized by covalently cross-linking tris(4,4'-dicarboxylic acid-2,2'-bipyridyl) ruthenium(II) dichloride ([Ru(dcbpy)₃]Cl₂) with branched polyethylenimine (BPEI) in one molecule (BPEI-Ru(II)), which then self-assembled into nanoparticles (BRuNPs). The nanoparticles exhibited stable and strong CL emission with potassium persulfate (K₂S₂O₈) as the oxidant. After the redox reaction between K₂S₂O₈ and BRuNPs, and the subsequent intramolecular electron-transfer reaction, excited state luminophores were generated to emit light. This self-enhanced CL system shortened the electron transfer distance and reduced energy loss, thus improving the luminous efficiency. In addition, the CL lifetime of BRuNPs/K₂S₂O₈ was longer than classical luminophores such as N-(4-aminobutyl)-N-ethylisoluminol (ABEI), indicating the potential application of this system in CL imaging. Surprisingly, Ag⁺ was found to greatly improve the CL efficiency of BRuNPs/K₂S₂O₈ by catalyzing the decomposition of K₂S₂O₈ to generate SO₄^•-. On the basis of the enhancement effect of Ag⁺, a simple and rapid CL method was proposed for Ag⁺ detection. The chemosensor showed a wide linear range from 25 to 3000 nM and low detection limit of 9.03 nM, as well as good stability and excellent selectivity. More importantly, this result indicated that Ag⁺ can be used as a coreaction accelerator to develop a ternary self-enhanced CL system, BRuNPs/K₂S₂O₈/Ag⁺.

Utilizing Ag-Au core-satellite structures for colorimetric and surface-enhanced Raman scattering dual-sensing of Cu (II)

This study develops a dual-channel colorimetric and surface-enhanced Raman scattering (SERS) strategy for detection of Cu²⁺ utilizing Ag-Au core-satellite nanostructures. 4-mercaptobenzoic acid (MBA) modified Ag nanoparticles (AgNPs@MBA) and 4-mercaptopyridine (Mpy) capped AuNPs (GNPs@Mpy) are first designed via metal-sulfur bonds, respectively. Benefiting from the Cu²⁺-triggered NPs self-aggregation, the dispersion of AgNPs-GNPs (AgNPs@MBA + GNPs@Mpy) is turned into AgNPs-Cu²⁺-GNPs core-satellite structures. Because of the presence of pyridyl nitrogen and carboxy group which have specific coordination ability towards Cu²⁺, induces a certain aggregation of NPs. As well it can be obviously discerned by the visual assay and easily captured by SERS analysis. The UV-Vis method exhibits good linearity in the ranging from 0.1 μM-200 μM for Cu²⁺, while SERS method displays good linear response from 1 pM to 100 μM. The detection limit of Cu²⁺ is 0.032 μM by colorimetry and 0.6 pM by SERS method, which is significantly lower than the acceptable limit of Cu²⁺ in drinking water (20 μM) set by the US EPA. Furthermore, colorimetric and SERS assay based on AgNPs-Cu²⁺-GNPs core-satellite structures is used to determine Cu²⁺ in various waters and soils, and the detection results are consistent with the traditional atomic analysis methods. This work offers a new method for detecting Cu²⁺ in environmental samples, and the plasmonic nanostructure provides new entry point for development of multiplexed sensing platform for in-field application.

Multiple logic operations based on chemically triggered upconversion fluorescence switching

The development of upconversion nanoparticles based logic systems, especially integrated logic systems is still a challenge until now. In this work, an upconversion nanocomposite system is developed and studied for the sensing abilities toward hydrion, hydroxyl ions, metal ions and anions (S^2-, I^-) by taking the advantages of turn-on and turn-off upconversion fluorescence switching response. Triggering by different kinds of ions, the upconversion system can act as a fluorescence switch due to the specific recognition abilities of Rhodamine 6G functionalized PEI for specific ions and the energy transfer process from upconversion nanoparticles to recognition molecules. Based on these results, multiple molecular logic gates, including single-input logic operation (YES, NOT), double-inputs logic operation (OR, AND, NOR, INHIBIT) and multiple-input integrative logic operation (INHIBIT+OR) are developed by employing hydrion, hydroxyl ions, metal ions and anions as inputs and the changes in the upconversion fluorescence intensity as output. The multiple logic operations are of great significance for the applications in biomedicine and molecular calculation.

A highly sensitive fluorescence sensor based on lucigenin/chitosan/SiO2 composite nanoparticles for microRNA detection using magnetic separation

In this paper, a convenient reverse-phase microemulsion method for the synthesis of SiO₂ nanoparticles (NPs) by simply introducing the chitosan and fluorescent dye of lucigenin during the formation reaction of SiO₂ NPs was proposed. Addition of chitosan can make the SiO₂ NPs porous, and increases lucigenin molecule incorporation into chitosan/SiO₂ NPs nanopores based on electrostatic interaction and supermolecular forces. Therefore, fluorescence quantum yield of the lucigenin/chitosan/SiO₂ composite nanoparticles was increased by introduction of chitosan and compared with lucigenin/SiO₂ NPs without chitosan. Because the number of negative charges carried when using single-stranded DNA (ssDNA) was different from that of double-stranded DNA (dsDNA), the numbers of lucigenin/chitosan/SiO₂ composite nanoparticles with positive charge adsorbed using ssDNA or dsDNA were different. Consequently, fluorescence intensity caused using ssDNA or dsDNA/miRNA was clearly discriminative. With increase in target DNA/miRNA concentration, the difference in fluorescence intensity also increased, resulting in a good linear relationship between fluorescence intensity sensitizing value and target miRNA concentrations. Therefore, a new fluorescence analysis method for direct detection of let-7a in human gastric cancer cell samples without enzyme, label free and no immobilization was established using lucigenin/chitosan/SiO₂ composite nanoparticles as a DNA hybrid indicator. The proposed method had high sensitivity and selectivity, low cost and the detection limit was 10 fM (S/N = 3).

Colloidal clusters of icosahedrons and face-centred cubes

Synthetically colloidal clusters with new functions and well-controlled size distribution can in principle be constructed using colloidal particles. The building units could be integrated into dense-packed and desired structured with novel functions by means of an efficient strategy or binding patterns. Here we synthesized colloidal clusters of icosahedrons and long-range ordered face-centered cubes (FCCs) via emulsion self-assembly using fluorescence upconversion nanoparticles NaGdF₄: Yb³⁺, Er³⁺ as building blocks. The icosahedrons and FCCs structure may generate spontaneously due to an entropy-driven process. The morphology and structure of colloidal clusters have noticeable transformation from icosahedron-like symmetry to FCC symmetry with the increasing size of clusters. Furthermore, the colloidal clusters could be decorated with cationic polyethyleneimine (PEI) via electrostatic interaction. When copper ions are added, the amino groups of PEI could coordinate with Cu²⁺ forming low toxic PEI-Cu²⁺ layers, which can further serve as energy receptors to quench upconversion fluorescence with 980 nm laser excitation. Our results reflect that the colloidal clusters not only can serve as a fluorescence platform of detection and analysis but also may represent advancement in the field of colloidal and interface sciences.

Ratiometric Fluorescent Quantum Dot-Based Biosensor for Chlorothalonil Detection via an Inner-Filter Effect

A new sensitive sensor for detecting chlorothalonil (CHL) based on the inner-filter effect (IFE) between gold nanoparticles (AuNPs) and ratiometric fluorescent quantum dots (RF-QDs) was developed. Here, RF-QDs were designed by two different color CdTe QDs. Based on the IFE, the AuNPs can quench the fluorescence of the RF-QDs. Because of the electrostatic attraction between protamine (PRO) and the AuNPs, the PRO can restore fluorescence effectively. Papain (PAP) can easily hydrolyze PRO and causes the quench of fluorescence quenching. The addition of CHL can inhibit PAP activity and restore the fluorescent signal. Through the characterization of the structural changes of PAP, the inhibition and mechanism of CHL on PAP activity were studied. The ability of CHL to inhibit PAP activity was evaluated by measuring the fluorescence of the RF-QDs. Under the optimal conditions, this sensing platform shows a response to CHL in the range of 0.34-2320 ng/mL and a detection limit of 0.0017 ng/mL. Based on the CHL inhibition of PAP activity, the RF-QDs showed good selectivity for CHL. The practical application of the proposed system was demonstrated by detecting CHL in food and environmental samples with satisfying results.

Silica nanoparticles with thermally activated delayed fluorescence for live cell imaging

Thermally activated delayed fluorescence (TADF) has revolutionized the field of organic light emitting diodes owing to the possibility of harvesting non-emissive triplet states and converting them in emissive singlet states. This mechanism generates a long-lived delayed fluorescence component which can also be used in sensing oxygen concentration, measuring local temperature, or on imaging. Despite this strong potential, only recently TADF has emerged as a powerful tool to develop metal-free long-lived luminescent probes for imaging and sensing. The application of TADF molecules in aqueous and/or biological media requires specific structural features that allow complexation with biomolecules or enable emission in the aggregated state, in order to retain the delayed fluorescence that is characteristic of these compounds. Herein we demonstrate a facile method that maintains the optical properties of solvated dyes by dispersing TADF molecules in nanoparticles. TADF dye-doped silica nanoparticles are prepared using a modified fluorescein fluorophore. However, the strategy can be used with many other TADF dyes. The covalent grafting of the TADF emitter into the inorganic matrix effectively preserves and transfers the optical properties of the free dye into the luminescent nanomaterials. Importantly, the silica matrix is efficient in shielding the dye from solvent polarity effects and increases delayed fluorescence lifetime. The prepared nanoparticles are effectively internalized by human cells, even at low incubation concentrations, localizing primarily in the cytosol, enabling fluorescence microscopy imaging at low dye concentrations.

Rhodamine B derivative-modified up-conversion nanoparticle probes based on fluorescence resonance energy transfer (FRET) for the solid-based detection of copper ions

Herein, a novel solid-based up-conversion fluorescence resonance energy transfer (FRET) sensor was developed using rhodamine B hydrazide, which provided a selective fluorescence response and suitable affinity towards Cu²⁺ ions over other biologically relevant metal ions because the Cu²⁺ ion could promote the hydrolysis of α-amino acid esters of rhodamine B hydrazide and yield the Cu·α-amino acid chelate. This solid-based detection system is more convenient for the detection of Cu²⁺ based on color change and emission spectra instead of the complicated and tedious measurements than other up-conversion sensors and up-conversion luminescent nanoparticles used as an excitation source; moreover, the proposed system shows high selectivity, minimum photo-damage to living organisms, and high chemical stability.

Nitrogen-doped carbon dots as a probe for the detection of Cu2+ and its cellular imaging

Nitrogen-doped carbon dots were synthesized using citric acid monohydrate and glutathione as raw materials. The synthesized nitrogen-doped carbon dots were characterized by multiple analytical techniques, including transmission electron microscopy, Fourier transform infrared spectroscopy, ultraviolet–visible absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractometry, and fluorescence spectra. The fluorescence intensity of the nitrogen-doped carbon dots gradually quenched with different concentrations of Cu2+ ions. The effect of the pH value, the nitrogen-doped carbon dot concentration, and the reaction time on the fluorescence intensity of the N-CDs-Cu2+ system was investigated, and the experimental conditions were optimized. A rapid and sensitive method for the determination of Cu2+ ions was established that exhibited a good linearity in the concentration range 0.20–200.0 μM with a detection limit of 0.27 nM. Meanwhile, the fluorescence quenching mechanism of the interaction between nitrogen-doped carbon dots and Cu2+ was preliminarily discussed. The method was used to detect trace Cu2+ in tap water and lake water, with recoveries ranging from 98.1% to 102.0%. Furthermore, due to low cytotoxicity and good biocompatibility, nitrogen-doped carbon dots as a probe were also successfully used in bioimaging.

The synthesis of PEI core@silica shell nanoparticles and its application for sensitive electrochemical detecting mi-RNA

Although the silica-based nanoparticles (NPs) have been widely explored as the labels for sensing different targets, the simple and novel scheme, to impose a large number of signal molecules inside silica NPs, is challenge. Herein, a new scheme for this purpose was developed. This new strategy was based on densely doped polyethyleneimine (PEI) inside silica nanoparticles and forming the PEI@silica nanoparticles. Then, the Cu²⁺ was selected as the electrochemical signal molecule model to be loaded in PEI@silica nanoparticles the based on the strong coordination reaction of Cu²⁺ with PEI and test its signal amplification ability. Our results showed that 7.6 × 10⁵ Cu²⁺signal ions could be loaded in a single PEI@silica nanoparticles. Thereafter, based on the discriminating interaction of this PEI/Cu²⁺/SiO₂ NPs towards both ssDNA probes and ssDNA probe/mi-RNA complex, as well as the specific adsorption effect of this NPs on chemically modified electrode, a highly sensitive electrochemical method for detecting mi-RNA was developed and successfully used to detect mi-RNA in the human serum samples.

Label-free gold nanorod-based plasmonic sensing of arsenic(iii) in contaminated water

An efficient label-free strategy for arsenic(iii) sensing in water through the suppression of iron(iii)-catalyzed oxidative shortening of gold nanorods.

A bis-benzimidazole PMO ratiometric fluorescence sensor exhibiting AIEE and ESIPT for sensitive detection of Cu2+

A novel bis-benzimidazole organic siloxane precursor (BBM-Si) was prepared, and was combined with tetraethylorthosilicate (TEOS) as a mixed Si source. Then, bridged periodic mesoporous organosilica (BBM-PMO) spherical nanoparticles were synthesized by co-condensation using cetyltrimethylammonium bromide (CTAB) as structure directing agent. The optical properties showed that BBM qualifies as an “aggregation induced emission enhanced” (AIEE) molecule, exhibiting characteristics of excited-state intramolecular proton transfer (ESIPT), such as a large Stokes shift and dual fluorescence emission. For the BBM-PMO materials, the silica skeleton provides a rigid environment that limits molecular rotation, resulting in improved fluorescence emission. In particular, the BBM-PMOs exhibited dual emission of the enol and keto forms, achieving a ratiometric response to Cu²⁺ with high sensitivity and selectivity in a broad pH range. Additionally, the limit of detection was as low as 7.15 × 10⁻⁹ M in aqueous solution. The X-ray absorption near-edge spectroscopy (XANES) showed the coordination structure through the interaction between copper ions and N atoms of benzimidazole in the BBM-PMO coordinated to Cu²⁺. These results demonstrate that BBM-PMO hybrid materials have potential applications in the fields of bio-imaging and environmental monitoring.

A novel bis-benzimidazole organic siloxane precursor (BBM-Si) was prepared, and was combined with tetraethylorthosilicate (TEOS) as a mixed Si source.

A FRET-based colorimetric and ratiometric fluorescent probe for the detection of Cu2+ with a new trimethylindolin fluorophore

The possible interaction mechanism between probe RhF and Cu²⁺ ions.

Exploration of surface plasmon resonance for sensing copper ion based on nanocrystalline cellulose-modified thin film

In this research, surface plasmon resonance (SPR) spectroscopy was used for sensing copper ion by combining the SPR with nanocrystalline cellulose modified by hexadecyltrimethylammonium bromide and graphene oxide composite (CTA-NCC/GO) thin film. The binding of Cu²⁺ on CTA-NCC/GO thin film was monitored by using SPR spectroscopy. By using the obtained SPR curve, detection range, binding affinity, sensitivity, full width at half maximum (FWHM), data accuracy (DA), and signal-to-noise ratio (SNR) have been calculated. The results showed that the sensor detection range was 0.01 until 0.5 ppm, and that it reached a saturation value. Moreover, the resonance angle shift followed the Langmuir isotherm model with a binding affinity constant of 4.075 × 10³ M^-1. A high sensitivity of 3.271° ppm^-1 also was obtained for low Cu²⁺ concentration ranged from 0.01 to 0.1 ppm. For the FWHM, the lowest value calculated was at 0.08 and 0.1 ppm, which is 3.35°. The DA of the SPR signal consecutively highest at 0.08 and 0.1 ppm. Besides that, the SNR of the SPR signal increases with the Cu²⁺ concentrations. The CTA-NCC/GO thin film morphological properties were also studied by using atomic force microscopy. The rms roughness values, which were obtained before and after in contact with Cu^2+, were 3.51 nm and 2.46 nm, respectively.

Facile synthesis of BCNO quantum dots with applications for ion detection, chemosensor and fingerprint identification

Boron carbon oxynitride quantum dots (BCNO QDs) with blue emission were prepared via the template of SBA-15 (a typical mesoporous silica). A modulated photoluminescence sensor was developed based on the different quenching effects of Cu²⁺ or Hg²⁺ ions on the luminescence intensity of BCNO QDs. The Cu²⁺ or Hg²⁺ ions have an interaction with BCNO QDs due to the electrons transfer between the BCNO and Cu²⁺ or Hg²⁺ ions, and the detection limit of Cu²⁺ or Hg²⁺ ion concentration can be as less as 10 nM. The BCNO-Cr⁶⁺ mixture can be served as a turn-on fluorescent sensor for detecting the ascorbic acid based on the inner filter effect since overlapping of excitation and emission spectra between Cr⁶⁺ ions and BCNO QDs. Moreover, the BCNO QDs can also be applied to fingerprint identification and organic fluorescent films under ultraviolet excitation.