Fluorescence Color Change Research Articles

Novel Easy‐to‐Synthesize Hydrazine Multi‐channel Detection and Adsorption Materials

Comprehensive SummaryHydrazine hydrate (DH) is a widely used chemical agent, but it is highly toxic. Thus, the development of low‐cost and easy‐to‐prepare materials for the detection and adsorption of DH is very significant. Herein, a novel and easy‐to‐prepare supramolecular smart material based on bisquinoline‐functionalized naphthalene diimide (DQ8) has been designed and synthesized. In the DQ8, the synergistic effect between quinoline and naphthalene diimide groups has been employed to improve the selectivity and sensitivity for binding of DH. The DQ8‐based crystalline porous material (DQ8‐CPM) can simultaneously detect and adsorb DH and produce noticeable fluorescence color changes after adsorption of DH vapor. More significantly, the DQ8‐CPM shows nice recycling performance on DH detection and adsorption. Meanwhile, a smart gel based on DQ8 (DQ8‐G) shows multi‐channel response for DH through color, fluorescence, and state changes. The DQ8 shows high selectivity and sensitivity for DH. The detection limit of DQ8 for DH is 8.6 × 10–7 mol/L. According to the investigation of the DH binding and response mechanism, the synergistic effect between quinoline and naphthalene diimide groups plays an important role in the DH response process. It's a simple and feasible way to develop materials for detection and adsorption of DH through synergistic effects.

Multicolor Gold Clusterzyme-Enabled Construction of Ratiometric Fluorescent Sensor Array for Visual Biosensing.

The simultaneous detection of multiple bioanalytes with similar structures has been a long-standing challenge for biological research and disease diagnosis. Bioreceptor-inspired sensor arrays provide an attractive and competitive solution for addressing this challenge, but applying this technique to biosensing in practical application scenarios is complicated by many factors such as the lack of robust probes, interference from the biological matrix, and difficulty for on-site analysis. In this work, by taking advantage of the intrinsic fluorescence and enzyme-mimic properties of gold nanoclusters (AuNCs), we report the design of an innovative ratiometric sensor array toward enhanced fluorescent visual biosensing. With biologically important phosphates as an example, we show that the present fluorescent clusterzyme-based ratiometric sensor array could effectively discriminate and detect eight types of phosphates. In particular, AuNCs with three different emission colors (blue, green, and red) and good peroxidase-mimic properties were employed as the sensing units, and the presence of phosphates affected both the intrinsic fluorescence and the enzymatic activity of these AuNCs, yielding distinct optical responses in a ratiometric manner. Moreover, a portable sensor array was established by further integrating these fluorescent clusterzymes into a hydrogel matrix, which could visually identify different phosphates based on their distinct fluorescence color changes. Consequently, the point-of-care diagnosis of urinary tract infections at different levels was achieved by analyzing urinary microbial ATP via the present strategy. This study illustrates the great potential of clusterzyme-based fluorescent sensor arrays as a promising biosensing platform for disease diagnosis.

Dual-mode sensing platform for Bisphenol A detection via bifunctional CsPbBr3@Cu-MOF assisted fluorescence and colorimetric analysis

BackgroundBisphenol A (BPA) has been identified as an endocrine disruptor with numerous detrimental effects on human health. There is an urgent need to develop fluorescence/colorimetric dual-mode sensing approaches with expanded detection linear range, increased accuracy, and enhanced application flexibility for BPA detection. The utilization of fluorescence and colorimetric signals in point-of-care applications and real-time sensitive sensing further highlights the significance of developing novel and efficient fluorescence/colorimetric dual-mode sensing platform with high-efficiency probes. ResultsHerein, a fluorescence and colorimetric dual-mode aptasensor was developed by using CsPbBr3@Cu-MOF as the aptamer immobilization matrix and signal generator. CsPbBr3 was functionalized with Cu-MOF using a simple two-step strategy. This strategy involved in-situ formation and modified ligand-assisted precipitation technique with 4,4′-bipyridine (4,4-Bpy) serving as the bifunctional linker. The resulting CsPbBr3@Cu-MOF exhibited improved stability in water and enhanced fluorescence. Additionally, it functioned as peroxidase mimetic to oxidize 3,3′,5,5′-tetramethyl benzidine (TMB), leading to a colorimetric change from colorless to blue. In the presence of BPA, aptamers were removed from CsPbBr3@Cu-MOF. Consequently, the fluorescence and peroxidase-activity of CsPbBr3@Cu-MOF were recovered, resulting in the enhanced fluorescence intensity and color change of TMB. Using this system, the proposed aptasensor demonstrated detection ranges of 1.0–80.0 nM with a LOD of 0.60 nM for the colorimetric method, and a linearity range of 0.1–100 nM with a LOD of 0.02 nM for the fluorescence method. SignificanceThe obtained CsPbBr3@Cu-MOF composites showed excellent fluorescence properties, good peroxidase-like activity, and aqueous stability. Furthermore, the proposed dual-mode aptasensor demonstrated simplicity, cost-effectiveness and good anti-interference abilities. This can be extended to the construction of other dual-mode sensors by changing aptamers and provides novel insights on the potential applications of perovskites in bioanalysis.

Ultrabright silicon nanoparticles combined with o-phenylenediamine for ratiometric fluorescence and smartphone imaging dual-mode detection of nitrite

Nitrite (NO2−) is widely present in the natural environment and human daily life. Excessive NO2− can cause harm to the environment and human health. Herein, silicon nanoparticles (SiNPs) with a fluorescence quantum yield of up to 70 % were synthesised using a one-pot hydrothermal method and combined with the common and inexpensive o-phenylenediamine (OPD) to achieve the detection of NO2−. Upon the addition of NO2−, the blue fluorescence of the SiNPs was quenched due to static quenching and Förster resonance energy transfer (FRET), while the yellow fluorescence of benzotriazole, the reaction product of OPD and NO2−, was enhanced, resulting in the fluorescence color change from blue to yellow. Based on these phenomena, a ratiometric fluorescence sensor integrated with smartphone imaging technology was developed. This sensor is notable for its portability, cost-effectiveness, and satisfactory detection limits (0.016 μM for ratiometric fluorescence and 1.64 μM for smartphone imaging). Importantly, it demonstrates high reliability and practicability in detecting NO2− in real water and food samples. This broadens the application of SiNPs in the sensing field and introduces new possibilities for NO2− detection in complex sample matrices.

Highly sensitive and selective ratiometric fluorescence and colorimetric detection of Cr(VI) via in situ encapsulation of green/red carbon quantum dots in zeolite

To overcome the limitations arising from non-uniform particle size and solid-state aggregation of carbon quantum dots (CQDs), a novel dual-emissive ratiometric fluorescence probe, GCQDs@SBA-15/RCQDs@SBA-15 (G-RCQDs@SBA-15), has been successfully constructed by simplifying the synthesis process through in situ synthesis of CQDs in SBA-15 to further enhance their optical properties for highly sensitive detection of Cr(VI). The probe G-RCDs@SBA-15, based on green-emission carbon quantum dots (GCQDs) encapsulated in mesoporous molecular sieves SBA-15, provides the response signal, while red-emission carbon quantum dots (RCQDs) encapsulated in SBA-15 serve as an internal reference. The probe exhibits a satisfactory limit of detection (LOD) of 0.336 μM, which is 52 % lower than GCQDs/RCQDs. Importantly, the probe shows superior selectivity in detecting Cr(VI) compared to other metal ions. The fluorescence signal ratio of the probe decreases with increasing Cr(VI) concentration, resulting in a distinct change of fluorescence color from green to red. Based on UV–vis and fluorescence lifetime analysis, Inner filter effect (IFE) is considered the primary potential mechanism for the fluorescence color transition of G-RCDs@SBA-15 following the addition of Cr(VI). G-RCQDs@SBA-15 not only inherits the excellent optical properties of GCQDs and RCQDs but also shows high fluorescence and chemical stability. Considering the sensitive photoconversion properties of G-RCQDs@SBA-15, a smartphone-based laboratory device in combination with RGB analysis software has been used for Cr(VI) detection by directly capturing and analyzing fluorescence images. In addition, the sensing system is validated in the actual lake water samples, exhibiting recoveries from 83.3 % to 96.3 %, indicating its excellent practicality for Cr(VI) detection in real samples.

Rational Design of Regenerable Amino-Functionalized Fluorescent Covalent Organic Framework for the Exclusive Detection of Mercury(II).

Goal-oriented development of novel covalent organic frameworks (COFs) to construct a sensing platform for highly toxic mercury (II, Hg2+) is of tremendous significance. Recently, numerous COFs with sulfur-based ligands were developed for Hg2+ monitoring; however, strong binding of Hg2+ by sulfur makes their regeneration very tough. Herein, we designed and developed an amino-functionalized fluorescent COF (COF-NH2) through facile postmodification for Hg2+ detection in which the π-conjugation skeleton is the signal reader and the nitrogen-based side is the highly selective Hg2+ receptor. More importantly, this nitrogen-based receptor permits the reversible binding of Hg2+. As a sensing platform, the outstanding performance of COF-NH2 for Hg2+ detection was reached with respect to high sensitivity with an ultralow detection of 15.3 nM, real-time response with rapid signal change of 10 s, and facile visualization with significant fluorescence color change. Expectedly, COF-NH2 obtained facile recycling which still shows excellent response performance toward Hg2+ after six cycles based on the reversible interaction between amino groups and Hg2+. Our work not only shows an attractive foreground of fluorescent COF for Hg2+ detection but also emphasizes the easy construction of novel COF materials via the rational introduction of metal ligands for the recognition of other metal ions.

Multifunctional Au–Ag NCs for luminescence and colorimetric double signal sensing of H2S and catalytic reduction of nitrophenol

In this study, the N-Acetyl-l-Cysteine (NAC)-capped gold and silver bimetallic nanoclusters (NAC@Au–Ag NCs) was synthesized by reflux method. Due to the silver effect, the NAC@Au–Ag NCs exhibited strong photoluminescence at far-red/near-infrared regions and better catalytic performance than Au or Ag NCs. Upon addition of H2S, the Au–Ag NCs exhibited obvious fluorescence quench and color changes through the generation of metal sulfides and a static quenching process. The Au–Ag NCs displayed a wide linear luminescence response for H2S (18.5–217 μmol/L) with a detection limit of 0.269 μmol/L. Moreover, the visible color of Au–Ag NCs changed from white to brown-yellow along with increased H2S, the corresponding RGB values also displayed good linearity with the concentration of H2S (90.1–678 μmol/L). Notably, the fabrication of test strips provided a convenient and intuitive tool to screen the freshness of eggs by the color change of test strips. Au–Ag NCs could be used for living HeLa cells bioimaging and recognition of H2S abnormalities. Furthermore, it can be used as a catalyst to reduction of nitrophenols (NPhs), specific included 2NP, 3NP and 4NP. The reaction was regarded as a pseudo-first-order kinetic reaction due to the presence of excess NaBH4. At 298K, the catalytic rate constants(k) of 2NP, 3NP and 4NP were 0.1754 min−1, 0.1734 min−1 and 0.2782 min−1, respectively. The NAC@Au–Ag NCs catalyst still showed good catalytic activity and reusability after five cycles. Therefore, this study developed a H2S sensor for food samples and biological systems. And this nanocatalyst had great application potential for removed the nitrophenol pollutants in water.

A Carbazole-based Fluorescent Probe with AIE Performance and a Large Stokes Shift for Peroxynitrite Detection and Imaging in Live Cells.

A carbazole-based fluorescent probe YCN with AIE performance and a large Stokes shift (242nm) shift was synthesized by attaching 4-acetonitrile pyridine to the 3-phenylaldehyde butylcarbazole. Its structure was characterized by 1H NMR, 13C NMR and MS. Probe YCN has high selectivity and sensitivity toward ONOO-. The addition of ONOO- to the probe YCN solution results in a noticeable color change from pale yellow to colorless under natural light, and a fluorescent color change from bright orange-yellow to bright yellow-green under a 365nm UV lamp, which can be distinguished by the naked eye. The research results on the reaction mechanism showed that when YCN reacted with ONOO-, -C = C- was oxidized and broken into -CHO, and the ICT effect was significantly inhibited, resulting in changes in UV absorption and fluorescence emission phenomenon. The recognition mechanism was verified by 1H NMR, mass spectrometry (MS) and density function theory (DFT) calculations. The experiments of live cells imaging suggested that compound YCN can be used as a fluorescent probe for the detection of ONOO- in HeLa cells. This result indicates that YCN has potential application prospects in the biological aspects.

Nanozyme-mediated ratiometric fluorescence hydrogel for on-site detection of sulfite in food

In this work, a ratiometric fluorescence hydrogel nanosensor was developed by integrating a composite consisting of o-phenylenediamine (OPD), manganese dioxide nanoflakes (MnO2 NFs), and N-doped carbon dots (N-CDs) into an agarose hydrogel for sulfite detection. MnO2 NFs demonstrated intense oxidase-like activity, facilitating the conversion of non-fluorescent OPD into yellow-emissive 2,3-diaminophenazine (DAP). As a result, a significant emission peak belongs to DAP, alongside the fluorescence quenching of N-CDs through FRET. Upon interaction with sulfite, MnO2 NFs lost their oxidase-like function. This process decreased the fluorescence of DAP and restored the blue fluorescence of N-CDs, producing a typical ratiometric response, ranging from 3 nM ∼ 400 μM, with a detection limit (LOD) of 3.79 nM. Employing a smartphone, the fluorescence color change demonstrated by the hydrogel sensor was translated into quantitative data (LOD: 8.44 nM). This hydrogel sensor offers an affordable, portable, and user-friendly solution for sulfite detection and food safety monitoring.

Expanding the Color Range of Photoresponsive Multicolor Luminescent System Through Host-Guest Interaction.

Photoresponsive multicolor luminescent systems offer interesting functions, which have led to applications in anticounterfeiting and biological imaging. However, expanding the color range of these materials remains a challenging task. Herein, a carbazole-modified dithienylethene derivative (DTE-CZ) that exhibits modulated fluorescence color changes through the photocyclization reaction and photolysis reaction is synthesized. DTE-CZ emits orange fluorescence, and it can release a fluorophore which emits blue fluorescence by the photolysis reaction, resulting in the color change. Upon complexation of DTE-CZ with cucurbit[10]uril (CB[10]), the fluorescence wavelength will have a blue shift and the photolysis reaction will be inhibited. Benefiting from the influence of CB[10] and the photolysis reaction of free guests, the color range of the photoresponsive system which is composed of free guests and host-guest complexes is further extended. White light emission along with a color shift from yellow-green to blue was achieved by adjusting the ratio of free guests to host-guest complexes. Finally, the photoresponsive multicolor systems are utilized to construct a photostimulated PVA film and an information encryption system. This work provides an alternative strategy for the preparing of photoresponsive multicolor luminescent system and modulation of its color range.

A dual-response fluorescent hemicyanine probe for the detection of mitochondrial hypochlorite and viscosity based on ESIPT/AIE and TICT

Viscosity and hypochlorite (ClO−) are two important factors affecting the physiological activity and function of mitochondria. Hypochlorite (ClO−) is a vital reactive oxygen species, and endogenous ClO− acts as an important germicidal oxidant in the immune system at low concentrations. While, fluctuations in viscosity can cause mitochondrial dysfunction that is linked to several diseases. We herein report on a hemicyanine-based probe (BDTB-PA) for the detection of hypochlorite (ClO−) and viscosity. The probe exhibits a very low fluorescence background in an aqueous solution due to twisted intramolecular charge transfer (TICT) and blocked excited-state intramolecular proton transfer (ESIPT). In a viscous solution, the TICT of the probe was inhibited, generating a strong emission at 580 nm. In contrast, upon treatment with ClO−, the phenylboronic acid pinacol ester group of probe BDTB-PA was removed, and the hydroxyl group was released, activating the ESIPT process. Coupled with its aggregation-induced emission (AIE) characteristics, the product of BDTB-PA with ClO− exhibited a distinct emission at 540 nm. As such a solution of the probe BDTB-PA exhibited a distinct fluorescent color change from colourless to green under UV light with the addition of ClO−. More importantly, probe BDTB-PA was used for monitoring ClO− and viscosity in the mitochondria of living cells, plants and zebrafish.

Design and synthesis of dicyanoethylene derivatives functionalized with carbazole possessing the properties of obvious aggregation-induced emission and reversible high-contrast mechanofluorochromism

This study devotes to the design, preparation, and examination of two novel D-A structured molecules, designated as CCEDBF and BCCEDBF, which are derived from carbazole unit, dicyanoethylene segment, and dibenzofuran unit. The distinctive D-A molecular architectures and highly twisted spatial configurations of these compounds facilitate pronounced intramolecular charge transfer (ICT) while also imparting robust solid-state luminescence, exhibiting emission efficiencies of 0.518 and 0.739, respectively, and notable aggregation-induced emission (AIE) with AIE factors of 43 and 30. Significantly, both CCEDBF and BCCEDBF demonstrate reversible mechanofluorochromic (MFC) behavior characterized by high fluorescence contrast. Mechanical grinding of the initial powders results in a shift in their emission colors, transitioning from green and yellow-green to yellow and orange-red, respectively, alongside a corresponding shift in emission peaks from 525 nm to 536 nm–558 nm and 597 nm. Powder X-ray diffraction (PXRD) examination of the initially synthesized, mechanically processed, and vaporized samples reveals that the observed fluorescence color change is due to a structural transformation between ordered crystalline and disordered amorphous configurations induced by the application of the external force. The red shift in photoluminescence (PL) spectra post-grinding is attributed to a reduced band gap, driven by factors such as extended π-conjugation length, enhanced planar intramolecular charge transfer (PICT) effect, strengthened π-π interactions and exciton coupling, as well as the increase in the orbitals overlap between neighboring molecular. Moreover, the presence or absence of tert-butyl substituents attaching to the 3- and 6-positions of the carbazole units significantly impacts the photophysical properties of these materials.

Reversible Emission Color, Brightness, and Shape Changes of AIEgen‐containing Bulk Polymers

AbstractBulk polymers generally exhibit faster response, higher shape‐deformation speed, and stronger mechanical properties than the hydrogels. However, it still remains a formidable challenge to enable bulk polymers to exhibit reversible changes in shape and fluorescence simultaneously. Herein, for the first time, the temperature‐responsive reversible changes in fluorescence color, brightness, and shape of semi‐crystalline poly(ε‐caprolactone) (PCL) network doped with a D‐A based aggregation‐induced emission luminogen (AIEgen) is realized. The fabricated flower‐like and dragonfly‐shaped actuators show reversible blooming‐closing and wing fanning behaviors, respectively, as well as reversible fluorescence‐changing effects. Notably, the response and shape‐deformation speed as well as mechanical properties of the system is much better than the reported hydrogels. Moreover, a smart switch is developed to demonstrate the potential applications. The stick fabricated by the sample can lift and release an object 1000 times larger than its weight, serving as a color‐changing artificial muscle. This material design strategy may shine light on the design and preparation of other reversible shape‐deformation polymers in combination with stimuli‐responsive luminescence‐changing AIEgens, such as mechanochromic, thermochromic, and photochromic luminogens.

Wavelength-Based luminescence sensing via Turn-On responses for acid detection in complex Environments

One possible way to address the shortcomings of current acid detection is to add fluorescence detection capabilities, however, there is little data regarding wavelength-based luminescence sensing, which makes possible for the naked eye to perceive various colors through wavelength variations. In this paper, we achieved turn-on response and wavelength-based luminescence sensing on acids detection by using donor-accepter complex Fe-L, which display significant fluorescence discoloration in the presence of a wide range of inorganic and organic acids, including benzoic acids, providing the fluorescence response for a more intuitive and convenient acid detection. The simultaneous achievement of fluorescence enhancement and color change as the acid concentration changes enables visual detection of the acid concentration, which provides a foundation for future research into convenient detection methods for various types of acids.

Fluorescent Microneedle‐Based Theranostic Patch for Naked‐Eye Monitoring and On‐Demand Photo‐Therapy of Bacterial Biofilm Infections

AbstractThe eradication of recalcitrant bacterial biofilm infections necessitates the development of speedy diagnostics and prompt therapeutics. However, constructing a portable versatile platform that enables in situ monitoring of biofilm infections accompanied by potent antibiofilm activity remains challenging. To address this conundrum, a microneedle theranostic patch (Mn: C/G@MN) is devised by incorporating an innovative biophotonic probe (manganese‐doped carbon dots, Mn: CDs) into methacrylated gelatin for visual monitoring of biofilm infection and on‐demand photo‐therapy. The Mn: C/G@MN patch penetrates the physical barrier of biofilms to track their acidic microenvironment, exhibiting a visualized fluorescence color change (from yellow to turquoise) to enable naked‐eye monitoring of biofilm infection. Furthermore, the Mn: C/G@MN patch can drastically eradicate biofilm on‐demand through the synergy of local hyperthermia and hydroxyl radical (•OH) storm under 808 nm near‐infrared light illumination, enabling the damaging of extracellular polymeric substances (EPS) matrix to disperse biofilms and subsequently kill detached bacteria. Both in vitro and in vivo findings authenticate that biofilm infection monitoring‐and‐treating can be achieved. Moreover, the versatile Mn: C/G@MN patch is conducive to suppressing inflammatory responses, expediting collagen deposition, stimulating angiogenesis, and accelerating biofilm‐infected wound healing. As envisaged, this work highlights the potential of such a versatile platform for application in integrated theranostics for biofilm infection.

Advanced multicolor dynamic fluorescence anti-counterfeiting and encryption strategy based on light-induced reversible perovskite lattice distortion

Time-dynamic fluorescence encryption and anti-counterfeiting technology have garnered significant attention in the high-end information security field. However, developing tunable multicolor solid-state photoluminescent systems that are low-cost, easy to manufacture, scalable, and convenient to verify remains a considerable challenge. In this study, we finely tuned the luminescence behavior of CsCdCl3 all-inorganic perovskite crystals using a halogen doping strategy, resulting in reversible lattice distortion under UV light and endowing them with photoactivated luminescence properties to produce dynamic fluorescence. Upon the introduction of Br-, the optical properties of CsCdCl3 changed significantly, with the fluorescence emission color shifting from orange to white-green under UV irradiation. By adjusting the Br- doping ratio and UV irradiation intensity, the fluorescence color change time of CsCdCl3 can be controlled. Multiple cycle light exposure tests demonstrated that the luminescence properties of CsCdCl3 remained identical to the initial state, indicating high stability in response to UV stimulation. Consequently, we successfully realized advanced anti-counterfeiting and 4D code encryption modes based on dynamic fluorescence. The introduction of a time variable imparts extremely high security to these strategies. This work provides an exciting approach for designing information encryption materials with higher security requirements and offers a promising high-sensitivity UV detection material.

Gold nanoclusters and amino-modified mesoporous silica-encapsulated carbon dot fluorescence nanosensors combined with LightGBM algorithm for ultra-fast detection of Co2+

In this study, we develop a novel ratiometric fluorescent nanosensor for the detection excess Co2+ in soil. This fluorescent nanosensor is fabricated using mesoporous silica-encapsulated nitrogen-doped carbon dots (N-CDs@mSiO2) and gold nanoclusters stabilized by bovine serum albumin (BSA-AuNCs). The green fluorescence of the carbon dots within the mesoporous silica spheres (mSiO2) serves as an internal reference signal. The red fluoresence BSA-AuNCs are covalently connected onto the surface of amino-functionalized nanospheres (N-CDs@mSiO2-NH2), providing the response signal. This nanosensor has dual emission peaks at 520 nm and 650 nm under excitation wavelength of 380 nm. The addition of Co2+ to this nanosensor causes the fluorescence quenching at 650 nm while the green fluorescence at 520 nm remains unchanged, resulting in fluorescence color change from yellow to green. The developed ratiometric fluorescence nanosensor exhibits excellent selectivity to Co2+ with a range of 2.00–200.00 μM and a detection limit as low as 0.74 μM. In addition, a Co2+ prediction model is developed using the Light Gradient Boosting Machine (LightGBM) algorithm. The entire detection process is within 10 s and the model prediction value is as high as 0.991 on average. This shows that the proposed fluorescent nanosensor, optimized with the LightGBM algorithm, provides an efficient, environmentally friendly and potentially practical solution for Co2+ detection.

Red-emitting copper nanoclusters for ultrasensitive and selective detection of creatinine and its application in portable smartphone-based paper strips and polymer thin film

In this work, a quantitative paper-based sensor integrated with smartphone-application was developed using poly(sodium 4-styrenesulfonate) stabilized copper nanoclusters (PSS-CuNCs) as a fluorescence probe to detect creatinine (CRN). The surface morphology and optical properties of PSS-CuNCs were verified using UV–vis absorption, zeta-potential, photoluminescence, high resolution transmission electron microscopy (HR-TEM) and Fourier-transform infrared (FI-IR) and X-ray photoelectron (XPS) spectroscopy. PSS-CuNCs exhibited strong red fluorescence with the emission peak centered at 654 nm upon excitation at 390 nm. PSS-CuNCs was also used to determine CRN because of their excellent fluorescence properties. The fluorescence of PSS-CuNCs was quenched significantly by adding different concentrations of CRN, which mainly originated from the formation of ground state complexation. The PSS-CuNCs probe showed high sensitivity with a low limit of detection (LOD) of 2.48 nM and high selectivity even in the presence of other interfering analytes. This assay was also used to measure CRN in real samples. Additionally, test paper-based assay has been developed to detect CRN using smartphones. The developed assay provides a reliable, cost-effective, sensitive and portable on-site method to measure CRN levels by utilizing fluorescence color changes. Incorporation of PSS-CuNCs into poly(vinyl alcohol) resulted in the formation of fluorescent transparent polymer thin films with high photostability.

Highly Reversible "On-Off-On" Fluorescence Switch Governed by pH, Utilizing Bis(Benzimidazole) Derivatives with Varied Link Groups.

In this work, a series of dibenzimidazole derivatives 1-4, act as highly reversible colorimetric and fluorescent pH chemosensor, were designed and synthesized. Excellent reversible pH response of these sensors could be found by a specific pH change through obvious fluorescent color changes. The response is not affected by common cations (including Al3+, Cu2+, Ca2+, Cd2+, Co2+, Cr3+, Mg2+, Na+, K+, Ni2+, Pb2+ and Zn2+) and anions (including F-, Cl-, Br-, I-, ClO4-, H2PO4-, HSO4-, HCO3- and CH3COO-). Notably, these sensors can be reused more than 10 times without losing functionality. Unlike previous reports, the distinct properties of 1-4 are attributed to the varied link groups. Based on comprehensive experimental data and mechanistic analyses, it is concluded that sensors 1-4 are promising candidates for use as highly reversible "on-off-on" fluorescence switches under precise pH control.

Fluorogenic Monitoring of α-Amylase in Human Urine for Straightforward Diagnosis of Pancreatic Diseases.

In this study, we developed a sensitive method for monitoring α-amylase using a fluorogenic approach based on the host-guest complexation between an amphiphilic pyrenyl derivative (1) and γ-cyclodextrins (γ-CDs). The compound 1 self-assembles into nanofibrils in aqueous solutions. Upon the introduction of γ-CD, compound 1 forms an inclusion complex with it. This complex then participates in the formation of a 2 : 2 complex with another complex, leading to strong excimer fluorescence. Upon interaction with α-amylase, γ-CD undergoes hydrolysis, leading to the regeneration of nanofibrils, which is accompanied by a decrease in excimer fluorescence and an increase in monomeric fluorescence. This ratiometric fluorescence color change enables the sensitive detection of low levels of α-amylase in human urine, offering a practical approach for early screening of pancreatic-related diseases.